=head1 NAME
-perlguts - Perl's Internal Functions
+perlguts - Introduction to the Perl API
=head1 DESCRIPTION
-This document attempts to describe some of the internal functions of the
-Perl executable. It is far from complete and probably contains many errors.
-Please refer any questions or comments to the author below.
+This document attempts to describe how to use the Perl API, as well as
+to provide some info on the basic workings of the Perl core. It is far
+from complete and probably contains many errors. Please refer any
+questions or comments to the author below.
=head1 Variables
=head2 What is an "IV"?
-Perl uses a special typedef IV which is a simple integer type that is
+Perl uses a special typedef IV which is a simple signed integer type that is
guaranteed to be large enough to hold a pointer (as well as an integer).
+Additionally, there is the UV, which is simply an unsigned IV.
Perl also uses two special typedefs, I32 and I16, which will always be at
-least 32-bits and 16-bits long, respectively.
+least 32-bits and 16-bits long, respectively. (Again, there are U32 and U16,
+as well.) They will usually be exactly 32 and 16 bits long, but on Crays
+they will both be 64 bits.
=head2 Working with SVs
-An SV can be created and loaded with one command. There are four types of
-values that can be loaded: an integer value (IV), a double (NV), a string,
-(PV), and another scalar (SV).
+An SV can be created and loaded with one command. There are five types of
+values that can be loaded: an integer value (IV), an unsigned integer
+value (UV), a double (NV), a string (PV), and another scalar (SV).
-The four routines are:
+The seven routines are:
SV* newSViv(IV);
+ SV* newSVuv(UV);
SV* newSVnv(double);
- SV* newSVpv(char*, int);
+ SV* newSVpv(const char*, STRLEN);
+ SV* newSVpvn(const char*, STRLEN);
+ SV* newSVpvf(const char*, ...);
SV* newSVsv(SV*);
-To change the value of an *already-existing* SV, there are five routines:
+C<STRLEN> is an integer type (Size_t, usually defined as size_t in
+F<config.h>) guaranteed to be large enough to represent the size of
+any string that perl can handle.
+
+In the unlikely case of a SV requiring more complex initialisation, you
+can create an empty SV with newSV(len). If C<len> is 0 an empty SV of
+type NULL is returned, else an SV of type PV is returned with len + 1 (for
+the NUL) bytes of storage allocated, accessible via SvPVX. In both cases
+the SV has value undef.
+
+ SV *sv = newSV(0); /* no storage allocated */
+ SV *sv = newSV(10); /* 10 (+1) bytes of uninitialised storage allocated */
+
+To change the value of an I<already-existing> SV, there are eight routines:
void sv_setiv(SV*, IV);
+ void sv_setuv(SV*, UV);
void sv_setnv(SV*, double);
- void sv_setpvn(SV*, char*, int)
- void sv_setpv(SV*, char*);
+ void sv_setpv(SV*, const char*);
+ void sv_setpvn(SV*, const char*, STRLEN)
+ void sv_setpvf(SV*, const char*, ...);
+ void sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool *);
void sv_setsv(SV*, SV*);
Notice that you can choose to specify the length of the string to be
-assigned by using C<sv_setpvn> or C<newSVpv>, or you may allow Perl to
-calculate the length by using C<sv_setpv> or by specifying 0 as the second
-argument to C<newSVpv>. Be warned, though, that Perl will determine the
-string's length by using C<strlen>, which depends on the string terminating
-with a NUL character.
-
-All SVs that will contain strings should, but need not, be terminated
-with a NUL character. If it is not NUL-terminated there is a risk of
+assigned by using C<sv_setpvn>, C<newSVpvn>, or C<newSVpv>, or you may
+allow Perl to calculate the length by using C<sv_setpv> or by specifying
+0 as the second argument to C<newSVpv>. Be warned, though, that Perl will
+determine the string's length by using C<strlen>, which depends on the
+string terminating with a NUL character.
+
+The arguments of C<sv_setpvf> are processed like C<sprintf>, and the
+formatted output becomes the value.
+
+C<sv_vsetpvfn> is an analogue of C<vsprintf>, but it allows you to specify
+either a pointer to a variable argument list or the address and length of
+an array of SVs. The last argument points to a boolean; on return, if that
+boolean is true, then locale-specific information has been used to format
+the string, and the string's contents are therefore untrustworthy (see
+L<perlsec>). This pointer may be NULL if that information is not
+important. Note that this function requires you to specify the length of
+the format.
+
+The C<sv_set*()> functions are not generic enough to operate on values
+that have "magic". See L<Magic Virtual Tables> later in this document.
+
+All SVs that contain strings should be terminated with a NUL character.
+If it is not NUL-terminated there is a risk of
core dumps and corruptions from code which passes the string to C
functions or system calls which expect a NUL-terminated string.
Perl's own functions typically add a trailing NUL for this reason.
To access the actual value that an SV points to, you can use the macros:
SvIV(SV*)
+ SvUV(SV*)
SvNV(SV*)
SvPV(SV*, STRLEN len)
+ SvPV_nolen(SV*)
-which will automatically coerce the actual scalar type into an IV, double,
+which will automatically coerce the actual scalar type into an IV, UV, double,
or string.
In the C<SvPV> macro, the length of the string returned is placed into the
-variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
-care what the length of the data is, use the global variable C<na>. Remember,
-however, that Perl allows arbitrary strings of data that may both contain
-NULs and might not be terminated by a NUL.
+variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do
+not care what the length of the data is, use the C<SvPV_nolen> macro.
+Historically the C<SvPV> macro with the global variable C<PL_na> has been
+used in this case. But that can be quite inefficient because C<PL_na> must
+be accessed in thread-local storage in threaded Perl. In any case, remember
+that Perl allows arbitrary strings of data that may both contain NULs and
+might not be terminated by a NUL.
+
+Also remember that C doesn't allow you to safely say C<foo(SvPV(s, len),
+len);>. It might work with your compiler, but it won't work for everyone.
+Break this sort of statement up into separate assignments:
+
+ SV *s;
+ STRLEN len;
+ char * ptr;
+ ptr = SvPV(s, len);
+ foo(ptr, len);
If you want to know if the scalar value is TRUE, you can use:
If you want to append something to the end of string stored in an C<SV*>,
you can use the following functions:
- void sv_catpv(SV*, char*);
- void sv_catpvn(SV*, char*, int);
+ void sv_catpv(SV*, const char*);
+ void sv_catpvn(SV*, const char*, STRLEN);
+ void sv_catpvf(SV*, const char*, ...);
+ void sv_vcatpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
void sv_catsv(SV*, SV*);
The first function calculates the length of the string to be appended by
using C<strlen>. In the second, you specify the length of the string
-yourself. The third function extends the string stored in the first SV
-with the string stored in the second SV. It also forces the second SV to
-be interpreted as a string.
+yourself. The third function processes its arguments like C<sprintf> and
+appends the formatted output. The fourth function works like C<vsprintf>.
+You can specify the address and length of an array of SVs instead of the
+va_list argument. The fifth function extends the string stored in the first
+SV with the string stored in the second SV. It also forces the second SV
+to be interpreted as a string.
+
+The C<sv_cat*()> functions are not generic enough to operate on values that
+have "magic". See L<Magic Virtual Tables> later in this document.
If you know the name of a scalar variable, you can get a pointer to its SV
by using the following:
- SV* perl_get_sv("package::varname", FALSE);
+ SV* get_sv("package::varname", FALSE);
This returns NULL if the variable does not exist.
SvOK(SV*)
-The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
-address can be used whenever an C<SV*> is needed.
+The scalar C<undef> value is stored in an SV instance called C<PL_sv_undef>.
+
+Its address can be used whenever an C<SV*> is needed. Make sure that
+you don't try to compare a random sv with C<&PL_sv_undef>. For example
+when interfacing Perl code, it'll work correctly for:
+
+ foo(undef);
+
+But won't work when called as:
+
+ $x = undef;
+ foo($x);
-There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
-TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
-be used whenever an C<SV*> is needed.
+So to repeat always use SvOK() to check whether an sv is defined.
-Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
+Also you have to be careful when using C<&PL_sv_undef> as a value in
+AVs or HVs (see L<AVs, HVs and undefined values>).
+
+There are also the two values C<PL_sv_yes> and C<PL_sv_no>, which contain
+boolean TRUE and FALSE values, respectively. Like C<PL_sv_undef>, their
+addresses can be used whenever an C<SV*> is needed.
+
+Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>.
Take this code:
SV* sv = (SV*) 0;
sv_setsv(ST(0), sv);
This code tries to return a new SV (which contains the value 42) if it should
-return a real value, or undef otherwise. Instead it has returned a null
+return a real value, or undef otherwise. Instead it has returned a NULL
pointer which, somewhere down the line, will cause a segmentation violation,
-bus error, or just weird results. Change the zero to C<&sv_undef> in the first
-line and all will be well.
+bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the
+first line and all will be well.
To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
call is not necessary (see L<Reference Counts and Mortality>).
+=head2 Offsets
+
+Perl provides the function C<sv_chop> to efficiently remove characters
+from the beginning of a string; you give it an SV and a pointer to
+somewhere inside the PV, and it discards everything before the
+pointer. The efficiency comes by means of a little hack: instead of
+actually removing the characters, C<sv_chop> sets the flag C<OOK>
+(offset OK) to signal to other functions that the offset hack is in
+effect, and it puts the number of bytes chopped off into the IV field
+of the SV. It then moves the PV pointer (called C<SvPVX>) forward that
+many bytes, and adjusts C<SvCUR> and C<SvLEN>.
+
+Hence, at this point, the start of the buffer that we allocated lives
+at C<SvPVX(sv) - SvIV(sv)> in memory and the PV pointer is pointing
+into the middle of this allocated storage.
+
+This is best demonstrated by example:
+
+ % ./perl -Ilib -MDevel::Peek -le '$a="12345"; $a=~s/.//; Dump($a)'
+ SV = PVIV(0x8128450) at 0x81340f0
+ REFCNT = 1
+ FLAGS = (POK,OOK,pPOK)
+ IV = 1 (OFFSET)
+ PV = 0x8135781 ( "1" . ) "2345"\0
+ CUR = 4
+ LEN = 5
+
+Here the number of bytes chopped off (1) is put into IV, and
+C<Devel::Peek::Dump> helpfully reminds us that this is an offset. The
+portion of the string between the "real" and the "fake" beginnings is
+shown in parentheses, and the values of C<SvCUR> and C<SvLEN> reflect
+the fake beginning, not the real one.
+
+Something similar to the offset hack is performed on AVs to enable
+efficient shifting and splicing off the beginning of the array; while
+C<AvARRAY> points to the first element in the array that is visible from
+Perl, C<AvALLOC> points to the real start of the C array. These are
+usually the same, but a C<shift> operation can be carried out by
+increasing C<AvARRAY> by one and decreasing C<AvFILL> and C<AvLEN>.
+Again, the location of the real start of the C array only comes into
+play when freeing the array. See C<av_shift> in F<av.c>.
+
=head2 What's Really Stored in an SV?
Recall that the usual method of determining the type of scalar you have is
These will tell you if you truly have an integer, double, or string pointer
stored in your SV. The "p" stands for private.
+The are various ways in which the private and public flags may differ.
+For example, a tied SV may have a valid underlying value in the IV slot
+(so SvIOKp is true), but the data should be accessed via the FETCH
+routine rather than directly, so SvIOK is false. Another is when
+numeric conversion has occurred and precision has been lost: only the
+private flag is set on 'lossy' values. So when an NV is converted to an
+IV with loss, SvIOKp, SvNOKp and SvNOK will be set, while SvIOK wont be.
+
In general, though, it's best to use the C<Sv*V> macros.
=head2 Working with AVs
like $#array in Perl). If the array is empty, -1 is returned. The
C<av_fetch> function returns the value at index C<key>, but if C<lval>
is non-zero, then C<av_fetch> will store an undef value at that index.
-The C<av_store> function stores the value C<val> at index C<key>.
-note that C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s
-as their return value.
+The C<av_store> function stores the value C<val> at index C<key>, and does
+not increment the reference count of C<val>. Thus the caller is responsible
+for taking care of that, and if C<av_store> returns NULL, the caller will
+have to decrement the reference count to avoid a memory leak. Note that
+C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
+return value.
void av_clear(AV*);
void av_undef(AV*);
The C<av_clear> function deletes all the elements in the AV* array, but
does not actually delete the array itself. The C<av_undef> function will
delete all the elements in the array plus the array itself. The
-C<av_extend> function extends the array so that it contains C<key>
-elements. If C<key> is less than the current length of the array, then
-nothing is done.
+C<av_extend> function extends the array so that it contains at least C<key+1>
+elements. If C<key+1> is less than the currently allocated length of the array,
+then nothing is done.
If you know the name of an array variable, you can get a pointer to its AV
by using the following:
- AV* perl_get_av("package::varname", FALSE);
+ AV* get_av("package::varname", FALSE);
This returns NULL if the variable does not exist.
+See L<Understanding the Magic of Tied Hashes and Arrays> for more
+information on how to use the array access functions on tied arrays.
+
=head2 Working with HVs
To create an HV, you use the following routine:
Once the HV has been created, the following operations are possible on HVs:
- SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
- SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
+ SV** hv_store(HV*, const char* key, U32 klen, SV* val, U32 hash);
+ SV** hv_fetch(HV*, const char* key, U32 klen, I32 lval);
The C<klen> parameter is the length of the key being passed in (Note that
you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
These two functions check if a hash table entry exists, and deletes it.
- bool hv_exists(HV*, char* key, U32 klen);
- SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
+ bool hv_exists(HV*, const char* key, U32 klen);
+ SV* hv_delete(HV*, const char* key, U32 klen, I32 flags);
If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
create and return a mortal copy of the deleted value.
/* Get the key from an HE structure and also return
the length of the key string */
SV* hv_iterval(HV*, HE* entry);
- /* Return a SV pointer to the value of the HE
+ /* Return an SV pointer to the value of the HE
structure */
SV* hv_iternextsv(HV*, char** key, I32* retlen);
/* This convenience routine combines hv_iternext,
If you know the name of a hash variable, you can get a pointer to its HV
by using the following:
- HV* perl_get_hv("package::varname", FALSE);
+ HV* get_hv("package::varname", FALSE);
This returns NULL if the variable does not exist.
The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
- i = klen;
hash = 0;
- s = key;
- while (i--)
- hash = hash * 33 + *s++;
+ while (klen--)
+ hash = (hash * 33) + *key++;
+ hash = hash + (hash >> 5); /* after 5.6 */
+
+The last step was added in version 5.6 to improve distribution of
+lower bits in the resulting hash value.
+
+See L<Understanding the Magic of Tied Hashes and Arrays> for more
+information on how to use the hash access functions on tied hashes.
=head2 Hash API Extensions
HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
-
+
bool hv_exists_ent (HV* tb, SV* key, U32 hash);
SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
-
+
SV* hv_iterkeysv (HE* entry);
Note that these functions take C<SV*> keys, which simplifies writing
They also return and accept whole hash entries (C<HE*>), making their
use more efficient (since the hash number for a particular string
-doesn't have to be recomputed every time). See L<API LISTING> later in
-this document for detailed descriptions.
+doesn't have to be recomputed every time). See L<perlapi> for detailed
+descriptions.
The following macros must always be used to access the contents of hash
entries. Note that the arguments to these macros must be simple
variables, since they may get evaluated more than once. See
-L<API LISTING> later in this document for detailed descriptions of these
-macros.
+L<perlapi> for detailed descriptions of these macros.
HePV(HE* he, STRLEN len)
HeVAL(HE* he)
HeKEY(HE* he)
HeKLEN(HE* he)
+Note that both C<hv_store> and C<hv_store_ent> do not increment the
+reference count of the stored C<val>, which is the caller's responsibility.
+If these functions return a NULL value, the caller will usually have to
+decrement the reference count of C<val> to avoid a memory leak.
+
+=head2 AVs, HVs and undefined values
+
+Sometimes you have to store undefined values in AVs or HVs. Although
+this may be a rare case, it can be tricky. That's because you're
+used to using C<&PL_sv_undef> if you need an undefined SV.
+
+For example, intuition tells you that this XS code:
+
+ AV *av = newAV();
+ av_store( av, 0, &PL_sv_undef );
+
+is equivalent to this Perl code:
+
+ my @av;
+ $av[0] = undef;
+
+Unfortunately, this isn't true. AVs use C<&PL_sv_undef> as a marker
+for indicating that an array element has not yet been initialized.
+Thus, C<exists $av[0]> would be true for the above Perl code, but
+false for the array generated by the XS code.
+
+Other problems can occur when storing C<&PL_sv_undef> in HVs:
+
+ hv_store( hv, "key", 3, &PL_sv_undef, 0 );
+
+This will indeed make the value C<undef>, but if you try to modify
+the value of C<key>, you'll get the following error:
+
+ Modification of non-creatable hash value attempted
+
+In perl 5.8.0, C<&PL_sv_undef> was also used to mark placeholders
+in restricted hashes. This caused such hash entries not to appear
+when iterating over the hash or when checking for the keys
+with the C<hv_exists> function.
+
+You can run into similar problems when you store C<&PL_sv_true> or
+C<&PL_sv_false> into AVs or HVs. Trying to modify such elements
+will give you the following error:
+
+ Modification of a read-only value attempted
+
+To make a long story short, you can use the special variables
+C<&PL_sv_undef>, C<&PL_sv_true> and C<&PL_sv_false> with AVs and
+HVs, but you have to make sure you know what you're doing.
+
+Generally, if you want to store an undefined value in an AV
+or HV, you should not use C<&PL_sv_undef>, but rather create a
+new undefined value using the C<newSV> function, for example:
+
+ av_store( av, 42, newSV(0) );
+ hv_store( hv, "foo", 3, newSV(0), 0 );
=head2 References
=head2 Blessed References and Class Objects
-References are also used to support object-oriented programming. In the
+References are also used to support object-oriented programming. In perl's
OO lexicon, an object is simply a reference that has been blessed into a
package (or class). Once blessed, the programmer may now use the reference
to access the various methods in the class.
SV* sv_bless(SV* sv, HV* stash);
-The C<sv> argument must be a reference. The C<stash> argument specifies
-which class the reference will belong to. See
+The C<sv> argument must be a reference value. The C<stash> argument
+specifies which class the reference will belong to. See
L<Stashes and Globs> for information on converting class names into stashes.
/* Still under construction */
point to. If C<classname> is non-null, the SV is blessed into the specified
class. SV is returned.
- SV* newSVrv(SV* rv, char* classname);
+ SV* newSVrv(SV* rv, const char* classname);
-Copies integer or double into an SV whose reference is C<rv>. SV is blessed
+Copies integer, unsigned integer or double into an SV whose reference is C<rv>. SV is blessed
if C<classname> is non-null.
- SV* sv_setref_iv(SV* rv, char* classname, IV iv);
- SV* sv_setref_nv(SV* rv, char* classname, NV iv);
+ SV* sv_setref_iv(SV* rv, const char* classname, IV iv);
+ SV* sv_setref_uv(SV* rv, const char* classname, UV uv);
+ SV* sv_setref_nv(SV* rv, const char* classname, NV iv);
Copies the pointer value (I<the address, not the string!>) into an SV whose
reference is rv. SV is blessed if C<classname> is non-null.
- SV* sv_setref_pv(SV* rv, char* classname, PV iv);
+ SV* sv_setref_pv(SV* rv, const char* classname, PV iv);
Copies string into an SV whose reference is C<rv>. Set length to 0 to let
Perl calculate the string length. SV is blessed if C<classname> is non-null.
- SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
+ SV* sv_setref_pvn(SV* rv, const char* classname, PV iv, STRLEN length);
+
+Tests whether the SV is blessed into the specified class. It does not
+check inheritance relationships.
+
+ int sv_isa(SV* sv, const char* name);
+
+Tests whether the SV is a reference to a blessed object.
+
+ int sv_isobject(SV* sv);
+
+Tests whether the SV is derived from the specified class. SV can be either
+a reference to a blessed object or a string containing a class name. This
+is the function implementing the C<UNIVERSAL::isa> functionality.
+
+ bool sv_derived_from(SV* sv, const char* name);
- int sv_isa(SV* sv, char* name);
- int sv_isobject(SV* sv);
+To check if you've got an object derived from a specific class you have
+to write:
+
+ if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... }
=head2 Creating New Variables
To create a new Perl variable with an undef value which can be accessed from
your Perl script, use the following routines, depending on the variable type.
- SV* perl_get_sv("package::varname", TRUE);
- AV* perl_get_av("package::varname", TRUE);
- HV* perl_get_hv("package::varname", TRUE);
+ SV* get_sv("package::varname", TRUE);
+ AV* get_av("package::varname", TRUE);
+ HV* get_hv("package::varname", TRUE);
Notice the use of TRUE as the second parameter. The new variable can now
be set, using the routines appropriate to the data type.
There are additional macros whose values may be bitwise OR'ed with the
C<TRUE> argument to enable certain extra features. Those bits are:
- GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
- "Name <varname> used only once: possible typo" warning.
- GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
- the variable did not exist before the function was called.
+=over
+
+=item GV_ADDMULTI
+
+Marks the variable as multiply defined, thus preventing the:
+
+ Name <varname> used only once: possible typo
+
+warning.
+
+=item GV_ADDWARN
+
+Issues the warning:
+
+ Had to create <varname> unexpectedly
+
+if the variable did not exist before the function was called.
+
+=back
If you do not specify a package name, the variable is created in the current
package.
=head2 Reference Counts and Mortality
-Perl uses an reference count-driven garbage collection mechanism. SVs,
+Perl uses a reference count-driven garbage collection mechanism. SVs,
AVs, or HVs (xV for short in the following) start their life with a
reference count of 1. If the reference count of an xV ever drops to 0,
then it will be destroyed and its memory made available for reuse.
However, if you mortalize a variable twice, the reference count will
later be decremented twice.
-You should be careful about creating mortal variables. Strange things
-can happen if you make the same value mortal within multiple contexts,
-or if you make a variable mortal multiple times.
+"Mortal" SVs are mainly used for SVs that are placed on perl's stack.
+For example an SV which is created just to pass a number to a called sub
+is made mortal to have it cleaned up automatically when it's popped off
+the stack. Similarly, results returned by XSUBs (which are pushed on the
+stack) are often made mortal.
To create a mortal variable, use the functions:
SV* sv_2mortal(SV*)
SV* sv_mortalcopy(SV*)
-The first call creates a mortal SV, the second converts an existing
+The first call creates a mortal SV (with no value), the second converts an existing
SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
third creates a mortal copy of an existing SV.
+Because C<sv_newmortal> gives the new SV no value,it must normally be given one
+via C<sv_setpv>, C<sv_setiv>, etc. :
+
+ SV *tmp = sv_newmortal();
+ sv_setiv(tmp, an_integer);
+
+As that is multiple C statements it is quite common so see this idiom instead:
+
+ SV *tmp = sv_2mortal(newSViv(an_integer));
+
+
+You should be careful about creating mortal variables. Strange things
+can happen if you make the same value mortal within multiple contexts,
+or if you make a variable mortal multiple times. Thinking of "Mortalization"
+as deferred C<SvREFCNT_dec> should help to minimize such problems.
+For example if you are passing an SV which you I<know> has high enough REFCNT
+to survive its use on the stack you need not do any mortalization.
+If you are not sure then doing an C<SvREFCNT_inc> and C<sv_2mortal>, or
+making a C<sv_mortalcopy> is safer.
The mortal routines are not just for SVs -- AVs and HVs can be
made mortal by passing their address (type-casted to C<SV*>) to the
=head2 Stashes and Globs
-A "stash" is a hash that contains all of the different objects that
-are contained within a package. Each key of the stash is a symbol
+A B<stash> is a hash that contains all variables that are defined
+within a package. Each key of the stash is a symbol
name (shared by all the different types of objects that have the same
name), and each value in the hash table is a GV (Glob Value). This GV
in turn contains references to the various objects of that name,
Scalar Value
Array Value
Hash Value
- File Handle
- Directory Handle
+ I/O Handle
Format
Subroutine
-There is a single stash called "defstash" that holds the items that exist
-in the "main" package. To get at the items in other packages, append the
-string "::" to the package name. The items in the "Foo" package are in
-the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
-in the stash "Baz::" in "Bar::"'s stash.
+There is a single stash called C<PL_defstash> that holds the items that exist
+in the C<main> package. To get at the items in other packages, append the
+string "::" to the package name. The items in the C<Foo> package are in
+the stash C<Foo::> in PL_defstash. The items in the C<Bar::Baz> package are
+in the stash C<Baz::> in C<Bar::>'s stash.
To get the stash pointer for a particular package, use the function:
- HV* gv_stashpv(char* name, I32 create)
- HV* gv_stashsv(SV*, I32 create)
+ HV* gv_stashpv(const char* name, I32 flags)
+ HV* gv_stashsv(SV*, I32 flags)
The first function takes a literal string, the second uses the string stored
in the SV. Remember that a stash is just a hash table, so you get back an
-C<HV*>. The C<create> flag will create a new package if it is set.
+C<HV*>. The C<flags> flag will create a new package if it is set to GV_ADD.
The name that C<gv_stash*v> wants is the name of the package whose symbol table
you want. The default package is called C<main>. If you have multiply nested
extern int dberror;
extern char *dberror_list;
- SV* sv = perl_get_sv("dberror", TRUE);
+ SV* sv = get_sv("dberror", TRUE);
sv_setiv(sv, (IV) dberror);
sv_setpv(sv, dberror_list[dberror]);
SvIOK_on(sv);
U16 mg_private;
char mg_type;
U8 mg_flags;
+ I32 mg_len;
SV* mg_obj;
char* mg_ptr;
- I32 mg_len;
};
Note this is current as of patchlevel 0, and could change at any time.
Perl adds magic to an SV using the sv_magic function:
- void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
+ void sv_magic(SV* sv, SV* obj, int how, const char* name, I32 namlen);
The C<sv> argument is a pointer to the SV that is to acquire a new magical
feature.
If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
-set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
-it to the beginning of the linked list of magical features. Any prior
-entry of the same type of magic is deleted. Note that this can be
-overridden, and multiple instances of the same type of magic can be
-associated with an SV.
+convert C<sv> to type C<SVt_PVMG>. Perl then continues by adding new magic
+to the beginning of the linked list of magical features. Any prior entry
+of the same type of magic is deleted. Note that this can be overridden,
+and multiple instances of the same type of magic can be associated with an
+SV.
The C<name> and C<namlen> arguments are used to associate a string with
the magic, typically the name of a variable. C<namlen> is stored in the
-C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
-copy of the name is stored in C<mg_ptr> field.
+C<mg_len> field and if C<name> is non-null then either a C<savepvn> copy of
+C<name> or C<name> itself is stored in the C<mg_ptr> field, depending on
+whether C<namlen> is greater than zero or equal to zero respectively. As a
+special case, if C<(name && namlen == HEf_SVKEY)> then C<name> is assumed
+to contain an C<SV*> and is stored as-is with its REFCNT incremented.
The sv_magic function uses C<how> to determine which, if any, predefined
"Magic Virtual Table" should be assigned to the C<mg_virtual> field.
-See the "Magic Virtual Table" section below. The C<how> argument is also
-stored in the C<mg_type> field.
+See the L<Magic Virtual Tables> section below. The C<how> argument is also
+stored in the C<mg_type> field. The value of C<how> should be chosen
+from the set of macros C<PERL_MAGIC_foo> found in F<perl.h>. Note that before
+these macros were added, Perl internals used to directly use character
+literals, so you may occasionally come across old code or documentation
+referring to 'U' magic rather than C<PERL_MAGIC_uvar> for example.
The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
structure. If it is not the same as the C<sv> argument, the reference
count of the C<obj> object is incremented. If it is the same, or if
-the C<how> argument is "#", or if it is a null pointer, then C<obj> is
-merely stored, without the reference count being incremented.
+the C<how> argument is C<PERL_MAGIC_arylen>, or if it is a NULL pointer,
+then C<obj> is merely stored, without the reference count being incremented.
+
+See also C<sv_magicext> in L<perlapi> for a more flexible way to add magic
+to an SV.
There is also a function to add magic to an C<HV>:
=head2 Magic Virtual Tables
-The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
+The C<mg_virtual> field in the C<MAGIC> structure is a pointer to an
C<MGVTBL>, which is a structure of function pointers and stands for
"Magic Virtual Table" to handle the various operations that might be
applied to that variable.
-The C<MGVTBL> has five pointers to the following routine types:
+The C<MGVTBL> has five (or sometimes eight) pointers to the following
+routine types:
int (*svt_get)(SV* sv, MAGIC* mg);
int (*svt_set)(SV* sv, MAGIC* mg);
int (*svt_clear)(SV* sv, MAGIC* mg);
int (*svt_free)(SV* sv, MAGIC* mg);
-This MGVTBL structure is set at compile-time in C<perl.h> and there are
+ int (*svt_copy)(SV *sv, MAGIC* mg, SV *nsv, const char *name, I32 namlen);
+ int (*svt_dup)(MAGIC *mg, CLONE_PARAMS *param);
+ int (*svt_local)(SV *nsv, MAGIC *mg);
+
+
+This MGVTBL structure is set at compile-time in F<perl.h> and there are
currently 19 types (or 21 with overloading turned on). These different
structures contain pointers to various routines that perform additional
actions depending on which function is being called.
Function pointer Action taken
---------------- ------------
- svt_get Do something after the value of the SV is retrieved.
+ svt_get Do something before the value of the SV is retrieved.
svt_set Do something after the SV is assigned a value.
svt_len Report on the SV's length.
- svt_clear Clear something the SV represents.
+ svt_clear Clear something the SV represents.
svt_free Free any extra storage associated with the SV.
+ svt_copy copy tied variable magic to a tied element
+ svt_dup duplicate a magic structure during thread cloning
+ svt_local copy magic to local value during 'local'
+
For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
-to an C<mg_type> of '\0') contains:
+to an C<mg_type> of C<PERL_MAGIC_sv>) contains:
{ magic_get, magic_set, magic_len, 0, 0 }
-Thus, when an SV is determined to be magical and of type '\0', if a get
-operation is being performed, the routine C<magic_get> is called. All
-the various routines for the various magical types begin with C<magic_>.
+Thus, when an SV is determined to be magical and of type C<PERL_MAGIC_sv>,
+if a get operation is being performed, the routine C<magic_get> is
+called. All the various routines for the various magical types begin
+with C<magic_>. NOTE: the magic routines are not considered part of
+the Perl API, and may not be exported by the Perl library.
+
+The last three slots are a recent addition, and for source code
+compatibility they are only checked for if one of the three flags
+MGf_COPY, MGf_DUP or MGf_LOCAL is set in mg_flags. This means that most
+code can continue declaring a vtable as a 5-element value. These three are
+currently used exclusively by the threading code, and are highly subject
+to change.
The current kinds of Magic Virtual Tables are:
- mg_type MGVTBL Type of magical
- ------- ------ ----------------------------
- \0 vtbl_sv Regexp???
- A vtbl_amagic Operator Overloading
- a vtbl_amagicelem Operator Overloading
- c 0 Used in Operator Overloading
- B vtbl_bm Boyer-Moore???
- E vtbl_env %ENV hash
- e vtbl_envelem %ENV hash element
- g vtbl_mglob Regexp /g flag???
- I vtbl_isa @ISA array
- i vtbl_isaelem @ISA array element
- L 0 (but sets RMAGICAL) Perl Module/Debugger???
- l vtbl_dbline Debugger?
- o vtbl_collxfrm Locale transformation
- P vtbl_pack Tied Array or Hash
- p vtbl_packelem Tied Array or Hash element
- q vtbl_packelem Tied Scalar or Handle
- S vtbl_sig Signal Hash
- s vtbl_sigelem Signal Hash element
- t vtbl_taint Taintedness
- U vtbl_uvar ???
- v vtbl_vec Vector
- x vtbl_substr Substring???
- y vtbl_itervar Shadow "foreach" iterator variable
- * vtbl_glob GV???
- # vtbl_arylen Array Length
- . vtbl_pos $. scalar variable
- ~ None Used by certain extensions
+ mg_type
+ (old-style char and macro) MGVTBL Type of magic
+ -------------------------- ------ -------------
+ \0 PERL_MAGIC_sv vtbl_sv Special scalar variable
+ A PERL_MAGIC_overload vtbl_amagic %OVERLOAD hash
+ a PERL_MAGIC_overload_elem vtbl_amagicelem %OVERLOAD hash element
+ c PERL_MAGIC_overload_table (none) Holds overload table (AMT)
+ on stash
+ B PERL_MAGIC_bm vtbl_bm Boyer-Moore (fast string search)
+ D PERL_MAGIC_regdata vtbl_regdata Regex match position data
+ (@+ and @- vars)
+ d PERL_MAGIC_regdatum vtbl_regdatum Regex match position data
+ element
+ E PERL_MAGIC_env vtbl_env %ENV hash
+ e PERL_MAGIC_envelem vtbl_envelem %ENV hash element
+ f PERL_MAGIC_fm vtbl_fm Formline ('compiled' format)
+ g PERL_MAGIC_regex_global vtbl_mglob m//g target / study()ed string
+ H PERL_MAGIC_hints vtbl_sig %^H hash
+ h PERL_MAGIC_hintselem vtbl_hintselem %^H hash element
+ I PERL_MAGIC_isa vtbl_isa @ISA array
+ i PERL_MAGIC_isaelem vtbl_isaelem @ISA array element
+ k PERL_MAGIC_nkeys vtbl_nkeys scalar(keys()) lvalue
+ L PERL_MAGIC_dbfile (none) Debugger %_<filename
+ l PERL_MAGIC_dbline vtbl_dbline Debugger %_<filename element
+ o PERL_MAGIC_collxfrm vtbl_collxfrm Locale collate transformation
+ P PERL_MAGIC_tied vtbl_pack Tied array or hash
+ p PERL_MAGIC_tiedelem vtbl_packelem Tied array or hash element
+ q PERL_MAGIC_tiedscalar vtbl_packelem Tied scalar or handle
+ r PERL_MAGIC_qr vtbl_qr precompiled qr// regex
+ S PERL_MAGIC_sig vtbl_sig %SIG hash
+ s PERL_MAGIC_sigelem vtbl_sigelem %SIG hash element
+ t PERL_MAGIC_taint vtbl_taint Taintedness
+ U PERL_MAGIC_uvar vtbl_uvar Available for use by extensions
+ v PERL_MAGIC_vec vtbl_vec vec() lvalue
+ V PERL_MAGIC_vstring (none) v-string scalars
+ w PERL_MAGIC_utf8 vtbl_utf8 UTF-8 length+offset cache
+ x PERL_MAGIC_substr vtbl_substr substr() lvalue
+ y PERL_MAGIC_defelem vtbl_defelem Shadow "foreach" iterator
+ variable / smart parameter
+ vivification
+ # PERL_MAGIC_arylen vtbl_arylen Array length ($#ary)
+ . PERL_MAGIC_pos vtbl_pos pos() lvalue
+ < PERL_MAGIC_backref vtbl_backref back pointer to a weak ref
+ ~ PERL_MAGIC_ext (none) Available for use by extensions
+ : PERL_MAGIC_symtab (none) hash used as symbol table
+ % PERL_MAGIC_rhash (none) hash used as restricted hash
+ @ PERL_MAGIC_arylen_p vtbl_arylen_p pointer to $#a from @a
+
When an uppercase and lowercase letter both exist in the table, then the
-uppercase letter is used to represent some kind of composite type (a list
-or a hash), and the lowercase letter is used to represent an element of
-that composite type.
-
-The '~' magic type is defined specifically for use by extensions and
-will not be used by perl itself. Extensions can use ~ magic to 'attach'
-private information to variables (typically objects). This is especially
-useful because there is no way for normal perl code to corrupt this
-private information (unlike using extra elements of a hash object).
-
-Note that because multiple extensions may be using ~ magic it is
-important for extensions to take extra care with it. Typically only
-using it on objects blessed into the same class as the extension
-is sufficient. It may also be appropriate to add an I32 'signature'
-at the top of the private data area and check that.
+uppercase letter is typically used to represent some kind of composite type
+(a list or a hash), and the lowercase letter is used to represent an element
+of that composite type. Some internals code makes use of this case
+relationship. However, 'v' and 'V' (vec and v-string) are in no way related.
+
+The C<PERL_MAGIC_ext> and C<PERL_MAGIC_uvar> magic types are defined
+specifically for use by extensions and will not be used by perl itself.
+Extensions can use C<PERL_MAGIC_ext> magic to 'attach' private information
+to variables (typically objects). This is especially useful because
+there is no way for normal perl code to corrupt this private information
+(unlike using extra elements of a hash object).
+
+Similarly, C<PERL_MAGIC_uvar> magic can be used much like tie() to call a
+C function any time a scalar's value is used or changed. The C<MAGIC>'s
+C<mg_ptr> field points to a C<ufuncs> structure:
+
+ struct ufuncs {
+ I32 (*uf_val)(pTHX_ IV, SV*);
+ I32 (*uf_set)(pTHX_ IV, SV*);
+ IV uf_index;
+ };
+
+When the SV is read from or written to, the C<uf_val> or C<uf_set>
+function will be called with C<uf_index> as the first arg and a pointer to
+the SV as the second. A simple example of how to add C<PERL_MAGIC_uvar>
+magic is shown below. Note that the ufuncs structure is copied by
+sv_magic, so you can safely allocate it on the stack.
+
+ void
+ Umagic(sv)
+ SV *sv;
+ PREINIT:
+ struct ufuncs uf;
+ CODE:
+ uf.uf_val = &my_get_fn;
+ uf.uf_set = &my_set_fn;
+ uf.uf_index = 0;
+ sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf));
+
+Attaching C<PERL_MAGIC_uvar> to arrays is permissible but has no effect.
+
+For hashes there is a specialized hook that gives control over hash
+keys (but not values). This hook calls C<PERL_MAGIC_uvar> 'get' magic
+if the "set" function in the C<ufuncs> structure is NULL. The hook
+is activated whenever the hash is accessed with a key specified as
+an C<SV> through the functions C<hv_store_ent>, C<hv_fetch_ent>,
+C<hv_delete_ent>, and C<hv_exists_ent>. Accessing the key as a string
+through the functions without the C<..._ent> suffix circumvents the
+hook. See L<Hash::Util::Fieldhash/Guts> for a detailed description.
+
+Note that because multiple extensions may be using C<PERL_MAGIC_ext>
+or C<PERL_MAGIC_uvar> magic, it is important for extensions to take
+extra care to avoid conflict. Typically only using the magic on
+objects blessed into the same class as the extension is sufficient.
+For C<PERL_MAGIC_ext> magic, it may also be appropriate to add an I32
+'signature' at the top of the private data area and check that.
+
+Also note that the C<sv_set*()> and C<sv_cat*()> functions described
+earlier do B<not> invoke 'set' magic on their targets. This must
+be done by the user either by calling the C<SvSETMAGIC()> macro after
+calling these functions, or by using one of the C<sv_set*_mg()> or
+C<sv_cat*_mg()> functions. Similarly, generic C code must call the
+C<SvGETMAGIC()> macro to invoke any 'get' magic if they use an SV
+obtained from external sources in functions that don't handle magic.
+See L<perlapi> for a description of these functions.
+For example, calls to the C<sv_cat*()> functions typically need to be
+followed by C<SvSETMAGIC()>, but they don't need a prior C<SvGETMAGIC()>
+since their implementation handles 'get' magic.
=head2 Finding Magic
If the SV does not have that magical feature, C<NULL> is returned. Also,
if the SV is not of type SVt_PVMG, Perl may core dump.
- int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
+ int mg_copy(SV* sv, SV* nsv, const char* key, STRLEN klen);
This routine checks to see what types of magic C<sv> has. If the mg_type
field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
the mg_type field is changed to be the lowercase letter.
+=head2 Understanding the Magic of Tied Hashes and Arrays
+
+Tied hashes and arrays are magical beasts of the C<PERL_MAGIC_tied>
+magic type.
+
+WARNING: As of the 5.004 release, proper usage of the array and hash
+access functions requires understanding a few caveats. Some
+of these caveats are actually considered bugs in the API, to be fixed
+in later releases, and are bracketed with [MAYCHANGE] below. If
+you find yourself actually applying such information in this section, be
+aware that the behavior may change in the future, umm, without warning.
+
+The perl tie function associates a variable with an object that implements
+the various GET, SET, etc methods. To perform the equivalent of the perl
+tie function from an XSUB, you must mimic this behaviour. The code below
+carries out the necessary steps - firstly it creates a new hash, and then
+creates a second hash which it blesses into the class which will implement
+the tie methods. Lastly it ties the two hashes together, and returns a
+reference to the new tied hash. Note that the code below does NOT call the
+TIEHASH method in the MyTie class -
+see L<Calling Perl Routines from within C Programs> for details on how
+to do this.
+
+ SV*
+ mytie()
+ PREINIT:
+ HV *hash;
+ HV *stash;
+ SV *tie;
+ CODE:
+ hash = newHV();
+ tie = newRV_noinc((SV*)newHV());
+ stash = gv_stashpv("MyTie", GV_ADD);
+ sv_bless(tie, stash);
+ hv_magic(hash, (GV*)tie, PERL_MAGIC_tied);
+ RETVAL = newRV_noinc(hash);
+ OUTPUT:
+ RETVAL
+
+The C<av_store> function, when given a tied array argument, merely
+copies the magic of the array onto the value to be "stored", using
+C<mg_copy>. It may also return NULL, indicating that the value did not
+actually need to be stored in the array. [MAYCHANGE] After a call to
+C<av_store> on a tied array, the caller will usually need to call
+C<mg_set(val)> to actually invoke the perl level "STORE" method on the
+TIEARRAY object. If C<av_store> did return NULL, a call to
+C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
+leak. [/MAYCHANGE]
+
+The previous paragraph is applicable verbatim to tied hash access using the
+C<hv_store> and C<hv_store_ent> functions as well.
+
+C<av_fetch> and the corresponding hash functions C<hv_fetch> and
+C<hv_fetch_ent> actually return an undefined mortal value whose magic
+has been initialized using C<mg_copy>. Note the value so returned does not
+need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
+need to call C<mg_get()> on the returned value in order to actually invoke
+the perl level "FETCH" method on the underlying TIE object. Similarly,
+you may also call C<mg_set()> on the return value after possibly assigning
+a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
+method on the TIE object. [/MAYCHANGE]
+
+[MAYCHANGE]
+In other words, the array or hash fetch/store functions don't really
+fetch and store actual values in the case of tied arrays and hashes. They
+merely call C<mg_copy> to attach magic to the values that were meant to be
+"stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
+do the job of invoking the TIE methods on the underlying objects. Thus
+the magic mechanism currently implements a kind of lazy access to arrays
+and hashes.
+
+Currently (as of perl version 5.004), use of the hash and array access
+functions requires the user to be aware of whether they are operating on
+"normal" hashes and arrays, or on their tied variants. The API may be
+changed to provide more transparent access to both tied and normal data
+types in future versions.
+[/MAYCHANGE]
+
+You would do well to understand that the TIEARRAY and TIEHASH interfaces
+are mere sugar to invoke some perl method calls while using the uniform hash
+and array syntax. The use of this sugar imposes some overhead (typically
+about two to four extra opcodes per FETCH/STORE operation, in addition to
+the creation of all the mortal variables required to invoke the methods).
+This overhead will be comparatively small if the TIE methods are themselves
+substantial, but if they are only a few statements long, the overhead
+will not be insignificant.
+
+=head2 Localizing changes
+
+Perl has a very handy construction
+
+ {
+ local $var = 2;
+ ...
+ }
+
+This construction is I<approximately> equivalent to
+
+ {
+ my $oldvar = $var;
+ $var = 2;
+ ...
+ $var = $oldvar;
+ }
+
+The biggest difference is that the first construction would
+reinstate the initial value of $var, irrespective of how control exits
+the block: C<goto>, C<return>, C<die>/C<eval>, etc. It is a little bit
+more efficient as well.
+
+There is a way to achieve a similar task from C via Perl API: create a
+I<pseudo-block>, and arrange for some changes to be automatically
+undone at the end of it, either explicit, or via a non-local exit (via
+die()). A I<block>-like construct is created by a pair of
+C<ENTER>/C<LEAVE> macros (see L<perlcall/"Returning a Scalar">).
+Such a construct may be created specially for some important localized
+task, or an existing one (like boundaries of enclosing Perl
+subroutine/block, or an existing pair for freeing TMPs) may be
+used. (In the second case the overhead of additional localization must
+be almost negligible.) Note that any XSUB is automatically enclosed in
+an C<ENTER>/C<LEAVE> pair.
+
+Inside such a I<pseudo-block> the following service is available:
+
+=over 4
+
+=item C<SAVEINT(int i)>
+
+=item C<SAVEIV(IV i)>
+
+=item C<SAVEI32(I32 i)>
+
+=item C<SAVELONG(long i)>
+
+These macros arrange things to restore the value of integer variable
+C<i> at the end of enclosing I<pseudo-block>.
+
+=item C<SAVESPTR(s)>
+
+=item C<SAVEPPTR(p)>
+
+These macros arrange things to restore the value of pointers C<s> and
+C<p>. C<s> must be a pointer of a type which survives conversion to
+C<SV*> and back, C<p> should be able to survive conversion to C<char*>
+and back.
+
+=item C<SAVEFREESV(SV *sv)>
+
+The refcount of C<sv> would be decremented at the end of
+I<pseudo-block>. This is similar to C<sv_2mortal> in that it is also a
+mechanism for doing a delayed C<SvREFCNT_dec>. However, while C<sv_2mortal>
+extends the lifetime of C<sv> until the beginning of the next statement,
+C<SAVEFREESV> extends it until the end of the enclosing scope. These
+lifetimes can be wildly different.
+
+Also compare C<SAVEMORTALIZESV>.
+
+=item C<SAVEMORTALIZESV(SV *sv)>
+
+Just like C<SAVEFREESV>, but mortalizes C<sv> at the end of the current
+scope instead of decrementing its reference count. This usually has the
+effect of keeping C<sv> alive until the statement that called the currently
+live scope has finished executing.
+
+=item C<SAVEFREEOP(OP *op)>
+
+The C<OP *> is op_free()ed at the end of I<pseudo-block>.
+
+=item C<SAVEFREEPV(p)>
+
+The chunk of memory which is pointed to by C<p> is Safefree()ed at the
+end of I<pseudo-block>.
+
+=item C<SAVECLEARSV(SV *sv)>
+
+Clears a slot in the current scratchpad which corresponds to C<sv> at
+the end of I<pseudo-block>.
+
+=item C<SAVEDELETE(HV *hv, char *key, I32 length)>
+
+The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
+string pointed to by C<key> is Safefree()ed. If one has a I<key> in
+short-lived storage, the corresponding string may be reallocated like
+this:
+
+ SAVEDELETE(PL_defstash, savepv(tmpbuf), strlen(tmpbuf));
+
+=item C<SAVEDESTRUCTOR(DESTRUCTORFUNC_NOCONTEXT_t f, void *p)>
+
+At the end of I<pseudo-block> the function C<f> is called with the
+only argument C<p>.
+
+=item C<SAVEDESTRUCTOR_X(DESTRUCTORFUNC_t f, void *p)>
+
+At the end of I<pseudo-block> the function C<f> is called with the
+implicit context argument (if any), and C<p>.
+
+=item C<SAVESTACK_POS()>
+
+The current offset on the Perl internal stack (cf. C<SP>) is restored
+at the end of I<pseudo-block>.
+
+=back
+
+The following API list contains functions, thus one needs to
+provide pointers to the modifiable data explicitly (either C pointers,
+or Perlish C<GV *>s). Where the above macros take C<int>, a similar
+function takes C<int *>.
+
+=over 4
+
+=item C<SV* save_scalar(GV *gv)>
+
+Equivalent to Perl code C<local $gv>.
+
+=item C<AV* save_ary(GV *gv)>
+
+=item C<HV* save_hash(GV *gv)>
+
+Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
+
+=item C<void save_item(SV *item)>
+
+Duplicates the current value of C<SV>, on the exit from the current
+C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
+using the stored value. It doesn't handle magic. Use C<save_scalar> if
+magic is affected.
+
+=item C<void save_list(SV **sarg, I32 maxsarg)>
+
+A variant of C<save_item> which takes multiple arguments via an array
+C<sarg> of C<SV*> of length C<maxsarg>.
+
+=item C<SV* save_svref(SV **sptr)>
+
+Similar to C<save_scalar>, but will reinstate an C<SV *>.
+
+=item C<void save_aptr(AV **aptr)>
+
+=item C<void save_hptr(HV **hptr)>
+
+Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
+
+=back
+
+The C<Alias> module implements localization of the basic types within the
+I<caller's scope>. People who are interested in how to localize things in
+the containing scope should take a look there too.
+
=head1 Subroutines
=head2 XSUBs and the Argument Stack
To handle this situation, the PPCODE directive is used and the stack is
extended using the macro:
- EXTEND(sp, num);
+ EXTEND(SP, num);
-where C<sp> is the stack pointer, and C<num> is the number of elements the
-stack should be extended by.
+where C<SP> is the macro that represents the local copy of the stack pointer,
+and C<num> is the number of elements the stack should be extended by.
-Now that there is room on the stack, values can be pushed on it using the
-macros to push IVs, doubles, strings, and SV pointers respectively:
+Now that there is room on the stack, values can be pushed on it using C<PUSHs>
+macro. The pushed values will often need to be "mortal" (See
+L</Reference Counts and Mortality>):
- PUSHi(IV)
- PUSHn(double)
- PUSHp(char*, I32)
- PUSHs(SV*)
+ PUSHs(sv_2mortal(newSViv(an_integer)))
+ PUSHs(sv_2mortal(newSVuv(an_unsigned_integer)))
+ PUSHs(sv_2mortal(newSVnv(a_double)))
+ PUSHs(sv_2mortal(newSVpv("Some String",0)))
And now the Perl program calling C<tzname>, the two values will be assigned
as in:
($standard_abbrev, $summer_abbrev) = POSIX::tzname;
An alternate (and possibly simpler) method to pushing values on the stack is
-to use the macros:
+to use the macro:
- XPUSHi(IV)
- XPUSHn(double)
- XPUSHp(char*, I32)
XPUSHs(SV*)
-These macros automatically adjust the stack for you, if needed. Thus, you
+This macro automatically adjust the stack for you, if needed. Thus, you
do not need to call C<EXTEND> to extend the stack.
+Despite their suggestions in earlier versions of this document the macros
+C<(X)PUSH[iunp]> are I<not> suited to XSUBs which return multiple results.
+For that, either stick to the C<(X)PUSHs> macros shown above, or use the new
+C<m(X)PUSH[iunp]> macros instead; see L</Putting a C value on Perl stack>.
+
For more information, consult L<perlxs> and L<perlxstut>.
=head2 Calling Perl Routines from within C Programs
There are four routines that can be used to call a Perl subroutine from
within a C program. These four are:
- I32 perl_call_sv(SV*, I32);
- I32 perl_call_pv(char*, I32);
- I32 perl_call_method(char*, I32);
- I32 perl_call_argv(char*, I32, register char**);
+ I32 call_sv(SV*, I32);
+ I32 call_pv(const char*, I32);
+ I32 call_method(const char*, I32);
+ I32 call_argv(const char*, I32, register char**);
-The routine most often used is C<perl_call_sv>. The C<SV*> argument
+The routine most often used is C<call_sv>. The C<SV*> argument
contains either the name of the Perl subroutine to be called, or a
reference to the subroutine. The second argument consists of flags
that control the context in which the subroutine is called, whether
All four routines return the number of arguments that the subroutine returned
on the Perl stack.
-When using any of these routines (except C<perl_call_argv>), the programmer
+These routines used to be called C<perl_call_sv>, etc., before Perl v5.6.0,
+but those names are now deprecated; macros of the same name are provided for
+compatibility.
+
+When using any of these routines (except C<call_argv>), the programmer
must manipulate the Perl stack. These include the following macros and
functions:
dSP
+ SP
PUSHMARK()
PUTBACK
SPAGAIN
=head2 Memory Allocation
-It is suggested that you use the version of malloc that is distributed
+=head3 Allocation
+
+All memory meant to be used with the Perl API functions should be manipulated
+using the macros described in this section. The macros provide the necessary
+transparency between differences in the actual malloc implementation that is
+used within perl.
+
+It is suggested that you enable the version of malloc that is distributed
with Perl. It keeps pools of various sizes of unallocated memory in
order to satisfy allocation requests more quickly. However, on some
platforms, it may cause spurious malloc or free errors.
- New(x, pointer, number, type);
- Newc(x, pointer, number, type, cast);
- Newz(x, pointer, number, type);
+The following three macros are used to initially allocate memory :
-These three macros are used to initially allocate memory.
+ Newx(pointer, number, type);
+ Newxc(pointer, number, type, cast);
+ Newxz(pointer, number, type);
-The first argument C<x> was a "magic cookie" that was used to keep track
-of who called the macro, to help when debugging memory problems. However,
-the current code makes no use of this feature (most Perl developers now
-use run-time memory checkers), so this argument can be any number.
-
-The second argument C<pointer> should be the name of a variable that will
+The first argument C<pointer> should be the name of a variable that will
point to the newly allocated memory.
-The third and fourth arguments C<number> and C<type> specify how many of
+The second and third arguments C<number> and C<type> specify how many of
the specified type of data structure should be allocated. The argument
-C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
+C<type> is passed to C<sizeof>. The final argument to C<Newxc>, C<cast>,
should be used if the C<pointer> argument is different from the C<type>
argument.
-Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
+Unlike the C<Newx> and C<Newxc> macros, the C<Newxz> macro calls C<memzero>
to zero out all the newly allocated memory.
+=head3 Reallocation
+
Renew(pointer, number, type);
Renewc(pointer, number, type, cast);
Safefree(pointer)
match those of C<New> and C<Newc> with the exception of not needing the
"magic cookie" argument.
+=head3 Moving
+
Move(source, dest, number, type);
Copy(source, dest, number, type);
Zero(dest, number, type);
The macro to put this target on stack is C<PUSHTARG>, and it is
directly used in some opcodes, as well as indirectly in zillions of
-others, which use it via C<(X)PUSH[pni]>.
+others, which use it via C<(X)PUSH[iunp]>.
+
+Because the target is reused, you must be careful when pushing multiple
+values on the stack. The following code will not do what you think:
+
+ XPUSHi(10);
+ XPUSHi(20);
+
+This translates as "set C<TARG> to 10, push a pointer to C<TARG> onto
+the stack; set C<TARG> to 20, push a pointer to C<TARG> onto the stack".
+At the end of the operation, the stack does not contain the values 10
+and 20, but actually contains two pointers to C<TARG>, which we have set
+to 20.
+
+If you need to push multiple different values then you should either use
+the C<(X)PUSHs> macros, or else use the new C<m(X)PUSH[iunp]> macros,
+none of which make use of C<TARG>. The C<(X)PUSHs> macros simply push an
+SV* on the stack, which, as noted under L</XSUBs and the Argument Stack>,
+will often need to be "mortal". The new C<m(X)PUSH[iunp]> macros make
+this a little easier to achieve by creating a new mortal for you (via
+C<(X)PUSHmortal>), pushing that onto the stack (extending it if necessary
+in the case of the C<mXPUSH[iunp]> macros), and then setting its value.
+Thus, instead of writing this to "fix" the example above:
+
+ XPUSHs(sv_2mortal(newSViv(10)))
+ XPUSHs(sv_2mortal(newSViv(20)))
+
+you can simply write:
+
+ mXPUSHi(10)
+ mXPUSHi(20)
+
+On a related note, if you do use C<(X)PUSH[iunp]>, then you're going to
+need a C<dTARG> in your variable declarations so that the C<*PUSH*>
+macros can make use of the local variable C<TARG>. See also C<dTARGET>
+and C<dXSTARG>.
=head2 Scratchpads
(initially) one element, and this element is the scratchpad AV. Why do
we need an extra level of indirection?
-The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
+The answer is B<recursion>, and maybe B<threads>. Both
these can create several execution pointers going into the same
subroutine. For the subroutine-child not write over the temporaries
for the subroutine-parent (lifespan of which covers the call to the
/ \
$b $c
-(but slightly more complicated). This tree reflect the way Perl
+(but slightly more complicated). This tree reflects the way Perl
parsed your code, but has nothing to do with the execution order.
There is an additional "thread" going through the nodes of the tree
which shows the order of execution of the nodes. In our simplified
=head2 Examining the tree
-If you have your perl compiled for debugging (usually done with C<-D
-optimize=-g> on C<Configure> command line), you may examine the
+If you have your perl compiled for debugging (usually done with
+C<-DDEBUGGING> on the C<Configure> command line), you may examine the
compiled tree by specifying C<-Dx> on the Perl command line. The
output takes several lines per node, and for C<$b+$c> it looks like
this:
4 5 6> (node C<6> is not included into above listing), i.e.,
C<gvsv gvsv add whatever>.
+Each of these nodes represents an op, a fundamental operation inside the
+Perl core. The code which implements each operation can be found in the
+F<pp*.c> files; the function which implements the op with type C<gvsv>
+is C<pp_gvsv>, and so on. As the tree above shows, different ops have
+different numbers of children: C<add> is a binary operator, as one would
+expect, and so has two children. To accommodate the various different
+numbers of children, there are various types of op data structure, and
+they link together in different ways.
+
+The simplest type of op structure is C<OP>: this has no children. Unary
+operators, C<UNOP>s, have one child, and this is pointed to by the
+C<op_first> field. Binary operators (C<BINOP>s) have not only an
+C<op_first> field but also an C<op_last> field. The most complex type of
+op is a C<LISTOP>, which has any number of children. In this case, the
+first child is pointed to by C<op_first> and the last child by
+C<op_last>. The children in between can be found by iteratively
+following the C<op_sibling> pointer from the first child to the last.
+
+There are also two other op types: a C<PMOP> holds a regular expression,
+and has no children, and a C<LOOP> may or may not have children. If the
+C<op_children> field is non-zero, it behaves like a C<LISTOP>. To
+complicate matters, if a C<UNOP> is actually a C<null> op after
+optimization (see L</Compile pass 2: context propagation>) it will still
+have children in accordance with its former type.
+
+Another way to examine the tree is to use a compiler back-end module, such
+as L<B::Concise>.
+
=head2 Compile pass 1: check routines
-The tree is created by the I<pseudo-compiler> while yacc code feeds it
-the constructions it recognizes. Since yacc works bottom-up, so does
+The tree is created by the compiler while I<yacc> code feeds it
+the constructions it recognizes. Since I<yacc> works bottom-up, so does
the first pass of perl compilation.
What makes this pass interesting for perl developers is that some
optimization may be performed on this pass. This is optimization by
-so-called I<check routines>. The correspondence between node names
+so-called "check routines". The correspondence between node names
and corresponding check routines is described in F<opcode.pl> (do not
forget to run C<make regen_headers> if you modify this file).
A check routine is called when the node is fully constructed except
-for the execution-order thread. Since at this time there is no
+for the execution-order thread. Since at this time there are no
back-links to the currently constructed node, one can do most any
operation to the top-level node, including freeing it and/or creating
new nodes above/below it.
=head2 Compile pass 2: context propagation
When a context for a part of compile tree is known, it is propagated
-down through the tree. Aat this time the context can have 5 values
+down through the tree. At this time the context can have 5 values
(instead of 2 for runtime context): void, boolean, scalar, list, and
lvalue. In contrast with the pass 1 this pass is processed from top
to bottom: a node's context determines the context for its children.
After the compile tree for a subroutine (or for an C<eval> or a file)
is created, an additional pass over the code is performed. This pass
is neither top-down or bottom-up, but in the execution order (with
-additional compilications for conditionals). These optimizations are
+additional complications for conditionals). These optimizations are
done in the subroutine peep(). Optimizations performed at this stage
are subject to the same restrictions as in the pass 2.
-=head1 API LISTING
-
-This is a listing of functions, macros, flags, and variables that may be
-useful to extension writers or that may be found while reading other
-extensions.
-
-=over 8
-
-=item AvFILL
-
-See C<av_len>.
-
-=item av_clear
-
-Clears an array, making it empty.
-
- void av_clear _((AV* ar));
-
-=item av_extend
-
-Pre-extend an array. The C<key> is the index to which the array should be
-extended.
-
- void av_extend _((AV* ar, I32 key));
-
-=item av_fetch
-
-Returns the SV at the specified index in the array. The C<key> is the
-index. If C<lval> is set then the fetch will be part of a store. Check
-that the return value is non-null before dereferencing it to a C<SV*>.
-
- SV** av_fetch _((AV* ar, I32 key, I32 lval));
-
-=item av_len
-
-Returns the highest index in the array. Returns -1 if the array is empty.
-
- I32 av_len _((AV* ar));
-
-=item av_make
-
-Creates a new AV and populates it with a list of SVs. The SVs are copied
-into the array, so they may be freed after the call to av_make. The new AV
-will have a reference count of 1.
-
- AV* av_make _((I32 size, SV** svp));
-
-=item av_pop
-
-Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
-empty.
-
- SV* av_pop _((AV* ar));
-
-=item av_push
-
-Pushes an SV onto the end of the array. The array will grow automatically
-to accommodate the addition.
-
- void av_push _((AV* ar, SV* val));
-
-=item av_shift
-
-Shifts an SV off the beginning of the array.
-
- SV* av_shift _((AV* ar));
-
-=item av_store
-
-Stores an SV in an array. The array index is specified as C<key>. The
-return value will be null if the operation failed, otherwise it can be
-dereferenced to get the original C<SV*>.
-
- SV** av_store _((AV* ar, I32 key, SV* val));
-
-=item av_undef
-
-Undefines the array.
-
- void av_undef _((AV* ar));
-
-=item av_unshift
-
-Unshift an SV onto the beginning of the array. The array will grow
-automatically to accommodate the addition.
-
- void av_unshift _((AV* ar, I32 num));
-
-=item CLASS
-
-Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
-constructor. This is always a C<char*>. See C<THIS> and
-L<perlxs/"Using XS With C++">.
-
-=item Copy
-
-The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
-source, C<d> is the destination, C<n> is the number of items, and C<t> is
-the type.
-
- (void) Copy( s, d, n, t );
-
-=item croak
-
-This is the XSUB-writer's interface to Perl's C<die> function. Use this
-function the same way you use the C C<printf> function. See C<warn>.
-
-=item CvSTASH
-
-Returns the stash of the CV.
-
- HV * CvSTASH( SV* sv )
-
-=item DBsingle
-
-When Perl is run in debugging mode, with the B<-d> switch, this SV is a
-boolean which indicates whether subs are being single-stepped.
-Single-stepping is automatically turned on after every step. This is the C
-variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
-
-=item DBsub
-
-When Perl is run in debugging mode, with the B<-d> switch, this GV contains
-the SV which holds the name of the sub being debugged. This is the C
-variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
-The sub name can be found by
-
- SvPV( GvSV( DBsub ), na )
-
-=item DBtrace
-
-Trace variable used when Perl is run in debugging mode, with the B<-d>
-switch. This is the C variable which corresponds to Perl's $DB::trace
-variable. See C<DBsingle>.
-
-=item dMARK
-
-Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
-C<dORIGMARK>.
-
-=item dORIGMARK
-
-Saves the original stack mark for the XSUB. See C<ORIGMARK>.
-
-=item dowarn
-
-The C variable which corresponds to Perl's $^W warning variable.
+=head2 Pluggable runops
-=item dSP
+The compile tree is executed in a runops function. There are two runops
+functions, in F<run.c> and in F<dump.c>. C<Perl_runops_debug> is used
+with DEBUGGING and C<Perl_runops_standard> is used otherwise. For fine
+control over the execution of the compile tree it is possible to provide
+your own runops function.
-Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
+It's probably best to copy one of the existing runops functions and
+change it to suit your needs. Then, in the BOOT section of your XS
+file, add the line:
-=item dXSARGS
+ PL_runops = my_runops;
-Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
-usually handled automatically by C<xsubpp>. Declares the C<items> variable
-to indicate the number of items on the stack.
+This function should be as efficient as possible to keep your programs
+running as fast as possible.
-=item dXSI32
+=head1 Examining internal data structures with the C<dump> functions
+
+To aid debugging, the source file F<dump.c> contains a number of
+functions which produce formatted output of internal data structures.
-Sets up the C<ix> variable for an XSUB which has aliases. This is usually
-handled automatically by C<xsubpp>.
+The most commonly used of these functions is C<Perl_sv_dump>; it's used
+for dumping SVs, AVs, HVs, and CVs. The C<Devel::Peek> module calls
+C<sv_dump> to produce debugging output from Perl-space, so users of that
+module should already be familiar with its format.
-=item dXSI32
+C<Perl_op_dump> can be used to dump an C<OP> structure or any of its
+derivatives, and produces output similar to C<perl -Dx>; in fact,
+C<Perl_dump_eval> will dump the main root of the code being evaluated,
+exactly like C<-Dx>.
-Sets up the C<ix> variable for an XSUB which has aliases. This is usually
-handled automatically by C<xsubpp>.
+Other useful functions are C<Perl_dump_sub>, which turns a C<GV> into an
+op tree, C<Perl_dump_packsubs> which calls C<Perl_dump_sub> on all the
+subroutines in a package like so: (Thankfully, these are all xsubs, so
+there is no op tree)
-=item ENTER
+ (gdb) print Perl_dump_packsubs(PL_defstash)
+
+ SUB attributes::bootstrap = (xsub 0x811fedc 0)
-Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
+ SUB UNIVERSAL::can = (xsub 0x811f50c 0)
+
+ SUB UNIVERSAL::isa = (xsub 0x811f304 0)
+
+ SUB UNIVERSAL::VERSION = (xsub 0x811f7ac 0)
+
+ SUB DynaLoader::boot_DynaLoader = (xsub 0x805b188 0)
+
+and C<Perl_dump_all>, which dumps all the subroutines in the stash and
+the op tree of the main root.
+
+=head1 How multiple interpreters and concurrency are supported
+
+=head2 Background and PERL_IMPLICIT_CONTEXT
+
+The Perl interpreter can be regarded as a closed box: it has an API
+for feeding it code or otherwise making it do things, but it also has
+functions for its own use. This smells a lot like an object, and
+there are ways for you to build Perl so that you can have multiple
+interpreters, with one interpreter represented either as a C structure,
+or inside a thread-specific structure. These structures contain all
+the context, the state of that interpreter.
+
+One macro controls the major Perl build flavor: MULTIPLICITY. The
+MULTIPLICITY build has a C structure that packages all the interpreter
+state. With multiplicity-enabled perls, PERL_IMPLICIT_CONTEXT is also
+normally defined, and enables the support for passing in a "hidden" first
+argument that represents all three data structures. MULTIPLICITY makes
+mutli-threaded perls possible (with the ithreads threading model, related
+to the macro USE_ITHREADS.)
+
+Two other "encapsulation" macros are the PERL_GLOBAL_STRUCT and
+PERL_GLOBAL_STRUCT_PRIVATE (the latter turns on the former, and the
+former turns on MULTIPLICITY.) The PERL_GLOBAL_STRUCT causes all the
+internal variables of Perl to be wrapped inside a single global struct,
+struct perl_vars, accessible as (globals) &PL_Vars or PL_VarsPtr or
+the function Perl_GetVars(). The PERL_GLOBAL_STRUCT_PRIVATE goes
+one step further, there is still a single struct (allocated in main()
+either from heap or from stack) but there are no global data symbols
+pointing to it. In either case the global struct should be initialised
+as the very first thing in main() using Perl_init_global_struct() and
+correspondingly tear it down after perl_free() using Perl_free_global_struct(),
+please see F<miniperlmain.c> for usage details. You may also need
+to use C<dVAR> in your coding to "declare the global variables"
+when you are using them. dTHX does this for you automatically.
+
+To see whether you have non-const data you can use a BSD-compatible C<nm>:
+
+ nm libperl.a | grep -v ' [TURtr] '
+
+If this displays any C<D> or C<d> symbols, you have non-const data.
+
+For backward compatibility reasons defining just PERL_GLOBAL_STRUCT
+doesn't actually hide all symbols inside a big global struct: some
+PerlIO_xxx vtables are left visible. The PERL_GLOBAL_STRUCT_PRIVATE
+then hides everything (see how the PERLIO_FUNCS_DECL is used).
+
+All this obviously requires a way for the Perl internal functions to be
+either subroutines taking some kind of structure as the first
+argument, or subroutines taking nothing as the first argument. To
+enable these two very different ways of building the interpreter,
+the Perl source (as it does in so many other situations) makes heavy
+use of macros and subroutine naming conventions.
+
+First problem: deciding which functions will be public API functions and
+which will be private. All functions whose names begin C<S_> are private
+(think "S" for "secret" or "static"). All other functions begin with
+"Perl_", but just because a function begins with "Perl_" does not mean it is
+part of the API. (See L</Internal Functions>.) The easiest way to be B<sure> a
+function is part of the API is to find its entry in L<perlapi>.
+If it exists in L<perlapi>, it's part of the API. If it doesn't, and you
+think it should be (i.e., you need it for your extension), send mail via
+L<perlbug> explaining why you think it should be.
+
+Second problem: there must be a syntax so that the same subroutine
+declarations and calls can pass a structure as their first argument,
+or pass nothing. To solve this, the subroutines are named and
+declared in a particular way. Here's a typical start of a static
+function used within the Perl guts:
+
+ STATIC void
+ S_incline(pTHX_ char *s)
+
+STATIC becomes "static" in C, and may be #define'd to nothing in some
+configurations in future.
+
+A public function (i.e. part of the internal API, but not necessarily
+sanctioned for use in extensions) begins like this:
+
+ void
+ Perl_sv_setiv(pTHX_ SV* dsv, IV num)
+
+C<pTHX_> is one of a number of macros (in perl.h) that hide the
+details of the interpreter's context. THX stands for "thread", "this",
+or "thingy", as the case may be. (And no, George Lucas is not involved. :-)
+The first character could be 'p' for a B<p>rototype, 'a' for B<a>rgument,
+or 'd' for B<d>eclaration, so we have C<pTHX>, C<aTHX> and C<dTHX>, and
+their variants.
+
+When Perl is built without options that set PERL_IMPLICIT_CONTEXT, there is no
+first argument containing the interpreter's context. The trailing underscore
+in the pTHX_ macro indicates that the macro expansion needs a comma
+after the context argument because other arguments follow it. If
+PERL_IMPLICIT_CONTEXT is not defined, pTHX_ will be ignored, and the
+subroutine is not prototyped to take the extra argument. The form of the
+macro without the trailing underscore is used when there are no additional
+explicit arguments.
+
+When a core function calls another, it must pass the context. This
+is normally hidden via macros. Consider C<sv_setiv>. It expands into
+something like this:
+
+ #ifdef PERL_IMPLICIT_CONTEXT
+ #define sv_setiv(a,b) Perl_sv_setiv(aTHX_ a, b)
+ /* can't do this for vararg functions, see below */
+ #else
+ #define sv_setiv Perl_sv_setiv
+ #endif
+
+This works well, and means that XS authors can gleefully write:
+
+ sv_setiv(foo, bar);
+
+and still have it work under all the modes Perl could have been
+compiled with.
+
+This doesn't work so cleanly for varargs functions, though, as macros
+imply that the number of arguments is known in advance. Instead we
+either need to spell them out fully, passing C<aTHX_> as the first
+argument (the Perl core tends to do this with functions like
+Perl_warner), or use a context-free version.
+
+The context-free version of Perl_warner is called
+Perl_warner_nocontext, and does not take the extra argument. Instead
+it does dTHX; to get the context from thread-local storage. We
+C<#define warner Perl_warner_nocontext> so that extensions get source
+compatibility at the expense of performance. (Passing an arg is
+cheaper than grabbing it from thread-local storage.)
+
+You can ignore [pad]THXx when browsing the Perl headers/sources.
+Those are strictly for use within the core. Extensions and embedders
+need only be aware of [pad]THX.
- ENTER;
+=head2 So what happened to dTHR?
-=item EXTEND
+C<dTHR> was introduced in perl 5.005 to support the older thread model.
+The older thread model now uses the C<THX> mechanism to pass context
+pointers around, so C<dTHR> is not useful any more. Perl 5.6.0 and
+later still have it for backward source compatibility, but it is defined
+to be a no-op.
+
+=head2 How do I use all this in extensions?
+
+When Perl is built with PERL_IMPLICIT_CONTEXT, extensions that call
+any functions in the Perl API will need to pass the initial context
+argument somehow. The kicker is that you will need to write it in
+such a way that the extension still compiles when Perl hasn't been
+built with PERL_IMPLICIT_CONTEXT enabled.
+
+There are three ways to do this. First, the easy but inefficient way,
+which is also the default, in order to maintain source compatibility
+with extensions: whenever XSUB.h is #included, it redefines the aTHX
+and aTHX_ macros to call a function that will return the context.
+Thus, something like:
+
+ sv_setiv(sv, num);
+
+in your extension will translate to this when PERL_IMPLICIT_CONTEXT is
+in effect:
+
+ Perl_sv_setiv(Perl_get_context(), sv, num);
-Used to extend the argument stack for an XSUB's return values.
+or to this otherwise:
- EXTEND( sp, int x );
+ Perl_sv_setiv(sv, num);
+
+You have to do nothing new in your extension to get this; since
+the Perl library provides Perl_get_context(), it will all just
+work.
-=item FREETMPS
+The second, more efficient way is to use the following template for
+your Foo.xs:
-Closing bracket for temporaries on a callback. See C<SAVETMPS> and
-L<perlcall>.
+ #define PERL_NO_GET_CONTEXT /* we want efficiency */
+ #include "EXTERN.h"
+ #include "perl.h"
+ #include "XSUB.h"
- FREETMPS;
+ STATIC void my_private_function(int arg1, int arg2);
+
+ STATIC void
+ my_private_function(int arg1, int arg2)
+ {
+ dTHX; /* fetch context */
+ ... call many Perl API functions ...
+ }
+
+ [... etc ...]
+
+ MODULE = Foo PACKAGE = Foo
+
+ /* typical XSUB */
+
+ void
+ my_xsub(arg)
+ int arg
+ CODE:
+ my_private_function(arg, 10);
-=item G_ARRAY
+Note that the only two changes from the normal way of writing an
+extension is the addition of a C<#define PERL_NO_GET_CONTEXT> before
+including the Perl headers, followed by a C<dTHX;> declaration at
+the start of every function that will call the Perl API. (You'll
+know which functions need this, because the C compiler will complain
+that there's an undeclared identifier in those functions.) No changes
+are needed for the XSUBs themselves, because the XS() macro is
+correctly defined to pass in the implicit context if needed.
-Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
+The third, even more efficient way is to ape how it is done within
+the Perl guts:
+
+
+ #define PERL_NO_GET_CONTEXT /* we want efficiency */
+ #include "EXTERN.h"
+ #include "perl.h"
+ #include "XSUB.h"
+
+ /* pTHX_ only needed for functions that call Perl API */
+ STATIC void my_private_function(pTHX_ int arg1, int arg2);
+
+ STATIC void
+ my_private_function(pTHX_ int arg1, int arg2)
+ {
+ /* dTHX; not needed here, because THX is an argument */
+ ... call Perl API functions ...
+ }
-=item G_DISCARD
+ [... etc ...]
-Indicates that arguments returned from a callback should be discarded. See
-L<perlcall>.
+ MODULE = Foo PACKAGE = Foo
-=item G_EVAL
+ /* typical XSUB */
-Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
+ void
+ my_xsub(arg)
+ int arg
+ CODE:
+ my_private_function(aTHX_ arg, 10);
-=item GIMME
+This implementation never has to fetch the context using a function
+call, since it is always passed as an extra argument. Depending on
+your needs for simplicity or efficiency, you may mix the previous
+two approaches freely.
-A backward-compatible version of C<GIMME_V> which can only return
-C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
+Never add a comma after C<pTHX> yourself--always use the form of the
+macro with the underscore for functions that take explicit arguments,
+or the form without the argument for functions with no explicit arguments.
-=item GIMME_V
+If one is compiling Perl with the C<-DPERL_GLOBAL_STRUCT> the C<dVAR>
+definition is needed if the Perl global variables (see F<perlvars.h>
+or F<globvar.sym>) are accessed in the function and C<dTHX> is not
+used (the C<dTHX> includes the C<dVAR> if necessary). One notices
+the need for C<dVAR> only with the said compile-time define, because
+otherwise the Perl global variables are visible as-is.
-The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
-C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
-context, respectively.
+=head2 Should I do anything special if I call perl from multiple threads?
-=item G_NOARGS
+If you create interpreters in one thread and then proceed to call them in
+another, you need to make sure perl's own Thread Local Storage (TLS) slot is
+initialized correctly in each of those threads.
-Indicates that no arguments are being sent to a callback. See L<perlcall>.
+The C<perl_alloc> and C<perl_clone> API functions will automatically set
+the TLS slot to the interpreter they created, so that there is no need to do
+anything special if the interpreter is always accessed in the same thread that
+created it, and that thread did not create or call any other interpreters
+afterwards. If that is not the case, you have to set the TLS slot of the
+thread before calling any functions in the Perl API on that particular
+interpreter. This is done by calling the C<PERL_SET_CONTEXT> macro in that
+thread as the first thing you do:
-=item G_SCALAR
+ /* do this before doing anything else with some_perl */
+ PERL_SET_CONTEXT(some_perl);
-Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
+ ... other Perl API calls on some_perl go here ...
-=item G_VOID
+=head2 Future Plans and PERL_IMPLICIT_SYS
-Used to indicate void context. See C<GIMME_V> and L<perlcall>.
+Just as PERL_IMPLICIT_CONTEXT provides a way to bundle up everything
+that the interpreter knows about itself and pass it around, so too are
+there plans to allow the interpreter to bundle up everything it knows
+about the environment it's running on. This is enabled with the
+PERL_IMPLICIT_SYS macro. Currently it only works with USE_ITHREADS on
+Windows.
-=item gv_fetchmeth
+This allows the ability to provide an extra pointer (called the "host"
+environment) for all the system calls. This makes it possible for
+all the system stuff to maintain their own state, broken down into
+seven C structures. These are thin wrappers around the usual system
+calls (see win32/perllib.c) for the default perl executable, but for a
+more ambitious host (like the one that would do fork() emulation) all
+the extra work needed to pretend that different interpreters are
+actually different "processes", would be done here.
-Returns the glob with the given C<name> and a defined subroutine or
-C<NULL>. The glob lives in the given C<stash>, or in the stashes
-accessable via @ISA and @<UNIVERSAL>.
+The Perl engine/interpreter and the host are orthogonal entities.
+There could be one or more interpreters in a process, and one or
+more "hosts", with free association between them.
-The argument C<level> should be either 0 or -1. If C<level==0>, as a
-side-effect creates a glob with the given C<name> in the given
-C<stash> which in the case of success contains an alias for the
-subroutine, and sets up caching info for this glob. Similarly for all
-the searched stashes.
+=head1 Internal Functions
-This function grants C<"SUPER"> token as a postfix of the stash name.
+All of Perl's internal functions which will be exposed to the outside
+world are prefixed by C<Perl_> so that they will not conflict with XS
+functions or functions used in a program in which Perl is embedded.
+Similarly, all global variables begin with C<PL_>. (By convention,
+static functions start with C<S_>.)
-The GV returned from C<gv_fetchmeth> may be a method cache entry,
-which is not visible to Perl code. So when calling C<perl_call_sv>,
-you should not use the GV directly; instead, you should use the
-method's CV, which can be obtained from the GV with the C<GvCV> macro.
+Inside the Perl core, you can get at the functions either with or
+without the C<Perl_> prefix, thanks to a bunch of defines that live in
+F<embed.h>. This header file is generated automatically from
+F<embed.pl> and F<embed.fnc>. F<embed.pl> also creates the prototyping
+header files for the internal functions, generates the documentation
+and a lot of other bits and pieces. It's important that when you add
+a new function to the core or change an existing one, you change the
+data in the table in F<embed.fnc> as well. Here's a sample entry from
+that table:
- GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
+ Apd |SV** |av_fetch |AV* ar|I32 key|I32 lval
-=item gv_fetchmethod
+The second column is the return type, the third column the name. Columns
+after that are the arguments. The first column is a set of flags:
-=item gv_fetchmethod_autoload
+=over 3
-Returns the glob which contains the subroutine to call to invoke the
-method on the C<stash>. In fact in the presense of autoloading this may
-be the glob for "AUTOLOAD". In this case the corresponding variable
-$AUTOLOAD is already setup.
+=item A
-The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
-lookup is performed if the given method is not present: non-zero means
-yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
-C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
-non-zero C<autoload> parameter.
+This function is a part of the public API. All such functions should also
+have 'd', very few do not.
-These functions grant C<"SUPER"> token as a prefix of the method name.
+=item p
-Note that if you want to keep the returned glob for a long time, you
-need to check for it being "AUTOLOAD", since at the later time the call
-may load a different subroutine due to $AUTOLOAD changing its value.
-Use the glob created via a side effect to do this.
+This function has a C<Perl_> prefix; i.e. it is defined as
+C<Perl_av_fetch>.
-These functions have the same side-effects and as C<gv_fetchmeth> with
-C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
-The warning against passing the GV returned by C<gv_fetchmeth> to
-C<perl_call_sv> apply equally to these functions.
+=item d
+
+This function has documentation using the C<apidoc> feature which we'll
+look at in a second. Some functions have 'd' but not 'A'; docs are good.
- GV* gv_fetchmethod _((HV* stash, char* name));
- GV* gv_fetchmethod_autoload _((HV* stash, char* name,
- I32 autoload));
-
-=item gv_stashpv
-
-Returns a pointer to the stash for a specified package. If C<create> is set
-then the package will be created if it does not already exist. If C<create>
-is not set and the package does not exist then NULL is returned.
-
- HV* gv_stashpv _((char* name, I32 create));
-
-=item gv_stashsv
-
-Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
-
- HV* gv_stashsv _((SV* sv, I32 create));
-
-=item GvSV
-
-Return the SV from the GV.
-
-=item HEf_SVKEY
-
-This flag, used in the length slot of hash entries and magic
-structures, specifies the structure contains a C<SV*> pointer where a
-C<char*> pointer is to be expected. (For information only--not to be used).
-
-=item HeHASH
-
-Returns the computed hash (type C<U32>) stored in the hash entry.
-
- HeHASH(HE* he)
-
-=item HeKEY
-
-Returns the actual pointer stored in the key slot of the hash entry.
-The pointer may be either C<char*> or C<SV*>, depending on the value of
-C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
-are usually preferable for finding the value of a key.
-
- HeKEY(HE* he)
-
-=item HeKLEN
-
-If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
-holds an C<SV*> key. Otherwise, holds the actual length of the key.
-Can be assigned to. The C<HePV()> macro is usually preferable for finding
-key lengths.
-
- HeKLEN(HE* he)
-
-=item HePV
-
-Returns the key slot of the hash entry as a C<char*> value, doing any
-necessary dereferencing of possibly C<SV*> keys. The length of
-the string is placed in C<len> (this is a macro, so do I<not> use
-C<&len>). If you do not care about what the length of the key is,
-you may use the global variable C<na>. Remember though, that hash
-keys in perl are free to contain embedded nulls, so using C<strlen()>
-or similar is not a good way to find the length of hash keys.
-This is very similar to the C<SvPV()> macro described elsewhere in
-this document.
-
- HePV(HE* he, STRLEN len)
-
-=item HeSVKEY
-
-Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
-does not contain an C<SV*> key.
-
- HeSVKEY(HE* he)
-
-=item HeSVKEY_force
-
-Returns the key as an C<SV*>. Will create and return a temporary
-mortal C<SV*> if the hash entry contains only a C<char*> key.
-
- HeSVKEY_force(HE* he)
-
-=item HeSVKEY_set
-
-Sets the key to a given C<SV*>, taking care to set the appropriate flags
-to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
-
- HeSVKEY_set(HE* he, SV* sv)
-
-=item HeVAL
-
-Returns the value slot (type C<SV*>) stored in the hash entry.
-
- HeVAL(HE* he)
-
-=item hv_clear
-
-Clears a hash, making it empty.
-
- void hv_clear _((HV* tb));
-
-=item hv_delayfree_ent
-
-Releases a hash entry, such as while iterating though the hash, but
-delays actual freeing of key and value until the end of the current
-statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>
-and C<hv_free_ent>.
-
- void hv_delayfree_ent _((HV* hv, HE* entry));
-
-=item hv_delete
-
-Deletes a key/value pair in the hash. The value SV is removed from the hash
-and returned to the caller. The C<klen> is the length of the key. The
-C<flags> value will normally be zero; if set to G_DISCARD then null will be
-returned.
-
- SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
-
-=item hv_delete_ent
-
-Deletes a key/value pair in the hash. The value SV is removed from the hash
-and returned to the caller. The C<flags> value will normally be zero; if set
-to G_DISCARD then null will be returned. C<hash> can be a valid precomputed
-hash value, or 0 to ask for it to be computed.
-
- SV* hv_delete_ent _((HV* tb, SV* key, I32 flags, U32 hash));
-
-=item hv_exists
-
-Returns a boolean indicating whether the specified hash key exists. The
-C<klen> is the length of the key.
-
- bool hv_exists _((HV* tb, char* key, U32 klen));
-
-=item hv_exists_ent
-
-Returns a boolean indicating whether the specified hash key exists. C<hash>
-can be a valid precomputed hash value, or 0 to ask for it to be computed.
-
- bool hv_exists_ent _((HV* tb, SV* key, U32 hash));
-
-=item hv_fetch
-
-Returns the SV which corresponds to the specified key in the hash. The
-C<klen> is the length of the key. If C<lval> is set then the fetch will be
-part of a store. Check that the return value is non-null before
-dereferencing it to a C<SV*>.
-
- SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
-
-=item hv_fetch_ent
-
-Returns the hash entry which corresponds to the specified key in the hash.
-C<hash> must be a valid precomputed hash number for the given C<key>, or
-0 if you want the function to compute it. IF C<lval> is set then the
-fetch will be part of a store. Make sure the return value is non-null
-before accessing it. The return value when C<tb> is a tied hash
-is a pointer to a static location, so be sure to make a copy of the
-structure if you need to store it somewhere.
-
- HE* hv_fetch_ent _((HV* tb, SV* key, I32 lval, U32 hash));
-
-=item hv_free_ent
-
-Releases a hash entry, such as while iterating though the hash. See
-C<hv_iternext> and C<hv_delayfree_ent>.
-
- void hv_free_ent _((HV* hv, HE* entry));
+=back
-=item hv_iterinit
+Other available flags are:
-Prepares a starting point to traverse a hash table.
+=over 3
- I32 hv_iterinit _((HV* tb));
+=item s
-=item hv_iterkey
+This is a static function and is defined as C<STATIC S_whatever>, and
+usually called within the sources as C<whatever(...)>.
-Returns the key from the current position of the hash iterator. See
-C<hv_iterinit>.
+=item n
- char* hv_iterkey _((HE* entry, I32* retlen));
+This does not need a interpreter context, so the definition has no
+C<pTHX>, and it follows that callers don't use C<aTHX>. (See
+L<perlguts/Background and PERL_IMPLICIT_CONTEXT>.)
-=item hv_iterkeysv
+=item r
-Returns the key as an C<SV*> from the current position of the hash
-iterator. The return value will always be a mortal copy of the
-key. Also see C<hv_iterinit>.
+This function never returns; C<croak>, C<exit> and friends.
- SV* hv_iterkeysv _((HE* entry));
+=item f
-=item hv_iternext
+This function takes a variable number of arguments, C<printf> style.
+The argument list should end with C<...>, like this:
-Returns entries from a hash iterator. See C<hv_iterinit>.
+ Afprd |void |croak |const char* pat|...
- HE* hv_iternext _((HV* tb));
+=item M
-=item hv_iternextsv
+This function is part of the experimental development API, and may change
+or disappear without notice.
-Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
-operation.
+=item o
- SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
+This function should not have a compatibility macro to define, say,
+C<Perl_parse> to C<parse>. It must be called as C<Perl_parse>.
-=item hv_iterval
+=item x
-Returns the value from the current position of the hash iterator. See
-C<hv_iterkey>.
+This function isn't exported out of the Perl core.
- SV* hv_iterval _((HV* tb, HE* entry));
+=item m
-=item hv_magic
+This is implemented as a macro.
-Adds magic to a hash. See C<sv_magic>.
+=item X
- void hv_magic _((HV* hv, GV* gv, int how));
+This function is explicitly exported.
-=item HvNAME
+=item E
-Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
+This function is visible to extensions included in the Perl core.
- char *HvNAME (HV* stash)
+=item b
-=item hv_store
+Binary backward compatibility; this function is a macro but also has
+a C<Perl_> implementation (which is exported).
-Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
-the length of the key. The C<hash> parameter is the precomputed hash
-value; if it is zero then Perl will compute it. The return value will be
-null if the operation failed, otherwise it can be dereferenced to get the
-original C<SV*>.
+=item others
- SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
+See the comments at the top of C<embed.fnc> for others.
-=item hv_store_ent
+=back
-Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
-parameter is the precomputed hash value; if it is zero then Perl will
-compute it. The return value is the new hash entry so created. It will be
-null if the operation failed or if the entry was stored in a tied hash.
-Otherwise the contents of the return value can be accessed using the
-C<He???> macros described here.
+If you edit F<embed.pl> or F<embed.fnc>, you will need to run
+C<make regen_headers> to force a rebuild of F<embed.h> and other
+auto-generated files.
- HE* hv_store_ent _((HV* tb, SV* key, SV* val, U32 hash));
+=head2 Formatted Printing of IVs, UVs, and NVs
-=item hv_undef
+If you are printing IVs, UVs, or NVS instead of the stdio(3) style
+formatting codes like C<%d>, C<%ld>, C<%f>, you should use the
+following macros for portability
-Undefines the hash.
+ IVdf IV in decimal
+ UVuf UV in decimal
+ UVof UV in octal
+ UVxf UV in hexadecimal
+ NVef NV %e-like
+ NVff NV %f-like
+ NVgf NV %g-like
- void hv_undef _((HV* tb));
+These will take care of 64-bit integers and long doubles.
+For example:
-=item isALNUM
+ printf("IV is %"IVdf"\n", iv);
-Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
-character or digit.
+The IVdf will expand to whatever is the correct format for the IVs.
- int isALNUM (char c)
+If you are printing addresses of pointers, use UVxf combined
+with PTR2UV(), do not use %lx or %p.
-=item isALPHA
+=head2 Pointer-To-Integer and Integer-To-Pointer
-Returns a boolean indicating whether the C C<char> is an ascii alphabetic
-character.
+Because pointer size does not necessarily equal integer size,
+use the follow macros to do it right.
- int isALPHA (char c)
+ PTR2UV(pointer)
+ PTR2IV(pointer)
+ PTR2NV(pointer)
+ INT2PTR(pointertotype, integer)
-=item isDIGIT
+For example:
-Returns a boolean indicating whether the C C<char> is an ascii digit.
+ IV iv = ...;
+ SV *sv = INT2PTR(SV*, iv);
- int isDIGIT (char c)
+and
-=item isLOWER
+ AV *av = ...;
+ UV uv = PTR2UV(av);
-Returns a boolean indicating whether the C C<char> is a lowercase character.
+=head2 Exception Handling
- int isLOWER (char c)
+There are a couple of macros to do very basic exception handling in XS
+modules. You have to define C<NO_XSLOCKS> before including F<XSUB.h> to
+be able to use these macros:
-=item isSPACE
+ #define NO_XSLOCKS
+ #include "XSUB.h"
-Returns a boolean indicating whether the C C<char> is whitespace.
+You can use these macros if you call code that may croak, but you need
+to do some cleanup before giving control back to Perl. For example:
- int isSPACE (char c)
+ dXCPT; /* set up necessary variables */
-=item isUPPER
+ XCPT_TRY_START {
+ code_that_may_croak();
+ } XCPT_TRY_END
-Returns a boolean indicating whether the C C<char> is an uppercase character.
+ XCPT_CATCH
+ {
+ /* do cleanup here */
+ XCPT_RETHROW;
+ }
- int isUPPER (char c)
+Note that you always have to rethrow an exception that has been
+caught. Using these macros, it is not possible to just catch the
+exception and ignore it. If you have to ignore the exception, you
+have to use the C<call_*> function.
-=item items
+The advantage of using the above macros is that you don't have
+to setup an extra function for C<call_*>, and that using these
+macros is faster than using C<call_*>.
-Variable which is setup by C<xsubpp> to indicate the number of items on the
-stack. See L<perlxs/"Variable-length Parameter Lists">.
+=head2 Source Documentation
-=item ix
+There's an effort going on to document the internal functions and
+automatically produce reference manuals from them - L<perlapi> is one
+such manual which details all the functions which are available to XS
+writers. L<perlintern> is the autogenerated manual for the functions
+which are not part of the API and are supposedly for internal use only.
-Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
-was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
+Source documentation is created by putting POD comments into the C
+source, like this:
-=item LEAVE
+ /*
+ =for apidoc sv_setiv
-Closing bracket on a callback. See C<ENTER> and L<perlcall>.
+ Copies an integer into the given SV. Does not handle 'set' magic. See
+ C<sv_setiv_mg>.
- LEAVE;
+ =cut
+ */
-=item MARK
+Please try and supply some documentation if you add functions to the
+Perl core.
-Stack marker variable for the XSUB. See C<dMARK>.
+=head2 Backwards compatibility
-=item mg_clear
+The Perl API changes over time. New functions are added or the interfaces
+of existing functions are changed. The C<Devel::PPPort> module tries to
+provide compatibility code for some of these changes, so XS writers don't
+have to code it themselves when supporting multiple versions of Perl.
-Clear something magical that the SV represents. See C<sv_magic>.
+C<Devel::PPPort> generates a C header file F<ppport.h> that can also
+be run as a Perl script. To generate F<ppport.h>, run:
- int mg_clear _((SV* sv));
+ perl -MDevel::PPPort -eDevel::PPPort::WriteFile
-=item mg_copy
+Besides checking existing XS code, the script can also be used to retrieve
+compatibility information for various API calls using the C<--api-info>
+command line switch. For example:
-Copies the magic from one SV to another. See C<sv_magic>.
+ % perl ppport.h --api-info=sv_magicext
- int mg_copy _((SV *, SV *, char *, STRLEN));
+For details, see C<perldoc ppport.h>.
-=item mg_find
+=head1 Unicode Support
-Finds the magic pointer for type matching the SV. See C<sv_magic>.
+Perl 5.6.0 introduced Unicode support. It's important for porters and XS
+writers to understand this support and make sure that the code they
+write does not corrupt Unicode data.
- MAGIC* mg_find _((SV* sv, int type));
+=head2 What B<is> Unicode, anyway?
-=item mg_free
+In the olden, less enlightened times, we all used to use ASCII. Most of
+us did, anyway. The big problem with ASCII is that it's American. Well,
+no, that's not actually the problem; the problem is that it's not
+particularly useful for people who don't use the Roman alphabet. What
+used to happen was that particular languages would stick their own
+alphabet in the upper range of the sequence, between 128 and 255. Of
+course, we then ended up with plenty of variants that weren't quite
+ASCII, and the whole point of it being a standard was lost.
-Free any magic storage used by the SV. See C<sv_magic>.
+Worse still, if you've got a language like Chinese or
+Japanese that has hundreds or thousands of characters, then you really
+can't fit them into a mere 256, so they had to forget about ASCII
+altogether, and build their own systems using pairs of numbers to refer
+to one character.
+
+To fix this, some people formed Unicode, Inc. and
+produced a new character set containing all the characters you can
+possibly think of and more. There are several ways of representing these
+characters, and the one Perl uses is called UTF-8. UTF-8 uses
+a variable number of bytes to represent a character. You can learn more
+about Unicode and Perl's Unicode model in L<perlunicode>.
+
+=head2 How can I recognise a UTF-8 string?
+
+You can't. This is because UTF-8 data is stored in bytes just like
+non-UTF-8 data. The Unicode character 200, (C<0xC8> for you hex types)
+capital E with a grave accent, is represented by the two bytes
+C<v196.172>. Unfortunately, the non-Unicode string C<chr(196).chr(172)>
+has that byte sequence as well. So you can't tell just by looking - this
+is what makes Unicode input an interesting problem.
+
+In general, you either have to know what you're dealing with, or you
+have to guess. The API function C<is_utf8_string> can help; it'll tell
+you if a string contains only valid UTF-8 characters. However, it can't
+do the work for you. On a character-by-character basis, C<is_utf8_char>
+will tell you whether the current character in a string is valid UTF-8.
+
+=head2 How does UTF-8 represent Unicode characters?
+
+As mentioned above, UTF-8 uses a variable number of bytes to store a
+character. Characters with values 0...127 are stored in one byte, just
+like good ol' ASCII. Character 128 is stored as C<v194.128>; this
+continues up to character 191, which is C<v194.191>. Now we've run out of
+bits (191 is binary C<10111111>) so we move on; 192 is C<v195.128>. And
+so it goes on, moving to three bytes at character 2048.
+
+Assuming you know you're dealing with a UTF-8 string, you can find out
+how long the first character in it is with the C<UTF8SKIP> macro:
+
+ char *utf = "\305\233\340\240\201";
+ I32 len;
+
+ len = UTF8SKIP(utf); /* len is 2 here */
+ utf += len;
+ len = UTF8SKIP(utf); /* len is 3 here */
+
+Another way to skip over characters in a UTF-8 string is to use
+C<utf8_hop>, which takes a string and a number of characters to skip
+over. You're on your own about bounds checking, though, so don't use it
+lightly.
+
+All bytes in a multi-byte UTF-8 character will have the high bit set,
+so you can test if you need to do something special with this
+character like this (the UTF8_IS_INVARIANT() is a macro that tests
+whether the byte can be encoded as a single byte even in UTF-8):
+
+ U8 *utf;
+ UV uv; /* Note: a UV, not a U8, not a char */
+
+ if (!UTF8_IS_INVARIANT(*utf))
+ /* Must treat this as UTF-8 */
+ uv = utf8_to_uv(utf);
+ else
+ /* OK to treat this character as a byte */
+ uv = *utf;
+
+You can also see in that example that we use C<utf8_to_uv> to get the
+value of the character; the inverse function C<uv_to_utf8> is available
+for putting a UV into UTF-8:
+
+ if (!UTF8_IS_INVARIANT(uv))
+ /* Must treat this as UTF8 */
+ utf8 = uv_to_utf8(utf8, uv);
+ else
+ /* OK to treat this character as a byte */
+ *utf8++ = uv;
+
+You B<must> convert characters to UVs using the above functions if
+you're ever in a situation where you have to match UTF-8 and non-UTF-8
+characters. You may not skip over UTF-8 characters in this case. If you
+do this, you'll lose the ability to match hi-bit non-UTF-8 characters;
+for instance, if your UTF-8 string contains C<v196.172>, and you skip
+that character, you can never match a C<chr(200)> in a non-UTF-8 string.
+So don't do that!
+
+=head2 How does Perl store UTF-8 strings?
+
+Currently, Perl deals with Unicode strings and non-Unicode strings
+slightly differently. A flag in the SV, C<SVf_UTF8>, indicates that the
+string is internally encoded as UTF-8. Without it, the byte value is the
+codepoint number and vice versa (in other words, the string is encoded
+as iso-8859-1). You can check and manipulate this flag with the
+following macros:
+
+ SvUTF8(sv)
+ SvUTF8_on(sv)
+ SvUTF8_off(sv)
+
+This flag has an important effect on Perl's treatment of the string: if
+Unicode data is not properly distinguished, regular expressions,
+C<length>, C<substr> and other string handling operations will have
+undesirable results.
- int mg_free _((SV* sv));
+The problem comes when you have, for instance, a string that isn't
+flagged as UTF-8, and contains a byte sequence that could be UTF-8 -
+especially when combining non-UTF-8 and UTF-8 strings.
-=item mg_get
+Never forget that the C<SVf_UTF8> flag is separate to the PV value; you
+need be sure you don't accidentally knock it off while you're
+manipulating SVs. More specifically, you cannot expect to do this:
-Do magic after a value is retrieved from the SV. See C<sv_magic>.
+ SV *sv;
+ SV *nsv;
+ STRLEN len;
+ char *p;
- int mg_get _((SV* sv));
+ p = SvPV(sv, len);
+ frobnicate(p);
+ nsv = newSVpvn(p, len);
-=item mg_len
+The C<char*> string does not tell you the whole story, and you can't
+copy or reconstruct an SV just by copying the string value. Check if the
+old SV has the UTF8 flag set, and act accordingly:
-Report on the SV's length. See C<sv_magic>.
+ p = SvPV(sv, len);
+ frobnicate(p);
+ nsv = newSVpvn(p, len);
+ if (SvUTF8(sv))
+ SvUTF8_on(nsv);
- U32 mg_len _((SV* sv));
+In fact, your C<frobnicate> function should be made aware of whether or
+not it's dealing with UTF-8 data, so that it can handle the string
+appropriately.
-=item mg_magical
+Since just passing an SV to an XS function and copying the data of
+the SV is not enough to copy the UTF8 flags, even less right is just
+passing a C<char *> to an XS function.
-Turns on the magical status of an SV. See C<sv_magic>.
+=head2 How do I convert a string to UTF-8?
- void mg_magical _((SV* sv));
+If you're mixing UTF-8 and non-UTF-8 strings, it is necessary to upgrade
+one of the strings to UTF-8. If you've got an SV, the easiest way to do
+this is:
-=item mg_set
+ sv_utf8_upgrade(sv);
-Do magic after a value is assigned to the SV. See C<sv_magic>.
+However, you must not do this, for example:
- int mg_set _((SV* sv));
+ if (!SvUTF8(left))
+ sv_utf8_upgrade(left);
-=item Move
+If you do this in a binary operator, you will actually change one of the
+strings that came into the operator, and, while it shouldn't be noticeable
+by the end user, it can cause problems in deficient code.
-The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
-source, C<d> is the destination, C<n> is the number of items, and C<t> is
-the type.
+Instead, C<bytes_to_utf8> will give you a UTF-8-encoded B<copy> of its
+string argument. This is useful for having the data available for
+comparisons and so on, without harming the original SV. There's also
+C<utf8_to_bytes> to go the other way, but naturally, this will fail if
+the string contains any characters above 255 that can't be represented
+in a single byte.
- (void) Move( s, d, n, t );
+=head2 Is there anything else I need to know?
-=item na
+Not really. Just remember these things:
-A variable which may be used with C<SvPV> to tell Perl to calculate the
-string length.
+=over 3
-=item New
+=item *
-The XSUB-writer's interface to the C C<malloc> function.
+There's no way to tell if a string is UTF-8 or not. You can tell if an SV
+is UTF-8 by looking at is C<SvUTF8> flag. Don't forget to set the flag if
+something should be UTF-8. Treat the flag as part of the PV, even though
+it's not - if you pass on the PV to somewhere, pass on the flag too.
- void * New( x, void *ptr, int size, type )
+=item *
-=item Newc
+If a string is UTF-8, B<always> use C<utf8_to_uv> to get at the value,
+unless C<UTF8_IS_INVARIANT(*s)> in which case you can use C<*s>.
-The XSUB-writer's interface to the C C<malloc> function, with cast.
+=item *
- void * Newc( x, void *ptr, int size, type, cast )
+When writing a character C<uv> to a UTF-8 string, B<always> use
+C<uv_to_utf8>, unless C<UTF8_IS_INVARIANT(uv))> in which case
+you can use C<*s = uv>.
-=item Newz
+=item *
-The XSUB-writer's interface to the C C<malloc> function. The allocated
-memory is zeroed with C<memzero>.
+Mixing UTF-8 and non-UTF-8 strings is tricky. Use C<bytes_to_utf8> to get
+a new string which is UTF-8 encoded. There are tricks you can use to
+delay deciding whether you need to use a UTF-8 string until you get to a
+high character - C<HALF_UPGRADE> is one of those.
- void * Newz( x, void *ptr, int size, type )
+=back
-=item newAV
-
-Creates a new AV. The reference count is set to 1.
-
- AV* newAV _((void));
-
-=item newHV
-
-Creates a new HV. The reference count is set to 1.
-
- HV* newHV _((void));
-
-=item newRV_inc
-
-Creates an RV wrapper for an SV. The reference count for the original SV is
-incremented.
-
- SV* newRV_inc _((SV* ref));
-
-For historical reasons, "newRV" is a synonym for "newRV_inc".
-
-=item newRV_noinc
-
-Creates an RV wrapper for an SV. The reference count for the original
-SV is B<not> incremented.
-
- SV* newRV_noinc _((SV* ref));
-
-=item newSV
-
-Creates a new SV. The C<len> parameter indicates the number of bytes of
-preallocated string space the SV should have. The reference count for the
-new SV is set to 1.
-
- SV* newSV _((STRLEN len));
-
-=item newSViv
-
-Creates a new SV and copies an integer into it. The reference count for the
-SV is set to 1.
-
- SV* newSViv _((IV i));
-
-=item newSVnv
-
-Creates a new SV and copies a double into it. The reference count for the
-SV is set to 1.
-
- SV* newSVnv _((NV i));
-
-=item newSVpv
-
-Creates a new SV and copies a string into it. The reference count for the
-SV is set to 1. If C<len> is zero then Perl will compute the length.
-
- SV* newSVpv _((char* s, STRLEN len));
-
-=item newSVrv
-
-Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
-it will be upgraded to one. If C<classname> is non-null then the new SV will
-be blessed in the specified package. The new SV is returned and its
-reference count is 1.
-
- SV* newSVrv _((SV* rv, char* classname));
-
-=item newSVsv
-
-Creates a new SV which is an exact duplicate of the original SV.
-
- SV* newSVsv _((SV* old));
-
-=item newXS
-
-Used by C<xsubpp> to hook up XSUBs as Perl subs.
-
-=item newXSproto
-
-Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
-the subs.
-
-=item Nullav
-
-Null AV pointer.
-
-=item Nullch
-
-Null character pointer.
-
-=item Nullcv
-
-Null CV pointer.
-
-=item Nullhv
-
-Null HV pointer.
-
-=item Nullsv
-
-Null SV pointer.
-
-=item ORIGMARK
-
-The original stack mark for the XSUB. See C<dORIGMARK>.
-
-=item perl_alloc
-
-Allocates a new Perl interpreter. See L<perlembed>.
-
-=item perl_call_argv
-
-Performs a callback to the specified Perl sub. See L<perlcall>.
-
- I32 perl_call_argv _((char* subname, I32 flags, char** argv));
-
-=item perl_call_method
-
-Performs a callback to the specified Perl method. The blessed object must
-be on the stack. See L<perlcall>.
-
- I32 perl_call_method _((char* methname, I32 flags));
-
-=item perl_call_pv
-
-Performs a callback to the specified Perl sub. See L<perlcall>.
-
- I32 perl_call_pv _((char* subname, I32 flags));
-
-=item perl_call_sv
-
-Performs a callback to the Perl sub whose name is in the SV. See
-L<perlcall>.
-
- I32 perl_call_sv _((SV* sv, I32 flags));
-
-=item perl_construct
-
-Initializes a new Perl interpreter. See L<perlembed>.
-
-=item perl_destruct
-
-Shuts down a Perl interpreter. See L<perlembed>.
-
-=item perl_eval_sv
-
-Tells Perl to C<eval> the string in the SV.
-
- I32 perl_eval_sv _((SV* sv, I32 flags));
-
-=item perl_eval_pv
-
-Tells Perl to C<eval> the given string and return an SV* result.
-
- SV* perl_eval_pv _((char* p, I32 croak_on_error));
-
-=item perl_free
-
-Releases a Perl interpreter. See L<perlembed>.
-
-=item perl_get_av
-
-Returns the AV of the specified Perl array. If C<create> is set and the
-Perl variable does not exist then it will be created. If C<create> is not
-set and the variable does not exist then null is returned.
-
- AV* perl_get_av _((char* name, I32 create));
-
-=item perl_get_cv
-
-Returns the CV of the specified Perl sub. If C<create> is set and the Perl
-variable does not exist then it will be created. If C<create> is not
-set and the variable does not exist then null is returned.
-
- CV* perl_get_cv _((char* name, I32 create));
-
-=item perl_get_hv
-
-Returns the HV of the specified Perl hash. If C<create> is set and the Perl
-variable does not exist then it will be created. If C<create> is not
-set and the variable does not exist then null is returned.
-
- HV* perl_get_hv _((char* name, I32 create));
-
-=item perl_get_sv
-
-Returns the SV of the specified Perl scalar. If C<create> is set and the
-Perl variable does not exist then it will be created. If C<create> is not
-set and the variable does not exist then null is returned.
-
- SV* perl_get_sv _((char* name, I32 create));
-
-=item perl_parse
-
-Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
-
-=item perl_require_pv
-
-Tells Perl to C<require> a module.
-
- void perl_require_pv _((char* pv));
-
-=item perl_run
-
-Tells a Perl interpreter to run. See L<perlembed>.
-
-=item POPi
-
-Pops an integer off the stack.
-
- int POPi();
-
-=item POPl
-
-Pops a long off the stack.
-
- long POPl();
-
-=item POPp
-
-Pops a string off the stack.
-
- char * POPp();
-
-=item POPn
-
-Pops a double off the stack.
-
- double POPn();
-
-=item POPs
-
-Pops an SV off the stack.
-
- SV* POPs();
-
-=item PUSHMARK
-
-Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
-
- PUSHMARK(p)
-
-=item PUSHi
-
-Push an integer onto the stack. The stack must have room for this element.
-See C<XPUSHi>.
-
- PUSHi(int d)
-
-=item PUSHn
-
-Push a double onto the stack. The stack must have room for this element.
-See C<XPUSHn>.
-
- PUSHn(double d)
-
-=item PUSHp
-
-Push a string onto the stack. The stack must have room for this element.
-The C<len> indicates the length of the string. See C<XPUSHp>.
-
- PUSHp(char *c, int len )
-
-=item PUSHs
-
-Push an SV onto the stack. The stack must have room for this element. See
-C<XPUSHs>.
-
- PUSHs(sv)
-
-=item PUTBACK
-
-Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
-See C<PUSHMARK> and L<perlcall> for other uses.
-
- PUTBACK;
-
-=item Renew
-
-The XSUB-writer's interface to the C C<realloc> function.
-
- void * Renew( void *ptr, int size, type )
-
-=item Renewc
-
-The XSUB-writer's interface to the C C<realloc> function, with cast.
-
- void * Renewc( void *ptr, int size, type, cast )
-
-=item RETVAL
-
-Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
-This is always the proper type for the XSUB.
-See L<perlxs/"The RETVAL Variable">.
-
-=item safefree
-
-The XSUB-writer's interface to the C C<free> function.
-
-=item safemalloc
-
-The XSUB-writer's interface to the C C<malloc> function.
-
-=item saferealloc
-
-The XSUB-writer's interface to the C C<realloc> function.
-
-=item savepv
-
-Copy a string to a safe spot. This does not use an SV.
-
- char* savepv _((char* sv));
-
-=item savepvn
-
-Copy a string to a safe spot. The C<len> indicates number of bytes to
-copy. This does not use an SV.
-
- char* savepvn _((char* sv, I32 len));
-
-=item SAVETMPS
-
-Opening bracket for temporaries on a callback. See C<FREETMPS> and
-L<perlcall>.
-
- SAVETMPS;
-
-=item SP
-
-Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
-C<SPAGAIN>.
-
-=item SPAGAIN
-
-Refetch the stack pointer. Used after a callback. See L<perlcall>.
-
- SPAGAIN;
-
-=item ST
-
-Used to access elements on the XSUB's stack.
-
- SV* ST(int x)
-
-=item strEQ
-
-Test two strings to see if they are equal. Returns true or false.
-
- int strEQ( char *s1, char *s2 )
-
-=item strGE
-
-Test two strings to see if the first, C<s1>, is greater than or equal to the
-second, C<s2>. Returns true or false.
-
- int strGE( char *s1, char *s2 )
-
-=item strGT
-
-Test two strings to see if the first, C<s1>, is greater than the second,
-C<s2>. Returns true or false.
-
- int strGT( char *s1, char *s2 )
-
-=item strLE
-
-Test two strings to see if the first, C<s1>, is less than or equal to the
-second, C<s2>. Returns true or false.
-
- int strLE( char *s1, char *s2 )
-
-=item strLT
-
-Test two strings to see if the first, C<s1>, is less than the second,
-C<s2>. Returns true or false.
-
- int strLT( char *s1, char *s2 )
-
-=item strNE
-
-Test two strings to see if they are different. Returns true or false.
-
- int strNE( char *s1, char *s2 )
-
-=item strnEQ
-
-Test two strings to see if they are equal. The C<len> parameter indicates
-the number of bytes to compare. Returns true or false.
-
- int strnEQ( char *s1, char *s2 )
-
-=item strnNE
-
-Test two strings to see if they are different. The C<len> parameter
-indicates the number of bytes to compare. Returns true or false.
-
- int strnNE( char *s1, char *s2, int len )
-
-=item sv_2mortal
-
-Marks an SV as mortal. The SV will be destroyed when the current context
-ends.
-
- SV* sv_2mortal _((SV* sv));
-
-=item sv_bless
-
-Blesses an SV into a specified package. The SV must be an RV. The package
-must be designated by its stash (see C<gv_stashpv()>). The reference count
-of the SV is unaffected.
-
- SV* sv_bless _((SV* sv, HV* stash));
-
-=item sv_catpv
-
-Concatenates the string onto the end of the string which is in the SV.
-
- void sv_catpv _((SV* sv, char* ptr));
-
-=item sv_catpvn
-
-Concatenates the string onto the end of the string which is in the SV. The
-C<len> indicates number of bytes to copy.
-
- void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
-
-=item sv_catsv
-
-Concatenates the string from SV C<ssv> onto the end of the string in SV
-C<dsv>.
-
- void sv_catsv _((SV* dsv, SV* ssv));
-
-=item sv_cmp
-
-Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
-string in C<sv1> is less than, equal to, or greater than the string in
-C<sv2>.
-
- I32 sv_cmp _((SV* sv1, SV* sv2));
-
-=item sv_cmp
-
-Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
-string in C<sv1> is less than, equal to, or greater than the string in
-C<sv2>.
-
- I32 sv_cmp _((SV* sv1, SV* sv2));
-
-=item SvCUR
-
-Returns the length of the string which is in the SV. See C<SvLEN>.
-
- int SvCUR (SV* sv)
-
-=item SvCUR_set
-
-Set the length of the string which is in the SV. See C<SvCUR>.
-
- SvCUR_set (SV* sv, int val )
-
-=item sv_dec
-
-Auto-decrement of the value in the SV.
-
- void sv_dec _((SV* sv));
-
-=item sv_dec
-
-Auto-decrement of the value in the SV.
-
- void sv_dec _((SV* sv));
-
-=item SvEND
-
-Returns a pointer to the last character in the string which is in the SV.
-See C<SvCUR>. Access the character as
-
- *SvEND(sv)
-
-=item sv_eq
-
-Returns a boolean indicating whether the strings in the two SVs are
-identical.
-
- I32 sv_eq _((SV* sv1, SV* sv2));
-
-=item SvGROW
-
-Expands the character buffer in the SV. Calls C<sv_grow> to perform the
-expansion if necessary. Returns a pointer to the character buffer.
-
- char * SvGROW( SV* sv, int len )
-
-=item sv_grow
-
-Expands the character buffer in the SV. This will use C<sv_unref> and will
-upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
-Use C<SvGROW>.
-
-=item sv_inc
-
-Auto-increment of the value in the SV.
-
- void sv_inc _((SV* sv));
-
-=item SvIOK
-
-Returns a boolean indicating whether the SV contains an integer.
-
- int SvIOK (SV* SV)
-
-=item SvIOK_off
-
-Unsets the IV status of an SV.
-
- SvIOK_off (SV* sv)
-
-=item SvIOK_on
-
-Tells an SV that it is an integer.
-
- SvIOK_on (SV* sv)
-
-=item SvIOK_only
-
-Tells an SV that it is an integer and disables all other OK bits.
-
- SvIOK_on (SV* sv)
-
-=item SvIOK_only
-
-Tells an SV that it is an integer and disables all other OK bits.
-
- SvIOK_on (SV* sv)
-
-=item SvIOKp
-
-Returns a boolean indicating whether the SV contains an integer. Checks the
-B<private> setting. Use C<SvIOK>.
-
- int SvIOKp (SV* SV)
-
-=item sv_isa
-
-Returns a boolean indicating whether the SV is blessed into the specified
-class. This does not know how to check for subtype, so it doesn't work in
-an inheritance relationship.
-
- int sv_isa _((SV* sv, char* name));
-
-=item SvIV
-
-Returns the integer which is in the SV.
-
- int SvIV (SV* sv)
-
-=item sv_isobject
-
-Returns a boolean indicating whether the SV is an RV pointing to a blessed
-object. If the SV is not an RV, or if the object is not blessed, then this
-will return false.
-
- int sv_isobject _((SV* sv));
-
-=item SvIVX
-
-Returns the integer which is stored in the SV.
-
- int SvIVX (SV* sv);
-
-=item SvLEN
-
-Returns the size of the string buffer in the SV. See C<SvCUR>.
-
- int SvLEN (SV* sv)
-
-=item sv_len
-
-Returns the length of the string in the SV. Use C<SvCUR>.
-
- STRLEN sv_len _((SV* sv));
-
-=item sv_len
-
-Returns the length of the string in the SV. Use C<SvCUR>.
-
- STRLEN sv_len _((SV* sv));
-
-=item sv_magic
-
-Adds magic to an SV.
-
- void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
-
-=item sv_mortalcopy
-
-Creates a new SV which is a copy of the original SV. The new SV is marked
-as mortal.
-
- SV* sv_mortalcopy _((SV* oldsv));
-
-=item SvOK
-
-Returns a boolean indicating whether the value is an SV.
-
- int SvOK (SV* sv)
-
-=item sv_newmortal
-
-Creates a new SV which is mortal. The reference count of the SV is set to 1.
-
- SV* sv_newmortal _((void));
-
-=item sv_no
-
-This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
-
-=item SvNIOK
-
-Returns a boolean indicating whether the SV contains a number, integer or
-double.
-
- int SvNIOK (SV* SV)
-
-=item SvNIOK_off
-
-Unsets the NV/IV status of an SV.
-
- SvNIOK_off (SV* sv)
-
-=item SvNIOKp
-
-Returns a boolean indicating whether the SV contains a number, integer or
-double. Checks the B<private> setting. Use C<SvNIOK>.
-
- int SvNIOKp (SV* SV)
-
-=item SvNOK
-
-Returns a boolean indicating whether the SV contains a double.
-
- int SvNOK (SV* SV)
-
-=item SvNOK_off
-
-Unsets the NV status of an SV.
-
- SvNOK_off (SV* sv)
-
-=item SvNOK_on
-
-Tells an SV that it is a double.
-
- SvNOK_on (SV* sv)
-
-=item SvNOK_only
-
-Tells an SV that it is a double and disables all other OK bits.
-
- SvNOK_on (SV* sv)
-
-=item SvNOK_only
-
-Tells an SV that it is a double and disables all other OK bits.
-
- SvNOK_on (SV* sv)
-
-=item SvNOKp
-
-Returns a boolean indicating whether the SV contains a double. Checks the
-B<private> setting. Use C<SvNOK>.
-
- int SvNOKp (SV* SV)
-
-=item SvNV
-
-Returns the double which is stored in the SV.
-
- double SvNV (SV* sv);
-
-=item SvNVX
-
-Returns the double which is stored in the SV.
-
- double SvNVX (SV* sv);
-
-=item SvPOK
-
-Returns a boolean indicating whether the SV contains a character string.
-
- int SvPOK (SV* SV)
-
-=item SvPOK_off
-
-Unsets the PV status of an SV.
-
- SvPOK_off (SV* sv)
-
-=item SvPOK_on
-
-Tells an SV that it is a string.
-
- SvPOK_on (SV* sv)
-
-=item SvPOK_only
-
-Tells an SV that it is a string and disables all other OK bits.
-
- SvPOK_on (SV* sv)
-
-=item SvPOK_only
-
-Tells an SV that it is a string and disables all other OK bits.
-
- SvPOK_on (SV* sv)
-
-=item SvPOKp
-
-Returns a boolean indicating whether the SV contains a character string.
-Checks the B<private> setting. Use C<SvPOK>.
-
- int SvPOKp (SV* SV)
-
-=item SvPV
-
-Returns a pointer to the string in the SV, or a stringified form of the SV
-if the SV does not contain a string. If C<len> is C<na> then Perl will
-handle the length on its own.
-
- char * SvPV (SV* sv, int len )
-
-=item SvPVX
-
-Returns a pointer to the string in the SV. The SV must contain a string.
-
- char * SvPVX (SV* sv)
-
-=item SvREFCNT
-
-Returns the value of the object's reference count.
-
- int SvREFCNT (SV* sv);
-
-=item SvREFCNT_dec
-
-Decrements the reference count of the given SV.
-
- void SvREFCNT_dec (SV* sv)
-
-=item SvREFCNT_inc
-
-Increments the reference count of the given SV.
-
- void SvREFCNT_inc (SV* sv)
-
-=item SvROK
-
-Tests if the SV is an RV.
-
- int SvROK (SV* sv)
-
-=item SvROK_off
-
-Unsets the RV status of an SV.
-
- SvROK_off (SV* sv)
-
-=item SvROK_on
-
-Tells an SV that it is an RV.
-
- SvROK_on (SV* sv)
-
-=item SvRV
-
-Dereferences an RV to return the SV.
-
- SV* SvRV (SV* sv);
-
-=item sv_setiv
-
-Copies an integer into the given SV.
-
- void sv_setiv _((SV* sv, IV num));
-
-=item sv_setnv
-
-Copies a double into the given SV.
-
- void sv_setnv _((SV* sv, double num));
-
-=item sv_setpv
-
-Copies a string into an SV. The string must be null-terminated.
-
- void sv_setpv _((SV* sv, char* ptr));
-
-=item sv_setpvn
-
-Copies a string into an SV. The C<len> parameter indicates the number of
-bytes to be copied.
-
- void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
-
-=item sv_setref_iv
-
-Copies an integer into a new SV, optionally blessing the SV. The C<rv>
-argument will be upgraded to an RV. That RV will be modified to point to
-the new SV. The C<classname> argument indicates the package for the
-blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
-will be returned and will have a reference count of 1.
-
- SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
-
-=item sv_setref_nv
-
-Copies a double into a new SV, optionally blessing the SV. The C<rv>
-argument will be upgraded to an RV. That RV will be modified to point to
-the new SV. The C<classname> argument indicates the package for the
-blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
-will be returned and will have a reference count of 1.
-
- SV* sv_setref_nv _((SV *rv, char *classname, double nv));
-
-=item sv_setref_pv
-
-Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
-argument will be upgraded to an RV. That RV will be modified to point to
-the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
-into the SV. The C<classname> argument indicates the package for the
-blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
-will be returned and will have a reference count of 1.
-
- SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
-
-Do not use with integral Perl types such as HV, AV, SV, CV, because those
-objects will become corrupted by the pointer copy process.
-
-Note that C<sv_setref_pvn> copies the string while this copies the pointer.
-
-=item sv_setref_pvn
-
-Copies a string into a new SV, optionally blessing the SV. The length of the
-string must be specified with C<n>. The C<rv> argument will be upgraded to
-an RV. That RV will be modified to point to the new SV. The C<classname>
-argument indicates the package for the blessing. Set C<classname> to
-C<Nullch> to avoid the blessing. The new SV will be returned and will have
-a reference count of 1.
-
- SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
-
-Note that C<sv_setref_pv> copies the pointer while this copies the string.
-
-=item sv_setsv
-
-Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
-The source SV may be destroyed if it is mortal.
-
- void sv_setsv _((SV* dsv, SV* ssv));
-
-=item SvSTASH
-
-Returns the stash of the SV.
-
- HV * SvSTASH (SV* sv)
-
-=item SVt_IV
-
-Integer type flag for scalars. See C<svtype>.
-
-=item SVt_PV
-
-Pointer type flag for scalars. See C<svtype>.
-
-=item SVt_PVAV
-
-Type flag for arrays. See C<svtype>.
-
-=item SVt_PVCV
-
-Type flag for code refs. See C<svtype>.
-
-=item SVt_PVHV
-
-Type flag for hashes. See C<svtype>.
-
-=item SVt_PVMG
-
-Type flag for blessed scalars. See C<svtype>.
-
-=item SVt_NV
-
-Double type flag for scalars. See C<svtype>.
-
-=item SvTRUE
-
-Returns a boolean indicating whether Perl would evaluate the SV as true or
-false, defined or undefined.
-
- int SvTRUE (SV* sv)
-
-=item SvTYPE
-
-Returns the type of the SV. See C<svtype>.
-
- svtype SvTYPE (SV* sv)
-
-=item svtype
-
-An enum of flags for Perl types. These are found in the file B<sv.h> in the
-C<svtype> enum. Test these flags with the C<SvTYPE> macro.
-
-=item SvUPGRADE
-
-Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
-the upgrade if necessary. See C<svtype>.
-
- bool SvUPGRADE _((SV* sv, svtype mt));
-
-=item sv_upgrade
-
-Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
-
-=item sv_undef
-
-This is the C<undef> SV. Always refer to this as C<&sv_undef>.
-
-=item sv_unref
-
-Unsets the RV status of the SV, and decrements the reference count of
-whatever was being referenced by the RV. This can almost be thought of
-as a reversal of C<newSVrv>. See C<SvROK_off>.
-
- void sv_unref _((SV* sv));
-
-=item sv_usepvn
-
-Tells an SV to use C<ptr> to find its string value. Normally the string is
-stored inside the SV but sv_usepvn allows the SV to use an outside string.
-The C<ptr> should point to memory that was allocated by C<malloc>. The
-string length, C<len>, must be supplied. This function will realloc the
-memory pointed to by C<ptr>, so that pointer should not be freed or used by
-the programmer after giving it to sv_usepvn.
-
- void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
-
-=item sv_yes
-
-This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
-
-=item THIS
-
-Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
-This is always the proper type for the C++ object. See C<CLASS> and
-L<perlxs/"Using XS With C++">.
-
-=item toLOWER
-
-Converts the specified character to lowercase.
-
- int toLOWER (char c)
-
-=item toUPPER
-
-Converts the specified character to uppercase.
-
- int toUPPER (char c)
-
-=item warn
-
-This is the XSUB-writer's interface to Perl's C<warn> function. Use this
-function the same way you use the C C<printf> function. See C<croak()>.
-
-=item XPUSHi
-
-Push an integer onto the stack, extending the stack if necessary. See
-C<PUSHi>.
-
- XPUSHi(int d)
-
-=item XPUSHn
-
-Push a double onto the stack, extending the stack if necessary. See
-C<PUSHn>.
-
- XPUSHn(double d)
-
-=item XPUSHp
-
-Push a string onto the stack, extending the stack if necessary. The C<len>
-indicates the length of the string. See C<PUSHp>.
-
- XPUSHp(char *c, int len)
-
-=item XPUSHs
-
-Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
-
- XPUSHs(sv)
-
-=item XS
-
-Macro to declare an XSUB and its C parameter list. This is handled by
-C<xsubpp>.
-
-=item XSRETURN
-
-Return from XSUB, indicating number of items on the stack. This is usually
-handled by C<xsubpp>.
-
- XSRETURN(int x);
-
-=item XSRETURN_EMPTY
-
-Return an empty list from an XSUB immediately.
-
- XSRETURN_EMPTY;
-
-=item XSRETURN_IV
-
-Return an integer from an XSUB immediately. Uses C<XST_mIV>.
-
- XSRETURN_IV(IV v);
-
-=item XSRETURN_NO
-
-Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
-
- XSRETURN_NO;
-
-=item XSRETURN_NV
-
-Return an double from an XSUB immediately. Uses C<XST_mNV>.
-
- XSRETURN_NV(NV v);
-
-=item XSRETURN_PV
-
-Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
-
- XSRETURN_PV(char *v);
-
-=item XSRETURN_UNDEF
-
-Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
-
- XSRETURN_UNDEF;
-
-=item XSRETURN_YES
-
-Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
-
- XSRETURN_YES;
-
-=item XST_mIV
-
-Place an integer into the specified position C<i> on the stack. The value is
-stored in a new mortal SV.
-
- XST_mIV( int i, IV v );
-
-=item XST_mNV
-
-Place a double into the specified position C<i> on the stack. The value is
-stored in a new mortal SV.
-
- XST_mNV( int i, NV v );
-
-=item XST_mNO
-
-Place C<&sv_no> into the specified position C<i> on the stack.
-
- XST_mNO( int i );
-
-=item XST_mPV
-
-Place a copy of a string into the specified position C<i> on the stack. The
-value is stored in a new mortal SV.
-
- XST_mPV( int i, char *v );
-
-=item XST_mUNDEF
-
-Place C<&sv_undef> into the specified position C<i> on the stack.
-
- XST_mUNDEF( int i );
-
-=item XST_mYES
-
-Place C<&sv_yes> into the specified position C<i> on the stack.
-
- XST_mYES( int i );
-
-=item XS_VERSION
-
-The version identifier for an XS module. This is usually handled
-automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
-
-=item XS_VERSION_BOOTCHECK
-
-Macro to verify that a PM module's $VERSION variable matches the XS module's
-C<XS_VERSION> variable. This is usually handled automatically by
-C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
-
-=item Zero
-
-The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
-destination, C<n> is the number of items, and C<t> is the type.
-
- (void) Zero( d, n, t );
-
-=back
-
-=head1 EDITOR
-
-Jeff Okamoto <F<okamoto@corp.hp.com>>
+=head1 Custom Operators
+
+Custom operator support is a new experimental feature that allows you to
+define your own ops. This is primarily to allow the building of
+interpreters for other languages in the Perl core, but it also allows
+optimizations through the creation of "macro-ops" (ops which perform the
+functions of multiple ops which are usually executed together, such as
+C<gvsv, gvsv, add>.)
+
+This feature is implemented as a new op type, C<OP_CUSTOM>. The Perl
+core does not "know" anything special about this op type, and so it will
+not be involved in any optimizations. This also means that you can
+define your custom ops to be any op structure - unary, binary, list and
+so on - you like.
+
+It's important to know what custom operators won't do for you. They
+won't let you add new syntax to Perl, directly. They won't even let you
+add new keywords, directly. In fact, they won't change the way Perl
+compiles a program at all. You have to do those changes yourself, after
+Perl has compiled the program. You do this either by manipulating the op
+tree using a C<CHECK> block and the C<B::Generate> module, or by adding
+a custom peephole optimizer with the C<optimize> module.
+
+When you do this, you replace ordinary Perl ops with custom ops by
+creating ops with the type C<OP_CUSTOM> and the C<pp_addr> of your own
+PP function. This should be defined in XS code, and should look like
+the PP ops in C<pp_*.c>. You are responsible for ensuring that your op
+takes the appropriate number of values from the stack, and you are
+responsible for adding stack marks if necessary.
+
+You should also "register" your op with the Perl interpreter so that it
+can produce sensible error and warning messages. Since it is possible to
+have multiple custom ops within the one "logical" op type C<OP_CUSTOM>,
+Perl uses the value of C<< o->op_ppaddr >> as a key into the
+C<PL_custom_op_descs> and C<PL_custom_op_names> hashes. This means you
+need to enter a name and description for your op at the appropriate
+place in the C<PL_custom_op_names> and C<PL_custom_op_descs> hashes.
+
+Forthcoming versions of C<B::Generate> (version 1.0 and above) should
+directly support the creation of custom ops by name.
+
+=head1 AUTHORS
+
+Until May 1997, this document was maintained by Jeff Okamoto
+E<lt>okamoto@corp.hp.comE<gt>. It is now maintained as part of Perl
+itself by the Perl 5 Porters E<lt>perl5-porters@perl.orgE<gt>.
With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
-Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
-
-API Listing by Dean Roehrich <F<roehrich@cray.com>>.
+Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
+Stephen McCamant, and Gurusamy Sarathy.
-=head1 DATE
+=head1 SEE ALSO
-Version 31.6: 1997/4/14
+perlapi(1), perlintern(1), perlxs(1), perlembed(1)
projects / p5sagit/p5-mst-13.2.git / blobdiff