X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlxs.pod;h=6d14bae275b9289560fce55fa0e5d0df765ceec7;hb=e40b81a3dd247b1a29fc78399677b77b78b5f183;hp=5146a1e45da04d4bbe55775962168155c7fe99a4;hpb=662a0f8c5d8b6f39576444a5a7208fca2f67099e;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlxs.pod b/pod/perlxs.pod index 5146a1e..6d14bae 100644 --- a/pod/perlxs.pod +++ b/pod/perlxs.pod @@ -276,6 +276,63 @@ some heuristic code which tries to disambiguate between "truly-void" and "old-practice-declared-as-void" functions. Hence your code is at mercy of this heuristics unless you use C as return value.) +=head2 Returning SVs, AVs and HVs through RETVAL + +When you're using RETVAL to return an C, there's some magic +going on behind the scenes that should be mentioned. When you're +manipulating the argument stack using the ST(x) macro, for example, +you usually have to pay special attention to reference counts. (For +more about reference counts, see L.) To make your life +easier, the typemap file automatically makes C mortal when +you're returning an C. Thus, the following two XSUBs are more +or less equivalent: + + void + alpha() + PPCODE: + ST(0) = newSVpv("Hello World",0); + sv_2mortal(ST(0)); + XSRETURN(1); + + SV * + beta() + CODE: + RETVAL = newSVpv("Hello World",0); + OUTPUT: + RETVAL + +This is quite useful as it usually improves readability. While +this works fine for an C, it's unfortunately not as easy +to have C or C as a return value. You I be +able to write: + + AV * + array() + CODE: + RETVAL = newAV(); + /* do something with RETVAL */ + OUTPUT: + RETVAL + +But due to an unfixable bug (fixing it would break lots of existing +CPAN modules) in the typemap file, the reference count of the C +is not properly decremented. Thus, the above XSUB would leak memory +whenever it is being called. The same problem exists for C. + +When you're returning an C or a C, you have make sure +their reference count is decremented by making the AV or HV mortal: + + AV * + array() + CODE: + RETVAL = newAV(); + sv_2mortal((SV*)RETVAL); + /* do something with RETVAL */ + OUTPUT: + RETVAL + +And also remember that you don't have to do this for an C. + =head2 The MODULE Keyword The MODULE keyword is used to start the XS code and to specify the package @@ -310,6 +367,10 @@ keyword and must follow immediately after it when used. [ XS code in package RPC ] +The same package name can be used more than once, allowing for +non-contiguous code. This is useful if you have a stronger ordering +principle than package names. + Although this keyword is optional and in some cases provides redundant information it should always be used. This keyword will ensure that the XSUBs appear in the desired package. @@ -527,7 +588,7 @@ Here's a truly obscure example: bool_t rpcb_gettime(host,timep) - time_t &timep ; /* \$v{timep}=@{[$v{timep}=$arg]} */ + time_t &timep; /* \$v{timep}=@{[$v{timep}=$arg]} */ char *host + SvOK($v{timep}) ? SvPV($arg,PL_na) : NULL; OUTPUT: timep @@ -839,6 +900,31 @@ However, the generated Perl function is called in very C-ish style: my ($day, $month); day_month($day, time, $month); +=head2 The C Keyword + +If one of the input arguments to the C function is the length of a string +argument C, one can substitute the name of the length-argument by +C in the XSUB declaration. This argument must be omitted when +the generated Perl function is called. E.g., + + void + dump_chars(char *s, short l) + { + short n = 0; + while (n < l) { + printf("s[%d] = \"\\%#03o\"\n", n, (int)s[n]); + n++; + } + } + + MODULE = x PACKAGE = x + + void dump_chars(char *s, short length(s)) + +should be called as C. + +This directive is supported with ANSI-type function declarations only. + =head2 Variable-length Parameter Lists XSUBs can have variable-length parameter lists by specifying an ellipsis @@ -1035,8 +1121,8 @@ then not push return values on the stack. Some people may be inclined to include an explicit C in the above XSUB, rather than letting control fall through to the end. In those situations C should be used, instead. This will ensure that -the XSUB stack is properly adjusted. Consult L for -other C macros. +the XSUB stack is properly adjusted. Consult L for other +C macros. Since C macros can be used with CODE blocks as well, one can rewrite this example as: @@ -1165,6 +1251,14 @@ prototypes. timep RETVAL +If the prototypes are enabled, you can disable it locally for a given +XSUB as in the following example: + + void + rpcb_gettime_noproto() + PROTOTYPE: DISABLE + ... + =head2 The ALIAS: Keyword The ALIAS: keyword allows an XSUB to have two or more unique Perl names @@ -1189,6 +1283,57 @@ C for this function. OUTPUT: timep +=head2 The OVERLOAD: Keyword + +Instead of writing an overloaded interface using pure Perl, you +can also use the OVERLOAD keyword to define additional Perl names +for your functions (like the ALIAS: keyword above). However, the +overloaded functions must be defined with three parameters (except +for the nomethod() function which needs four parameters). If any +function has the OVERLOAD: keyword, several additional lines +will be defined in the c file generated by xsubpp in order to +register with the overload magic. + +Since blessed objects are actually stored as RV's, it is useful +to use the typemap features to preprocess parameters and extract +the actual SV stored within the blessed RV. See the sample for +T_PTROBJ_SPECIAL below. + +To use the OVERLOAD: keyword, create an XS function which takes +three input parameters ( or use the c style '...' definition) like +this: + + SV * + cmp (lobj, robj, swap) + My_Module_obj lobj + My_Module_obj robj + IV swap + OVERLOAD: cmp <=> + { /* function defined here */} + +In this case, the function will overload both of the three way +comparison operators. For all overload operations using non-alpha +characters, you must type the parameter without quoting, seperating +multiple overloads with whitespace. Note that "" (the stringify +overload) should be entered as \"\" (i.e. escaped). + +=head2 The FALLBACK: Keyword + +In addition to the OVERLOAD keyword, if you need to control how +Perl autogenerates missing overloaded operators, you can set the +FALLBACK keyword in the module header section, like this: + + MODULE = RPC PACKAGE = RPC + + FALLBACK: TRUE + ... + +where FALLBACK can take any of the three values TRUE, FALSE, or +UNDEF. If you do not set any FALLBACK value when using OVERLOAD, +it defaults to UNDEF. FALLBACK is not used except when one or +more functions using OVERLOAD have been defined. Please see +L for more details. + =head2 The INTERFACE: Keyword This keyword declares the current XSUB as a keeper of the given @@ -1688,7 +1833,7 @@ double-colons (::), and declare C to be of that type: T_PTROBJ_SPECIAL if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) { IV tmp = SvIV((SV*)SvRV($arg)); - $var = ($type) tmp; + $var = INT2PTR($type, tmp); } else croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\") @@ -1702,6 +1847,11 @@ The INPUT and OUTPUT sections substitute underscores for double-colons on the fly, giving the desired effect. This example demonstrates some of the power and versatility of the typemap facility. +The INT2PTR macro (defined in perl.h) casts an integer to a pointer, +of a given type, taking care of the possible different size of integers +and pointers. There are also PTR2IV, PTR2UV, PTR2NV macros, +to map the other way, which may be useful in OUTPUT sections. + =head2 Safely Storing Static Data in XS Starting with Perl 5.8, a macro framework has been defined to allow @@ -1714,7 +1864,7 @@ have been designed so that they will work with non-threaded Perl as well. It is therefore strongly recommended that these macros be used by all XS modules that make use of static data. -The easiest way to get a template set of macros to use is by specifiying +The easiest way to get a template set of macros to use is by specifying the C<-g> (C<--global>) option with h2xs (see L). Below is an example module that makes use of the macros. @@ -1722,20 +1872,20 @@ Below is an example module that makes use of the macros. #include "EXTERN.h" #include "perl.h" #include "XSUB.h" - + /* Global Data */ - + #define MY_CXT_KEY "BlindMice::_guts" XS_VERSION - + typedef struct { int count; char name[3][100]; } my_cxt_t; - + START_MY_CXT - + MODULE = BlindMice PACKAGE = BlindMice - + BOOT: { MY_CXT_INIT; @@ -1752,7 +1902,7 @@ Below is an example module that makes use of the macros. dMY_CXT; CODE: if (MY_CXT.count >= 3) { - warn("Already have 3 blind mice") ; + warn("Already have 3 blind mice"); RETVAL = 0; } else { @@ -1771,6 +1921,10 @@ Below is an example module that makes use of the macros. else RETVAL = newSVpv(MY_CXT.name[index - 1]); + void + CLONE(...) + CODE: + MY_CXT_CLONE; B @@ -1806,7 +1960,10 @@ of C. The MY_CXT_INIT macro initialises storage for the C struct. -It I be called exactly once -- typically in a BOOT: section. +It I be called exactly once -- typically in a BOOT: section. If you +are maintaining multiple interpreters, it should be called once in each +interpreter instance, except for interpreters cloned from existing ones. +(But see C below.) =item dMY_CXT @@ -1827,8 +1984,64 @@ then use this to access the C member dMY_CXT; MY_CXT.index = 2; +=item aMY_CXT/pMY_CXT + +C may be quite expensive to calculate, and to avoid the overhead +of invoking it in each function it is possible to pass the declaration +onto other functions using the C/C macros, eg + + void sub1() { + dMY_CXT; + MY_CXT.index = 1; + sub2(aMY_CXT); + } + + void sub2(pMY_CXT) { + MY_CXT.index = 2; + } + +Analogously to C, there are equivalent forms for when the macro is the +first or last in multiple arguments, where an underscore represents a +comma, i.e. C<_aMY_CXT>, C, C<_pMY_CXT> and C. + +=item MY_CXT_CLONE + +By default, when a new interpreter is created as a copy of an existing one +(eg via C<new()>>), both interpreters share the same physical +my_cxt_t structure. Calling C (typically via the package's +C function), causes a byte-for-byte copy of the structure to be +taken, and any future dMY_CXT will cause the copy to be accessed instead. + +=item MY_CXT_INIT_INTERP(my_perl) + +=item dMY_CXT_INTERP(my_perl) + +These are versions of the macros which take an explicit interpreter as an +argument. + =back +Note that these macros will only work together within the I source +file; that is, a dMY_CTX in one source file will access a different structure +than a dMY_CTX in another source file. + +=head2 Thread-aware system interfaces + +Starting from Perl 5.8, in C/C++ level Perl knows how to wrap +system/library interfaces that have thread-aware versions +(e.g. getpwent_r()) into frontend macros (e.g. getpwent()) that +correctly handle the multithreaded interaction with the Perl +interpreter. This will happen transparently, the only thing +you need to do is to instantiate a Perl interpreter. + +This wrapping happens always when compiling Perl core source +(PERL_CORE is defined) or the Perl core extensions (PERL_EXT is +defined). When compiling XS code outside of Perl core the wrapping +does not take place. Note, however, that intermixing the _r-forms +(as Perl compiled for multithreaded operation will do) and the _r-less +forms is neither well-defined (inconsistent results, data corruption, +or even crashes become more likely), nor is it very portable. + =head1 EXAMPLES File C: Interface to some ONC+ RPC bind library functions.