X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlcall.pod;h=e691e759a1d22b0971b27bf1a5e475283b8f3677;hb=a3dfe201291c96fc01babd3d4782d52ba945f2a3;hp=865d3bf88de9a2ded5fb9e24792d39b859e7982f;hpb=1e62ac33a10830c28db17da2c54df825238f3e85;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlcall.pod b/pod/perlcall.pod index 865d3bf..e691e75 100644 --- a/pod/perlcall.pod +++ b/pod/perlcall.pod @@ -72,7 +72,7 @@ Each of the functions will now be discussed in turn. =over 5 -=item B +=item perl_call_sv I takes two parameters, the first, C, is an SV*. This allows you to specify the Perl subroutine to be called either as a @@ -80,7 +80,7 @@ C string (which has first been converted to an SV) or a reference to a subroutine. The section, I, shows how you can make use of I. -=item B +=item perl_call_pv The function, I, is similar to I except it expects its first parameter to be a C char* which identifies the Perl @@ -88,7 +88,7 @@ subroutine you want to call, e.g., C. If the subroutine you want to call is in another package, just include the package name in the string, e.g., C<"pkg::fred">. -=item B +=item perl_call_method The function I is used to call a method from a Perl class. The parameter C corresponds to the name of the method @@ -99,7 +99,7 @@ object (for a virtual method). See L for more information on static and virtual methods and L for an example of using I. -=item B +=item perl_call_argv I calls the Perl subroutine specified by the C string stored in the C parameter. It also takes the usual C @@ -116,7 +116,7 @@ subroutine are stored on the Perl stack. As a general rule you should I check the return value from these functions. Even if you are expecting only a particular number of values to be returned from the Perl subroutine, there is nothing to -stop someone from doing something unexpected - don't say you haven't +stop someone from doing something unexpected--don't say you haven't been warned. =head1 FLAG VALUES @@ -279,8 +279,8 @@ belongs to C. It is possible for the Perl subroutine you are calling to terminate abnormally, e.g., by calling I explicitly or by not actually -existing. By default, when either of these of events occurs, the -process will terminate immediately. If though, you want to trap this +existing. By default, when either of these events occurs, the +process will terminate immediately. If you want to trap this type of event, specify the G_EVAL flag. It will put an I around the subroutine call. @@ -505,9 +505,9 @@ returned from I. It will always be 0. =head2 Passing Parameters Now let's make a slightly more complex example. This time we want to -call a Perl subroutine, C, which will take 2 parameters - a -string (C<$s>) and an integer (C<$n>). The subroutine will simply -print the first C<$n> characters of the string. +call a Perl subroutine, C, which will take 2 parameters--a +string ($s) and an integer ($n). The subroutine will simply +print the first $n characters of the string. So the Perl subroutine would look like this @@ -526,12 +526,18 @@ The C function required to call I would look like this. { dSP ; + ENTER ; + SAVETMPS ; + PUSHMARK(SP) ; XPUSHs(sv_2mortal(newSVpv(a, 0))); XPUSHs(sv_2mortal(newSViv(b))); PUTBACK ; perl_call_pv("LeftString", G_DISCARD); + + FREETMPS ; + LEAVE ; } Here are a few notes on the C function I. @@ -549,7 +555,7 @@ as C. =item 2. If you are going to put something onto the Perl stack, you need to know -where to put it. This is the purpose of the macro C - it declares +where to put it. This is the purpose of the macro C--it declares and initializes a I copy of the Perl stack pointer. All the other macros which will be used in this example require you to @@ -557,7 +563,7 @@ have used this macro. The exception to this rule is if you are calling a Perl subroutine directly from an XSUB function. In this case it is not necessary to -use the C macro explicitly - it will be declared for you +use the C macro explicitly--it will be declared for you automatically. =item 3. @@ -572,12 +578,12 @@ The C macro tells Perl to make a mental note of the current stack pointer. Even if you aren't passing any parameters (like the example shown in the section I) you must still call the C macro before you can call any of the -I functions - Perl still needs to know that there are no +I functions--Perl still needs to know that there are no parameters. The C macro sets the global copy of the stack pointer to be the same as our local copy. If we didn't do this I -wouldn't know where the two parameters we pushed were - remember that +wouldn't know where the two parameters we pushed were--remember that up to now all the stack pointer manipulation we have done is with our local copy, I the global copy. @@ -598,6 +604,36 @@ on how the XPUSH macros work. =item 6. +Because we created temporary values (by means of sv_2mortal() calls) +we will have to tidy up the Perl stack and dispose of mortal SVs. + +This is the purpose of + + ENTER ; + SAVETMPS ; + +at the start of the function, and + + FREETMPS ; + LEAVE ; + +at the end. The C/C pair creates a boundary for any +temporaries we create. This means that the temporaries we get rid of +will be limited to those which were created after these calls. + +The C/C pair will get rid of any values returned by +the Perl subroutine (see next example), plus it will also dump the +mortal SVs we have created. Having C/C at the +beginning of the code makes sure that no other mortals are destroyed. + +Think of these macros as working a bit like using C<{> and C<}> in Perl +to limit the scope of local variables. + +See the section I for details of +an alternative to using these macros. + +=item 7. + Finally, I can now be called via the I function. @@ -660,40 +696,8 @@ The only flag specified this time was G_SCALAR. That means the C<@_> array will be created and that the value returned by I will still exist after the call to I. - - =item 2. -Because we are interested in what is returned from I we cannot -specify G_DISCARD. This means that we will have to tidy up the Perl -stack and dispose of any temporary values ourselves. This is the -purpose of - - ENTER ; - SAVETMPS ; - -at the start of the function, and - - FREETMPS ; - LEAVE ; - -at the end. The C/C pair creates a boundary for any -temporaries we create. This means that the temporaries we get rid of -will be limited to those which were created after these calls. - -The C/C pair will get rid of any values returned by -the Perl subroutine, plus it will also dump the mortal SVs we have -created. Having C/C at the beginning of the code -makes sure that no other mortals are destroyed. - -Think of these macros as working a bit like using C<{> and C<}> in Perl -to limit the scope of local variables. - -See the section I for details of -an alternative to using these macros. - -=item 3. - The purpose of the macro C is to refresh the local copy of the stack pointer. This is necessary because it is possible that the memory allocated to the Perl stack has been reallocated whilst in the @@ -703,7 +707,7 @@ If you are making use of the Perl stack pointer in your code you must always refresh the local copy using SPAGAIN whenever you make use of the I functions or any other Perl internal function. -=item 4. +=item 3. Although only a single value was expected to be returned from I, it is still good practice to check the return code from I @@ -715,7 +719,7 @@ didn't check for that possibility and take appropriate action the Perl stack would end up in an inconsistent state. That is something you I don't want to happen ever. -=item 5. +=item 4. The C macro is used here to pop the return value from the stack. In this case we wanted an integer, so C was used. @@ -730,7 +734,7 @@ they return. POPi integer POPl long -=item 6. +=item 5. The final C is used to leave the Perl stack in a consistent state before exiting the function. This is necessary because when we @@ -918,7 +922,7 @@ and here is a C function to call it. To be able to access the two parameters that were pushed onto the stack after they return from I it is necessary to make a note -of their addresses - thus the two variables C and C. +of their addresses--thus the two variables C and C. The reason this is necessary is that the area of the Perl stack which held them will very likely have been overwritten by something else by @@ -965,9 +969,10 @@ and some C to call it SPAGAIN ; /* Check the eval first */ - if (SvTRUE(GvSV(errgv))) + if (SvTRUE(ERRSV)) { - printf ("Uh oh - %s\n", SvPV(GvSV(errgv), na)) ; + STRLEN n_a; + printf ("Uh oh - %s\n", SvPV(ERRSV, n_a)) ; POPs ; } else @@ -1007,9 +1012,10 @@ I. The code - if (SvTRUE(GvSV(errgv))) + if (SvTRUE(ERRSV)) { - printf ("Uh oh - %s\n", SvPV(GvSV(errgv), na)) ; + STRLEN n_a; + printf ("Uh oh - %s\n", SvPV(ERRSV, n_a)) ; POPs ; } @@ -1017,14 +1023,14 @@ is the direct equivalent of this bit of Perl print "Uh oh - $@\n" if $@ ; -C is a perl global of type C that points to the -symbol table entry containing the error. C therefore +C is a perl global of type C that points to the +symbol table entry containing the error. C therefore refers to the C equivalent of C<$@>. =item 3. Note that the stack is popped using C in the block where -C is true. This is necessary because whenever a +C is true. This is necessary because whenever a I function invoked with G_EVAL|G_SCALAR returns an error, the top of the stack holds the value I. Because we want the program to continue after detecting this error, it is essential that @@ -1169,11 +1175,11 @@ the version of Perl you are using) Not a CODE reference at ... Undefined subroutine &main::47 called ... -The variable C<$ref> may have referred to the subroutine C +The variable $ref may have referred to the subroutine C whenever the call to C was made but by the time C gets called it now holds the number C<47>. Because we saved only a pointer to the original SV in C, any changes to -C<$ref> will be tracked by the pointer C. This means that +$ref will be tracked by the pointer C. This means that whenever C gets called, it will attempt to execute the code which is referenced by the SV* C. In this case though, it now refers to the integer C<47>, so expect Perl to complain @@ -1345,7 +1351,7 @@ So the methods C and C can be invoked like this call_PrintID('Mine', 'PrintID') ; The only thing to note is that in both the static and virtual methods, -the method name is not passed via the stack - it is used as the first +the method name is not passed via the stack--it is used as the first parameter to I. =head2 Using GIMME_V @@ -1479,9 +1485,9 @@ enclosing scope at some stage. In the event driven scenario that may never happen. This means that as time goes on, your program will create more and more temporaries, none of which will ever be freed. As each of these temporaries consumes some memory your program will -eventually consume all the available memory in your system - kapow! +eventually consume all the available memory in your system--kapow! -So here is the bottom line - if you are sure that control will revert +So here is the bottom line--if you are sure that control will revert back to the enclosing Perl scope fairly quickly after the end of your callback, then it isn't absolutely necessary to dispose explicitly of any temporaries you may have created. Mind you, if you are at all @@ -1573,7 +1579,7 @@ require is a means of storing the mapping between the opened file and the Perl subroutine we want to be called for that file. Say the i/o library has a function C which associates a C -function C with a file handle C - this assumes that it +function C with a file handle C--this assumes that it has also provided some routine to open the file and so obtain the file handle. @@ -1873,7 +1879,7 @@ of values> recoded to use C instead of C. SPAGAIN ; SP -= count ; - ax = (SP - stack_base) + 1 ; + ax = (SP - PL_stack_base) + 1 ; if (count != 2) croak("Big trouble\n") ; @@ -1903,7 +1909,7 @@ The code SPAGAIN ; SP -= count ; - ax = (SP - stack_base) + 1 ; + ax = (SP - PL_stack_base) + 1 ; sets the stack up so that we can use the C macro. @@ -1918,9 +1924,9 @@ refers to the last. =head2 Creating and calling an anonymous subroutine in C -As we've already shown, L can be used to invoke an -anonymous subroutine. However, our example showed how Perl script -invoking an XSUB to preform this operation. Let's see how it can be +As we've already shown, C can be used to invoke an +anonymous subroutine. However, our example showed a Perl script +invoking an XSUB to perform this operation. Let's see how it can be done inside our C code: ... @@ -1931,8 +1937,9 @@ done inside our C code: perl_call_sv(cvrv, G_VOID|G_NOARGS); -L is used to compile the anonymous subroutine, which -will be the return value as well. Once this code reference is in hand, it +C is used to compile the anonymous subroutine, which +will be the return value as well (read more about C in +L). Once this code reference is in hand, it can be mixed in with all the previous examples we've shown. =head1 SEE ALSO @@ -1941,7 +1948,7 @@ L, L, L =head1 AUTHOR -Paul Marquess > +Paul Marquess Special thanks to the following people who assisted in the creation of the document.