3 perlembed - how to embed perl in your C program
13 =item B<Use C from Perl?>
15 Read L<perlxstut>, L<perlxs>, L<h2xs>, L<perlguts>, and L<perlapi>.
17 =item B<Use a Unix program from Perl?>
19 Read about back-quotes and about C<system> and C<exec> in L<perlfunc>.
21 =item B<Use Perl from Perl?>
23 Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlfunc/require>
26 =item B<Use C from C?>
30 =item B<Use Perl from C?>
42 Compiling your C program
46 Adding a Perl interpreter to your C program
50 Calling a Perl subroutine from your C program
54 Evaluating a Perl statement from your C program
58 Performing Perl pattern matches and substitutions from your C program
62 Fiddling with the Perl stack from your C program
66 Maintaining a persistent interpreter
70 Maintaining multiple interpreter instances
74 Using Perl modules, which themselves use C libraries, from your C program
78 Embedding Perl under Win32
82 =head2 Compiling your C program
84 If you have trouble compiling the scripts in this documentation,
85 you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY
86 THE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.)
88 Also, every C program that uses Perl must link in the I<perl library>.
89 What's that, you ask? Perl is itself written in C; the perl library
90 is the collection of compiled C programs that were used to create your
91 perl executable (I</usr/bin/perl> or equivalent). (Corollary: you
92 can't use Perl from your C program unless Perl has been compiled on
93 your machine, or installed properly--that's why you shouldn't blithely
94 copy Perl executables from machine to machine without also copying the
97 When you use Perl from C, your C program will--usually--allocate,
98 "run", and deallocate a I<PerlInterpreter> object, which is defined by
101 If your copy of Perl is recent enough to contain this documentation
102 (version 5.002 or later), then the perl library (and I<EXTERN.h> and
103 I<perl.h>, which you'll also need) will reside in a directory
104 that looks like this:
106 /usr/local/lib/perl5/your_architecture_here/CORE
110 /usr/local/lib/perl5/CORE
112 or maybe something like
116 Execute this statement for a hint about where to find CORE:
118 perl -MConfig -e 'print $Config{archlib}'
120 Here's how you'd compile the example in the next section,
121 L</Adding a Perl interpreter to your C program>, on my Linux box:
123 % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
124 -I/usr/local/lib/perl5/i586-linux/5.003/CORE
125 -L/usr/local/lib/perl5/i586-linux/5.003/CORE
126 -o interp interp.c -lperl -lm
128 (That's all one line.) On my DEC Alpha running old 5.003_05, the
129 incantation is a bit different:
131 % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
132 -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
133 -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
134 -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
136 How can you figure out what to add? Assuming your Perl is post-5.001,
137 execute a C<perl -V> command and pay special attention to the "cc" and
138 "ccflags" information.
140 You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for
141 your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what
144 You'll also have to choose the appropriate library directory
145 (I</usr/local/lib/...>) for your machine. If your compiler complains
146 that certain functions are undefined, or that it can't locate
147 I<-lperl>, then you need to change the path following the C<-L>. If it
148 complains that it can't find I<EXTERN.h> and I<perl.h>, you need to
149 change the path following the C<-I>.
151 You may have to add extra libraries as well. Which ones?
152 Perhaps those printed by
154 perl -MConfig -e 'print $Config{libs}'
156 Provided your perl binary was properly configured and installed the
157 B<ExtUtils::Embed> module will determine all of this information for
160 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
162 If the B<ExtUtils::Embed> module isn't part of your Perl distribution,
163 you can retrieve it from
164 http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils/
165 (If this documentation came from your Perl distribution, then you're
166 running 5.004 or better and you already have it.)
168 The B<ExtUtils::Embed> kit on CPAN also contains all source code for
169 the examples in this document, tests, additional examples and other
170 information you may find useful.
172 =head2 Adding a Perl interpreter to your C program
174 In a sense, perl (the C program) is a good example of embedding Perl
175 (the language), so I'll demonstrate embedding with I<miniperlmain.c>,
176 included in the source distribution. Here's a bastardized, non-portable
177 version of I<miniperlmain.c> containing the essentials of embedding:
179 #include <EXTERN.h> /* from the Perl distribution */
180 #include <perl.h> /* from the Perl distribution */
182 static PerlInterpreter *my_perl; /*** The Perl interpreter ***/
184 int main(int argc, char **argv, char **env)
186 PERL_SYS_INIT3(&argc,&argv,&env);
187 my_perl = perl_alloc();
188 perl_construct(my_perl);
189 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
190 perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
192 perl_destruct(my_perl);
197 Notice that we don't use the C<env> pointer. Normally handed to
198 C<perl_parse> as its final argument, C<env> here is replaced by
199 C<NULL>, which means that the current environment will be used.
201 The macros PERL_SYS_INIT3() and PERL_SYS_TERM() provide system-specific
202 tune up of the C runtime environment necessary to run Perl interpreters;
203 they should only be called once regardless of how many interpreters you
204 create or destroy. Call PERL_SYS_INIT3() before you create your first
205 interpreter, and PERL_SYS_TERM() after you free your last interpreter.
207 Since PERL_SYS_INIT3() may change C<env>, it may be more appropriate to
208 provide C<env> as an argument to perl_parse().
210 Also notice that no matter what arguments you pass to perl_parse(),
211 PERL_SYS_INIT3() must be invoked on the C main() argc, argv and env and
214 Mind that argv[argc] must be NULL, same as those passed to a main
217 Now compile this program (I'll call it I<interp.c>) into an executable:
219 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
221 After a successful compilation, you'll be able to use I<interp> just
225 print "Pretty Good Perl \n";
226 print "10890 - 9801 is ", 10890 - 9801;
233 % interp -e 'printf("%x", 3735928559)'
236 You can also read and execute Perl statements from a file while in the
237 midst of your C program, by placing the filename in I<argv[1]> before
240 =head2 Calling a Perl subroutine from your C program
242 To call individual Perl subroutines, you can use any of the B<call_*>
243 functions documented in L<perlcall>.
244 In this example we'll use C<call_argv>.
246 That's shown below, in a program I'll call I<showtime.c>.
251 static PerlInterpreter *my_perl;
253 int main(int argc, char **argv, char **env)
255 char *args[] = { NULL };
256 PERL_SYS_INIT3(&argc,&argv,&env);
257 my_perl = perl_alloc();
258 perl_construct(my_perl);
260 perl_parse(my_perl, NULL, argc, argv, NULL);
261 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
263 /*** skipping perl_run() ***/
265 call_argv("showtime", G_DISCARD | G_NOARGS, args);
267 perl_destruct(my_perl);
272 where I<showtime> is a Perl subroutine that takes no arguments (that's the
273 I<G_NOARGS>) and for which I'll ignore the return value (that's the
274 I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>.
276 I'll define the I<showtime> subroutine in a file called I<showtime.pl>:
278 print "I shan't be printed.";
284 Simple enough. Now compile and run:
286 % cc -o showtime showtime.c \
287 `perl -MExtUtils::Embed -e ccopts -e ldopts`
288 % showtime showtime.pl
291 yielding the number of seconds that elapsed between January 1, 1970
292 (the beginning of the Unix epoch), and the moment I began writing this
295 In this particular case we don't have to call I<perl_run>, as we set
296 the PL_exit_flag PERL_EXIT_DESTRUCT_END which executes END blocks in
299 If you want to pass arguments to the Perl subroutine, you can add
300 strings to the C<NULL>-terminated C<args> list passed to
301 I<call_argv>. For other data types, or to examine return values,
302 you'll need to manipulate the Perl stack. That's demonstrated in
303 L</Fiddling with the Perl stack from your C program>.
305 =head2 Evaluating a Perl statement from your C program
307 Perl provides two API functions to evaluate pieces of Perl code.
308 These are L<perlapi/eval_sv> and L<perlapi/eval_pv>.
310 Arguably, these are the only routines you'll ever need to execute
311 snippets of Perl code from within your C program. Your code can be as
312 long as you wish; it can contain multiple statements; it can employ
313 L<perlfunc/use>, L<perlfunc/require>, and L<perlfunc/do> to
314 include external Perl files.
316 I<eval_pv> lets us evaluate individual Perl strings, and then
317 extract variables for coercion into C types. The following program,
318 I<string.c>, executes three Perl strings, extracting an C<int> from
319 the first, a C<float> from the second, and a C<char *> from the third.
324 static PerlInterpreter *my_perl;
326 main (int argc, char **argv, char **env)
328 char *embedding[] = { "", "-e", "0" };
330 PERL_SYS_INIT3(&argc,&argv,&env);
331 my_perl = perl_alloc();
332 perl_construct( my_perl );
334 perl_parse(my_perl, NULL, 3, embedding, NULL);
335 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
338 /** Treat $a as an integer **/
339 eval_pv("$a = 3; $a **= 2", TRUE);
340 printf("a = %d\n", SvIV(get_sv("a", 0)));
342 /** Treat $a as a float **/
343 eval_pv("$a = 3.14; $a **= 2", TRUE);
344 printf("a = %f\n", SvNV(get_sv("a", 0)));
346 /** Treat $a as a string **/
348 "$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
349 printf("a = %s\n", SvPV_nolen(get_sv("a", 0)));
351 perl_destruct(my_perl);
356 All of those strange functions with I<sv> in their names help convert Perl
357 scalars to C types. They're described in L<perlguts> and L<perlapi>.
359 If you compile and run I<string.c>, you'll see the results of using
360 I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
361 I<SvPV()> to create a string:
365 a = Just Another Perl Hacker
367 In the example above, we've created a global variable to temporarily
368 store the computed value of our eval'ed expression. It is also
369 possible and in most cases a better strategy to fetch the return value
370 from I<eval_pv()> instead. Example:
373 SV *val = eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
374 printf("%s\n", SvPV_nolen(val));
377 This way, we avoid namespace pollution by not creating global
378 variables and we've simplified our code as well.
380 =head2 Performing Perl pattern matches and substitutions from your C program
382 The I<eval_sv()> function lets us evaluate strings of Perl code, so we can
383 define some functions that use it to "specialize" in matches and
384 substitutions: I<match()>, I<substitute()>, and I<matches()>.
386 I32 match(SV *string, char *pattern);
388 Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
389 in your C program might appear as "/\\b\\w*\\b/"), match()
390 returns 1 if the string matches the pattern and 0 otherwise.
392 int substitute(SV **string, char *pattern);
394 Given a pointer to an C<SV> and an C<=~> operation (e.g.,
395 C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
396 within the C<SV> as according to the operation, returning the number of
399 SSize_t matches(SV *string, char *pattern, AV **matches);
401 Given an C<SV>, a pattern, and a pointer to an empty C<AV>,
402 matches() evaluates C<$string =~ $pattern> in a list context, and
403 fills in I<matches> with the array elements, returning the number of matches
406 Here's a sample program, I<match.c>, that uses all three (long lines have
412 static PerlInterpreter *my_perl;
414 /** my_eval_sv(code, error_check)
415 ** kinda like eval_sv(),
416 ** but we pop the return value off the stack
418 SV* my_eval_sv(SV *sv, I32 croak_on_error)
425 eval_sv(sv, G_SCALAR);
431 if (croak_on_error && SvTRUE(ERRSV))
432 croak(SvPVx_nolen(ERRSV));
437 /** match(string, pattern)
439 ** Used for matches in a scalar context.
441 ** Returns 1 if the match was successful; 0 otherwise.
444 I32 match(SV *string, char *pattern)
446 SV *command = newSV(0), *retval;
448 sv_setpvf(command, "my $string = '%s'; $string =~ %s",
449 SvPV_nolen(string), pattern);
451 retval = my_eval_sv(command, TRUE);
452 SvREFCNT_dec(command);
457 /** substitute(string, pattern)
459 ** Used for =~ operations that
460 ** modify their left-hand side (s/// and tr///)
462 ** Returns the number of successful matches, and
463 ** modifies the input string if there were any.
466 I32 substitute(SV **string, char *pattern)
468 SV *command = newSV(0), *retval;
470 sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
471 SvPV_nolen(*string), pattern);
473 retval = my_eval_sv(command, TRUE);
474 SvREFCNT_dec(command);
476 *string = get_sv("string", 0);
480 /** matches(string, pattern, matches)
482 ** Used for matches in a list context.
484 ** Returns the number of matches,
485 ** and fills in **matches with the matching substrings
488 SSize_t matches(SV *string, char *pattern, AV **match_list)
490 SV *command = newSV(0);
493 sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
494 SvPV_nolen(string), pattern);
496 my_eval_sv(command, TRUE);
497 SvREFCNT_dec(command);
499 *match_list = get_av("array", 0);
500 num_matches = av_top_index(*match_list) + 1;
505 main (int argc, char **argv, char **env)
507 char *embedding[] = { "", "-e", "0" };
512 PERL_SYS_INIT3(&argc,&argv,&env);
513 my_perl = perl_alloc();
514 perl_construct(my_perl);
515 perl_parse(my_perl, NULL, 3, embedding, NULL);
516 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
519 sv_setpv(text, "When he is at a convenience store and the "
520 "bill comes to some amount like 76 cents, Maynard is "
521 "aware that there is something he *should* do, something "
522 "that will enable him to get back a quarter, but he has "
523 "no idea *what*. He fumbles through his red squeezey "
524 "changepurse and gives the boy three extra pennies with "
525 "his dollar, hoping that he might luck into the correct "
526 "amount. The boy gives him back two of his own pennies "
527 "and then the big shiny quarter that is his prize. "
530 if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
531 printf("match: Text contains the word 'quarter'.\n\n");
533 printf("match: Text doesn't contain the word 'quarter'.\n\n");
535 if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
536 printf("match: Text contains the word 'eighth'.\n\n");
538 printf("match: Text doesn't contain the word 'eighth'.\n\n");
540 /** Match all occurrences of /wi../ **/
541 num_matches = matches(text, "m/(wi..)/g", &match_list);
542 printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
544 for (i = 0; i < num_matches; i++)
545 printf("match: %s\n",
546 SvPV_nolen(*av_fetch(match_list, i, FALSE)));
549 /** Remove all vowels from text **/
550 num_matches = substitute(&text, "s/[aeiou]//gi");
552 printf("substitute: s/[aeiou]//gi...%lu substitutions made.\n",
553 (unsigned long)num_matches);
554 printf("Now text is: %s\n\n", SvPV_nolen(text));
557 /** Attempt a substitution **/
558 if (!substitute(&text, "s/Perl/C/")) {
559 printf("substitute: s/Perl/C...No substitution made.\n\n");
563 PL_perl_destruct_level = 1;
564 perl_destruct(my_perl);
569 which produces the output (again, long lines have been wrapped here)
571 match: Text contains the word 'quarter'.
573 match: Text doesn't contain the word 'eighth'.
575 matches: m/(wi..)/g found 2 matches...
579 substitute: s/[aeiou]//gi...139 substitutions made.
580 Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
581 Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt
582 bck qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd
583 gvs th by thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct
584 mnt. Th by gvs hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s
587 substitute: s/Perl/C...No substitution made.
589 =head2 Fiddling with the Perl stack from your C program
591 When trying to explain stacks, most computer science textbooks mumble
592 something about spring-loaded columns of cafeteria plates: the last
593 thing you pushed on the stack is the first thing you pop off. That'll
594 do for our purposes: your C program will push some arguments onto "the Perl
595 stack", shut its eyes while some magic happens, and then pop the
596 results--the return value of your Perl subroutine--off the stack.
598 First you'll need to know how to convert between C types and Perl
599 types, with newSViv() and sv_setnv() and newAV() and all their
600 friends. They're described in L<perlguts> and L<perlapi>.
602 Then you'll need to know how to manipulate the Perl stack. That's
603 described in L<perlcall>.
605 Once you've understood those, embedding Perl in C is easy.
607 Because C has no builtin function for integer exponentiation, let's
608 make Perl's ** operator available to it (this is less useful than it
609 sounds, because Perl implements ** with C's I<pow()> function). First
610 I'll create a stub exponentiation function in I<power.pl>:
617 Now I'll create a C program, I<power.c>, with a function
618 I<PerlPower()> that contains all the perlguts necessary to push the
619 two arguments into I<expo()> and to pop the return value out. Take a
625 static PerlInterpreter *my_perl;
628 PerlPower(int a, int b)
630 dSP; /* initialize stack pointer */
631 ENTER; /* everything created after here */
632 SAVETMPS; /* ...is a temporary variable. */
633 PUSHMARK(SP); /* remember the stack pointer */
634 XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
635 XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
636 PUTBACK; /* make local stack pointer global */
637 call_pv("expo", G_SCALAR); /* call the function */
638 SPAGAIN; /* refresh stack pointer */
639 /* pop the return value from stack */
640 printf ("%d to the %dth power is %d.\n", a, b, POPi);
642 FREETMPS; /* free that return value */
643 LEAVE; /* ...and the XPUSHed "mortal" args.*/
646 int main (int argc, char **argv, char **env)
648 char *my_argv[] = { "", "power.pl" };
650 PERL_SYS_INIT3(&argc,&argv,&env);
651 my_perl = perl_alloc();
652 perl_construct( my_perl );
654 perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);
655 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
658 PerlPower(3, 4); /*** Compute 3 ** 4 ***/
660 perl_destruct(my_perl);
669 % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
672 3 to the 4th power is 81.
674 =head2 Maintaining a persistent interpreter
676 When developing interactive and/or potentially long-running
677 applications, it's a good idea to maintain a persistent interpreter
678 rather than allocating and constructing a new interpreter multiple
679 times. The major reason is speed: since Perl will only be loaded into
682 However, you have to be more cautious with namespace and variable
683 scoping when using a persistent interpreter. In previous examples
684 we've been using global variables in the default package C<main>. We
685 knew exactly what code would be run, and assumed we could avoid
686 variable collisions and outrageous symbol table growth.
688 Let's say your application is a server that will occasionally run Perl
689 code from some arbitrary file. Your server has no way of knowing what
690 code it's going to run. Very dangerous.
692 If the file is pulled in by C<perl_parse()>, compiled into a newly
693 constructed interpreter, and subsequently cleaned out with
694 C<perl_destruct()> afterwards, you're shielded from most namespace
697 One way to avoid namespace collisions in this scenario is to translate
698 the filename into a guaranteed-unique package name, and then compile
699 the code into that package using L<perlfunc/eval>. In the example
700 below, each file will only be compiled once. Or, the application
701 might choose to clean out the symbol table associated with the file
702 after it's no longer needed. Using L<perlapi/call_argv>, We'll
703 call the subroutine C<Embed::Persistent::eval_file> which lives in the
704 file C<persistent.pl> and pass the filename and boolean cleanup/cache
707 Note that the process will continue to grow for each file that it
708 uses. In addition, there might be C<AUTOLOAD>ed subroutines and other
709 conditions that cause Perl's symbol table to grow. You might want to
710 add some logic that keeps track of the process size, or restarts
711 itself after a certain number of requests, to ensure that memory
712 consumption is minimized. You'll also want to scope your variables
713 with L<perlfunc/my> whenever possible.
716 package Embed::Persistent;
721 use Symbol qw(delete_package);
723 sub valid_package_name {
725 $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
726 # second pass only for words starting with a digit
727 $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
729 # Dress it up as a real package name
731 return "Embed" . $string;
735 my($filename, $delete) = @_;
736 my $package = valid_package_name($filename);
737 my $mtime = -M $filename;
738 if(defined $Cache{$package}{mtime}
740 $Cache{$package}{mtime} <= $mtime)
742 # we have compiled this subroutine already,
743 # it has not been updated on disk, nothing left to do
744 print STDERR "already compiled $package->handler\n";
748 open FH, $filename or die "open '$filename' $!";
753 #wrap the code into a subroutine inside our unique package
754 my $eval = qq{package $package; sub handler { $sub; }};
756 # hide our variables within this block
757 my($filename,$mtime,$package,$sub);
762 #cache it unless we're cleaning out each time
763 $Cache{$package}{mtime} = $mtime unless $delete;
766 eval {$package->handler;};
769 delete_package($package) if $delete;
771 #take a look if you want
772 #print Devel::Symdump->rnew($package)->as_string, $/;
783 /* 1 = clean out filename's symbol table after each request,
790 #define BUFFER_SIZE 1024
792 static PerlInterpreter *my_perl = NULL;
795 main(int argc, char **argv, char **env)
797 char *embedding[] = { "", "persistent.pl" };
798 char *args[] = { "", DO_CLEAN, NULL };
799 char filename[BUFFER_SIZE];
802 PERL_SYS_INIT3(&argc,&argv,&env);
803 if((my_perl = perl_alloc()) == NULL) {
804 fprintf(stderr, "no memory!");
807 perl_construct(my_perl);
809 PL_origalen = 1; /* don't let $0 assignment update the
810 proctitle or embedding[0] */
811 exitstatus = perl_parse(my_perl, NULL, 2, embedding, NULL);
812 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
814 exitstatus = perl_run(my_perl);
816 while(printf("Enter file name: ") &&
817 fgets(filename, BUFFER_SIZE, stdin)) {
819 filename[strlen(filename)-1] = '\0'; /* strip \n */
820 /* call the subroutine,
821 passing it the filename as an argument */
823 call_argv("Embed::Persistent::eval_file",
824 G_DISCARD | G_EVAL, args);
828 fprintf(stderr, "eval error: %s\n", SvPV_nolen(ERRSV));
832 PL_perl_destruct_level = 0;
833 perl_destruct(my_perl);
841 % cc -o persistent persistent.c \
842 `perl -MExtUtils::Embed -e ccopts -e ldopts`
844 Here's an example script file:
847 my $string = "hello";
851 print "foo says: @_\n";
857 Enter file name: test.pl
859 Enter file name: test.pl
860 already compiled Embed::test_2epl->handler
864 =head2 Execution of END blocks
866 Traditionally END blocks have been executed at the end of the perl_run.
867 This causes problems for applications that never call perl_run. Since
868 perl 5.7.2 you can specify C<PL_exit_flags |= PERL_EXIT_DESTRUCT_END>
869 to get the new behaviour. This also enables the running of END blocks if
870 the perl_parse fails and C<perl_destruct> will return the exit value.
872 =head2 $0 assignments
874 When a perl script assigns a value to $0 then the perl runtime will
875 try to make this value show up as the program name reported by "ps" by
876 updating the memory pointed to by the argv passed to perl_parse() and
877 also calling API functions like setproctitle() where available. This
878 behaviour might not be appropriate when embedding perl and can be
879 disabled by assigning the value C<1> to the variable C<PL_origalen>
880 before perl_parse() is called.
882 The F<persistent.c> example above is for instance likely to segfault
883 when $0 is assigned to if the C<PL_origalen = 1;> assignment is
884 removed. This because perl will try to write to the read only memory
885 of the C<embedding[]> strings.
887 =head2 Maintaining multiple interpreter instances
889 Some rare applications will need to create more than one interpreter
890 during a session. Such an application might sporadically decide to
891 release any resources associated with the interpreter.
893 The program must take care to ensure that this takes place I<before>
894 the next interpreter is constructed. By default, when perl is not
895 built with any special options, the global variable
896 C<PL_perl_destruct_level> is set to C<0>, since extra cleaning isn't
897 usually needed when a program only ever creates a single interpreter
898 in its entire lifetime.
900 Setting C<PL_perl_destruct_level> to C<1> makes everything squeaky clean:
904 /* reset global variables here with PL_perl_destruct_level = 1 */
905 PL_perl_destruct_level = 1;
906 perl_construct(my_perl);
908 /* clean and reset _everything_ during perl_destruct */
909 PL_perl_destruct_level = 1;
910 perl_destruct(my_perl);
913 /* let's go do it again! */
916 When I<perl_destruct()> is called, the interpreter's syntax parse tree
917 and symbol tables are cleaned up, and global variables are reset. The
918 second assignment to C<PL_perl_destruct_level> is needed because
919 perl_construct resets it to C<0>.
921 Now suppose we have more than one interpreter instance running at the
922 same time. This is feasible, but only if you used the Configure option
923 C<-Dusemultiplicity> or the options C<-Dusethreads -Duseithreads> when
924 building perl. By default, enabling one of these Configure options
925 sets the per-interpreter global variable C<PL_perl_destruct_level> to
926 C<1>, so that thorough cleaning is automatic and interpreter variables
927 are initialized correctly. Even if you don't intend to run two or
928 more interpreters at the same time, but to run them sequentially, like
929 in the above example, it is recommended to build perl with the
930 C<-Dusemultiplicity> option otherwise some interpreter variables may
931 not be initialized correctly between consecutive runs and your
932 application may crash.
934 See also L<perlxs/Thread-aware system interfaces>.
936 Using C<-Dusethreads -Duseithreads> rather than C<-Dusemultiplicity>
937 is more appropriate if you intend to run multiple interpreters
938 concurrently in different threads, because it enables support for
939 linking in the thread libraries of your system with the interpreter.
947 /* we're going to embed two interpreters */
949 #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
951 int main(int argc, char **argv, char **env)
953 PerlInterpreter *one_perl, *two_perl;
954 char *one_args[] = { "one_perl", SAY_HELLO };
955 char *two_args[] = { "two_perl", SAY_HELLO };
957 PERL_SYS_INIT3(&argc,&argv,&env);
958 one_perl = perl_alloc();
959 two_perl = perl_alloc();
961 PERL_SET_CONTEXT(one_perl);
962 perl_construct(one_perl);
963 PERL_SET_CONTEXT(two_perl);
964 perl_construct(two_perl);
966 PERL_SET_CONTEXT(one_perl);
967 perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
968 PERL_SET_CONTEXT(two_perl);
969 perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
971 PERL_SET_CONTEXT(one_perl);
973 PERL_SET_CONTEXT(two_perl);
976 PERL_SET_CONTEXT(one_perl);
977 perl_destruct(one_perl);
978 PERL_SET_CONTEXT(two_perl);
979 perl_destruct(two_perl);
981 PERL_SET_CONTEXT(one_perl);
983 PERL_SET_CONTEXT(two_perl);
988 Note the calls to PERL_SET_CONTEXT(). These are necessary to initialize
989 the global state that tracks which interpreter is the "current" one on
990 the particular process or thread that may be running it. It should
991 always be used if you have more than one interpreter and are making
992 perl API calls on both interpreters in an interleaved fashion.
994 PERL_SET_CONTEXT(interp) should also be called whenever C<interp> is
995 used by a thread that did not create it (using either perl_alloc(), or
996 the more esoteric perl_clone()).
1000 % cc -o multiplicity multiplicity.c \
1001 `perl -MExtUtils::Embed -e ccopts -e ldopts`
1009 =head2 Using Perl modules, which themselves use C libraries, from your C
1012 If you've played with the examples above and tried to embed a script
1013 that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++
1014 library, this probably happened:
1017 Can't load module Socket, dynamic loading not available in this perl.
1018 (You may need to build a new perl executable which either supports
1019 dynamic loading or has the Socket module statically linked into it.)
1024 Your interpreter doesn't know how to communicate with these extensions
1025 on its own. A little glue will help. Up until now you've been
1026 calling I<perl_parse()>, handing it NULL for the second argument:
1028 perl_parse(my_perl, NULL, argc, my_argv, NULL);
1030 That's where the glue code can be inserted to create the initial contact
1031 between Perl and linked C/C++ routines. Let's take a look some pieces of
1032 I<perlmain.c> to see how Perl does this:
1034 static void xs_init (pTHX);
1036 EXTERN_C void boot_DynaLoader (pTHX_ CV* cv);
1037 EXTERN_C void boot_Socket (pTHX_ CV* cv);
1043 char *file = __FILE__;
1044 /* DynaLoader is a special case */
1045 newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
1046 newXS("Socket::bootstrap", boot_Socket, file);
1049 Simply put: for each extension linked with your Perl executable
1050 (determined during its initial configuration on your
1051 computer or when adding a new extension),
1052 a Perl subroutine is created to incorporate the extension's
1053 routines. Normally, that subroutine is named
1054 I<Module::bootstrap()> and is invoked when you say I<use Module>. In
1055 turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
1056 counterpart for each of the extension's XSUBs. Don't worry about this
1057 part; leave that to the I<xsubpp> and extension authors. If your
1058 extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
1059 for you on the fly. In fact, if you have a working DynaLoader then there
1060 is rarely any need to link in any other extensions statically.
1063 Once you have this code, slap it into the second argument of I<perl_parse()>:
1066 perl_parse(my_perl, xs_init, argc, my_argv, NULL);
1071 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
1075 use SomeDynamicallyLoadedModule;
1077 print "Now I can use extensions!\n"'
1079 B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
1081 % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
1082 % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
1083 % cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
1084 % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
1086 Consult L<perlxs>, L<perlguts>, and L<perlapi> for more details.
1088 =head2 Using embedded Perl with POSIX locales
1090 (See L<perllocale> for information about these.)
1091 When a Perl interpreter normally starts up, it tells the system it wants
1092 to use the system's default locale. This is often, but not necessarily,
1093 the "C" or "POSIX" locale. Absent a S<C<"use locale">> within the perl
1094 code, this mostly has no effect (but see L<perllocale/Not within the
1095 scope of "use locale">). Also, there is not a problem if the
1096 locale you want to use in your embedded Perl is the same as the system
1097 default. However, this doesn't work if you have set up and want to use
1098 a locale that isn't the system default one. Starting in Perl v5.20, you
1099 can tell the embedded Perl interpreter that the locale is already
1100 properly set up, and to skip doing its own normal initialization. It
1101 skips if the environment variable C<PERL_SKIP_LOCALE_INIT> is set (even
1102 if set to 0 or C<"">). A Perl that has this capability will define the
1103 C pre-processor symbol C<HAS_SKIP_LOCALE_INIT>. This allows code that
1104 has to work with multiple Perl versions to do some sort of work-around
1105 when confronted with an earlier Perl.
1109 If you completely hide the short forms of the Perl public API,
1110 add -DPERL_NO_SHORT_NAMES to the compilation flags. This means that
1111 for example instead of writing
1113 warn("%d bottles of beer on the wall", bottlecount);
1115 you will have to write the explicit full form
1117 Perl_warn(aTHX_ "%d bottles of beer on the wall", bottlecount);
1119 (See L<perlguts/"Background and PERL_IMPLICIT_CONTEXT"> for the explanation
1120 of the C<aTHX_>. ) Hiding the short forms is very useful for avoiding
1121 all sorts of nasty (C preprocessor or otherwise) conflicts with other
1122 software packages (Perl defines about 2400 APIs with these short names,
1123 take or leave few hundred, so there certainly is room for conflict.)
1127 You can sometimes I<write faster code> in C, but
1128 you can always I<write code faster> in Perl. Because you can use
1129 each from the other, combine them as you wish.
1134 Jon Orwant <F<orwant@media.mit.edu>> and Doug MacEachern
1135 <F<dougm@covalent.net>>, with small contributions from Tim Bunce, Tom
1136 Christiansen, Guy Decoux, Hallvard Furuseth, Dov Grobgeld, and Ilya
1139 Doug MacEachern has an article on embedding in Volume 1, Issue 4 of
1140 The Perl Journal ( http://www.tpj.com/ ). Doug is also the developer of the
1141 most widely-used Perl embedding: the mod_perl system
1142 (perl.apache.org), which embeds Perl in the Apache web server.
1143 Oracle, Binary Evolution, ActiveState, and Ben Sugars's nsapi_perl
1144 have used this model for Oracle, Netscape and Internet Information
1145 Server Perl plugins.
1149 Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant. All
1152 This document may be distributed under the same terms as Perl itself.