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 Now compile this program (I'll call it I<interp.c>) into an executable:
216 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
218 After a successful compilation, you'll be able to use I<interp> just
222 print "Pretty Good Perl \n";
223 print "10890 - 9801 is ", 10890 - 9801;
230 % interp -e 'printf("%x", 3735928559)'
233 You can also read and execute Perl statements from a file while in the
234 midst of your C program, by placing the filename in I<argv[1]> before
237 =head2 Calling a Perl subroutine from your C program
239 To call individual Perl subroutines, you can use any of the B<call_*>
240 functions documented in L<perlcall>.
241 In this example we'll use C<call_argv>.
243 That's shown below, in a program I'll call I<showtime.c>.
248 static PerlInterpreter *my_perl;
250 int main(int argc, char **argv, char **env)
252 char *args[] = { NULL };
253 PERL_SYS_INIT3(&argc,&argv,&env);
254 my_perl = perl_alloc();
255 perl_construct(my_perl);
257 perl_parse(my_perl, NULL, argc, argv, NULL);
258 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
260 /*** skipping perl_run() ***/
262 call_argv("showtime", G_DISCARD | G_NOARGS, args);
264 perl_destruct(my_perl);
269 where I<showtime> is a Perl subroutine that takes no arguments (that's the
270 I<G_NOARGS>) and for which I'll ignore the return value (that's the
271 I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>.
273 I'll define the I<showtime> subroutine in a file called I<showtime.pl>:
275 print "I shan't be printed.";
281 Simple enough. Now compile and run:
283 % cc -o showtime showtime.c \
284 `perl -MExtUtils::Embed -e ccopts -e ldopts`
285 % showtime showtime.pl
288 yielding the number of seconds that elapsed between January 1, 1970
289 (the beginning of the Unix epoch), and the moment I began writing this
292 In this particular case we don't have to call I<perl_run>, as we set
293 the PL_exit_flag PERL_EXIT_DESTRUCT_END which executes END blocks in
296 If you want to pass arguments to the Perl subroutine, you can add
297 strings to the C<NULL>-terminated C<args> list passed to
298 I<call_argv>. For other data types, or to examine return values,
299 you'll need to manipulate the Perl stack. That's demonstrated in
300 L<Fiddling with the Perl stack from your C program>.
302 =head2 Evaluating a Perl statement from your C program
304 Perl provides two API functions to evaluate pieces of Perl code.
305 These are L<perlapi/eval_sv> and L<perlapi/eval_pv>.
307 Arguably, these are the only routines you'll ever need to execute
308 snippets of Perl code from within your C program. Your code can be as
309 long as you wish; it can contain multiple statements; it can employ
310 L<perlfunc/use>, L<perlfunc/require>, and L<perlfunc/do> to
311 include external Perl files.
313 I<eval_pv> lets us evaluate individual Perl strings, and then
314 extract variables for coercion into C types. The following program,
315 I<string.c>, executes three Perl strings, extracting an C<int> from
316 the first, a C<float> from the second, and a C<char *> from the third.
321 static PerlInterpreter *my_perl;
323 main (int argc, char **argv, char **env)
325 char *embedding[] = { "", "-e", "0" };
327 PERL_SYS_INIT3(&argc,&argv,&env);
328 my_perl = perl_alloc();
329 perl_construct( my_perl );
331 perl_parse(my_perl, NULL, 3, embedding, NULL);
332 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
335 /** Treat $a as an integer **/
336 eval_pv("$a = 3; $a **= 2", TRUE);
337 printf("a = %d\n", SvIV(get_sv("a", 0)));
339 /** Treat $a as a float **/
340 eval_pv("$a = 3.14; $a **= 2", TRUE);
341 printf("a = %f\n", SvNV(get_sv("a", 0)));
343 /** Treat $a as a string **/
345 "$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
346 printf("a = %s\n", SvPV_nolen(get_sv("a", 0)));
348 perl_destruct(my_perl);
353 All of those strange functions with I<sv> in their names help convert Perl
354 scalars to C types. They're described in L<perlguts> and L<perlapi>.
356 If you compile and run I<string.c>, you'll see the results of using
357 I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
358 I<SvPV()> to create a string:
362 a = Just Another Perl Hacker
364 In the example above, we've created a global variable to temporarily
365 store the computed value of our eval'ed expression. It is also
366 possible and in most cases a better strategy to fetch the return value
367 from I<eval_pv()> instead. Example:
370 SV *val = eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
371 printf("%s\n", SvPV_nolen(val));
374 This way, we avoid namespace pollution by not creating global
375 variables and we've simplified our code as well.
377 =head2 Performing Perl pattern matches and substitutions from your C program
379 The I<eval_sv()> function lets us evaluate strings of Perl code, so we can
380 define some functions that use it to "specialize" in matches and
381 substitutions: I<match()>, I<substitute()>, and I<matches()>.
383 I32 match(SV *string, char *pattern);
385 Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
386 in your C program might appear as "/\\b\\w*\\b/"), match()
387 returns 1 if the string matches the pattern and 0 otherwise.
389 int substitute(SV **string, char *pattern);
391 Given a pointer to an C<SV> and an C<=~> operation (e.g.,
392 C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
393 within the C<SV> as according to the operation, returning the number of
396 SSize_t matches(SV *string, char *pattern, AV **matches);
398 Given an C<SV>, a pattern, and a pointer to an empty C<AV>,
399 matches() evaluates C<$string =~ $pattern> in a list context, and
400 fills in I<matches> with the array elements, returning the number of matches
403 Here's a sample program, I<match.c>, that uses all three (long lines have
409 static PerlInterpreter *my_perl;
411 /** my_eval_sv(code, error_check)
412 ** kinda like eval_sv(),
413 ** but we pop the return value off the stack
415 SV* my_eval_sv(SV *sv, I32 croak_on_error)
422 eval_sv(sv, G_SCALAR);
428 if (croak_on_error && SvTRUE(ERRSV))
429 croak(SvPVx_nolen(ERRSV));
434 /** match(string, pattern)
436 ** Used for matches in a scalar context.
438 ** Returns 1 if the match was successful; 0 otherwise.
441 I32 match(SV *string, char *pattern)
443 SV *command = newSV(0), *retval;
445 sv_setpvf(command, "my $string = '%s'; $string =~ %s",
446 SvPV_nolen(string), pattern);
448 retval = my_eval_sv(command, TRUE);
449 SvREFCNT_dec(command);
454 /** substitute(string, pattern)
456 ** Used for =~ operations that
457 ** modify their left-hand side (s/// and tr///)
459 ** Returns the number of successful matches, and
460 ** modifies the input string if there were any.
463 I32 substitute(SV **string, char *pattern)
465 SV *command = newSV(0), *retval;
467 sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
468 SvPV_nolen(*string), pattern);
470 retval = my_eval_sv(command, TRUE);
471 SvREFCNT_dec(command);
473 *string = get_sv("string", 0);
477 /** matches(string, pattern, matches)
479 ** Used for matches in a list context.
481 ** Returns the number of matches,
482 ** and fills in **matches with the matching substrings
485 SSize_t matches(SV *string, char *pattern, AV **match_list)
487 SV *command = newSV(0);
490 sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
491 SvPV_nolen(string), pattern);
493 my_eval_sv(command, TRUE);
494 SvREFCNT_dec(command);
496 *match_list = get_av("array", 0);
497 num_matches = av_top_index(*match_list) + 1;
502 main (int argc, char **argv, char **env)
504 char *embedding[] = { "", "-e", "0" };
509 PERL_SYS_INIT3(&argc,&argv,&env);
510 my_perl = perl_alloc();
511 perl_construct(my_perl);
512 perl_parse(my_perl, NULL, 3, embedding, NULL);
513 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
516 sv_setpv(text, "When he is at a convenience store and the "
517 "bill comes to some amount like 76 cents, Maynard is "
518 "aware that there is something he *should* do, something "
519 "that will enable him to get back a quarter, but he has "
520 "no idea *what*. He fumbles through his red squeezey "
521 "changepurse and gives the boy three extra pennies with "
522 "his dollar, hoping that he might luck into the correct "
523 "amount. The boy gives him back two of his own pennies "
524 "and then the big shiny quarter that is his prize. "
527 if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
528 printf("match: Text contains the word 'quarter'.\n\n");
530 printf("match: Text doesn't contain the word 'quarter'.\n\n");
532 if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
533 printf("match: Text contains the word 'eighth'.\n\n");
535 printf("match: Text doesn't contain the word 'eighth'.\n\n");
537 /** Match all occurrences of /wi../ **/
538 num_matches = matches(text, "m/(wi..)/g", &match_list);
539 printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
541 for (i = 0; i < num_matches; i++)
542 printf("match: %s\n",
543 SvPV_nolen(*av_fetch(match_list, i, FALSE)));
546 /** Remove all vowels from text **/
547 num_matches = substitute(&text, "s/[aeiou]//gi");
549 printf("substitute: s/[aeiou]//gi...%lu substitutions made.\n",
550 (unsigned long)num_matches);
551 printf("Now text is: %s\n\n", SvPV_nolen(text));
554 /** Attempt a substitution **/
555 if (!substitute(&text, "s/Perl/C/")) {
556 printf("substitute: s/Perl/C...No substitution made.\n\n");
560 PL_perl_destruct_level = 1;
561 perl_destruct(my_perl);
566 which produces the output (again, long lines have been wrapped here)
568 match: Text contains the word 'quarter'.
570 match: Text doesn't contain the word 'eighth'.
572 matches: m/(wi..)/g found 2 matches...
576 substitute: s/[aeiou]//gi...139 substitutions made.
577 Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
578 Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt
579 bck qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd
580 gvs th by thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct
581 mnt. Th by gvs hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s
584 substitute: s/Perl/C...No substitution made.
586 =head2 Fiddling with the Perl stack from your C program
588 When trying to explain stacks, most computer science textbooks mumble
589 something about spring-loaded columns of cafeteria plates: the last
590 thing you pushed on the stack is the first thing you pop off. That'll
591 do for our purposes: your C program will push some arguments onto "the Perl
592 stack", shut its eyes while some magic happens, and then pop the
593 results--the return value of your Perl subroutine--off the stack.
595 First you'll need to know how to convert between C types and Perl
596 types, with newSViv() and sv_setnv() and newAV() and all their
597 friends. They're described in L<perlguts> and L<perlapi>.
599 Then you'll need to know how to manipulate the Perl stack. That's
600 described in L<perlcall>.
602 Once you've understood those, embedding Perl in C is easy.
604 Because C has no builtin function for integer exponentiation, let's
605 make Perl's ** operator available to it (this is less useful than it
606 sounds, because Perl implements ** with C's I<pow()> function). First
607 I'll create a stub exponentiation function in I<power.pl>:
614 Now I'll create a C program, I<power.c>, with a function
615 I<PerlPower()> that contains all the perlguts necessary to push the
616 two arguments into I<expo()> and to pop the return value out. Take a
622 static PerlInterpreter *my_perl;
625 PerlPower(int a, int b)
627 dSP; /* initialize stack pointer */
628 ENTER; /* everything created after here */
629 SAVETMPS; /* ...is a temporary variable. */
630 PUSHMARK(SP); /* remember the stack pointer */
631 XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
632 XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
633 PUTBACK; /* make local stack pointer global */
634 call_pv("expo", G_SCALAR); /* call the function */
635 SPAGAIN; /* refresh stack pointer */
636 /* pop the return value from stack */
637 printf ("%d to the %dth power is %d.\n", a, b, POPi);
639 FREETMPS; /* free that return value */
640 LEAVE; /* ...and the XPUSHed "mortal" args.*/
643 int main (int argc, char **argv, char **env)
645 char *my_argv[] = { "", "power.pl" };
647 PERL_SYS_INIT3(&argc,&argv,&env);
648 my_perl = perl_alloc();
649 perl_construct( my_perl );
651 perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);
652 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
655 PerlPower(3, 4); /*** Compute 3 ** 4 ***/
657 perl_destruct(my_perl);
666 % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
669 3 to the 4th power is 81.
671 =head2 Maintaining a persistent interpreter
673 When developing interactive and/or potentially long-running
674 applications, it's a good idea to maintain a persistent interpreter
675 rather than allocating and constructing a new interpreter multiple
676 times. The major reason is speed: since Perl will only be loaded into
679 However, you have to be more cautious with namespace and variable
680 scoping when using a persistent interpreter. In previous examples
681 we've been using global variables in the default package C<main>. We
682 knew exactly what code would be run, and assumed we could avoid
683 variable collisions and outrageous symbol table growth.
685 Let's say your application is a server that will occasionally run Perl
686 code from some arbitrary file. Your server has no way of knowing what
687 code it's going to run. Very dangerous.
689 If the file is pulled in by C<perl_parse()>, compiled into a newly
690 constructed interpreter, and subsequently cleaned out with
691 C<perl_destruct()> afterwards, you're shielded from most namespace
694 One way to avoid namespace collisions in this scenario is to translate
695 the filename into a guaranteed-unique package name, and then compile
696 the code into that package using L<perlfunc/eval>. In the example
697 below, each file will only be compiled once. Or, the application
698 might choose to clean out the symbol table associated with the file
699 after it's no longer needed. Using L<perlapi/call_argv>, We'll
700 call the subroutine C<Embed::Persistent::eval_file> which lives in the
701 file C<persistent.pl> and pass the filename and boolean cleanup/cache
704 Note that the process will continue to grow for each file that it
705 uses. In addition, there might be C<AUTOLOAD>ed subroutines and other
706 conditions that cause Perl's symbol table to grow. You might want to
707 add some logic that keeps track of the process size, or restarts
708 itself after a certain number of requests, to ensure that memory
709 consumption is minimized. You'll also want to scope your variables
710 with L<perlfunc/my> whenever possible.
713 package Embed::Persistent;
718 use Symbol qw(delete_package);
720 sub valid_package_name {
722 $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
723 # second pass only for words starting with a digit
724 $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
726 # Dress it up as a real package name
728 return "Embed" . $string;
732 my($filename, $delete) = @_;
733 my $package = valid_package_name($filename);
734 my $mtime = -M $filename;
735 if(defined $Cache{$package}{mtime}
737 $Cache{$package}{mtime} <= $mtime)
739 # we have compiled this subroutine already,
740 # it has not been updated on disk, nothing left to do
741 print STDERR "already compiled $package->handler\n";
745 open FH, $filename or die "open '$filename' $!";
750 #wrap the code into a subroutine inside our unique package
751 my $eval = qq{package $package; sub handler { $sub; }};
753 # hide our variables within this block
754 my($filename,$mtime,$package,$sub);
759 #cache it unless we're cleaning out each time
760 $Cache{$package}{mtime} = $mtime unless $delete;
763 eval {$package->handler;};
766 delete_package($package) if $delete;
768 #take a look if you want
769 #print Devel::Symdump->rnew($package)->as_string, $/;
780 /* 1 = clean out filename's symbol table after each request,
787 #define BUFFER_SIZE 1024
789 static PerlInterpreter *my_perl = NULL;
792 main(int argc, char **argv, char **env)
794 char *embedding[] = { "", "persistent.pl" };
795 char *args[] = { "", DO_CLEAN, NULL };
796 char filename[BUFFER_SIZE];
799 PERL_SYS_INIT3(&argc,&argv,&env);
800 if((my_perl = perl_alloc()) == NULL) {
801 fprintf(stderr, "no memory!");
804 perl_construct(my_perl);
806 PL_origalen = 1; /* don't let $0 assignment update the
807 proctitle or embedding[0] */
808 exitstatus = perl_parse(my_perl, NULL, 2, embedding, NULL);
809 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
811 exitstatus = perl_run(my_perl);
813 while(printf("Enter file name: ") &&
814 fgets(filename, BUFFER_SIZE, stdin)) {
816 filename[strlen(filename)-1] = '\0'; /* strip \n */
817 /* call the subroutine,
818 passing it the filename as an argument */
820 call_argv("Embed::Persistent::eval_file",
821 G_DISCARD | G_EVAL, args);
825 fprintf(stderr, "eval error: %s\n", SvPV_nolen(ERRSV));
829 PL_perl_destruct_level = 0;
830 perl_destruct(my_perl);
838 % cc -o persistent persistent.c \
839 `perl -MExtUtils::Embed -e ccopts -e ldopts`
841 Here's an example script file:
844 my $string = "hello";
848 print "foo says: @_\n";
854 Enter file name: test.pl
856 Enter file name: test.pl
857 already compiled Embed::test_2epl->handler
861 =head2 Execution of END blocks
863 Traditionally END blocks have been executed at the end of the perl_run.
864 This causes problems for applications that never call perl_run. Since
865 perl 5.7.2 you can specify C<PL_exit_flags |= PERL_EXIT_DESTRUCT_END>
866 to get the new behaviour. This also enables the running of END blocks if
867 the perl_parse fails and C<perl_destruct> will return the exit value.
869 =head2 $0 assignments
871 When a perl script assigns a value to $0 then the perl runtime will
872 try to make this value show up as the program name reported by "ps" by
873 updating the memory pointed to by the argv passed to perl_parse() and
874 also calling API functions like setproctitle() where available. This
875 behaviour might not be appropriate when embedding perl and can be
876 disabled by assigning the value C<1> to the variable C<PL_origalen>
877 before perl_parse() is called.
879 The F<persistent.c> example above is for instance likely to segfault
880 when $0 is assigned to if the C<PL_origalen = 1;> assignment is
881 removed. This because perl will try to write to the read only memory
882 of the C<embedding[]> strings.
884 =head2 Maintaining multiple interpreter instances
886 Some rare applications will need to create more than one interpreter
887 during a session. Such an application might sporadically decide to
888 release any resources associated with the interpreter.
890 The program must take care to ensure that this takes place I<before>
891 the next interpreter is constructed. By default, when perl is not
892 built with any special options, the global variable
893 C<PL_perl_destruct_level> is set to C<0>, since extra cleaning isn't
894 usually needed when a program only ever creates a single interpreter
895 in its entire lifetime.
897 Setting C<PL_perl_destruct_level> to C<1> makes everything squeaky clean:
901 /* reset global variables here with PL_perl_destruct_level = 1 */
902 PL_perl_destruct_level = 1;
903 perl_construct(my_perl);
905 /* clean and reset _everything_ during perl_destruct */
906 PL_perl_destruct_level = 1;
907 perl_destruct(my_perl);
910 /* let's go do it again! */
913 When I<perl_destruct()> is called, the interpreter's syntax parse tree
914 and symbol tables are cleaned up, and global variables are reset. The
915 second assignment to C<PL_perl_destruct_level> is needed because
916 perl_construct resets it to C<0>.
918 Now suppose we have more than one interpreter instance running at the
919 same time. This is feasible, but only if you used the Configure option
920 C<-Dusemultiplicity> or the options C<-Dusethreads -Duseithreads> when
921 building perl. By default, enabling one of these Configure options
922 sets the per-interpreter global variable C<PL_perl_destruct_level> to
923 C<1>, so that thorough cleaning is automatic and interpreter variables
924 are initialized correctly. Even if you don't intend to run two or
925 more interpreters at the same time, but to run them sequentially, like
926 in the above example, it is recommended to build perl with the
927 C<-Dusemultiplicity> option otherwise some interpreter variables may
928 not be initialized correctly between consecutive runs and your
929 application may crash.
931 See also L<perlxs/Thread-aware system interfaces>.
933 Using C<-Dusethreads -Duseithreads> rather than C<-Dusemultiplicity>
934 is more appropriate if you intend to run multiple interpreters
935 concurrently in different threads, because it enables support for
936 linking in the thread libraries of your system with the interpreter.
944 /* we're going to embed two interpreters */
946 #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
948 int main(int argc, char **argv, char **env)
950 PerlInterpreter *one_perl, *two_perl;
951 char *one_args[] = { "one_perl", SAY_HELLO };
952 char *two_args[] = { "two_perl", SAY_HELLO };
954 PERL_SYS_INIT3(&argc,&argv,&env);
955 one_perl = perl_alloc();
956 two_perl = perl_alloc();
958 PERL_SET_CONTEXT(one_perl);
959 perl_construct(one_perl);
960 PERL_SET_CONTEXT(two_perl);
961 perl_construct(two_perl);
963 PERL_SET_CONTEXT(one_perl);
964 perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
965 PERL_SET_CONTEXT(two_perl);
966 perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
968 PERL_SET_CONTEXT(one_perl);
970 PERL_SET_CONTEXT(two_perl);
973 PERL_SET_CONTEXT(one_perl);
974 perl_destruct(one_perl);
975 PERL_SET_CONTEXT(two_perl);
976 perl_destruct(two_perl);
978 PERL_SET_CONTEXT(one_perl);
980 PERL_SET_CONTEXT(two_perl);
985 Note the calls to PERL_SET_CONTEXT(). These are necessary to initialize
986 the global state that tracks which interpreter is the "current" one on
987 the particular process or thread that may be running it. It should
988 always be used if you have more than one interpreter and are making
989 perl API calls on both interpreters in an interleaved fashion.
991 PERL_SET_CONTEXT(interp) should also be called whenever C<interp> is
992 used by a thread that did not create it (using either perl_alloc(), or
993 the more esoteric perl_clone()).
997 % cc -o multiplicity multiplicity.c \
998 `perl -MExtUtils::Embed -e ccopts -e ldopts`
1006 =head2 Using Perl modules, which themselves use C libraries, from your C
1009 If you've played with the examples above and tried to embed a script
1010 that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++
1011 library, this probably happened:
1014 Can't load module Socket, dynamic loading not available in this perl.
1015 (You may need to build a new perl executable which either supports
1016 dynamic loading or has the Socket module statically linked into it.)
1021 Your interpreter doesn't know how to communicate with these extensions
1022 on its own. A little glue will help. Up until now you've been
1023 calling I<perl_parse()>, handing it NULL for the second argument:
1025 perl_parse(my_perl, NULL, argc, my_argv, NULL);
1027 That's where the glue code can be inserted to create the initial contact
1028 between Perl and linked C/C++ routines. Let's take a look some pieces of
1029 I<perlmain.c> to see how Perl does this:
1031 static void xs_init (pTHX);
1033 EXTERN_C void boot_DynaLoader (pTHX_ CV* cv);
1034 EXTERN_C void boot_Socket (pTHX_ CV* cv);
1040 char *file = __FILE__;
1041 /* DynaLoader is a special case */
1042 newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
1043 newXS("Socket::bootstrap", boot_Socket, file);
1046 Simply put: for each extension linked with your Perl executable
1047 (determined during its initial configuration on your
1048 computer or when adding a new extension),
1049 a Perl subroutine is created to incorporate the extension's
1050 routines. Normally, that subroutine is named
1051 I<Module::bootstrap()> and is invoked when you say I<use Module>. In
1052 turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
1053 counterpart for each of the extension's XSUBs. Don't worry about this
1054 part; leave that to the I<xsubpp> and extension authors. If your
1055 extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
1056 for you on the fly. In fact, if you have a working DynaLoader then there
1057 is rarely any need to link in any other extensions statically.
1060 Once you have this code, slap it into the second argument of I<perl_parse()>:
1063 perl_parse(my_perl, xs_init, argc, my_argv, NULL);
1068 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
1072 use SomeDynamicallyLoadedModule;
1074 print "Now I can use extensions!\n"'
1076 B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
1078 % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
1079 % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
1080 % cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
1081 % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
1083 Consult L<perlxs>, L<perlguts>, and L<perlapi> for more details.
1085 =head2 Using embedded Perl with POSIX locales
1087 (See L<perllocale> for information about these.)
1088 When a Perl interpreter normally starts up, it tells the system it wants
1089 to use the system's default locale. This is often, but not necessarily,
1090 the "C" or "POSIX" locale. Absent a S<C<"use locale">> within the perl
1091 code, this mostly has no effect (but see L<perllocale/Not within the
1092 scope of any "use locale" variant>). Also, there is not a problem if the
1093 locale you want to use in your embedded Perl is the same as the system
1094 default. However, this doesn't work if you have set up and want to use
1095 a locale that isn't the system default one. Starting in Perl v5.20, you
1096 can tell the embedded Perl interpreter that the locale is already
1097 properly set up, and to skip doing its own normal initialization. It
1098 skips if the environment variable C<PERL_SKIP_LOCALE_INIT> is set (even
1099 if set to 0 or C<"">). A Perl that has this capability will define the
1100 C pre-processor symbol C<HAS_SKIP_LOCALE_INIT>. This allows code that
1101 has to work with multiple Perl versions to do some sort of work-around
1102 when confronted with an earlier Perl.
1106 If you completely hide the short forms of the Perl public API,
1107 add -DPERL_NO_SHORT_NAMES to the compilation flags. This means that
1108 for example instead of writing
1110 warn("%d bottles of beer on the wall", bottlecount);
1112 you will have to write the explicit full form
1114 Perl_warn(aTHX_ "%d bottles of beer on the wall", bottlecount);
1116 (See L<perlguts/"Background and PERL_IMPLICIT_CONTEXT"> for the explanation
1117 of the C<aTHX_>. ) Hiding the short forms is very useful for avoiding
1118 all sorts of nasty (C preprocessor or otherwise) conflicts with other
1119 software packages (Perl defines about 2400 APIs with these short names,
1120 take or leave few hundred, so there certainly is room for conflict.)
1124 You can sometimes I<write faster code> in C, but
1125 you can always I<write code faster> in Perl. Because you can use
1126 each from the other, combine them as you wish.
1131 Jon Orwant <F<orwant@media.mit.edu>> and Doug MacEachern
1132 <F<dougm@covalent.net>>, with small contributions from Tim Bunce, Tom
1133 Christiansen, Guy Decoux, Hallvard Furuseth, Dov Grobgeld, and Ilya
1136 Doug MacEachern has an article on embedding in Volume 1, Issue 4 of
1137 The Perl Journal ( http://www.tpj.com/ ). Doug is also the developer of the
1138 most widely-used Perl embedding: the mod_perl system
1139 (perl.apache.org), which embeds Perl in the Apache web server.
1140 Oracle, Binary Evolution, ActiveState, and Ben Sugars's nsapi_perl
1141 have used this model for Oracle, Netscape and Internet Information
1142 Server Perl plugins.
1146 Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant. All
1149 This document may be distributed under the same terms as Perl itself.