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, nonportable
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. The macros
200 PERL_SYS_INIT3() and PERL_SYS_TERM() provide system-specific tune up
201 of the C runtime environment necessary to run Perl interpreters; since
202 PERL_SYS_INIT3() may change C<env>, it may be more appropriate to provide
203 C<env> as an argument to perl_parse().
205 Now compile this program (I'll call it I<interp.c>) into an executable:
207 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
209 After a successful compilation, you'll be able to use I<interp> just
213 print "Pretty Good Perl \n";
214 print "10890 - 9801 is ", 10890 - 9801;
221 % interp -e 'printf("%x", 3735928559)'
224 You can also read and execute Perl statements from a file while in the
225 midst of your C program, by placing the filename in I<argv[1]> before
228 =head2 Calling a Perl subroutine from your C program
230 To call individual Perl subroutines, you can use any of the B<call_*>
231 functions documented in L<perlcall>.
232 In this example we'll use C<call_argv>.
234 That's shown below, in a program I'll call I<showtime.c>.
239 static PerlInterpreter *my_perl;
241 int main(int argc, char **argv, char **env)
243 char *args[] = { NULL };
244 PERL_SYS_INIT3(&argc,&argv,&env);
245 my_perl = perl_alloc();
246 perl_construct(my_perl);
248 perl_parse(my_perl, NULL, argc, argv, NULL);
249 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
251 /*** skipping perl_run() ***/
253 call_argv("showtime", G_DISCARD | G_NOARGS, args);
255 perl_destruct(my_perl);
260 where I<showtime> is a Perl subroutine that takes no arguments (that's the
261 I<G_NOARGS>) and for which I'll ignore the return value (that's the
262 I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>.
264 I'll define the I<showtime> subroutine in a file called I<showtime.pl>:
266 print "I shan't be printed.";
272 Simple enough. Now compile and run:
274 % cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
276 % showtime showtime.pl
279 yielding the number of seconds that elapsed between January 1, 1970
280 (the beginning of the Unix epoch), and the moment I began writing this
283 In this particular case we don't have to call I<perl_run>, as we set
284 the PL_exit_flag PERL_EXIT_DESTRUCT_END which executes END blocks in
287 If you want to pass arguments to the Perl subroutine, you can add
288 strings to the C<NULL>-terminated C<args> list passed to
289 I<call_argv>. For other data types, or to examine return values,
290 you'll need to manipulate the Perl stack. That's demonstrated in
291 L<Fiddling with the Perl stack from your C program>.
293 =head2 Evaluating a Perl statement from your C program
295 Perl provides two API functions to evaluate pieces of Perl code.
296 These are L<perlapi/eval_sv> and L<perlapi/eval_pv>.
298 Arguably, these are the only routines you'll ever need to execute
299 snippets of Perl code from within your C program. Your code can be as
300 long as you wish; it can contain multiple statements; it can employ
301 L<perlfunc/use>, L<perlfunc/require>, and L<perlfunc/do> to
302 include external Perl files.
304 I<eval_pv> lets us evaluate individual Perl strings, and then
305 extract variables for coercion into C types. The following program,
306 I<string.c>, executes three Perl strings, extracting an C<int> from
307 the first, a C<float> from the second, and a C<char *> from the third.
312 static PerlInterpreter *my_perl;
314 main (int argc, char **argv, char **env)
317 char *embedding[] = { "", "-e", "0" };
319 PERL_SYS_INIT3(&argc,&argv,&env);
320 my_perl = perl_alloc();
321 perl_construct( my_perl );
323 perl_parse(my_perl, NULL, 3, embedding, NULL);
324 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
327 /** Treat $a as an integer **/
328 eval_pv("$a = 3; $a **= 2", TRUE);
329 printf("a = %d\n", SvIV(get_sv("a", FALSE)));
331 /** Treat $a as a float **/
332 eval_pv("$a = 3.14; $a **= 2", TRUE);
333 printf("a = %f\n", SvNV(get_sv("a", FALSE)));
335 /** Treat $a as a string **/
336 eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
337 printf("a = %s\n", SvPV(get_sv("a", FALSE), n_a));
339 perl_destruct(my_perl);
344 All of those strange functions with I<sv> in their names help convert Perl scalars to C types. They're described in L<perlguts> and L<perlapi>.
346 If you compile and run I<string.c>, you'll see the results of using
347 I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
348 I<SvPV()> to create a string:
352 a = Just Another Perl Hacker
354 In the example above, we've created a global variable to temporarily
355 store the computed value of our eval'd expression. It is also
356 possible and in most cases a better strategy to fetch the return value
357 from I<eval_pv()> instead. Example:
361 SV *val = eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
362 printf("%s\n", SvPV(val,n_a));
365 This way, we avoid namespace pollution by not creating global
366 variables and we've simplified our code as well.
368 =head2 Performing Perl pattern matches and substitutions from your C program
370 The I<eval_sv()> function lets us evaluate strings of Perl code, so we can
371 define some functions that use it to "specialize" in matches and
372 substitutions: I<match()>, I<substitute()>, and I<matches()>.
374 I32 match(SV *string, char *pattern);
376 Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
377 in your C program might appear as "/\\b\\w*\\b/"), match()
378 returns 1 if the string matches the pattern and 0 otherwise.
380 int substitute(SV **string, char *pattern);
382 Given a pointer to an C<SV> and an C<=~> operation (e.g.,
383 C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
384 within the C<SV> as according to the operation, returning the number of substitutions
387 int matches(SV *string, char *pattern, AV **matches);
389 Given an C<SV>, a pattern, and a pointer to an empty C<AV>,
390 matches() evaluates C<$string =~ $pattern> in a list context, and
391 fills in I<matches> with the array elements, returning the number of matches found.
393 Here's a sample program, I<match.c>, that uses all three (long lines have
399 static PerlInterpreter *my_perl;
401 /** my_eval_sv(code, error_check)
402 ** kinda like eval_sv(),
403 ** but we pop the return value off the stack
405 SV* my_eval_sv(SV *sv, I32 croak_on_error)
412 eval_sv(sv, G_SCALAR);
418 if (croak_on_error && SvTRUE(ERRSV))
419 croak(SvPVx(ERRSV, n_a));
424 /** match(string, pattern)
426 ** Used for matches in a scalar context.
428 ** Returns 1 if the match was successful; 0 otherwise.
431 I32 match(SV *string, char *pattern)
433 SV *command = NEWSV(1099, 0), *retval;
436 sv_setpvf(command, "my $string = '%s'; $string =~ %s",
437 SvPV(string,n_a), pattern);
439 retval = my_eval_sv(command, TRUE);
440 SvREFCNT_dec(command);
445 /** substitute(string, pattern)
447 ** Used for =~ operations that modify their left-hand side (s/// and tr///)
449 ** Returns the number of successful matches, and
450 ** modifies the input string if there were any.
453 I32 substitute(SV **string, char *pattern)
455 SV *command = NEWSV(1099, 0), *retval;
458 sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
459 SvPV(*string,n_a), pattern);
461 retval = my_eval_sv(command, TRUE);
462 SvREFCNT_dec(command);
464 *string = get_sv("string", FALSE);
468 /** matches(string, pattern, matches)
470 ** Used for matches in a list context.
472 ** Returns the number of matches,
473 ** and fills in **matches with the matching substrings
476 I32 matches(SV *string, char *pattern, AV **match_list)
478 SV *command = NEWSV(1099, 0);
482 sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
483 SvPV(string,n_a), pattern);
485 my_eval_sv(command, TRUE);
486 SvREFCNT_dec(command);
488 *match_list = get_av("array", FALSE);
489 num_matches = av_len(*match_list) + 1; /** assume $[ is 0 **/
494 main (int argc, char **argv, char **env)
496 char *embedding[] = { "", "-e", "0" };
502 PERL_SYS_INIT3(&argc,&argv,&env);
503 my_perl = perl_alloc();
504 perl_construct(my_perl);
505 perl_parse(my_perl, NULL, 3, embedding, NULL);
506 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
508 text = NEWSV(1099,0);
509 sv_setpv(text, "When he is at a convenience store and the bill comes to some amount like 76 cents, Maynard is aware that there is something he *should* do, something that will enable him to get back a quarter, but he has no idea *what*. He fumbles through his red squeezey changepurse and gives the boy three extra pennies with his dollar, hoping that he might luck into the correct amount. The boy gives him back two of his own pennies and then the big shiny quarter that is his prize. -RICHH");
511 if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
512 printf("match: Text contains the word 'quarter'.\n\n");
514 printf("match: Text doesn't contain the word 'quarter'.\n\n");
516 if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
517 printf("match: Text contains the word 'eighth'.\n\n");
519 printf("match: Text doesn't contain the word 'eighth'.\n\n");
521 /** Match all occurrences of /wi../ **/
522 num_matches = matches(text, "m/(wi..)/g", &match_list);
523 printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
525 for (i = 0; i < num_matches; i++)
526 printf("match: %s\n", SvPV(*av_fetch(match_list, i, FALSE),n_a));
529 /** Remove all vowels from text **/
530 num_matches = substitute(&text, "s/[aeiou]//gi");
532 printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
534 printf("Now text is: %s\n\n", SvPV(text,n_a));
537 /** Attempt a substitution **/
538 if (!substitute(&text, "s/Perl/C/")) {
539 printf("substitute: s/Perl/C...No substitution made.\n\n");
543 PL_perl_destruct_level = 1;
544 perl_destruct(my_perl);
549 which produces the output (again, long lines have been wrapped here)
551 match: Text contains the word 'quarter'.
553 match: Text doesn't contain the word 'eighth'.
555 matches: m/(wi..)/g found 2 matches...
559 substitute: s/[aeiou]//gi...139 substitutions made.
560 Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
561 Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
562 qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by
563 thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs
564 hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH
566 substitute: s/Perl/C...No substitution made.
568 =head2 Fiddling with the Perl stack from your C program
570 When trying to explain stacks, most computer science textbooks mumble
571 something about spring-loaded columns of cafeteria plates: the last
572 thing you pushed on the stack is the first thing you pop off. That'll
573 do for our purposes: your C program will push some arguments onto "the Perl
574 stack", shut its eyes while some magic happens, and then pop the
575 results--the return value of your Perl subroutine--off the stack.
577 First you'll need to know how to convert between C types and Perl
578 types, with newSViv() and sv_setnv() and newAV() and all their
579 friends. They're described in L<perlguts> and L<perlapi>.
581 Then you'll need to know how to manipulate the Perl stack. That's
582 described in L<perlcall>.
584 Once you've understood those, embedding Perl in C is easy.
586 Because C has no builtin function for integer exponentiation, let's
587 make Perl's ** operator available to it (this is less useful than it
588 sounds, because Perl implements ** with C's I<pow()> function). First
589 I'll create a stub exponentiation function in I<power.pl>:
596 Now I'll create a C program, I<power.c>, with a function
597 I<PerlPower()> that contains all the perlguts necessary to push the
598 two arguments into I<expo()> and to pop the return value out. Take a
604 static PerlInterpreter *my_perl;
607 PerlPower(int a, int b)
609 dSP; /* initialize stack pointer */
610 ENTER; /* everything created after here */
611 SAVETMPS; /* ...is a temporary variable. */
612 PUSHMARK(SP); /* remember the stack pointer */
613 XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
614 XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
615 PUTBACK; /* make local stack pointer global */
616 call_pv("expo", G_SCALAR); /* call the function */
617 SPAGAIN; /* refresh stack pointer */
618 /* pop the return value from stack */
619 printf ("%d to the %dth power is %d.\n", a, b, POPi);
621 FREETMPS; /* free that return value */
622 LEAVE; /* ...and the XPUSHed "mortal" args.*/
625 int main (int argc, char **argv, char **env)
627 char *my_argv[] = { "", "power.pl" };
629 PERL_SYS_INIT3(&argc,&argv,&env);
630 my_perl = perl_alloc();
631 perl_construct( my_perl );
633 perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);
634 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
637 PerlPower(3, 4); /*** Compute 3 ** 4 ***/
639 perl_destruct(my_perl);
648 % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
651 3 to the 4th power is 81.
653 =head2 Maintaining a persistent interpreter
655 When developing interactive and/or potentially long-running
656 applications, it's a good idea to maintain a persistent interpreter
657 rather than allocating and constructing a new interpreter multiple
658 times. The major reason is speed: since Perl will only be loaded into
661 However, you have to be more cautious with namespace and variable
662 scoping when using a persistent interpreter. In previous examples
663 we've been using global variables in the default package C<main>. We
664 knew exactly what code would be run, and assumed we could avoid
665 variable collisions and outrageous symbol table growth.
667 Let's say your application is a server that will occasionally run Perl
668 code from some arbitrary file. Your server has no way of knowing what
669 code it's going to run. Very dangerous.
671 If the file is pulled in by C<perl_parse()>, compiled into a newly
672 constructed interpreter, and subsequently cleaned out with
673 C<perl_destruct()> afterwards, you're shielded from most namespace
676 One way to avoid namespace collisions in this scenario is to translate
677 the filename into a guaranteed-unique package name, and then compile
678 the code into that package using L<perlfunc/eval>. In the example
679 below, each file will only be compiled once. Or, the application
680 might choose to clean out the symbol table associated with the file
681 after it's no longer needed. Using L<perlapi/call_argv>, We'll
682 call the subroutine C<Embed::Persistent::eval_file> which lives in the
683 file C<persistent.pl> and pass the filename and boolean cleanup/cache
686 Note that the process will continue to grow for each file that it
687 uses. In addition, there might be C<AUTOLOAD>ed subroutines and other
688 conditions that cause Perl's symbol table to grow. You might want to
689 add some logic that keeps track of the process size, or restarts
690 itself after a certain number of requests, to ensure that memory
691 consumption is minimized. You'll also want to scope your variables
692 with L<perlfunc/my> whenever possible.
695 package Embed::Persistent;
700 use Symbol qw(delete_package);
702 sub valid_package_name {
704 $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
705 # second pass only for words starting with a digit
706 $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
708 # Dress it up as a real package name
710 return "Embed" . $string;
714 my($filename, $delete) = @_;
715 my $package = valid_package_name($filename);
716 my $mtime = -M $filename;
717 if(defined $Cache{$package}{mtime}
719 $Cache{$package}{mtime} <= $mtime)
721 # we have compiled this subroutine already,
722 # it has not been updated on disk, nothing left to do
723 print STDERR "already compiled $package->handler\n";
727 open FH, $filename or die "open '$filename' $!";
732 #wrap the code into a subroutine inside our unique package
733 my $eval = qq{package $package; sub handler { $sub; }};
735 # hide our variables within this block
736 my($filename,$mtime,$package,$sub);
741 #cache it unless we're cleaning out each time
742 $Cache{$package}{mtime} = $mtime unless $delete;
745 eval {$package->handler;};
748 delete_package($package) if $delete;
750 #take a look if you want
751 #print Devel::Symdump->rnew($package)->as_string, $/;
762 /* 1 = clean out filename's symbol table after each request, 0 = don't */
767 #define BUFFER_SIZE 1024
769 static PerlInterpreter *my_perl = NULL;
772 main(int argc, char **argv, char **env)
774 char *embedding[] = { "", "persistent.pl" };
775 char *args[] = { "", DO_CLEAN, NULL };
776 char filename[BUFFER_SIZE];
780 PERL_SYS_INIT3(&argc,&argv,&env);
781 if((my_perl = perl_alloc()) == NULL) {
782 fprintf(stderr, "no memory!");
785 perl_construct(my_perl);
787 exitstatus = perl_parse(my_perl, NULL, 2, embedding, NULL);
788 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
790 exitstatus = perl_run(my_perl);
792 while(printf("Enter file name: ") &&
793 fgets(filename, BUFFER_SIZE, stdin)) {
795 filename[strlen(filename)-1] = '\0'; /* strip \n */
796 /* call the subroutine, passing it the filename as an argument */
798 call_argv("Embed::Persistent::eval_file",
799 G_DISCARD | G_EVAL, args);
803 fprintf(stderr, "eval error: %s\n", SvPV(ERRSV,n_a));
807 PL_perl_destruct_level = 0;
808 perl_destruct(my_perl);
816 % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
818 Here's an example script file:
821 my $string = "hello";
825 print "foo says: @_\n";
831 Enter file name: test.pl
833 Enter file name: test.pl
834 already compiled Embed::test_2epl->handler
838 =head2 Execution of END blocks
840 Traditionally END blocks have been executed at the end of the perl_run.
841 This causes problems for applications that never call perl_run. Since
842 perl 5.7.2 you can specify C<PL_exit_flags |= PERL_EXIT_DESTRUCT_END>
843 to get the new behaviour. This also enables the running of END blocks if
844 the perl_parse fails and C<perl_destruct> will return the exit value.
846 =head2 Maintaining multiple interpreter instances
848 Some rare applications will need to create more than one interpreter
849 during a session. Such an application might sporadically decide to
850 release any resources associated with the interpreter.
852 The program must take care to ensure that this takes place I<before>
853 the next interpreter is constructed. By default, when perl is not
854 built with any special options, the global variable
855 C<PL_perl_destruct_level> is set to C<0>, since extra cleaning isn't
856 usually needed when a program only ever creates a single interpreter
857 in its entire lifetime.
859 Setting C<PL_perl_destruct_level> to C<1> makes everything squeaky clean:
863 /* reset global variables here with PL_perl_destruct_level = 1 */
864 PL_perl_destruct_level = 1;
865 perl_construct(my_perl);
867 /* clean and reset _everything_ during perl_destruct */
868 PL_perl_destruct_level = 1;
869 perl_destruct(my_perl);
872 /* let's go do it again! */
875 When I<perl_destruct()> is called, the interpreter's syntax parse tree
876 and symbol tables are cleaned up, and global variables are reset. The
877 second assignment to C<PL_perl_destruct_level> is needed because
878 perl_construct resets it to C<0>.
880 Now suppose we have more than one interpreter instance running at the
881 same time. This is feasible, but only if you used the Configure option
882 C<-Dusemultiplicity> or the options C<-Dusethreads -Duseithreads> when
883 building perl. By default, enabling one of these Configure options
884 sets the per-interpreter global variable C<PL_perl_destruct_level> to
885 C<1>, so that thorough cleaning is automatic and interpreter variables
886 are initialized correctly. Even if you don't intend to run two or
887 more interpreters at the same time, but to run them sequentially, like
888 in the above example, it is recommended to build perl with the
889 C<-Dusemultiplicity> option otherwise some interpreter variables may
890 not be initialized correctly between consecutive runs and your
891 application may crash.
893 Using C<-Dusethreads -Duseithreads> rather than C<-Dusemultiplicity>
894 is more appropriate if you intend to run multiple interpreters
895 concurrently in different threads, because it enables support for
896 linking in the thread libraries of your system with the interpreter.
904 /* we're going to embed two interpreters */
905 /* we're going to embed two interpreters */
907 #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
909 int main(int argc, char **argv, char **env)
911 PerlInterpreter *one_perl, *two_perl;
912 char *one_args[] = { "one_perl", SAY_HELLO };
913 char *two_args[] = { "two_perl", SAY_HELLO };
915 PERL_SYS_INIT3(&argc,&argv,&env);
916 one_perl = perl_alloc();
917 two_perl = perl_alloc();
919 PERL_SET_CONTEXT(one_perl);
920 perl_construct(one_perl);
921 PERL_SET_CONTEXT(two_perl);
922 perl_construct(two_perl);
924 PERL_SET_CONTEXT(one_perl);
925 perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
926 PERL_SET_CONTEXT(two_perl);
927 perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
929 PERL_SET_CONTEXT(one_perl);
931 PERL_SET_CONTEXT(two_perl);
934 PERL_SET_CONTEXT(one_perl);
935 perl_destruct(one_perl);
936 PERL_SET_CONTEXT(two_perl);
937 perl_destruct(two_perl);
939 PERL_SET_CONTEXT(one_perl);
941 PERL_SET_CONTEXT(two_perl);
946 Note the calls to PERL_SET_CONTEXT(). These are necessary to initialize
947 the global state that tracks which interpreter is the "current" one on
948 the particular process or thread that may be running it. It should
949 always be used if you have more than one interpreter and are making
950 perl API calls on both interpreters in an interleaved fashion.
952 PERL_SET_CONTEXT(interp) should also be called whenever C<interp> is
953 used by a thread that did not create it (using either perl_alloc(), or
954 the more esoteric perl_clone()).
958 % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
966 =head2 Using Perl modules, which themselves use C libraries, from your C program
968 If you've played with the examples above and tried to embed a script
969 that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ library,
970 this probably happened:
973 Can't load module Socket, dynamic loading not available in this perl.
974 (You may need to build a new perl executable which either supports
975 dynamic loading or has the Socket module statically linked into it.)
980 Your interpreter doesn't know how to communicate with these extensions
981 on its own. A little glue will help. Up until now you've been
982 calling I<perl_parse()>, handing it NULL for the second argument:
984 perl_parse(my_perl, NULL, argc, my_argv, NULL);
986 That's where the glue code can be inserted to create the initial contact between
987 Perl and linked C/C++ routines. Let's take a look some pieces of I<perlmain.c>
988 to see how Perl does this:
990 static void xs_init (pTHX);
992 EXTERN_C void boot_DynaLoader (pTHX_ CV* cv);
993 EXTERN_C void boot_Socket (pTHX_ CV* cv);
999 char *file = __FILE__;
1000 /* DynaLoader is a special case */
1001 newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
1002 newXS("Socket::bootstrap", boot_Socket, file);
1005 Simply put: for each extension linked with your Perl executable
1006 (determined during its initial configuration on your
1007 computer or when adding a new extension),
1008 a Perl subroutine is created to incorporate the extension's
1009 routines. Normally, that subroutine is named
1010 I<Module::bootstrap()> and is invoked when you say I<use Module>. In
1011 turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
1012 counterpart for each of the extension's XSUBs. Don't worry about this
1013 part; leave that to the I<xsubpp> and extension authors. If your
1014 extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
1015 for you on the fly. In fact, if you have a working DynaLoader then there
1016 is rarely any need to link in any other extensions statically.
1019 Once you have this code, slap it into the second argument of I<perl_parse()>:
1022 perl_parse(my_perl, xs_init, argc, my_argv, NULL);
1027 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
1031 use SomeDynamicallyLoadedModule;
1033 print "Now I can use extensions!\n"'
1035 B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
1037 % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
1038 % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
1039 % cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
1040 % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
1042 Consult L<perlxs>, L<perlguts>, and L<perlapi> for more details.
1044 =head1 Embedding Perl under Win32
1046 In general, all of the source code shown here should work unmodified under
1049 However, there are some caveats about the command-line examples shown.
1050 For starters, backticks won't work under the Win32 native command shell.
1051 The ExtUtils::Embed kit on CPAN ships with a script called
1052 B<genmake>, which generates a simple makefile to build a program from
1053 a single C source file. It can be used like this:
1055 C:\ExtUtils-Embed\eg> perl genmake interp.c
1056 C:\ExtUtils-Embed\eg> nmake
1057 C:\ExtUtils-Embed\eg> interp -e "print qq{I'm embedded in Win32!\n}"
1059 You may wish to use a more robust environment such as the Microsoft
1060 Developer Studio. In this case, run this to generate perlxsi.c:
1062 perl -MExtUtils::Embed -e xsinit
1064 Create a new project and Insert -> Files into Project: perlxsi.c,
1065 perl.lib, and your own source files, e.g. interp.c. Typically you'll
1066 find perl.lib in B<C:\perl\lib\CORE>, if not, you should see the
1067 B<CORE> directory relative to C<perl -V:archlib>. The studio will
1068 also need this path so it knows where to find Perl include files.
1069 This path can be added via the Tools -> Options -> Directories menu.
1070 Finally, select Build -> Build interp.exe and you're ready to go.
1074 If you completely hide the short forms forms of the Perl public API,
1075 add -DPERL_NO_SHORT_NAMES to the compilation flags. This means that
1076 for example instead of writing
1078 warn("%d bottles of beer on the wall", bottlecount);
1080 you will have to write the explicit full form
1082 Perl_warn(aTHX_ "%d bottles of beer on the wall", bottlecount);
1084 (See L<perlguts/Background and PERL_IMPLICIT_CONTEXT for the explanation
1085 of the C<aTHX_>.> ) Hiding the short forms is very useful for avoiding
1086 all sorts of nasty (C preprocessor or otherwise) conflicts with other
1087 software packages (Perl defines about 2400 APIs with these short names,
1088 take or leave few hundred, so there certainly is room for conflict.)
1092 You can sometimes I<write faster code> in C, but
1093 you can always I<write code faster> in Perl. Because you can use
1094 each from the other, combine them as you wish.
1099 Jon Orwant <F<orwant@media.mit.edu>> and Doug MacEachern
1100 <F<dougm@covalent.net>>, with small contributions from Tim Bunce, Tom
1101 Christiansen, Guy Decoux, Hallvard Furuseth, Dov Grobgeld, and Ilya
1104 Doug MacEachern has an article on embedding in Volume 1, Issue 4 of
1105 The Perl Journal ( http://www.tpj.com/ ). Doug is also the developer of the
1106 most widely-used Perl embedding: the mod_perl system
1107 (perl.apache.org), which embeds Perl in the Apache web server.
1108 Oracle, Binary Evolution, ActiveState, and Ben Sugars's nsapi_perl
1109 have used this model for Oracle, Netscape and Internet Information
1110 Server Perl plugins.
1116 Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant. All
1119 Permission is granted to make and distribute verbatim copies of this
1120 documentation provided the copyright notice and this permission notice are
1121 preserved on all copies.
1123 Permission is granted to copy and distribute modified versions of this
1124 documentation under the conditions for verbatim copying, provided also
1125 that they are marked clearly as modified versions, that the authors'
1126 names and title are unchanged (though subtitles and additional
1127 authors' names may be added), and that the entire resulting derived
1128 work is distributed under the terms of a permission notice identical
1131 Permission is granted to copy and distribute translations of this
1132 documentation into another language, under the above conditions for