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PERLEMBED(1)	       Perl Programmers Reference Guide 	  PERLEMBED(1)

       perlembed - how to embed perl in your C program


       Do you want to:

       Use C from Perl?
	    Read perlxstut, perlxs, h2xs, perlguts, and perlapi.

       Use a Unix program from Perl?
	    Read about back-quotes and about "system" and "exec" in perlfunc.

       Use Perl from Perl?
	    Read about "do" in perlfunc and "eval" in perlfunc and "require"
	    in perlfunc and "use" in perlfunc.

       Use C from C?
	    Rethink your design.

       Use Perl from C?
	    Read on...


	   Compiling your C program

	   Adding a Perl interpreter to your C program

	   Calling a Perl subroutine from your C program

	   Evaluating a Perl statement from your C program

	   Performing Perl pattern matches and substitutions from your C pro

	   Fiddling with the Perl stack from your C program

	   Maintaining a persistent interpreter

	   Maintaining multiple interpreter instances

	   Using Perl modules, which themselves use C libraries, from your C

	   Embedding Perl under Win32

       Compiling your C program

       If you have trouble compiling the scripts in this documentation, youre
       not alone.  The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY THE SAME
       WAY THAT YOUR PERL WAS COMPILED.  (Sorry for yelling.)

       Also, every C program that uses Perl must link in the perl library.
       Whats that, you ask?  Perl is itself written in C; the perl library is
       the collection of compiled C programs that were used to create your
       perl executable (/usr/bin/perl or equivalent).  (Corollary: you cant
       use Perl from your C program unless Perl has been compiled on your
       machine, or installed properly--thats why you shouldnt blithely copy
       Perl executables from machine to machine without also copying the lib

       When you use Perl from C, your C program will--usually--allocate,
       "run", and deallocate a PerlInterpreter object, which is defined by the
       perl library.

       If your copy of Perl is recent enough to contain this documentation
       (version 5.002 or later), then the perl library (and EXTERN.h and
       perl.h, which youll also need) will reside in a directory that looks
       like this:


       or perhaps just


       or maybe something like


       Execute this statement for a hint about where to find CORE:

	   perl -MConfig -e print $Config{archlib}

       Heres how youd compile the example in the next section, "Adding a
       Perl interpreter to your C program", on my Linux box:

	   % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
	   -o interp interp.c -lperl -lm

       (Thats all one line.)  On my DEC Alpha running old 5.003_05, the
       incantation is a bit different:

	   % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
	   -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
	   -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm

       How can you figure out what to add?  Assuming your Perl is post-5.001,
       execute a "perl -V" command and pay special attention to the "cc" and
       "ccflags" information.

       Youll have to choose the appropriate compiler (cc, gcc, et al.) for
       your machine: "perl -MConfig -e print $Config{cc}" will tell you what
       to use.

       Youll also have to choose the appropriate library directory
       (/usr/local/lib/...) for your machine.  If your compiler complains that
       certain functions are undefined, or that it cant locate -lperl, then
       you need to change the path following the "-L".	If it complains that
       it cant find EXTERN.h and perl.h, you need to change the path follow
       ing the "-I".

       You may have to add extra libraries as well.  Which ones?  Perhaps
       those printed by

	  perl -MConfig -e print $Config{libs}

       Provided your perl binary was properly configured and installed the
       ExtUtils::Embed module will determine all of this information for you:

	  % cc -o interp interp.c perl -MExtUtils::Embed -e ccopts -e ldopts

       If the ExtUtils::Embed module isnt part of your Perl distribution, you
       can retrieve it from http://www.perl.com/perl/CPAN/modules/by-mod
       ule/ExtUtils/ (If this documentation came from your Perl distribution,
       then youre running 5.004 or better and you already have it.)

       The ExtUtils::Embed kit on CPAN also contains all source code for the
       examples in this document, tests, additional examples and other infor
       mation you may find useful.

       Adding a Perl interpreter to your C program

       In a sense, perl (the C program) is a good example of embedding Perl
       (the language), so Ill demonstrate embedding with miniperlmain.c,
       included in the source distribution.  Heres a bastardized, nonportable
       version of miniperlmain.c containing the essentials of embedding:

	   #include 		     /* from the Perl distribution     */
	   #include 		     /* from the Perl distribution     */

	   static PerlInterpreter *my_perl;  /***    The Perl interpreter    ***/

	   int main(int argc, char **argv, char **env)
	       my_perl = perl_alloc();
	       PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
	       perl_parse(my_perl, NULL, argc, argv, (char **)NULL);

       Notice that we dont use the "env" pointer.  Normally handed to
       "perl_parse" as its final argument, "env" here is replaced by "NULL",
       which means that the current environment will be used.  The macros
       PERL_SYS_INIT3() and PERL_SYS_TERM() provide system-specific tune up of
       the C runtime environment necessary to run Perl interpreters; since
       PERL_SYS_INIT3() may change "env", it may be more appropriate to pro
       vide "env" as an argument to perl_parse().

       Now compile this program (Ill call it interp.c) into an executable:

	   % cc -o interp interp.c perl -MExtUtils::Embed -e ccopts -e ldopts

       After a successful compilation, youll be able to use interp just like
       perl itself:

	   % interp
	   print "Pretty Good Perl \n";
	   print "10890 - 9801 is ", 10890 - 9801;
	   Pretty Good Perl
	   10890 - 9801 is 1089


	   % interp -e printf("%x", 3735928559)

       You can also read and execute Perl statements from a file while in the
       midst of your C program, by placing the filename in argv[1] before
       calling perl_run.

       Calling a Perl subroutine from your C program

       To call individual Perl subroutines, you can use any of the call_*
       functions documented in perlcall.  In this example well use

       Thats shown below, in a program Ill call showtime.c.


	   static PerlInterpreter *my_perl;

	   int main(int argc, char **argv, char **env)
	       char *args[] = { NULL };
	       my_perl = perl_alloc();

	       perl_parse(my_perl, NULL, argc, argv, NULL);
	       PL_exit_flags |= PERL_EXIT_DESTRUCT_END;

	       /*** skipping perl_run() ***/

	       call_argv("showtime", G_DISCARD | G_NOARGS, args);


       where showtime is a Perl subroutine that takes no arguments (thats the
       G_NOARGS) and for which Ill ignore the return value (thats the G_DIS
       CARD).  Those flags, and others, are discussed in perlcall.

       Ill define the showtime subroutine in a file called showtime.pl:

	   print "I shant be printed.";

	   sub showtime {
	       print time;

       Simple enough.  Now compile and run:

	   % cc -o showtime showtime.c perl -MExtUtils::Embed -e ccopts -e ldopts

	   % showtime showtime.pl

       yielding the number of seconds that elapsed between January 1, 1970
       (the beginning of the Unix epoch), and the moment I began writing this

       In this particular case we dont have to call perl_run, as we set the
       PL_exit_flag PERL_EXIT_DESTRUCT_END which executes END blocks in

       If you want to pass arguments to the Perl subroutine, you can add
       strings to the "NULL"-terminated "args" list passed to call_argv.  For
       other data types, or to examine return values, youll need to manipu
       late the Perl stack.  Thats demonstrated in "Fiddling with the Perl
       stack from your C program".

       Evaluating a Perl statement from your C program

       Perl provides two API functions to evaluate pieces of Perl code.  These
       are "eval_sv" in perlapi and "eval_pv" in perlapi.

       Arguably, these are the only routines youll ever need to execute snip
       pets of Perl code from within your C program.  Your code can be as long
       as you wish; it can contain multiple statements; it can employ "use" in
       perlfunc, "require" in perlfunc, and "do" in perlfunc to include exter
       nal Perl files.

       eval_pv lets us evaluate individual Perl strings, and then extract
       variables for coercion into C types.  The following program, string.c,
       executes three Perl strings, extracting an "int" from the first, a
       "float" from the second, and a "char *" from the third.


	  static PerlInterpreter *my_perl;

	  main (int argc, char **argv, char **env)
	      STRLEN n_a;
	      char *embedding[] = { "", "-e", "0" };

	      my_perl = perl_alloc();
	      perl_construct( my_perl );

	      perl_parse(my_perl, NULL, 3, embedding, NULL);
	      PL_exit_flags |= PERL_EXIT_DESTRUCT_END;

	      /** Treat $a as an integer **/
	      eval_pv("$a = 3; $a **= 2", TRUE);
	      printf("a = %d\n", SvIV(get_sv("a", FALSE)));

	      /** Treat $a as a float **/
	      eval_pv("$a = 3.14; $a **= 2", TRUE);
	      printf("a = %f\n", SvNV(get_sv("a", FALSE)));

	      /** Treat $a as a string **/
	      eval_pv("$a = rekcaH lreP rehtonA tsuJ; $a = reverse($a);", TRUE);
	      printf("a = %s\n", SvPV(get_sv("a", FALSE), n_a));


       All of those strange functions with sv in their names help convert Perl
       scalars to C types.  Theyre described in perlguts and perlapi.

       If you compile and run string.c, youll see the results of using SvIV()
       to create an "int", SvNV() to create a "float", and SvPV() to create a

	  a = 9
	  a = 9.859600
	  a = Just Another Perl Hacker

       In the example above, weve created a global variable to temporarily
       store the computed value of our evald expression.  It is also possible
       and in most cases a better strategy to fetch the return value from
       eval_pv() instead.  Example:

	  STRLEN n_a;
	  SV *val = eval_pv("reverse rekcaH lreP rehtonA tsuJ", TRUE);
	  printf("%s\n", SvPV(val,n_a));

       This way, we avoid namespace pollution by not creating global variables
       and weve simplified our code as well.

       Performing Perl pattern matches and substitutions from your C program

       The eval_sv() function lets us evaluate strings of Perl code, so we can
       define some functions that use it to "specialize" in matches and sub
       stitutions: match(), substitute(), and matches().

	  I32 match(SV *string, char *pattern);

       Given a string and a pattern (e.g., "m/clasp/" or "/\b\w*\b/", which in
       your C program might appear as "/\\b\\w*\\b/"), match() returns 1 if
       the string matches the pattern and 0 otherwise.

	  int substitute(SV **string, char *pattern);

       Given a pointer to an "SV" and an "=~" operation (e.g.,
       "s/bob/robert/g" or "tr[A-Z][a-z]"), substitute() modifies the string
       within the "SV" as according to the operation, returning the number of
       substitutions made.

	  int matches(SV *string, char *pattern, AV **matches);

       Given an "SV", a pattern, and a pointer to an empty "AV", matches()
       evaluates "$string =~ $pattern" in a list context, and fills in matches
       with the array elements, returning the number of matches found.

       Heres a sample program, match.c, that uses all three (long lines have
       been wrapped here):


	static PerlInterpreter *my_perl;

	/** my_eval_sv(code, error_check)
	** kinda like eval_sv(),
	** but we pop the return value off the stack
	SV* my_eval_sv(SV *sv, I32 croak_on_error)
	    SV* retval;
	    STRLEN n_a;

	    eval_sv(sv, G_SCALAR);

	    retval = POPs;

	    if (croak_on_error && SvTRUE(ERRSV))
	       croak(SvPVx(ERRSV, n_a));

	    return retval;

	/** match(string, pattern)
	** Used for matches in a scalar context.
	** Returns 1 if the match was successful; 0 otherwise.

	I32 match(SV *string, char *pattern)
	    SV *command = NEWSV(1099, 0), *retval;
	    STRLEN n_a;

	    sv_setpvf(command, "my $string = %s; $string =~ %s",
		     SvPV(string,n_a), pattern);

	    retval = my_eval_sv(command, TRUE);

	    return SvIV(retval);

	/** substitute(string, pattern)
	** Used for =~ operations that modify their left-hand side (s/// and tr///)
	** Returns the number of successful matches, and
	** modifies the input string if there were any.

	I32 substitute(SV **string, char *pattern)
	    SV *command = NEWSV(1099, 0), *retval;
	    STRLEN n_a;

	    sv_setpvf(command, "$string = %s; ($string =~ %s)",
		     SvPV(*string,n_a), pattern);

	    retval = my_eval_sv(command, TRUE);

	    *string = get_sv("string", FALSE);
	    return SvIV(retval);

	/** matches(string, pattern, matches)
	** Used for matches in a list context.
	** Returns the number of matches,
	** and fills in **matches with the matching substrings

	I32 matches(SV *string, char *pattern, AV **match_list)
	    SV *command = NEWSV(1099, 0);
	    I32 num_matches;
	    STRLEN n_a;

	    sv_setpvf(command, "my $string = %s; @array = ($string =~ %s)",
		     SvPV(string,n_a), pattern);

	    my_eval_sv(command, TRUE);

	    *match_list = get_av("array", FALSE);
	    num_matches = av_len(*match_list) + 1; /** assume $[ is 0 **/

	    return num_matches;

	main (int argc, char **argv, char **env)
	    char *embedding[] = { "", "-e", "0" };
	    AV *match_list;
	    I32 num_matches, i;
	    SV *text;
	    STRLEN n_a;

	    my_perl = perl_alloc();
	    perl_parse(my_perl, NULL, 3, embedding, NULL);
	    PL_exit_flags |= PERL_EXIT_DESTRUCT_END;

	    text = NEWSV(1099,0);
	    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. "

	    if (match(text, "m/quarter/")) /** Does text contain quarter? **/
	       printf("match: Text contains the word quarter.\n\n");
	       printf("match: Text doesnt contain the word quarter.\n\n");

	    if (match(text, "m/eighth/")) /** Does text contain eighth? **/
	       printf("match: Text contains the word eighth.\n\n");
	       printf("match: Text doesnt contain the word eighth.\n\n");

	    /** Match all occurrences of /wi../ **/
	    num_matches = matches(text, "m/(wi..)/g", &match_list);
	    printf("matches: m/(wi..)/g found %d matches...\n", num_matches);

	    for (i = 0; i < num_matches; i++)
	       printf("match: %s\n", SvPV(*av_fetch(match_list, i, FALSE),n_a));

	    /** Remove all vowels from text **/
	    num_matches = substitute(&text, "s/[aeiou]//gi");
	    if (num_matches) {
	       printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
	       printf("Now text is: %s\n\n", SvPV(text,n_a));

	    /** Attempt a substitution **/
	    if (!substitute(&text, "s/Perl/C/")) {
	       printf("substitute: s/Perl/C...No substitution made.\n\n");

	    PL_perl_destruct_level = 1;

       which produces the output (again, long lines have been wrapped here)

	  match: Text contains the word quarter.

	  match: Text doesnt contain the word eighth.

	  matches: m/(wi..)/g found 2 matches...
	  match: will
	  match: with

	  substitute: s/[aeiou]//gi...139 substitutions made.
	  Now text is: Whn h s t  cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
	  Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
	  qrtr, bt h hs n d *wht*.  H fmbls thrgh hs rd sqzy chngprs nd gvs th by
	  thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt.  Th by gvs
	  hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH

	  substitute: s/Perl/C...No substitution made.

       Fiddling with the Perl stack from your C program

       When trying to explain stacks, most computer science textbooks mumble
       something about spring-loaded columns of cafeteria plates: the last
       thing you pushed on the stack is the first thing you pop off.  Thatll
       do for our purposes: your C program will push some arguments onto "the
       Perl stack", shut its eyes while some magic happens, and then pop the
       results--the return value of your Perl subroutine--off the stack.

       First youll need to know how to convert between C types and Perl
       types, with newSViv() and sv_setnv() and newAV() and all their friends.
       Theyre described in perlguts and perlapi.

       Then youll need to know how to manipulate the Perl stack.  Thats
       described in perlcall.

       Once youve understood those, embedding Perl in C is easy.

       Because C has no builtin function for integer exponentiation, lets
       make Perls ** operator available to it (this is less useful than it
       sounds, because Perl implements ** with Cs pow() function).  First
       Ill create a stub exponentiation function in power.pl:

	   sub expo {
	       my ($a, $b) = @_;
	       return $a ** $b;

       Now Ill create a C program, power.c, with a function PerlPower() that
       contains all the perlguts necessary to push the two arguments into
       expo() and to pop the return value out.	Take a deep breath...


	   static PerlInterpreter *my_perl;

	   static void
	   PerlPower(int a, int b)
	     dSP;			     /* initialize stack pointer      */
	     ENTER;			     /* everything created after here */
	     SAVETMPS;			     /* ...is a temporary variable.   */
	     PUSHMARK(SP);		     /* remember the stack pointer    */
	     XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack  */
	     XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack  */
	     PUTBACK;			   /* make local stack pointer global */
	     call_pv("expo", G_SCALAR);      /* call the function	      */
	     SPAGAIN;			     /* refresh stack pointer	      */
					   /* pop the return value from stack */
	     printf ("%d to the %dth power is %d.\n", a, b, POPi);
	     FREETMPS;			     /* free that return value	      */
	     LEAVE;			  /* ...and the XPUSHed "mortal" args.*/

	   int main (int argc, char **argv, char **env)
	     char *my_argv[] = { "", "power.pl" };

	     my_perl = perl_alloc();
	     perl_construct( my_perl );

	     perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);
	     PL_exit_flags |= PERL_EXIT_DESTRUCT_END;

	     PerlPower(3, 4);			   /*** Compute 3 ** 4 ***/


       Compile and run:

	   % cc -o power power.c perl -MExtUtils::Embed -e ccopts -e ldopts

	   % power
	   3 to the 4th power is 81.

       Maintaining a persistent interpreter

       When developing interactive and/or potentially long-running applica
       tions, its a good idea to maintain a persistent interpreter rather
       than allocating and constructing a new interpreter multiple times.  The
       major reason is speed: since Perl will only be loaded into memory once.

       However, you have to be more cautious with namespace and variable scop
       ing when using a persistent interpreter.  In previous examples weve
       been using global variables in the default package "main".  We knew
       exactly what code would be run, and assumed we could avoid variable
       collisions and outrageous symbol table growth.

       Lets say your application is a server that will occasionally run Perl
       code from some arbitrary file.  Your server has no way of knowing what
       code its going to run.  Very dangerous.

       If the file is pulled in by "perl_parse()", compiled into a newly con
       structed interpreter, and subsequently cleaned out with
       "perl_destruct()" afterwards, youre shielded from most namespace trou

       One way to avoid namespace collisions in this scenario is to translate
       the filename into a guaranteed-unique package name, and then compile
       the code into that package using "eval" in perlfunc.  In the example
       below, each file will only be compiled once.  Or, the application might
       choose to clean out the symbol table associated with the file after
       its no longer needed.  Using "call_argv" in perlapi, Well call the
       subroutine "Embed::Persistent::eval_file" which lives in the file "per
       sistent.pl" and pass the filename and boolean cleanup/cache flag as

       Note that the process will continue to grow for each file that it uses.
       In addition, there might be "AUTOLOAD"ed subroutines and other condi
       tions that cause Perls symbol table to grow.  You might want to add
       some logic that keeps track of the process size, or restarts itself
       after a certain number of requests, to ensure that memory consumption
       is minimized.  Youll also want to scope your variables with "my" in
       perlfunc whenever possible.

	package Embed::Persistent;

	use strict;
	our %Cache;
	use Symbol qw(delete_package);

	sub valid_package_name {
	    my($string) = @_;
	    $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
	    # second pass only for words starting with a digit
	    $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;

	    # Dress it up as a real package name
	    $string =~ s|/|::|g;
	    return "Embed" . $string;

	sub eval_file {
	    my($filename, $delete) = @_;
	    my $package = valid_package_name($filename);
	    my $mtime = -M $filename;
	    if(defined $Cache{$package}{mtime}
	       $Cache{$package}{mtime} <= $mtime)
	       # we have compiled this subroutine already,
	       # it has not been updated on disk, nothing left to do
	       print STDERR "already compiled $package->handler\n";
	    else {
	       local *FH;
	       open FH, $filename or die "open $filename $!";
	       local($/) = undef;
	       my $sub = ;
	       close FH;

	       #wrap the code into a subroutine inside our unique package
	       my $eval = qq{package $package; sub handler { $sub; }};
		   # hide our variables within this block
		   eval $eval;
	       die $@ if $@;

	       #cache it unless were cleaning out each time
	       $Cache{$package}{mtime} = $mtime unless $delete;

	    eval {$package->handler;};
	    die $@ if $@;

	    delete_package($package) if $delete;

	    #take a look if you want
	    #print Devel::Symdump->rnew($package)->as_string, $/;



	/* persistent.c */

	/* 1 = clean out filenames symbol table after each request, 0 = dont */
	#ifndef DO_CLEAN
	#define DO_CLEAN 0

	#define BUFFER_SIZE 1024

	static PerlInterpreter *my_perl = NULL;

	main(int argc, char **argv, char **env)
	    char *embedding[] = { "", "persistent.pl" };
	    char *args[] = { "", DO_CLEAN, NULL };
	    char filename[BUFFER_SIZE];
	    int exitstatus = 0;
	    STRLEN n_a;

	    if((my_perl = perl_alloc()) == NULL) {
	       fprintf(stderr, "no memory!");

	    exitstatus = perl_parse(my_perl, NULL, 2, embedding, NULL);
	    PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
	    if(!exitstatus) {
	       exitstatus = perl_run(my_perl);

	       while(printf("Enter file name: ") &&
		     fgets(filename, BUFFER_SIZE, stdin)) {

		   filename[strlen(filename)-1] = \0; /* strip \n */
		   /* call the subroutine, passing it the filename as an argument */
		   args[0] = filename;
				  G_DISCARD | G_EVAL, args);

		   /* check $@ */
		       fprintf(stderr, "eval error: %s\n", SvPV(ERRSV,n_a));

	    PL_perl_destruct_level = 0;

       Now compile:

	% cc -o persistent persistent.c perl -MExtUtils::Embed -e ccopts -e ldopts

       Heres an example script file:

	my $string = "hello";

	sub foo {
	    print "foo says: @_\n";

       Now run:

	% persistent
	Enter file name: test.pl
	foo says: hello
	Enter file name: test.pl
	already compiled Embed::test_2epl->handler
	foo says: hello
	Enter file name: ^C

       Execution of END blocks

       Traditionally END blocks have been executed at the end of the perl_run.
       This causes problems for applications that never call perl_run. Since
       perl 5.7.2 you can specify "PL_exit_flags |= PERL_EXIT_DESTRUCT_END" to
       get the new behaviour. This also enables the running of END blocks if
       the perl_parse fails and "perl_destruct" will return the exit value.

       Maintaining multiple interpreter instances

       Some rare applications will need to create more than one interpreter
       during a session.  Such an application might sporadically decide to
       release any resources associated with the interpreter.

       The program must take care to ensure that this takes place before the
       next interpreter is constructed.  By default, when perl is not built
       with any special options, the global variable "PL_perl_destruct_level"
       is set to 0, since extra cleaning isnt usually needed when a program
       only ever creates a single interpreter in its entire lifetime.

       Setting "PL_perl_destruct_level" to 1 makes everything squeaky clean:

	while(1) {
	    /* reset global variables here with PL_perl_destruct_level = 1 */
	    PL_perl_destruct_level = 1;
	    /* clean and reset _everything_ during perl_destruct */
	    PL_perl_destruct_level = 1;
	    /* lets go do it again! */

       When perl_destruct() is called, the interpreters syntax parse tree and
       symbol tables are cleaned up, and global variables are reset.  The sec
       ond assignment to "PL_perl_destruct_level" is needed because perl_con
       struct resets it to 0.

       Now suppose we have more than one interpreter instance running at the
       same time.  This is feasible, but only if you used the Configure option
       "-Dusemultiplicity" or the options "-Dusethreads -Duseithreads" when
       building perl.  By default, enabling one of these Configure options
       sets the per-interpreter global variable "PL_perl_destruct_level" to 1,
       so that thorough cleaning is automatic and interpreter variables are
       initialized correctly.  Even if you dont intend to run two or more
       interpreters at the same time, but to run them sequentially, like in
       the above example, it is recommended to build perl with the "-Dusemul
       tiplicity" option otherwise some interpreter variables may not be ini
       tialized correctly between consecutive runs and your application may

       Using "-Dusethreads -Duseithreads" rather than "-Dusemultiplicity" is
       more appropriate if you intend to run multiple interpreters concur
       rently in different threads, because it enables support for linking in
       the thread libraries of your system with the interpreter.

       Lets give it a try:


	/* were going to embed two interpreters */
	/* were going to embed two interpreters */

	#define SAY_HELLO "-e", "print qq(Hi, Im $^X\n)"

	int main(int argc, char **argv, char **env)
	    PerlInterpreter *one_perl, *two_perl;
	    char *one_args[] = { "one_perl", SAY_HELLO };
	    char *two_args[] = { "two_perl", SAY_HELLO };

	    one_perl = perl_alloc();
	    two_perl = perl_alloc();


	    perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
	    perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);




       Note the calls to PERL_SET_CONTEXT().  These are necessary to initial
       ize the global state that tracks which interpreter is the "current" one
       on the particular process or thread that may be running it.  It should
       always be used if you have more than one interpreter and are making
       perl API calls on both interpreters in an interleaved fashion.

       PERL_SET_CONTEXT(interp) should also be called whenever "interp" is
       used by a thread that did not create it (using either perl_alloc(), or
       the more esoteric perl_clone()).

       Compile as usual:

	% cc -o multiplicity multiplicity.c perl -MExtUtils::Embed -e ccopts -e ldopts

       Run it, Run it:

	% multiplicity
	Hi, Im one_perl
	Hi, Im two_perl

       Using Perl modules, which themselves use C libraries, from your C pro

       If youve played with the examples above and tried to embed a script
       that use()s a Perl module (such as Socket) which itself uses a C or C++
       library, this probably happened:

	Cant load module Socket, dynamic loading not available in this perl.
	 (You may need to build a new perl executable which either supports
	 dynamic loading or has the Socket module statically linked into it.)

       Whats wrong?

       Your interpreter doesnt know how to communicate with these extensions
       on its own.  A little glue will help.  Up until now youve been calling
       perl_parse(), handing it NULL for the second argument:

	perl_parse(my_perl, NULL, argc, my_argv, NULL);

       Thats where the glue code can be inserted to create the initial con
       tact between Perl and linked C/C++ routines.  Lets take a look some
       pieces of perlmain.c to see how Perl does this:

	static void xs_init (pTHX);

	EXTERN_C void boot_DynaLoader (pTHX_ CV* cv);
	EXTERN_C void boot_Socket (pTHX_ CV* cv);

	EXTERN_C void
	       char *file = __FILE__;
	       /* DynaLoader is a special case */
	       newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
	       newXS("Socket::bootstrap", boot_Socket, file);

       Simply put: for each extension linked with your Perl executable (deter
       mined during its initial configuration on your computer or when adding
       a new extension), a Perl subroutine is created to incorporate the
       extensions routines.  Normally, that subroutine is named Module::boot
       strap() and is invoked when you say use Module.	In turn, this hooks
       into an XSUB, boot_Module, which creates a Perl counterpart for each of
       the extensions XSUBs.  Dont worry about this part; leave that to the
       xsubpp and extension authors.  If your extension is dynamically loaded,
       DynaLoader creates Module::bootstrap() for you on the fly.  In fact, if
       you have a working DynaLoader then there is rarely any need to link in
       any other extensions statically.

       Once you have this code, slap it into the second argument of

	perl_parse(my_perl, xs_init, argc, my_argv, NULL);

       Then compile:

	% cc -o interp interp.c perl -MExtUtils::Embed -e ccopts -e ldopts

	% interp
	  use Socket;
	  use SomeDynamicallyLoadedModule;

	  print "Now I can use extensions!\n"

       ExtUtils::Embed can also automate writing the xs_init glue code.

	% perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
	% cc -c perlxsi.c perl -MExtUtils::Embed -e ccopts
	% cc -c interp.c  perl -MExtUtils::Embed -e ccopts
	% cc -o interp perlxsi.o interp.o perl -MExtUtils::Embed -e ldopts

       Consult perlxs, perlguts, and perlapi for more details.

Embedding Perl under Win32
       In general, all of the source code shown here should work unmodified
       under Windows.

       However, there are some caveats about the command-line examples shown.
       For starters, backticks wont work under the Win32 native command
       shell.  The ExtUtils::Embed kit on CPAN ships with a script called gen
       make, which generates a simple makefile to build a program from a sin
       gle C source file.  It can be used like this:

	C:\ExtUtils-Embed\eg> perl genmake interp.c
	C:\ExtUtils-Embed\eg> nmake
	C:\ExtUtils-Embed\eg> interp -e "print qq{Im embedded in Win32!\n}"

       You may wish to use a more robust environment such as the Microsoft
       Developer Studio.  In this case, run this to generate perlxsi.c:

	perl -MExtUtils::Embed -e xsinit

       Create a new project and Insert -> Files into Project: perlxsi.c,
       perl.lib, and your own source files, e.g. interp.c.  Typically youll
       find perl.lib in C:\perl\lib\CORE, if not, you should see the CORE
       directory relative to "perl -V:archlib".  The studio will also need
       this path so it knows where to find Perl include files.	This path can
       be added via the Tools -> Options -> Directories menu.  Finally, select
       Build -> Build interp.exe and youre ready to go.

Hiding Perl_
       If you completely hide the short forms forms of the Perl public API,
       add -DPERL_NO_SHORT_NAMES to the compilation flags.  This means that
       for example instead of writing

	   warn("%d bottles of beer on the wall", bottlecount);

       you will have to write the explicit full form

	   Perl_warn(aTHX_ "%d bottles of beer on the wall", bottlecount);

       (See "Background and PERL_IMPLICIT_CONTEXT for the explanation of the
       "aTHX_"." in perlguts )	Hiding the short forms is very useful for
       avoiding all sorts of nasty (C preprocessor or otherwise) conflicts
       with other software packages (Perl defines about 2400 APIs with these
       short names, take or leave few hundred, so there certainly is room for

       You can sometimes write faster code in C, but you can always write code
       faster in Perl.	Because you can use each from the other, combine them
       as you wish.

       Jon Orwant  and Doug MacEachern , with small contributions from Tim Bunce, Tom Christiansen,
       Guy Decoux, Hallvard Furuseth, Dov Grobgeld, and Ilya Zakharevich.

       Doug MacEachern has an article on embedding in Volume 1, Issue 4 of The
       Perl Journal ( http://www.tpj.com/ ).  Doug is also the developer of
       the most widely-used Perl embedding: the mod_perl system
       (perl.apache.org), which embeds Perl in the Apache web server.  Oracle,
       Binary Evolution, ActiveState, and Ben Sugarss nsapi_perl have used
       this model for Oracle, Netscape and Internet Information Server Perl

       Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant.
       All Rights Reserved.

       Permission is granted to make and distribute verbatim copies of this
       documentation provided the copyright notice and this permission notice
       are preserved on all copies.

       Permission is granted to copy and distribute modified versions of this
       documentation under the conditions for verbatim copying, provided also
       that they are marked clearly as modified versions, that the authors
       names and title are unchanged (though subtitles and additional authors
       names may be added), and that the entire resulting derived work is dis
       tributed under the terms of a permission notice identical to this one.

       Permission is granted to copy and distribute translations of this docu
       mentation into another language, under the above conditions for modi
       fied versions.

perl v5.8.8			  2008-04-25			  PERLEMBED(1)

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