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perlembed ()
  • >> perlembed (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
  • perlembed (1) ( Разные man: Команды и прикладные программы пользовательского уровня )
  • 
    
    

    NAME

         perlembed - how to embed perl in your C program
    
    
    

    DESCRIPTION

         PREAMBLE
    
         Do you want to:
    
         Use C from Perl?
              Read the perlxstut manpage, the perlxs manpage, the
              h2xs manpage, the perlguts manpage, and the perlapi
              manpage.
    
         Use a Unix program from Perl?
              Read about back-quotes and about `system' and `exec' in
              the perlfunc manpage.
    
         Use Perl from Perl?
              Read about the do entry in the perlfunc manpage and the
              eval entry in the perlfunc manpage and the require
              entry in the perlfunc manpage and the use entry in the
              perlfunc manpage.
    
         Use C from C?
              Rethink your design.
    
         Use Perl from C?
              Read on...
    
         ROADMAP
    
         the Compiling your C program entry elsewhere in this
         document
    
         the Adding a Perl interpreter to your C program entry
         elsewhere in this document
    
         the Calling a Perl subroutine from your C program entry
         elsewhere in this document
    
         the Evaluating a Perl statement from your C program entry
         elsewhere in this document
    
         the Performing Perl pattern matches and substitutions from
         your C program entry elsewhere in this document
    
         the Fiddling with the Perl stack from your C program entry
         elsewhere in this document
    
         the Maintaining a persistent interpreter entry elsewhere in
         this document
    
         the Maintaining multiple interpreter instances entry
         elsewhere in this document
    
         the Using Perl modules, which themselves use C libraries,
         from your C program entry elsewhere in this document
    
         the Embedding Perl under Win32 entry elsewhere in this
         document
    
         Compiling your C program
    
         If you have trouble compiling the scripts in this
         documentation, you're 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.  What's 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 can't use Perl from your C
         program unless Perl has been compiled on your machine, or
         installed properly--that's why you shouldn't blithely copy
         Perl executables from machine to machine without also
         copying the lib directory.)
    
         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 you'll also need)
         will reside in a directory that looks like this:
    
             /usr/local/lib/perl5/your_architecture_here/CORE
    
         or perhaps just
    
             /usr/local/lib/perl5/CORE
    
         or maybe something like
    
             /usr/opt/perl5/CORE
    
         Execute this statement for a hint about where to find CORE:
    
             perl -MConfig -e 'print $Config{archlib}'
    
         Here's how you'd compile the example in the next section,
         the Adding a Perl interpreter to your C program entry
         elsewhere in this document, on my Linux box:
             % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
             -I/usr/local/lib/perl5/i586-linux/5.003/CORE
             -L/usr/local/lib/perl5/i586-linux/5.003/CORE
             -o interp interp.c -lperl -lm
    
         (That's 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
             -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
             -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.
    
         You'll 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.
    
         You'll 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
         can't locate -lperl, then you need to change the path
         following the `-L'.  If it complains that it can't find
         EXTERN.h and perl.h, you need to change the path following
         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 isn't part of your Perl
         distribution, you can retrieve it from
         http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils/.
         (If this documentation came from your Perl distribution,
         then you're 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 information 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 I'll demonstrate embedding
         with miniperlmain.c, included in the source distribution.
         Here's a bastardized, nonportable version of miniperlmain.c
         containing the essentials of embedding:
    
             #include <EXTERN.h>               /* from the Perl distribution     */
             #include <perl.h>                 /* from the Perl distribution     */
    
             static PerlInterpreter *my_perl;  /***    The Perl interpreter    ***/
    
             int main(int argc, char **argv, char **env)
             {
                 my_perl = perl_alloc();
                 perl_construct(my_perl);
                 perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
                 perl_run(my_perl);
                 perl_destruct(my_perl);
                 perl_free(my_perl);
             }
    
         Notice that we don't 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.
    
         Now compile this program (I'll call it interp.c) into an
         executable:
    
             % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
    
         After a successful compilation, you'll be able to use interp
         just like perl itself:
    
             % interp
             print "Pretty Good Perl \n";
             print "10890 - 9801 is ", 10890 - 9801;
             <CTRL-D>
             Pretty Good Perl
             10890 - 9801 is 1089
    
         or
    
             % interp -e 'printf("%x", 3735928559)'
             deadbeef
    
         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 the perlcall manpage.  In
         this example we'll use `call_argv'.
    
         That's shown below, in a program I'll call showtime.c.
    
             #include <EXTERN.h>
             #include <perl.h>
    
             static PerlInterpreter *my_perl;
    
             int main(int argc, char **argv, char **env)
             {
                 char *args[] = { NULL };
                 my_perl = perl_alloc();
                 perl_construct(my_perl);
    
                 perl_parse(my_perl, NULL, argc, argv, NULL);
    
                 /*** skipping perl_run() ***/
    
                 call_argv("showtime", G_DISCARD | G_NOARGS, args);
    
                 perl_destruct(my_perl);
                 perl_free(my_perl);
             }
    
         where showtime is a Perl subroutine that takes no arguments
         (that's the G_NOARGS) and for which I'll ignore the return
         value (that's the G_DISCARD).  Those flags, and others, are
         discussed in the perlcall manpage.
    
         I'll define the showtime subroutine in a file called
         showtime.pl:
    
             print "I shan't 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
             818284590
    
         yielding the number of seconds that elapsed between January
         1, 1970 (the beginning of the Unix epoch), and the moment I
         began writing this sentence.
    
         In this particular case we don't have to call perl_run, but
         in general it's considered good practice to ensure proper
         initialization of library code, including execution of all
         object `DESTROY' methods and package `END {}' blocks.
    
         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, you'll need to manipulate the Perl stack.  That's
         demonstrated in the last section of this document: the
         Fiddling with the Perl stack from your C program entry
         elsewhere in this document.
    
         Evaluating a Perl statement from your C program
    
         Perl provides two API functions to evaluate pieces of Perl
         code.  These are the eval_sv entry in the perlapi manpage
         and the eval_pv entry in the perlapi manpage.
    
         Arguably, these are the only routines you'll ever need to
         execute snippets 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 the use entry in the
         perlfunc manpage, the require entry in the perlfunc manpage,
         and the do entry in the perlfunc manpage to include external
         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.
    
            #include <EXTERN.h>
            #include <perl.h>
    
            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);
                perl_run(my_perl);
    
    
                /** 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));
    
                perl_destruct(my_perl);
                perl_free(my_perl);
            }
    
         All of those strange functions with sv in their names help
         convert Perl scalars to C types.  They're described in the
         perlguts manpage and the perlapi manpage.
    
         If you compile and run string.c, you'll see the results of
         using SvIV() to create an `int', SvNV() to create a `float',
         and SvPV() to create a string:
    
            a = 9
            a = 9.859600
            a = Just Another Perl Hacker
    
         In the example above, we've created a global variable to
         temporarily store the computed value of our eval'd
         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 we've 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 substitutions: 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 `AV' at 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 an array
         context, and fills in matches with the array elements,
         returning the number of matches found.
    
         Here's a sample program, match.c, that uses all three (long
         lines have been wrapped here):
    
          #include <EXTERN.h>
          #include <perl.h>
    
          /** 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)
          {
              dSP;
              SV* retval;
              STRLEN n_a;
    
              PUSHMARK(SP);
              eval_sv(sv, G_SCALAR);
    
              SPAGAIN;
              retval = POPs;
              PUTBACK;
    
              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);
              SvREFCNT_dec(command);
    
              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);
              SvREFCNT_dec(command);
    
              *string = get_sv("string", FALSE);
              return SvIV(retval);
          }
    
          /** matches(string, pattern, matches)
          **
          ** Used for matches in an array 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);
              SvREFCNT_dec(command);
    
              *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)
          {
              PerlInterpreter *my_perl = perl_alloc();
              char *embedding[] = { "", "-e", "0" };
              AV *match_list;
              I32 num_matches, i;
              SV *text = NEWSV(1099,0);
              STRLEN n_a;
    
              perl_construct(my_perl);
              perl_parse(my_perl, NULL, 3, embedding, NULL);
    
              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");
    
              if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
                 printf("match: Text contains the word 'quarter'.\n\n");
              else
                 printf("match: Text doesn't contain the word 'quarter'.\n\n");
    
              if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
                 printf("match: Text contains the word 'eighth'.\n\n");
              else
                 printf("match: Text doesn't 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));
              printf("\n");
    
    
    
              /** Remove all vowels from text **/
              num_matches = substitute(&text, "s/[aeiou]//gi");
              if (num_matches) {
                 printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
                        num_matches);
                 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");
              }
    
              SvREFCNT_dec(text);
              PL_perl_destruct_level = 1;
              perl_destruct(my_perl);
              perl_free(my_perl);
          }
    
         which produces the output (again, long lines have been
         wrapped here)
    
            match: Text contains the word 'quarter'.
    
            match: Text doesn't 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.  That'll 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 you'll need to know how to convert between C types and
         Perl types, with newSViv() and sv_setnv() and newAV() and
         all their friends.  They're described in the perlguts
         manpage and the perlapi manpage.
    
         Then you'll need to know how to manipulate the Perl stack.
         That's described in the perlcall manpage.
    
         Once you've understood those, embedding Perl in C is easy.
    
         Because C has no builtin function for integer
         exponentiation, let's make Perl's ** operator available to
         it (this is less useful than it sounds, because Perl
         implements ** with C's pow() function).  First I'll create a
         stub exponentiation function in power.pl:
    
             sub expo {
                 my ($a, $b) = @_;
                 return $a ** $b;
             }
    
         Now I'll 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...
    
             #include <EXTERN.h>
             #include <perl.h>
    
             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);
               PUTBACK;
               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);
               perl_run(my_perl);
    
               PerlPower(3, 4);                      /*** Compute 3 ** 4 ***/
    
               perl_destruct(my_perl);
               perl_free(my_perl);
             }
    
         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
         applications, it's 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 scoping when using a persistent interpreter.  In
         previous examples we've 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.
    
         Let's 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 it's going to run.
         Very dangerous.
    
         If the file is pulled in by `perl_parse()', compiled into a
         newly constructed interpreter, and subsequently cleaned out
         with `perl_destruct()' afterwards, you're shielded from most
         namespace troubles.
    
         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 the
         eval entry in the perlfunc manpage.  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 it's no longer needed.  Using the call_argv
         entry in the perlapi manpage, We'll call the subroutine
         `Embed::Persistent::eval_file' which lives in the file
         `persistent.pl' and pass the filename and boolean
         cleanup/cache flag as arguments.
    
         Note that the process will continue to grow for each file
         that it uses.  In addition, there might be `AUTOLOAD'ed
         subroutines and other conditions that cause Perl's 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.  You'll also want to scope your
         variables with the my entry in the perlfunc manpage whenever
         possible.
    
          package Embed::Persistent;
          #persistent.pl
    
          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 = <FH>;
                 close FH;
    
                 #wrap the code into a subroutine inside our unique package
                 my $eval = qq{package $package; sub handler { $sub; }};
                 {
                     # hide our variables within this block
                     my($filename,$mtime,$package,$sub);
                     eval $eval;
                 }
                 die $@ if $@;
    
                 #cache it unless we're 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, $/;
          }
    
          1;
    
          __END__
    
          /* persistent.c */
          #include <EXTERN.h>
          #include <perl.h>
    
    
    
          /* 1 = clean out filename's symbol table after each request, 0 = don't */
          #ifndef DO_CLEAN
          #define DO_CLEAN 0
          #endif
    
          static PerlInterpreter *perl = NULL;
    
          int
          main(int argc, char **argv, char **env)
          {
              char *embedding[] = { "", "persistent.pl" };
              char *args[] = { "", DO_CLEAN, NULL };
              char filename [1024];
              int exitstatus = 0;
              STRLEN n_a;
    
              if((perl = perl_alloc()) == NULL) {
                 fprintf(stderr, "no memory!");
                 exit(1);
              }
              perl_construct(perl);
    
              exitstatus = perl_parse(perl, NULL, 2, embedding, NULL);
    
              if(!exitstatus) {
                 exitstatus = perl_run(perl);
    
                 while(printf("Enter file name: ") && gets(filename)) {
    
                     /* call the subroutine, passing it the filename as an argument */
                     args[0] = filename;
                     call_argv("Embed::Persistent::eval_file",
                                    G_DISCARD | G_EVAL, args);
    
                     /* check $@ */
                     if(SvTRUE(ERRSV))
                         fprintf(stderr, "eval error: %s\n", SvPV(ERRSV,n_a));
                 }
              }
    
              PL_perl_destruct_level = 0;
              perl_destruct(perl);
              perl_free(perl);
              exit(exitstatus);
          }
    
         Now compile:
    
          % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
    
         Here's a example script file:
    
          #test.pl
          my $string = "hello";
          foo($string);
    
          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
    
    
         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, the
         global variable `PL_perl_destruct_level' is set to `0',
         since extra cleaning isn't needed when a program has only
         one interpreter.
    
         Setting `PL_perl_destruct_level' to `1' makes everything
         squeaky clean:
    
          PL_perl_destruct_level = 1;
    
          while(1) {
              ...
              /* reset global variables here with PL_perl_destruct_level = 1 */
              perl_construct(my_perl);
              ...
              /* clean and reset _everything_ during perl_destruct */
              perl_destruct(my_perl);
              perl_free(my_perl);
              ...
              /* let's go do it again! */
          }
    
         When perl_destruct() is called, the interpreter's syntax
         parse tree and symbol tables are cleaned up, and global
         variables are reset.
         Now suppose we have more than one interpreter instance
         running at the same time.  This is feasible, but only if you
         used the `-DMULTIPLICITY' flag when building Perl.  By
         default, that sets `PL_perl_destruct_level' to `1'.
    
         Let's give it a try:
    
          #include <EXTERN.h>
          #include <perl.h>
    
          /* we're going to embed two interpreters */
          /* we're going to embed two interpreters */
    
          #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
    
          int main(int argc, char **argv, char **env)
          {
              PerlInterpreter
                  *one_perl = perl_alloc(),
                  *two_perl = perl_alloc();
              char *one_args[] = { "one_perl", SAY_HELLO };
              char *two_args[] = { "two_perl", SAY_HELLO };
    
              perl_construct(one_perl);
              perl_construct(two_perl);
    
              perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
              perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
    
              perl_run(one_perl);
              perl_run(two_perl);
    
              perl_destruct(one_perl);
              perl_destruct(two_perl);
    
              perl_free(one_perl);
              perl_free(two_perl);
          }
    
         Compile as usual:
    
          % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
    
         Run it, Run it:
    
          % multiplicity
          Hi, I'm one_perl
          Hi, I'm two_perl
    
    
    
         Using Perl modules, which themselves use C libraries, from
         your C program
    
         If you've 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:
    
          Can't 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.)
    
         What's wrong?
    
         Your interpreter doesn't know how to communicate with these
         extensions on its own.  A little glue will help.  Up until
         now you've been calling perl_parse(), handing it NULL for
         the second argument:
    
          perl_parse(my_perl, NULL, argc, my_argv, NULL);
    
         That's where the glue code can be inserted to create the
         initial contact between Perl and linked C/C++ routines.
         Let's take a look some pieces of perlmain.c to see how Perl
         does this:
    
          #ifdef __cplusplus
          #  define EXTERN_C extern "C"
          #else
          #  define EXTERN_C extern
          #endif
    
          static void xs_init (void);
    
          EXTERN_C void boot_DynaLoader (CV* cv);
          EXTERN_C void boot_Socket (CV* cv);
    
          EXTERN_C void
          xs_init()
          {
                 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 (determined during its initial configuration on
         your computer or when adding a new extension), a Perl
         subroutine is created to incorporate the extension's
         routines.  Normally, that subroutine is named
         Module::bootstrap() 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 extension's XSUBs.  Don't
         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():
    
          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 the perlxs manpage, the perlguts manpage, and the
         perlapi manpage for more details.
    
    
    

    Embedding Perl under Win32

         At the time of this writing (5.004), there are two versions
         of Perl which run under Win32.  (The two versions are
         merging in 5.005.)  Interfacing to ActiveState's Perl
         library is quite different from the examples in this
         documentation, as significant changes were made to the
         internal Perl API.  However, it is possible to embed
         ActiveState's Perl runtime.  For details, see the Perl for
         Win32 FAQ at
         http://www.perl.com/CPAN/doc/FAQs/win32/perlwin32faq.html.
    
         With the "official" Perl version 5.004 or higher, all the
         examples within this documentation will compile and run
         untouched, although the build process is slightly different
         between Unix and Win32.
    
         For starters, backticks don't work under the Win32 native
         command shell.  The ExtUtils::Embed kit on CPAN ships with a
         script called genmake, which generates a simple makefile to
         build a program from a single 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{I'm 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 you'll 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 you're ready to go.
    
    
    

    MORAL

         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.
    
    
    

    AUTHOR

         Jon Orwant <orwant@tpj.com> and Doug MacEachern
         <dougm@osf.org>, 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://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 Sugars's nsapi_perl have used this model for Oracle,
         Netscape and Internet Information Server Perl plugins.
    
         July 22, 1998
    
    
    

    COPYRIGHT

         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
         distributed under the terms of a permission notice identical
         to this one.
    
         Permission is granted to copy and distribute translations of
         this documentation into another language, under the above
         conditions for modified versions.
    
    
    
    


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