PERLEMBED(1) Perl Programmers Reference Guide PERLEMBED(1)NAMEperlembed - how to embed perl in your C program
DESCRIPTION
PREAMBLE
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...
ROADMAP
+ 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 program
+ 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 program
+ Embedding Perl under Win32
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Compiling your C program
If you have trouble compiling the scripts in this documenta-
tion, you're not alone. The cardinal rule: COMPILE THE PRO-
GRAMS 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 copy-
ing 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 docu-
mentation (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,
"Adding a Perl interpreter to your C program", 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:
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% 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 fol-
lowing 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 dis-
tribution, 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 embed-
ding 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 con-
taining the essentials of embedding:
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#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)
{
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
perl_run(my_perl);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}
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. 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 provide "env" as an argument to perl_parse().
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.
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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
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 };
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
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);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}
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 perlcall.
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
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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, as
we set the PL_exit_flag PERL_EXIT_DESTRUCT_END which exe-
cutes END blocks in perl_destruct.
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 "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 per-
lapi.
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 multi-
ple statements; it can employ "use" in perlfunc, "require"
in perlfunc, and "do" in perlfunc 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" };
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct( my_perl );
perl_parse(my_perl, NULL, 3, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
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/** 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);
PERL_SYS_TERM();
}
All of those strange functions with sv in their names help
convert Perl scalars to C types. They're described in perl-
guts and perlapi.
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 expres-
sion. It is also possible and in most cases a better stra-
tegy 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 glo-
bal 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 "spe-
cialize" in matches and substitutions: match(), substi-
tute(), and matches().
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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.
Here's a sample program, match.c, that uses all three (long
lines have been wrapped here):
#include <EXTERN.h>
#include <perl.h>
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)
{
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;
}
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/** 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 a list context.
**
** Returns the number of matches,
** and fills in **matches with the matching substrings
**/
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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)
{
char *embedding[] = { "", "-e", "0" };
AV *match_list;
I32 num_matches, i;
SV *text;
STRLEN n_a;
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
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. "
"-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");
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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);
PERL_SYS_TERM();
}
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
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substitute: s/Perl/C...No substitution made.
Fiddling with the Perl stack from your C program
When trying to explain stacks, most computer science text-
books 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 perlguts and per-
lapi.
Then you'll need to know how to manipulate the Perl stack.
That's described in perlcall.
Once you've understood those, embedding Perl in C is easy.
Because C has no builtin function for integer exponentia-
tion, 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 exponentia-
tion function in power.pl:
sub expo {
my ($a, $b) = @_;
return $a ** $b;
}
Now I'll create a C program, power.c, with a function Perl-
Power() 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;
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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" };
PERL_SYS_INIT3(&argc,&argv,&env);
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;
perl_run(my_perl);
PerlPower(3, 4); /*** Compute 3 ** 4 ***/
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}
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.
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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 occasion-
ally 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
"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
it's no longer needed. Using "call_argv" in perlapi, 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 sub-
routines 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
"my" in perlfunc 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;
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# 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__
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/* 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
#define BUFFER_SIZE 1024
static PerlInterpreter *my_perl = NULL;
int
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;
PERL_SYS_INIT3(&argc,&argv,&env);
if((my_perl = perl_alloc()) == NULL) {
fprintf(stderr, "no memory!");
exit(1);
}
perl_construct(my_perl);
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;
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));
}
}
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PL_perl_destruct_level = 0;
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
exit(exitstatus);
}
Now compile:
% cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
Here's an 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
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
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cleaning isn't 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;
perl_construct(my_perl);
...
/* clean and reset _everything_ during perl_destruct */
PL_perl_destruct_level = 1;
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. The second assignment to
"PL_perl_destruct_level" is needed because perl_construct
resets it to 0.
Now suppose we have more than one interpreter instance run-
ning 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 don't
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 "-Dusemultiplicity"
option otherwise some interpreter variables may not be ini-
tialized correctly between consecutive runs and your appli-
cation may crash.
Using "-Dusethreads -Duseithreads" rather than "-Dusemulti-
plicity" is more appropriate if you intend to run multiple
interpreters concurrently in different threads, because it
enables support for linking in the thread libraries of your
system with the interpreter.
Let's give it a try:
#include <EXTERN.h>
#include <perl.h>
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/* 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, *two_perl;
char *one_args[] = { "one_perl", SAY_HELLO };
char *two_args[] = { "two_perl", SAY_HELLO };
PERL_SYS_INIT3(&argc,&argv,&env);
one_perl = perl_alloc();
two_perl = perl_alloc();
PERL_SET_CONTEXT(one_perl);
perl_construct(one_perl);
PERL_SET_CONTEXT(two_perl);
perl_construct(two_perl);
PERL_SET_CONTEXT(one_perl);
perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
PERL_SET_CONTEXT(two_perl);
perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
PERL_SET_CONTEXT(one_perl);
perl_run(one_perl);
PERL_SET_CONTEXT(two_perl);
perl_run(two_perl);
PERL_SET_CONTEXT(one_perl);
perl_destruct(one_perl);
PERL_SET_CONTEXT(two_perl);
perl_destruct(two_perl);
PERL_SET_CONTEXT(one_perl);
perl_free(one_perl);
PERL_SET_CONTEXT(two_perl);
perl_free(two_perl);
PERL_SYS_TERM();
}
Note the calls to PERL_SET_CONTEXT(). These are necessary
to initialize 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()).
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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:
static void xs_init (pTHX);
EXTERN_C void boot_DynaLoader (pTHX_ CV* cv);
EXTERN_C void boot_Socket (pTHX_ CV* cv);
EXTERN_C void
xs_init(pTHX)
{
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 execut-
able (determined during its initial configuration on your
computer or when adding a new extension), a Perl subroutine
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is created to incorporate the extension's routines. Nor-
mally, 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 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 exam-
ples shown. For starters, backticks won'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}"
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You may wish to use a more robust environment such as the
Microsoft Developer Studio. In this case, run this to gen-
erate 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.
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 explana-
tion of the "aTHX_"." in perlguts ) Hiding the short forms
is very useful for avoiding all sorts of nasty (C preproces-
sor 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 con-
flict.)
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@media.mit.edu> and Doug MacEachern
<dougm@covalent.net>, 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 embed-
ding: 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
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model for Oracle, Netscape and Internet Information Server
Perl plugins.
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 ver-
sions of this documentation under the conditions for verba-
tim 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.
perl v5.8.8 2006-06-30 23
