PERLEMBED(1) Perl Programmers Reference Guide PERLEMBED(1)
NAME
perlembed - 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 pro
gram
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
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
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 youll 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}
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
-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
(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
-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.
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)
{
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 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
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 perlcall. In this example well use
"call_argv".
Thats shown below, in a program Ill call showtime.c.
#include
#include
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 (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
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 dont have to call perl_run, as we set the
PL_exit_flag PERL_EXIT_DESTRUCT_END which executes 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, 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.
#include
#include
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);
/** 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. 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
string:
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):
#include
#include
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;
}
/** 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
**/
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 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");
else
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));
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 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...
#include
#include
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" };
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 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
bles.
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
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 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;
#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 = ;
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 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, $/;
}
1;
__END__
/* persistent.c */
#include
#include
/* 1 = clean out filenames symbol table after each request, 0 = dont */
#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));
}
}
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
Heres 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 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;
perl_construct(my_perl);
...
/* clean and reset _everything_ during perl_destruct */
PL_perl_destruct_level = 1;
perl_destruct(my_perl);
perl_free(my_perl);
...
/* 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
crash.
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:
#include
#include
/* 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 };
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 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
gram
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
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 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():
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
conflict.)
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 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
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 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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