PERLEMBED(1) Perl Programmers Reference Guide PERLEMBED(1) #
PERLEMBED(1) Perl Programmers Reference Guide PERLEMBED(1)
NNAAMMEE #
perlembed - how to embed perl in your C program
DDEESSCCRRIIPPTTIIOONN #
PPRREEAAMMBBLLEE #
Do you want to:
UUssee CC ffrroomm PPeerrll??
Read perlxstut, perlxs, h2xs, perlguts, and perlapi.
UUssee aa UUnniixx pprrooggrraamm ffrroomm PPeerrll??
Read about back-quotes and about "system" and "exec" in perlfunc.
UUssee PPeerrll ffrroomm PPeerrll??
Read about "do" in perlfunc and "eval" in perlfunc and "require" in
perlfunc and "use" in perlfunc.
UUssee CC ffrroomm CC??
Rethink your design.
UUssee PPeerrll ffrroomm CC??
Read on...
RROOAADDMMAAPP #
• 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
CCoommppiilliinngg yyoouurr CC pprrooggrraamm 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 _p_e_r_l _l_i_b_r_a_r_y.
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 (_/_u_s_r_/_b_i_n_/_p_e_r_l 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 _l_i_b
directory.)
When you use Perl from C, your C program will--usually--allocate, "run",
and deallocate a _P_e_r_l_I_n_t_e_r_p_r_e_t_e_r 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 _E_X_T_E_R_N_._h and _p_e_r_l_._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:
% cc -O2 -Olimit 2900 -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 (_c_c, _g_c_c, 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
(_/_u_s_r_/_l_o_c_a_l_/_l_i_b_/_._._.) for your machine. If your compiler complains that
certain functions are undefined, or that it can't locate _-_l_p_e_r_l, then you
need to change the path following the "-L". If it complains that it
can't find _E_X_T_E_R_N_._h and _p_e_r_l_._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
EExxttUUttiillss::::EEmmbbeedd module will determine all of this information for you:
% cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
If the EExxttUUttiillss::::EEmmbbeedd module isn't part of your Perl distribution, you
can retrieve it from <https://metacpan.org/pod/ExtUtils::Embed> (If this
documentation came from your Perl distribution, then you're running 5.004
or better and you already have it.)
The EExxttUUttiillss::::EEmmbbeedd kit on CPAN also contains all source code for the
examples in this document, tests, additional examples and other
information you may find useful.
AAddddiinngg aa PPeerrll iinntteerrpprreetteerr ttoo yyoouurr CC pprrooggrraamm In a sense, perl (the C program) is a good example of embedding Perl (the language), so I’ll demonstrate embedding with _m_i_n_i_p_e_r_l_m_a_i_n_._c, included in the source distribution. Here’s a bastardized, non-portable version of _m_i_n_i_p_e_r_l_m_a_i_n_._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)
{
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(); #
exit(EXIT_SUCCESS);
}
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 PPEERRLL__SSYYSS__IINNIITT33(()) and PPEERRLL__SSYYSS__TTEERRMM(()) provide system-specific
tune up of the C runtime environment necessary to run Perl interpreters;
they should only be called once regardless of how many interpreters you
create or destroy. Call PPEERRLL__SSYYSS__IINNIITT33(()) before you create your first
interpreter, and PPEERRLL__SSYYSS__TTEERRMM(()) after you free your last interpreter.
Since PPEERRLL__SSYYSS__IINNIITT33(()) may change "env", it may be more appropriate to
provide "env" as an argument to ppeerrll__ppaarrssee(()).
Also notice that no matter what arguments you pass to ppeerrll__ppaarrssee(()),
PPEERRLL__SSYYSS__IINNIITT33(()) must be invoked on the C mmaaiinn(()) argc, argv and env and
only once.
Mind that argv[argc] must be NULL, same as those passed to a main
function in C.
Now compile this program (I'll call it _i_n_t_e_r_p_._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 _i_n_t_e_r_p 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 _a_r_g_v_[_1_] before
calling _p_e_r_l___r_u_n.
CCaalllliinngg aa PPeerrll ssuubbrroouuttiinnee ffrroomm yyoouurr CC pprrooggrraamm To call individual Perl subroutines, you can use any of the ccaallll__ functions documented in perlcall. In this example we’ll use “call_argv”.
That's shown below, in a program I'll call _s_h_o_w_t_i_m_e_._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(); #
exit(EXIT_SUCCESS);
}
where _s_h_o_w_t_i_m_e is a Perl subroutine that takes no arguments (that's the
_G___N_O_A_R_G_S) and for which I'll ignore the return value (that's the
_G___D_I_S_C_A_R_D). Those flags, and others, are discussed in perlcall.
I'll define the _s_h_o_w_t_i_m_e subroutine in a file called _s_h_o_w_t_i_m_e_._p_l:
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 _p_e_r_l___r_u_n, 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 _c_a_l_l___a_r_g_v. 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".
EEvvaalluuaattiinngg aa PPeerrll ssttaatteemmeenntt ffrroomm yyoouurr CC pprrooggrraamm 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 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 "use"
in perlfunc, "require" in perlfunc, and "do" in perlfunc to include
external Perl files.
_e_v_a_l___p_v lets us evaluate individual Perl strings, and then extract
variables for coercion into C types. The following program, _s_t_r_i_n_g_._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)
{
char *embedding[] = { "", "-e", "0", NULL };
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", 0)));
/** Treat $a as a float **/
eval_pv("$a = 3.14; $a **= 2", TRUE);
printf("a = %f\n", SvNV(get_sv("a", 0)));
/** Treat $a as a string **/
eval_pv(
"$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
printf("a = %s\n", SvPV_nolen(get_sv("a", 0)));
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM(); #
}
All of those strange functions with _s_v in their names help convert Perl
scalars to C types. They're described in perlguts and perlapi.
If you compile and run _s_t_r_i_n_g_._c, you'll see the results of using _SS_vv_II_VV_((_))
to create an "int", _SS_vv_NN_VV_((_)) to create a "float", and _SS_vv_PP_VV_((_)) 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'ed expression. It is also possible
and in most cases a better strategy to fetch the return value from
_ee_vv_aa_ll____pp_vv_((_)) instead. Example:
...
SV *val = eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
printf("%s\n", SvPV_nolen(val));
...
This way, we avoid namespace pollution by not creating global variables
and we've simplified our code as well.
PPeerrffoorrmmiinngg PPeerrll ppaatttteerrnn mmaattcchheess aanndd ssuubbssttiittuuttiioonnss ffrroomm yyoouurr CC pprrooggrraamm The _ee_vv_aa_ll____ss_vv_((_)) function lets us evaluate strings of Perl code, so we can define some functions that use it to “specialize” in matches and substitutions: _mm_aa_tt_cc_hh_((_)), _ss_uu_bb_ss_tt_ii_tt_uu_tt_ee_((_)), and _mm_aa_tt_cc_hh_ee_ss_((_)).
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/"), mmaattcchh(()) 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]"), ssuubbssttiittuuttee(()) modifies the string within the "SV" as
according to the operation, returning the number of substitutions made.
SSize_t matches(SV *string, char *pattern, AV **matches);
Given an "SV", a pattern, and a pointer to an empty "AV", mmaattcchheess(())
evaluates "$string =~ $pattern" in a list context, and fills in _m_a_t_c_h_e_s
with the array elements, returning the number of matches found.
Here's a sample program, _m_a_t_c_h_._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;
PUSHMARK(SP); #
eval_sv(sv, G_SCALAR);
SPAGAIN; #
retval = POPs;
PUTBACK; #
if (croak_on_error && SvTRUE(ERRSV))
croak_sv(ERRSV);
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(0), *retval;
sv_setpvf(command, "my $string = '%s'; $string =~ %s",
SvPV_nolen(string), pattern);
retval = my_eval_sv(command, TRUE);
SvREFCNT_dec(command);
return SvIV(retval);
}
/** substitute(string, pattern)
**
** Used for =~ operations that
** modify their left-hand side (s/// and tr///)
**
** Returns the number of successful matches, and
** modifies the input string if there were any.
**/
I32 substitute(SV **string, char *pattern)
{
SV *command = newSV(0), *retval;
sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
SvPV_nolen(*string), pattern);
retval = my_eval_sv(command, TRUE);
SvREFCNT_dec(command);
*string = get_sv("string", 0);
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
**/
SSize_t matches(SV *string, char *pattern, AV **match_list)
{
SV *command = newSV(0);
SSize_t num_matches;
sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
SvPV_nolen(string), pattern);
my_eval_sv(command, TRUE);
SvREFCNT_dec(command);
*match_list = get_av("array", 0);
num_matches = av_top_index(*match_list) + 1;
return num_matches;
}
main (int argc, char **argv, char **env)
{
char *embedding[] = { "", "-e", "0", NULL };
AV *match_list;
I32 num_matches, i;
SV *text;
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(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");
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_nolen(*av_fetch(match_list, i, FALSE)));
printf("\n");
/** Remove all vowels from text **/
num_matches = substitute(&text, "s/[aeiou]//gi");
if (num_matches) {
printf("substitute: s/[aeiou]//gi...%lu substitutions made.\n",
(unsigned long)num_matches);
printf("Now text is: %s\n\n", SvPV_nolen(text));
}
/** 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
substitute: s/Perl/C...No substitution made.
FFiiddddlliinngg wwiitthh tthhee PPeerrll ssttaacckk ffrroomm yyoouurr CC pprrooggrraamm 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 nneewwSSVViivv(()) and ssvv__sseettnnvv(()) and nneewwAAVV(()) and all their friends. They're
described in perlguts and perlapi.
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 exponentiation, let's make
Perl's ** operator available to it (this is less useful than it sounds,
because Perl implements ** with C's _pp_oo_ww_((_)) function). First I'll create a
stub exponentiation function in _p_o_w_e_r_._p_l:
sub expo {
my ($a, $b) = @_;
return $a ** $b;
}
Now I'll create a C program, _p_o_w_e_r_._c, with a function _PP_ee_rr_ll_PP_oo_ww_ee_rr_((_)) that
contains all the perlguts necessary to push the two arguments into _ee_xx_pp_oo_((_))
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", NULL };
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(); #
exit(EXIT_SUCCESS);
}
Compile and run:
% cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
% power
3 to the 4th power is 81.
MMaaiinnttaaiinniinngg aa ppeerrssiisstteenntt iinntteerrpprreetteerr 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 "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 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 "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 = <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
#define BUFFER_SIZE 1024
static PerlInterpreter *my_perl = NULL;
int
main(int argc, char **argv, char **env)
{
char *embedding[] = { "", "persistent.pl", NULL };
char *args[] = { "", DO_CLEAN, NULL };
char filename[BUFFER_SIZE];
int failing, exitstatus;
PERL_SYS_INIT3(&argc,&argv,&env);
if((my_perl = perl_alloc()) == NULL) {
fprintf(stderr, "no memory!");
exit(EXIT_FAILURE);
}
perl_construct(my_perl);
PL_origalen = 1; /* don't let $0 assignment update the
proctitle or embedding[0] */
failing = perl_parse(my_perl, NULL, 2, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
if(!failing)
failing = perl_run(my_perl);
if(!failing) {
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_nolen(ERRSV));
}
}
PL_perl_destruct_level = 0;
exitstatus = 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
EExxeeccuuttiioonn ooff EENNDD bblloocckkss 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.
$$00 aassssiiggnnmmeennttss When a perl script assigns a value to $0 then the perl runtime will try to make this value show up as the program name reported by “ps” by updating the memory pointed to by the argv passed to ppeerrll__ppaarrssee(()) and also calling API functions like sseettpprrooccttiittllee(()) where available. This behaviour might not be appropriate when embedding perl and can be disabled by assigning the value 1 to the variable “PL_origalen” before ppeerrll__ppaarrssee(()) is called.
The _p_e_r_s_i_s_t_e_n_t_._c example above is for instance likely to segfault when $0
is assigned to if the "PL_origalen = 1;" assignment is removed. This
because perl will try to write to the read only memory of the
"embedding[]" strings.
MMaaiinnttaaiinniinngg mmuullttiippllee iinntteerrpprreetteerr iinnssttaanncceess 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 _b_e_f_o_r_e 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 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 _pp_ee_rr_ll____dd_ee_ss_tt_rr_uu_cc_tt_((_)) 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 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 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 initialized correctly between consecutive runs and your application
may crash.
See also "Thread-aware system interfaces" in perlxs.
Using "-Dusethreads -Duseithreads" rather than "-Dusemultiplicity" 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>
/* 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, NULL };
char *two_args[] = { "two_perl", SAY_HELLO, NULL };
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(); #
exit(EXIT_SUCCESS);
}
Note the calls to PPEERRLL__SSEETT__CCOONNTTEEXXTT(()). 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 ppeerrll__aalllloocc(()), or the
more esoteric ppeerrll__cclloonnee(())).
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
UUssiinngg PPeerrll mmoodduulleess,, wwhhiicchh tthheemmsseellvveess uussee CC lliibbrraarriieess,, ffrroomm yyoouurr CC pprrooggrraamm If you’ve played with the examples above and tried to embed a script that _uu_ss_ee_((_))s a Perl module (such as _S_o_c_k_e_t) 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
_pp_ee_rr_ll____pp_aa_rr_ss_ee_((_)), 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
_p_e_r_l_m_a_i_n_._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
(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
_MM_oo_dd_uu_ll_ee_::_::_bb_oo_oo_tt_ss_tt_rr_aa_pp_((_)) and is invoked when you say _u_s_e _M_o_d_u_l_e. In turn,
this hooks into an XSUB, _b_o_o_t___M_o_d_u_l_e, which creates a Perl counterpart
for each of the extension's XSUBs. Don't worry about this part; leave
that to the _x_s_u_b_p_p and extension authors. If your extension is
dynamically loaded, DynaLoader creates _MM_oo_dd_uu_ll_ee_::_::_bb_oo_oo_tt_ss_tt_rr_aa_pp_((_)) 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
_pp_ee_rr_ll____pp_aa_rr_ss_ee_((_)):
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"'
EExxttUUttiillss::::EEmmbbeedd can also automate writing the _x_s___i_n_i_t 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.
UUssiinngg eemmbbeeddddeedd PPeerrll wwiitthh PPOOSSIIXX llooccaalleess (See perllocale for information about these.) When a Perl interpreter normally starts up, it tells the system it wants to use the system’s default locale. This is often, but not necessarily, the “C” or “POSIX” locale. Absent a “use locale” within the perl code, this mostly has no effect (but see “Not within the scope of “use locale”” in perllocale). Also, there is not a problem if the locale you want to use in your embedded perl is the same as the system default. However, this doesn’t work if you have set up and want to use a locale that isn’t the system default one. Starting in Perl v5.20, you can tell the embedded Perl interpreter that the locale is already properly set up, and to skip doing its own normal initialization. It skips if the environment variable “PERL_SKIP_LOCALE_INIT” is set (even if set to 0 or “”). A perl that has this capability will define the C pre-processor symbol “HAS_SKIP_LOCALE_INIT”. This allows code that has to work with multiple Perl versions to do some sort of work-around when confronted with an earlier Perl.
If your program is using the POSIX 2008 multi-thread locale
functionality, you should switch into the global locale and set that up
properly before starting the Perl interpreter. It will then properly
switch back to using the thread-safe functions.
HHiiddiinngg PPeerrll__ If you completely hide the short 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 MULTIPLICITY" in perlguts for the explanation of the
"aTHX_". ) 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.)
MMOORRAALL #
You can sometimes _w_r_i_t_e _f_a_s_t_e_r _c_o_d_e in C, but you can always _w_r_i_t_e _c_o_d_e
_f_a_s_t_e_r in Perl. Because you can use each from the other, combine them as
you wish.
AAUUTTHHOORR #
Jon Orwant <_o_r_w_a_n_t_@_m_e_d_i_a_._m_i_t_._e_d_u> and Doug MacEachern
<_d_o_u_g_m_@_c_o_v_a_l_e_n_t_._n_e_t>, 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 Sugars's nsapi_perl have used this
model for Oracle, Netscape and Internet Information Server Perl plugins.
CCOOPPYYRRIIGGHHTT #
Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant. All
Rights Reserved.
This document may be distributed under the same terms as Perl itself.
perl v5.36.3 2023-02-15 PERLEMBED(1)