w2learn at yahoo
Nov 20, 2009, 1:07 AM
Post #2 of 2
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Re: Multiple embed interpreters : seg fault due to incorrect use?
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Hello,
I have got this problem resolved by trying few ideas I got searchig archives, googling etc. Posting my solution here for others. There maybe better solutions and I suspect this may still have other issues (eg do I need to cleanup sv_dup return?)
a) I saved the original perl-interpreter during startup. In SWIG, I specify
%init %{
my_init();
%}
%inline %{
static PerlInterpreter *orig_perl=NULL;
void my_init(void)
{
orig_perl = PERL_GET_CONTEXT;
}
}
b) modified mythread_fn like this instead of perl_alloc(). This change essentially got rid of the core dump. But, the args were empty when the perl sub was entered.
PERL_SET_CONTEXT(orig_perl);
perl_for_cb = perl_clone(orig_perl, CLONEf_KEEP_PTR_TABLE);
PERL_SET_CONTEXT(perl_for_cb);
c) added this code to the callback_handler before invoking the perl-sub via call_sv(). With this sv cloning, the arguments are fine when sub was entered.
CLONE_PARAMS clone_param;
clone_param.stashes = NULL;
clone_param.flags = 0;
clone_param.proto_perl = perl_for_cb;
sv = sv_dup(sv, &clone_param);
d) Also, added this to the callback registration function ("coderef" is the ref to the perl sub).
SvSHARE(coderef);
The problem I now face is that a global variable updated in the perl callback (ie. executing in cloned interpreter?) isnt getting reflected in the "main" of the perl script (orig interpreter).
Adding this to the script throws a run-time error for a scalar that I did NOT declare/intend to be shared ("Invalid value for shared scalar at")
use threads;
use threads::shared;
#updated in the perl callback..but update is not reflected in main, so
#try sharing it.
my $my_flag :shared =0;
Thanks
--- On Tue, 11/3/09, Sri <w2learn [at] yahoo> wrote:
> From: Sri <w2learn [at] yahoo>
> Subject: Multiple embed interpreters : seg fault due to incorrect use?
> To: perl5-porters [at] perl
> Date: Tuesday, November 3, 2009, 2:46 AM
> Hi,
>
> I'm trying to provide a Perl interface to a C library
> (event-driven). I've used SWIG (www.swig.org) to
> create perl wrappings for this library. I'm getting a
> seg fault in the depths of perl and I'm at a loss reg how to
> proceed. I feel its related to multiple interpreter instance
> usage.
>
> The C library has APIs, ofcourse, but it also allows
> perl-subroutines to be registered as callbacks into the C
> library. The C library has a thread that monitors
> external events and invokes the perl-sub callbacks.
>
> The default perl interpreter is executing the script
> (interpreter instance one). Neither SWIG nor I have
> any code to create/initiaze this instance, as far as I can
> see. My library thread, creates a new
> interpreter. But, crashes in the call_sv(). If I
> execute the same code (call_handler below, unmodified) as
> part of an API call invoked from perl-script, it works just
> fine. So, I feel I'm not initializing/using the 2nd
> instance correctly or "coordinating" between the two
> instances properly. If anyone has pointers or other
> forums that may specialize in this topic, it would be great
> help.
>
> ---using perl 5.8.8, compiled with multiplicity,
> implicit_context---
>
> void mythread_fn(void)
> {
>
> static
> PerlInterpreter *my_perl=NULL;
>
> my_perl =
> perl_alloc();
>
> PERL_SET_CONTEXT(my_perl);
>
> perl_construct(my_perl);
> perl_run(my_perl);
>
> while (1)
> {
>
> /*
> monitor for events */
> if
> (event == xyz)
>
> callback_handler(event);
> }
>
> perl_destruct(my_perl);
> perl_free(my_perl);
> }
>
> void callback_handler(int event)
> {
> dTHX;
> dSP;
>
> ENTER;
> SAVETMPS;
>
> SV * sv = disc_callback; /*
> saved earlier in an API call */
> if (sv == (SV*)NULL)
> croak("Internal
> error...\n");
>
> PUSHMARK(SP);
> XPUSHs(sv_2mortal(newSViv(event)));
> PUTBACK;
>
> /* Call the Perl sub */
> call_sv(sv, G_DISCARD); /*
> crashes as shown below in gdb */
>
> FREETMPS;
> LEAVE;
> }
>
> Part of gdb stacktrace.
>
> #0 Perl_pp_entersub (my_perl=0x6587b0) at
> pp_hot.c:2945
> #1 0x00000000004224f3 in S_call_body
> (my_perl=0x6587b0, myop=0x65a6e0,
> is_eval=1 '\001') at perl.c:2728
> #2 0x00000000004223c4 in Perl_call_sv
> (my_perl=0x6587b0, sv=0x635420, flags=2)
> at perl.c:2607
>
>
>
>
>
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