Hello Perl Gurus,

I am having trouble updating a variable in a perl sub and using the updated value in the main body of the perl script. Ultimately, I'd like to share more complex data between the sub/callback and main. Any help would be greatly appreciated!

I am extending perl (with SWIG) to access a C library and also embedding a perl interepreter (via perl_clone) so that the library can invoke perl subroutines as callbacks.

The perl subs are getting called correctly. I need to wait in the main perl script until the callback is executed before other actions are taken. I initially initialized a simple scalar to "0" and changed its value in the subroutine and waited (sleep() ) until the value is updated. Though the callback updates the value, it is never reflected in the main body of the script. I'm not sure what is the reason?

As a possible solution, I declared the scalar as ":shared", but then I get this error on a unrelated line of code. The offending line is registering the perl-sub as a callback into the C library via a SWIG generated wrapper. Not sure of the link between "use threads:shared" and this message.

Perl version 5.8.8 threads version: 1.07, threads::shared version: 0.94

Original/ideal looking code sample.. 

#This is the SWIG generated module to my C library
use MyModule;
#shared scalar
$cb_done = 0;

#This cb would be invoked by the cloned interpreter in the
#C library.  This works fine.
sub cb_one
{
  ($event, $pdata) = @_;
  #This line is printed.
  print "event : ", $event, "\n";
  $cb_done = 1;
}

$status = MyModule::RegisterCB(\&main::cb_one);

do
{
   sleep (5);
} until ($cb_done == 1)

#This line is not printed as $cb_done never becomes 1 
#in the main of the perl script
print "CB was invoked : $cb_done\n";

[download]

Sample code using threads::shared 

use threads;
use threads::shared;

use MyModule;
#shared scalar
$cb_done : shared = 0;

[download]
But I get "Invalid value for shared scalar" for this line of code

 $status = MyModule::RegisterCB(\&main::cb_one);

In reply to Extending & Embedding Perl simultaneously: How to share a scalar between perl callback sub and main body? by perlmonk1729

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