If you want to use threads for anything serious, get a new version of perl (at least 5.8.0, but the latest version, 5.8.8 is probably best) compiled with threads enabled. update: and then get the latest versions of threads and threads::shared from CPAN.

See also threads and threads::shared.

As for IPC, threads (not really IPC, but similar), sockets, shared memory and signals are some of the more popular options. Which one is the best/easiest depends on what you're trying to achieve.

updated again: fixed link to threads::shared

#!/usr/bin/perl
use threads;
use threads::shared;
use strict;

our $a:shared = 1;

print "main start->$a\n";

threads->create(\&display);
threads->create(\&display1);

print "hit enter to finish\n";
<STDIN>; #pauses for keypress
print "main done-> $a\n";

sub display {
   our $a = 2;
   $a++;
   print "from t1->$a\n";
}

sub display1 {
  our $a = 99;
   print "front2->$a\n";
   $a++;
lock $a;
cond_broadcast($a);
}
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You effectively get a shared hash table across all your processes. Remember to clear out the cache on startup and shutdown otherwise data will persist between runs.