Programming Perl, 4th Edition

threads

Perl has used a couple of different threading models in its time. There were the old v5.005 threads through the Threads module, but those were removed in v5.10. The second way, introduced in v5.8, are “interpreter threads” (or “ithreads”) that give each new thread its own Perl interpreter. If you know about threads from some other language, forget all that for Perl’s threads because they are the same in name only.

To use threads, you need a perl compiled with threads support. You can check the output of perl –V and look for something like USE_ITHREADS in the compile-time options. You can also check the Config module, which lets you inspect the compile-time options inside your program:

use Config;
$Config{useithreads} 
or die("Recompile Perl with threads to run this program.");

Many perls distributed with operating systems have a thread-enabled Perl already since it’s easier to turn it on for everyone than have it off for everyone, making a few people complain (which means you might squeeze extra performance out of your Perl binary by recompiling it without thread support).

Here’s a short example that starts some threads, detaches them, and starts a final thread and joins it. The program doesn’t wait for the detached threads to finish, but it will wait for the joined thread to complete. You can create threads with a code reference or a subroutine name, or using the async function from threads:

#!/usr/bin/perl use v5.10; use Config; $Config{useithreads} || die "You need thread support ...