I recently added thead signalling capabilities to the threads module, and improved the functionality of calling exit inside a thread. These features can be used to provide kill/cancel threads as follows:

    use threads;

    sub thr_func
    {
        # Thread 'cancellation' signal handler
        $SIG{'KILL'} = sub { threads->exit(); };

        ...
    }

    # Create a thread
    my $thr = threads->create('thr_func');

    ...

    # Signal the thread to terminate, and then detach
    # it so that it will get cleaned up automatically
    $thr->kill('KILL')->detach();
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Be sure to get the latest version of the threads module from CPAN, and read the POD for more information and caveats.