#!/usr/bin/perl

use warnings;
use strict;
use threads;

sub set_alarm
{
    $SIG{'ALRM'} = sub {
        printf "Alarm went off in thread #%d\n", threads->tid();
        print qq{"Get up, get up!", says the clock.\n};
        exit 1;
    };

    alarm shift;
}

# If you set the SIGALRM handler HERE and ...
#     If you join the thread,   the alarm handler goes off after 10 seconds
#     ( The 'sleep' delay set inside the child thread. ) 
#     If you detach the thread, the alarm handler goes off after 3 seconds
#     ( The 'alarm' delay set inside the thread )
#         Or If you don't set 'alarm' inside the thread, the outer 'alarm'
#         delay is used.

set_alarm( 5 );

my $sleepy = threads->create ( sub {
                                   # If the SIGALRM handler is used in this thread
                                   # (comment out the set_alarm above)
                                   # it simply prints "Alarm clock" ! hahahaha
                                   set_alarm( 3 );
                                   sleep 10;
                                   print "Well, well, are you joining me in bed?\n";
                               } );

printf "Main thread  # is %d.\nChild thread # is %d.\n",
    threads->tid(), $sleepy->tid();

# Try commenting out detach/sleep and uncommenting join
# $sleepy->join;

$sleepy->detach;
sleep 15; # you only need to sleep when detach-ing

print "*Fart*\n"; # Luckily this never gets reached...
print "Oh crap I'm late for work!\n";