Thank you very much. Adding a sleep at the end of my code solved the problem. The actual problem I'm trying to solve is running multiple threads on a system with 4 processors. I don't want the actual number of running threads to be larger then the processors. Each thread is a calculation and it is not possible to predict how long it will take. My model code is: 
use threads;
use Thread::Semaphore;

my $semaphore = Thread::Semaphore->new(4);  # max number of proccesors
+ to use

for $i (1..10) {
    my $thr = threads->new(\&sub1, $i);
    $thr->detach();
}
sleep 20;

sub sub1 {
    $semaphore->down(1);
    $tn = shift;
    print "thread $tn is working\n";
    $s = int(rand 4) +1;                    # a long calculation
    sleep $s;
    $semaphore->up(1);
}

[download]
Can you suggest a more inteligent way to prevent the main thread from finishing. Thanks in advance.

In reply to Re^2: Thread detach by ilanv
in thread Thread detach by ilanv

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