bash $ (sleep 1; killall -HUP the_parent) & perl threads.pl
[1] 4842
Thread 1: Created
Thread 2: Created
Thread 3: Created
Shutting down 3 threads
Thread 1: Shutting down
Thread 3: Shutting down
1 still running. Giving up!

##</code><code>##

#!/usr/bin/env perl

use 5.012;
use warnings FATAL => 'all';
use autodie;
  
if (my $pid = fork) {
    $0 = 'the_parent';
    local $SIG{HUP} = sub { kill USR1 => $pid };
    exit(0 < waitpid $pid,0);
}


$0 = 'the_child';
use threads;
use threads::shared;

my $shutdown :shared = 0;

my @thr = map { threads->create(sub {
    printf "Thread %d: Created\n", threads->tid;
    sleep 1 + rand 2 until $shutdown;
    printf "Thread %d: Shutting down\n", threads->tid;
    lock($shutdown); cond_signal($shutdown);
}) } 1..3;

$SIG{USR1} = sub { $shutdown = 1 };

sleep until $shutdown;

say "Shutting down " . scalar threads->list . " threads";
my $until = 1 + time; # Wait this many seconds before abort

while (my $threads = threads->list(threads::running)) {
    lock($shutdown);
    cond_timedwait($shutdown, $until) or last;
}

if (my @remain = threads->list(threads::running)) {
    $_->detach for @remain;
    $_->join   for threads->list(threads::joinable);
    die scalar @remain . " still running. Giving up!\n";
}

$_->join for @thr;
say "All threads exited normally.";