#!/usr/local/bin/perl -l

BEGIN {
    # reverses the parent-child relationship
    # between main and "thread state" process
    $ENV{THREADS_DAEMON_MODEL} = 1;

    setpgrp;  # for sending signals to our process group
}

use forks;

$SIG{USR1} = 'IGNORE';

my @procs;

for (1..3) {    # fork a few processes
    push @procs,
        threads->new(
            sub {
                $SIG{USR1} = sub { print "hi! from 'thread' #$_" };
                print "running 'thread' #$_ (pid=$$) ...";
                sleep 3;
            }
        );
}
sleep 1;

my $ps = "ps fT -o pid,ppid,pgrp,cmd";

print "\ninitial processes:";
system $ps;
sleep 1;

my $pgrp = getpgrp;
print "\nsending process group $pgrp USR1 signal";
kill -10, $pgrp;

$_->join() for @procs;
sleep 1;

print "\nprocesses after join()";
system $ps;


__END__
$ ./833279.pl
running 'thread' #1 (pid=24090) ...
running 'thread' #2 (pid=24091) ...
running 'thread' #3 (pid=24092) ...

initial processes:
  PID  PPID  PGRP CMD
25932 25930 25932 bash -rcfile .bashrc
24088 25932 24088  \_ /usr/local/bin/perl -l ./833279.pl
24089 24088 24088      \_ /usr/local/bin/perl -l ./833279.pl
24090 24089 24088          \_ /usr/local/bin/perl -l ./833279.pl
24091 24089 24088          \_ /usr/local/bin/perl -l ./833279.pl
24092 24089 24088          \_ /usr/local/bin/perl -l ./833279.pl
24093 24089 24088          \_ ps fT -o pid,ppid,pgrp,cmd

sending process group 24088 USR1 signal
hi! from 'thread' #1
hi! from 'thread' #2
hi! from 'thread' #3

processes after join()
  PID  PPID  PGRP CMD
25932 25930 25932 bash -rcfile .bashrc
24088 25932 24088  \_ /usr/local/bin/perl -l ./833279.pl
24089 24088 24088      \_ /usr/local/bin/perl -l ./833279.pl
24094 24089 24088          \_ ps fT -o pid,ppid,pgrp,cmd