Read http://search.cpan.org/~yanick/Parallel-ForkManager-1.17/lib/Parallel/ForkManager.pm#BLOCKING_CALLS and then try this to see if it helps:

#!/usr/local/bin/perl
use strict;
use warnings;
use Parallel::ForkManager;

my $pm = new Parallel::ForkManager(24);
$pm->set_waitpid_blocking_sleep(0);
...
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