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#!/usr/bin/perl
use strict;
use warnings;
use threads 1.39;
use threads::shared;
use Thread::Queue;
### Global Variables ###
# Maximum working threads
my $MAX_THREADS = 10;
# Flag to inform all threads that application is terminating
my $TERM :shared = 0;
# Threads add their ID to this queue when they are ready for work
# Also, when app terminates a -1 is added to this queue
my $IDLE_QUEUE = Thread::Queue->new();
### Signal Handling ###
# Gracefully terminate application on ^C or command line 'kill'
$SIG{'INT'} = $SIG{'TERM'} =
sub {
print(">>> Terminating <<<\n");
$TERM = 1;
# Add -1 to head of idle queue to signal termination
$IDLE_QUEUE->insert(0, -1);
};
### Main Processing Section ###
MAIN:
{
### INITIALIZE ###
# Thread work queues referenced by thread ID
my %work_queues;
# Create the thread pool
for (1..$MAX_THREADS) {
# Create a work queue for a thread
my $work_q = Thread::Queue->new();
# Create the thread, and give it the work queue
my $thr = threads->create('worker', $work_q);
# Remember the thread's work queue
$work_queues{$thr->tid()} = $work_q;
}
### DO WORK ###
# Manage the thread pool until signalled to terminate
while (! $TERM) {
# Wait for an available thread
my $tid = $IDLE_QUEUE->dequeue();
# Check for termination condition
last if ($tid < 0);
# Give the thread some work to do
my $work = 5 + int(rand(10));
$work_queues{$tid}->enqueue($work);
}
### CLEANING UP ###
# Signal all threads that there is no more work
$work_queues{$_}->enqueue(-1) foreach keys(%work_queues);
# Wait for all the threads to finish
$_->join() foreach threads->list();
}
print("Done\n");
exit(0);
### Thread Entry Point Subroutines ###
# A worker thread
sub worker
{
my ($work_q) = @_;
# This thread's ID
my $tid = threads->tid();
# Work loop
do {
# Indicate that were are ready to do work
printf("Idle -> %2d\n", $tid);
$IDLE_QUEUE->enqueue($tid);
# Wait for work from the queue
my $work = $work_q->dequeue();
# If no more work, exit
last if ($work < 0);
# Do some work while monitoring $TERM
printf(" %2d <- Working\n", $tid);
while (($work > 0) && ! $TERM) {
$work -= sleep($work);
}
# Loop back to idle state if not told to terminate
} while (! $TERM);
# All done
printf("Finished -> %2d\n", $tid);
}
__END__
=head1 NAME
pool_reuse.pl - Simple 'threads' example with a reusable thread pool
=head1 DESCRIPTION
A simplistic example illustrating the following:
=over
=item * Creation of a pool of reusable threads
=item * Threads use a queue to indicate readiness for handling work
=item * Sending work to threads using queues
=item * Interrupting a threaded program
=item * Cleaning up threads before terminating
=back
=head1 SEE ALSO
L<threads>, L<threads::shared>, and L<Thread::Queue>
=head1 AUTHOR
Jerry D. Hedden, S<E<lt>jdhedden AT cpan DOT orgE<gt>>
=head1 COPYRIGHT AND LICENSE
Copyright 2006 - 2009 Jerry D. Hedden. All rights reserved.
This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.
=cut
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