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+package Thread::Semaphore;
+
+use strict;
+use warnings;
+
+our $VERSION = '2.09';
+
+use threads::shared;
+use Scalar::Util 1.10 qw(looks_like_number);
+
+# Create a new semaphore optionally with specified count (count defaults to 1)
+sub new {
+    my $class = shift;
+    my $val :shared = @_ ? shift : 1;
+    if (!defined($val) ||
+        ! looks_like_number($val) ||
+        (int($val) != $val))
+    {
+        require Carp;
+        $val = 'undef' if (! defined($val));
+        Carp::croak("Semaphore initializer is not an integer: $val");
+    }
+    return bless(\$val, $class);
+}
+
+# Decrement a semaphore's count (decrement amount defaults to 1)
+sub down {
+    my $sema = shift;
+    lock($$sema);
+    my $dec = @_ ? shift : 1;
+    if (! defined($dec) ||
+        ! looks_like_number($dec) ||
+        (int($dec) != $dec) ||
+        ($dec < 1))
+    {
+        require Carp;
+        $dec = 'undef' if (! defined($dec));
+        Carp::croak("Semaphore decrement is not a positive integer: $dec");
+    }
+    cond_wait($$sema) until ($$sema >= $dec);
+    $$sema -= $dec;
+}
+
+# Increment a semaphore's count (increment amount defaults to 1)
+sub up {
+    my $sema = shift;
+    lock($$sema);
+    my $inc = @_ ? shift : 1;
+    if (! defined($inc) ||
+        ! looks_like_number($inc) ||
+        (int($inc) != $inc) ||
+        ($inc < 1))
+    {
+        require Carp;
+        $inc = 'undef' if (! defined($inc));
+        Carp::croak("Semaphore increment is not a positive integer: $inc");
+    }
+    ($$sema += $inc) > 0 and cond_broadcast($$sema);
+}
+
+1;
+
+=head1 NAME
+
+Thread::Semaphore - Thread-safe semaphores
+
+=head1 VERSION
+
+This document describes Thread::Semaphore version 2.09
+
+=head1 SYNOPSIS
+
+    use Thread::Semaphore;
+    my $s = Thread::Semaphore->new();
+    $s->down();   # Also known as the semaphore P operation.
+    # The guarded section is here
+    $s->up();     # Also known as the semaphore V operation.
+
+    # The default semaphore value is 1
+    my $s = Thread::Semaphore-new($initial_value);
+    $s->down($down_value);
+    $s->up($up_value);
+
+=head1 DESCRIPTION
+
+Semaphores provide a mechanism to regulate access to resources.  Unlike
+locks, semaphores aren't tied to particular scalars, and so may be used to
+control access to anything you care to use them for.
+
+Semaphores don't limit their values to zero and one, so they can be used to
+control access to some resource that there may be more than one of (e.g.,
+filehandles).  Increment and decrement amounts aren't fixed at one either,
+so threads can reserve or return multiple resources at once.
+
+=head1 METHODS
+
+=over 8
+
+=item ->new()
+
+=item ->new(NUMBER)
+
+C<new> creates a new semaphore, and initializes its count to the specified
+number (which must be an integer).  If no number is specified, the
+semaphore's count defaults to 1.
+
+=item ->down()
+
+=item ->down(NUMBER)
+
+The C<down> method decreases the semaphore's count by the specified number
+(which must be an integer >= 1), or by one if no number is specified.
+
+If the semaphore's count would drop below zero, this method will block
+until such time as the semaphore's count is greater than or equal to the
+amount you're C<down>ing the semaphore's count by.
+
+This is the semaphore "P operation" (the name derives from the Dutch
+word "pak", which means "capture" -- the semaphore operations were
+named by the late Dijkstra, who was Dutch).
+
+=item ->up()
+
+=item ->up(NUMBER)
+
+The C<up> method increases the semaphore's count by the number specified
+(which must be an integer >= 1), or by one if no number is specified.
+
+This will unblock any thread that is blocked trying to C<down> the
+semaphore if the C<up> raises the semaphore's count above the amount that
+the C<down> is trying to decrement it by.  For example, if three threads
+are blocked trying to C<down> a semaphore by one, and another thread C<up>s
+the semaphore by two, then two of the blocked threads (which two is
+indeterminate) will become unblocked.
+
+This is the semaphore "V operation" (the name derives from the Dutch
+word "vrij", which means "release").
+
+=back
+
+=head1 NOTES
+
+Semaphores created by L<Thread::Semaphore> can be used in both threaded and
+non-threaded applications.  This allows you to write modules and packages
+that potentially make use of semaphores, and that will function in either
+environment.
+
+=head1 SEE ALSO
+
+Thread::Semaphore Discussion Forum on CPAN:
+L<http://www.cpanforum.com/dist/Thread-Semaphore>
+
+Annotated POD for Thread::Semaphore:
+L<http://annocpan.org/~JDHEDDEN/Thread-Semaphore-2.09/lib/Thread/Semaphore.pm>
+
+Source repository:
+L<http://code.google.com/p/thread-semaphore/>
+
+L<threads>, L<threads::shared>
+
+=head1 MAINTAINER
+
+Jerry D. Hedden, S<E<lt>jdhedden AT cpan DOT orgE<gt>>
+
+=head1 LICENSE
+
+This program is free software; you can redistribute it and/or modify it under
+the same terms as Perl itself.
+
+=cut