package Thread::Semaphore;
+use strict;
+use warnings;
+
+our $VERSION = '2.07';
+
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 $val :shared = @_ ? shift : 1;
+ if (! looks_like_number($val) || (int($val) != $val)) {
+ require Carp;
+ $val = 'undef' if (! defined($val));
+ Carp::croak("Semaphore initializer is not an integer: $val");
+ }
+ return bless(\$val, $class);
+}
-our $VERSION = '2.01';
+# Decrement a semaphore's count (decrement amount defaults to 1)
+sub down {
+ my $sema = shift;
+ lock($$sema);
+ my $dec = @_ ? shift : 1;
+ if (! looks_like_number($dec) || (int($dec) != $dec) || ($dec < 1)) {
+ require Carp;
+ $dec = 'undef' if (! defined($dec));
+ Carp::croak("Semaphore decrement is not a positive integer: $dec");
+ }
+ cond_wait($$sema) until ($$sema >= $dec);
+ $$sema -= $dec;
+}
+
+# Increment a semaphore's count (increment amount defaults to 1)
+sub up {
+ my $sema = shift;
+ lock($$sema);
+ my $inc = @_ ? shift : 1;
+ if (! looks_like_number($inc) || (int($inc) != $inc) || ($inc < 1)) {
+ require Carp;
+ $inc = 'undef' if (! defined($inc));
+ Carp::croak("Semaphore increment is not a positive integer: $inc");
+ }
+ ($$sema += $inc) > 0 and cond_broadcast($$sema);
+}
+
+1;
=head1 NAME
-Thread::Semaphore - thread-safe semaphores
+Thread::Semaphore - Thread-safe semaphores
+
+=head1 VERSION
+
+This document describes Thread::Semaphore version 2.07
=head1 SYNOPSIS
use Thread::Semaphore;
- my $s = new Thread::Semaphore;
- $s->down; # Also known as the semaphore P operation.
+ 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.
+ $s->up(); # Also known as the semaphore V operation.
- # The default semaphore value is 1.
- my $s = new Thread::Semaphore($initial_value);
+ # 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. Semaphores,
-unlike locks, aren't tied to particular scalars, and so may be used to
+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 or one, so they can be used to
-control access to some resource that there may be more than one of. (For
-example, filehandles.) Increment and decrement amounts aren't fixed at one
-either, so threads can reserve or return multiple resources at once.
+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 FUNCTIONS AND METHODS
+=head1 METHODS
=over 8
-=item new
+=item ->new()
+
+=item ->new(NUMBER)
-=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.
-C<new> creates a new semaphore, and initializes its count to the passed
-number. If no number is passed, the semaphore's count is set to one.
+=item ->down()
-=item down
+=item ->down(NUMBER)
-=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.
-The C<down> method decreases the semaphore's count by the specified number,
-or by one if no number has been specified. If the semaphore's count would drop
-below zero, this method will block until such time that the semaphore's
-count is equal to or larger than the amount you're C<down>ing the
-semaphore's count by.
+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()
-=item up NUMBER
+=item ->up(NUMBER)
-The C<up> method increases the semaphore's count by the number specified,
-or by one if no number has been specified. This will unblock any thread blocked
-trying to C<down> the semaphore if the C<up> raises the semaphore count
-above the amount that the C<down>s are trying to decrement it by.
+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
-=cut
+=head1 NOTES
-sub new {
- my $class = shift;
- my $val : shared = @_ ? shift : 1;
- bless \$val, $class;
-}
+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.
-sub down {
- my $s = shift;
- lock($$s);
- my $inc = @_ ? shift : 1;
- cond_wait $$s until $$s >= $inc;
- $$s -= $inc;
-}
+=head1 SEE ALSO
-sub up {
- my $s = shift;
- lock($$s);
- my $inc = @_ ? shift : 1;
- ($$s += $inc) > 0 and cond_broadcast $$s;
-}
+Thread::Semaphore Discussion Forum on CPAN:
+L<http://www.cpanforum.com/dist/Thread-Semaphore>
-1;
+Annotated POD for Thread::Semaphore:
+L<http://annocpan.org/~JDHEDDEN/Thread-Semaphore-2.07/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
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