Thread::Semaphore(3pm)                          Perl Programmers Reference Guide                          Thread::Semaphore(3pm)



NAME
       Thread::Semaphore - Thread-safe semaphores

VERSION
       This document describes Thread::Semaphore version 2.09

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);

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.

METHODS
       ->new()
       ->new(NUMBER)
               "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.

       ->down()
       ->down(NUMBER)
               The "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 "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).

       ->up()
       ->up(NUMBER)
               The "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 "down" the semaphore if the "up" raises the semaphore's
               count above the amount that the "down" is trying to decrement it by.  For example, if three threads are blocked
               trying to "down" a semaphore by one, and another thread "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").

NOTES
       Semaphores created by 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.

SEE ALSO
       Thread::Semaphore Discussion Forum on CPAN: http://www.cpanforum.com/dist/Thread-Semaphore
       <http://www.cpanforum.com/dist/Thread-Semaphore>;

       Annotated POD for Thread::Semaphore: http://annocpan.org/~JDHEDDEN/Thread-Semaphore-2.09/lib/Thread/Semaphore.pm
       <http://annocpan.org/~JDHEDDEN/Thread-Semaphore-2.09/lib/Thread/Semaphore.pm>;

       Source repository: http://code.google.com/p/thread-semaphore/ <http://code.google.com/p/thread-semaphore/>;

       threads, threads::shared

MAINTAINER
       Jerry D. Hedden, <jdhedden AT cpan DOT org>

LICENSE
       This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.



perl v5.12.4                                               2011-06-07                                     Thread::Semaphore(3pm)