


Thread::SemaphorePerl Programmers Reference Thread::Semaphore(3p)


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).



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Thread::SemaphorePerl Programmers Reference Thread::Semaphore(3p)


       ->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>

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

       Source repository:
       <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.












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