NAME

       Thread::Semaphore - Thread-safe semaphores

VERSION

       This document describes Thread::Semaphore version 2.13

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.

           # Decrement the semaphore only if it would immediately succeed.
           if ($s->down_nb()) {
               # The guarded section is here
               $s->up();
           }

           # Forcefully decrement the semaphore even if its count goes below 0.
           $s->down_force();

           # The default value for semaphore operations is 1
           my $s = Thread::Semaphore->new($initial_value);
           $s->down($down_value);
           $s->up($up_value);
           if ($s->down_nb($down_value)) {
               ...
               $s->up($up_value);
           }
           $s->down_force($down_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).

       ->down_nb()
       ->down_nb(NUMBER)
               The "down_nb" method attempts to decrease 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  return false, and the
               semaphore's count remains unchanged.  Otherwise, the semaphore's count is  decremented  and  this
               method returns true.

       ->down_force()
       ->down_force(NUMBER)
               The "down_force" method decreases the semaphore's count by the specified number (which must be an
               integer  >=  1),  or by one if no number is specified.  This method does not block, and may cause
               the semaphore's count to drop below zero.

       ->down_timed(TIMEOUT)
       ->down_timed(TIMEOUT, NUMBER)
               The "down_timed" method attempts to decrease the semaphore's count  by  1  or  by  the  specified
               number within the specified timeout period given in seconds (which must be an integer >= 0).

               If  the  semaphore's  count  would  drop  below  zero,  this  method  will block until either the
               semaphore's count is greater than or equal to the amount you're "down"ing the  semaphore's  count
               by, or until the timeout is reached.

               If  the  timeout  is  reached,  this  method will return false, and the semaphore's count remains
               unchanged.  Otherwise, the semaphore's count is decremented and this method returns true.

       ->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 on MetaCPAN: <https://metacpan.org/release/Thread-Semaphore>

       Code repository for CPAN distribution: <https://github.com/Dual-Life/Thread-Semaphore>

       threads, threads::shared

       Sample code in the examples directory of this distribution on CPAN.

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 v5.38.2                                       2025-04-08                           Thread::Semaphore(3perl)