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

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 v5.28.3			  2020-05-14		  Thread::Semaphore(3)

NAME | VERSION | SYNOPSIS | DESCRIPTION | METHODS | NOTES | SEE ALSO | MAINTAINER | LICENSE

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