Thread::Semaphore man page on CentOS

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

NAME
       Thread::Semaphore - thread-safe semaphores

SYNOPSIS
	   use Thread::Semaphore;
	   my $s = new Thread::Semaphore;
	   $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 $s = new Thread::Semaphore($initial_value);
	   $s->down($down_value);
	   $s->up($up_value);

DESCRIPTION
       Semaphores provide a mechanism to regulate access to resources. Sema‐
       phores, unlike locks, 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.

FUNCTIONS AND METHODS
       new
       new NUMBER
	       "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.

       down
       down NUMBER
	       The "down" method decreases the semaphore's count by the speci‐
	       fied 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 "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 opera‐
	       tions were named by the late Dijkstra, who was Dutch).

       up
       up NUMBER
	       The "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 "down" the semaphore if
	       the "up" raises the semaphore count above the amount that the
	       "down"s are trying to decrement it by.

	       This is the semaphore "V operation" (the name derives from the
	       Dutch word "vrij", which means "release").

perl v5.8.8			  2001-09-21		Thread::Semaphore(3pm)
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