Thread::Semaphore

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



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.
       Semaphores, 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 spec-
	       ified 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 oper-
	       ations 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(3)