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

       Thread::Semaphore - thread-safe semaphores

	   use Thread::Semaphore;
	   my $s = new Thread::Semaphore;
	   $s->up;     # Also known as the semaphore V -operation.
	   # The guarded section is here
	   $s->down;   # Also known as the semaphore P -operation.

	   # The default semaphore value is 1.
	   my $s = new Thread::Semaphore($initial_value);

       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 multi-
       ple resources at once.

       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 NUMBER
	       The "down" method decreases the semaphore's count by the specified 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.

       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.

perl v5.8.0				    2002-06-01			   Thread::Semaphore(3pm)
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