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Thread::SemaphorePerl Programmers Reference Thread::Semaphore(3p)


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 par-
       ticular 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 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.

               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).

       up
       up NUMBER
               The "up" method increases the semaphore's count by
               the number specified, or by one if no number has



perl v5.8.5                 2002-11-06                          1





Thread::SemaphorePerl Programmers Reference Thread::Semaphore(3p)


               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 v5.8.5                 2002-11-06                          2