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 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 v5.8.6                       2001-09-21              Thread::Semaphore(3)