Thread::SemaphorePerl Programmers Reference Thread::Semaphore(3p)
Thread::Semaphore - thread-safe semaphores
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);
Semaphores provide a mechanism to regulate access to resources. Semaphores, unlike locks, aren't tied to particu- lar scalars, and so may be used to control access to any- thing 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.) Incre- ment and decrement amounts aren't fixed at one either, so threads can reserve or return multiple resources at once.
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 "cap- ture" -- the semaphore operations were named by the late Dijkstra, who was Dutch). up up NUMBER The "up" method increases the semaphore's count by perl v5.8.8 2005-02-05 1 Thread::SemaphorePerl Programmers Reference Thread::Semaphore(3p) 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 2005-02-05 2
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