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); $s->up($up_value); $s->down($up_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 may have 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.