Thread::Semaphore(3pm) Perl Programmers Reference Guide Thread::Semaphore(3pm)
NAME
Thread::Semaphore - thread-safe semaphores
SYNOPSIS
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);
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 specified number, or by one if no number has been specified. If the sema-
phore'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
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)
