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Thread::Semaphore(3pm) Perl Programmers Reference Guide Thread::Semaphore(3pm)
Thread::Semaphore - thread-safe semaphores
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);
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 multi-
ple resources at once.
FUNCTIONS AND METHODS
"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.
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.
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)
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