Thread::SemaphorePerl Programmers Reference Thread::Semaphore(3p)NAMEThread::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 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.
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 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
