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Coro::Semaphore.3pm

NAME

Coro::Semaphore - non-binary semaphores

SYNOPSIS

  use Coro::Semaphore;
 
  $sig = new Coro::Semaphore [initial value];
 
  $sig->down; # wait for signal
 
  # ... some other "thread"
 
  $sig->up;
 
 

DESCRIPTION

This module implements counting semaphores. You can initialize a mutex with any level of parallel users, that is, you can intialize a sempahore that can be "down"ed more than once until it blocks. There is no owner associated with semaphores, so one coroutine can "down" it while another can "up" it.

Counting semaphores are typically used to coordinate access to resources, with the semaphore count initialized to the number of free resources. Coroutines then increment the count when resources are added and decrement the count when resources are removed.

new [inital count]

Creates a new sempahore object with the given initial lock count. The default lock count is 1, which means it is unlocked by default. Zero (or negative values) are also allowed, in which case the semaphore is locked by default.

$sem->count

Returns the current semaphore count.

$sem->adjust ($diff)

Atomically adds the amount given to the current semaphore count. If the count becomes positive, wakes up any waiters. Does not block if the count becomes negative, however.

$sem->down

Decrement the counter, therefore ``locking'' the semaphore. This method waits until the semaphore is available if the counter is zero.

$status = $sem->timed_down ($timeout)

Like "down", but returns false if semaphore couldn't be acquired within $timeout seconds, otherwise true.

$sem->up

Unlock the semaphore again.

$sem->try

Try to "down" the semaphore. Returns true when this was possible, otherwise return false and leave the semaphore unchanged.

$sem->waiters

In scalar context, returns the number of coroutines waiting for this semaphore.

$guard = $sem->guard

This method calls "down" and then creates a guard object. When the guard object is destroyed it automatically calls "up".

$guard = $sem->timed_guard ($timeout)

Like "guard", but returns undef if semaphore couldn't be acquired within $timeout seconds, otherwise the guard object.

AUTHOR

  Marc Lehmann <schmorp@schmorp.de>
  http://home.schmorp.de/