Semaphore(3) User Contributed Perl Documentation Semaphore(3)NAMECoro::Semaphore - counting semaphores
SYNOPSIS
use Coro;
$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 thread 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. Threads then increment the count when resources are added
and decrement the count when resources are removed.
You don't have to load "Coro::Semaphore" manually, it will be loaded
automatically when you "use Coro" and call the "new" constructor.
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.
$sem->wait
Similar to "down", but does not actually decrement the counter.
Instead, when this function returns, a following call to "down" or
"try" is guaranteed to succeed without blocking, until the next
thread switch ("cede" etc.).
Note that using "wait" is much less efficient than using "down", so
try to prefer "down" whenever possible.
$sem->wait ($callback)
If you pass a callback argument to "wait", it will not wait, but
immediately return. The callback will be called as soon as the
semaphore becomes available (which might be instantly), and gets
passed the semaphore as first argument.
The callback might "down" the semaphore exactly once, might wake up
other threads, but is NOT allowed to block (switch to other
threads).
$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 threads 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".
AUTHOR
Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/
perl v5.14.2 2011-11-11 Semaphore(3)
