Coro::Semaphore - counting semaphores
use Coro;
$sig = new Coro::Semaphore [initial value];
$sig->down; # wait for signal
# ... some other "thread"
$sig->up;
This module implements counting semaphores. You can initialize a mutex with any
level of parallel users, that is, you can initialize a semaphore 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 (or vice versa), "up" can be called
before "down" and so on: the semaphore is really just an integer
counter that optionally blocks when it is 0.
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 [initial count]
- Creates a new semaphore 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. The semaphore can be
down'ed without blocking when the count is strictly higher than 0.
- $sem->adjust ($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 or less.
- $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. Might accidentally cause WW3 if called in other
contexts, so don't use these.
- $guard = $sem->guard
- This method calls "down" and then creates a guard
object. When the guard object is destroyed it automatically calls
"up".
Marc A. Lehmann <[email protected]>
http://software.schmorp.de/pkg/Coro.html