twisted.internet.defer.DeferredSemaphore : API documentation

A semaphore for event driven systems.

If you are looking into this as a means of limiting parallelism, you might find twisted.internet.task.Cooperator more useful.

Instance Variable	tokens	At most this many users may acquire this semaphore at once. (type: `int`)
Instance Variable	limit	The difference between `tokens` and the number of users which have currently acquired this semaphore. (type: `int`)
Method	__init__	Undocumented
Method	acquire	Attempt to acquire the token.
Method	release	Release the token.
Method	_cancelAcquire	Remove a deferred d from our waiting list, as the deferred has been canceled.

Inherited from _ConcurrencyPrimitive:

Method	run	Acquire, run, release.
Method	_releaseAndReturn	Undocumented

tokens =

At most this many users may acquire this semaphore at once. (type: int)

limit =

The difference between tokens and the number of users which have currently acquired this semaphore. (type: int)

def _cancelAcquire(self, d): (source)

Remove a deferred d from our waiting list, as the deferred has been canceled.

Note: We do not need to wrap this in a try/except to catch d not being in self.waiting because this canceller will not be called if d has fired. release() pops a deferred out of self.waiting and calls it, so the canceller will no longer be called.

Parameters d The deferred that has been canceled.

def acquire(self): (source)

Attempt to acquire the token.

Returns a Deferred which fires on token acquisition.

def release(self): (source)

Release the token.

Should be called by whoever did the acquire() when the shared resource is free.

t.i.d.DeferredSemaphore(_ConcurrencyPrimitive) : class documentation