twisted.internet.defer.DeferredSemaphore : API documentation

class documentation

class twisted.internet.defer.DeferredSemaphore(_ConcurrencyPrimitive): (source)

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	limit	At most this many users may acquire this semaphore at once.
Instance Variable	tokens	The difference between `limit` and the number of users which have currently acquired this semaphore.
Method	__init__
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:

Instance Variable	waiting	Undocumented
Method	run	Acquire, run, release.
Method	__aenter__	We can be used as an asynchronous context manager.
Method	__aexit__	Undocumented
Method	_releaseAndReturn	Undocumented

limit = (source)

At most this many users may acquire this semaphore at once.

(type: int)

tokens = (source)

The difference between limit and the number of users which have currently acquired this semaphore.

(type: int)

def __init__(self, tokens): (source)

overrides twisted.internet.defer._ConcurrencyPrimitive.__init__

Parameters tokens initial value of tokens and limit (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.

API Documentation for Twisted, generated by pydoctor 20.12.1 at 2021-02-28 19:53:36.