twisted.internet.defer.DeferredSemaphore(_ConcurrencyPrimitive) class documentation

Part of twisted.internet.defer (View In Hierarchy)

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

Method run Acquire, run, release.
Method __aenter__ We can be used as an asynchronous context manager.
Method __aexit__ Undocumented
Method _releaseAndReturn Undocumented
limit =
At most this many users may acquire this semaphore at once. (type: int)
tokens =
The difference between limit and the number of users which have currently acquired this semaphore. (type: int)
def __init__(self, tokens):
overrides twisted.internet.defer._ConcurrencyPrimitive.__init__
Parameterstokensinitial value of tokens and limit (type: int)
def _cancelAcquire(self, d):

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.

ParametersdThe deferred that has been canceled.
def acquire(self):

Attempt to acquire the token.

Returnsa Deferred which fires on token acquisition.
def release(self):

Release the token.

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

API Documentation for twisted, generated by pydoctor at 2020-03-25 17:34:30.