twisted.internet.defer.DeferredSemaphore

class documentation

class DeferredSemaphore(_ConcurrencyPrimitive): (source)

Constructor: DeferredSemaphore(tokens)

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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.

Method __init__ No summary
Method acquire Attempt to acquire the token.
Method release Release the token.
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 _cancelAcquire Remove a deferred d from our waiting list, as the deferred has been canceled.

Inherited from _ConcurrencyPrimitive:

Method __aenter__ We can be used as an asynchronous context manager.
Method __aexit__ Undocumented
Method run Acquire, run, release.
Instance Variable waiting Undocumented
Method _releaseAndReturn Undocumented
def __init__(self, tokens: int): (source)
overrides twisted.internet.defer._ConcurrencyPrimitive.__init__
Parameters
tokens:intinitial value of tokens and limit
def acquire(self: Self) -> Deferred[Self]: (source)
overrides twisted.internet.defer._ConcurrencyPrimitive.acquire

Attempt to acquire the token.

Returns
Deferred[Self]a Deferred which fires on token acquisition.
def release(self: Self): (source)
overrides twisted.internet.defer._ConcurrencyPrimitive.release

Release the token.

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

limit = (source)

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

tokens = (source)

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

def _cancelAcquire(self: Self, d: Deferred[Self]): (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:Deferred[Self]The deferred that has been canceled.