twisted.internet.defer.DeferredLock

class documentation

class DeferredLock(_ConcurrencyPrimitive): (source)

A lock for event driven systems.

Method	`acquire`	Attempt to acquire the lock. Returns a `Deferred` that fires on lock acquisition with the `DeferredLock` as the value. If the lock is locked, then the Deferred is placed at the end of a waiting list.
Method	`release`	Release the lock. If there is a waiting list, then the first `Deferred` in that waiting list will be called back.
Instance Variable	`locked`	`True` when this Lock has been acquired, false at all other times. Do not change this value, but it is useful to examine for the equivalent of a "non-blocking" acquisition.
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	`__init__`	Undocumented
Method	`run`	Acquire, run, release.
Instance Variable	`waiting`	Undocumented
Method	`_releaseAndReturn`	Undocumented

def acquire(self: Self) -> Deferred[Self]: (source) ¶

overrides twisted.internet.defer._ConcurrencyPrimitive.acquire

Attempt to acquire the lock. Returns a Deferred that fires on lock acquisition with the DeferredLock as the value. If the lock is locked, then the Deferred is placed at the end of a waiting list.

Returns
a `Deferred`	a `Deferred` which fires on lock acquisition.

def release(self: Self): (source) ¶

overrides twisted.internet.defer._ConcurrencyPrimitive.release

Release the lock. If there is a waiting list, then the first Deferred in that waiting list will be called back.

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

locked: bool = (source) ¶

True when this Lock has been acquired, false at all other times. Do not change this value, but it is useful to examine for the equivalent of a "non-blocking" acquisition.

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.