gevent.lock
– Locking primitives¶BoundedSemaphore
(value=1) → BoundedSemaphore[source]¶A bounded semaphore checks to make sure its current value doesn’t
exceed its initial value. If it does, ValueError
is
raised. In most situations semaphores are used to guard resources
with limited capacity. If the semaphore is released too many times
it’s a sign of a bug.
If not given, value defaults to 1.
DummySemaphore
(value=None) → DummySemaphore[source]¶A Semaphore initialized with “infinite” initial value. None of its methods ever block.
This can be used to parameterize on whether or not to actually
guard access to a potentially limited resource. If the resource is
actually limited, such as a fixed-size thread pool, use a real
Semaphore
, but if the resource is unbounded, use an
instance of this class. In that way none of the supporting code
needs to change.
Similarly, it can be used to parameterize on whether or not to
enforce mutual exclusion to some underlying object. If the
underlying object is known to be thread-safe itself mutual
exclusion is not needed and a DummySemaphore
can be used, but
if that’s not true, use a real Semaphore
.
Changed in version 1.1rc3: Accept and ignore a value argument for compatibility with Semaphore.
Semaphore
(value=1) → Semaphore[source]¶A semaphore manages a counter representing the number of release() calls minus the number of acquire() calls, plus an initial value. The acquire() method blocks if necessary until it can return without making the counter negative.
If not given, value
defaults to 1.
The semaphore is a context manager and can be used in with
statements.
This Semaphore’s __exit__
method does not call the trace function
on CPython, but does under PyPy.
See also
BoundedSemaphore
for a safer version that prevents
some classes of bugs.
Changed in version 1.4.0: The order in which waiters are awakened is not specified. It was not specified previously, but usually went in FIFO order.
acquire
(blocking=True, timeout=None) → bool[source]¶Acquire the semaphore.
Caution
If this semaphore was initialized with a size of 0, this method will block forever (unless a timeout is given or blocking is set to false).
blocking (bool) – If True (the default), this function will block until the semaphore is acquired.
timeout (float) – If given, specifies the maximum amount of seconds this method will block.
A boolean indicating whether the semaphore was acquired.
If blocking
is True and timeout
is None (the default), then
(so long as this semaphore was initialized with a size greater than 0)
this will always return True. If a timeout was given, and it expired before
the semaphore was acquired, False will be returned. (Note that this can still
raise a Timeout
exception, if some other caller had already started a timer.)
locked
()[source]¶Return a boolean indicating whether the semaphore can be acquired. Most useful with binary semaphores.
wait
(timeout=None) → int[source]¶Wait until it is possible to acquire this semaphore, or until the optional timeout elapses.
Caution
If this semaphore was initialized with a size of 0, this method will block forever if no timeout is given.
timeout (float) – If given, specifies the maximum amount of seconds this method will block.
A number indicating how many times the semaphore can be acquired before blocking.
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