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188 lines
6.5 KiB
188 lines
6.5 KiB
# cython: auto_pickle=False,embedsignature=True,always_allow_keywords=False
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from __future__ import print_function, absolute_import, division
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__all__ = [
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'Semaphore',
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'BoundedSemaphore',
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]
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def _get_linkable():
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x = __import__('gevent._abstract_linkable')
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return x._abstract_linkable.AbstractLinkable
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locals()['AbstractLinkable'] = _get_linkable()
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del _get_linkable
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class Semaphore(AbstractLinkable): # pylint:disable=undefined-variable
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"""
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Semaphore(value=1) -> Semaphore
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A semaphore manages a counter representing the number of release()
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calls minus the number of acquire() calls, plus an initial value.
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The acquire() method blocks if necessary until it can return
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without making the counter negative.
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If not given, ``value`` defaults to 1.
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The semaphore is a context manager and can be used in ``with`` statements.
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This Semaphore's ``__exit__`` method does not call the trace function
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on CPython, but does under PyPy.
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.. seealso:: :class:`BoundedSemaphore` for a safer version that prevents
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some classes of bugs.
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.. versionchanged:: 1.4.0
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The order in which waiters are awakened is not specified. It was not
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specified previously, but usually went in FIFO order.
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"""
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def __init__(self, value=1):
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if value < 0:
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raise ValueError("semaphore initial value must be >= 0")
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super(Semaphore, self).__init__()
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self.counter = value
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self._notify_all = False
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def __str__(self):
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params = (self.__class__.__name__, self.counter, self.linkcount())
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return '<%s counter=%s _links[%s]>' % params
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def locked(self):
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"""Return a boolean indicating whether the semaphore can be acquired.
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Most useful with binary semaphores."""
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return self.counter <= 0
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def release(self):
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"""
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Release the semaphore, notifying any waiters if needed.
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"""
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self.counter += 1
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self._check_and_notify()
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return self.counter
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def ready(self):
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return self.counter > 0
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def _start_notify(self):
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self._check_and_notify()
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def _wait_return_value(self, waited, wait_success):
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if waited:
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return wait_success
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# We didn't even wait, we must be good to go.
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# XXX: This is probably dead code, we're careful not to go into the wait
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# state if we don't expect to need to
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return True
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def wait(self, timeout=None):
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"""
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wait(timeout=None) -> int
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Wait until it is possible to acquire this semaphore, or until the optional
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*timeout* elapses.
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.. caution:: If this semaphore was initialized with a size of 0,
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this method will block forever if no timeout is given.
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:keyword float timeout: If given, specifies the maximum amount of seconds
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this method will block.
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:return: A number indicating how many times the semaphore can be acquired
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before blocking.
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"""
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if self.counter > 0:
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return self.counter
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self._wait(timeout) # return value irrelevant, whether we got it or got a timeout
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return self.counter
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def acquire(self, blocking=True, timeout=None):
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"""
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acquire(blocking=True, timeout=None) -> bool
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Acquire the semaphore.
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.. caution:: If this semaphore was initialized with a size of 0,
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this method will block forever (unless a timeout is given or blocking is
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set to false).
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:keyword bool blocking: If True (the default), this function will block
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until the semaphore is acquired.
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:keyword float timeout: If given, specifies the maximum amount of seconds
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this method will block.
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:return: A boolean indicating whether the semaphore was acquired.
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If ``blocking`` is True and ``timeout`` is None (the default), then
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(so long as this semaphore was initialized with a size greater than 0)
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this will always return True. If a timeout was given, and it expired before
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the semaphore was acquired, False will be returned. (Note that this can still
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raise a ``Timeout`` exception, if some other caller had already started a timer.)
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"""
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if self.counter > 0:
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self.counter -= 1
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return True
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if not blocking:
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return False
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success = self._wait(timeout)
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if not success:
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# Our timer expired.
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return False
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# Neither our timer no another one expired, so we blocked until
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# awoke. Therefore, the counter is ours
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self.counter -= 1
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assert self.counter >= 0
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return True
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_py3k_acquire = acquire # PyPy needs this; it must be static for Cython
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def __enter__(self):
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self.acquire()
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def __exit__(self, t, v, tb):
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self.release()
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class BoundedSemaphore(Semaphore):
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"""
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BoundedSemaphore(value=1) -> BoundedSemaphore
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A bounded semaphore checks to make sure its current value doesn't
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exceed its initial value. If it does, :class:`ValueError` is
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raised. In most situations semaphores are used to guard resources
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with limited capacity. If the semaphore is released too many times
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it's a sign of a bug.
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If not given, *value* defaults to 1.
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"""
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#: For monkey-patching, allow changing the class of error we raise
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_OVER_RELEASE_ERROR = ValueError
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def __init__(self, *args, **kwargs):
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Semaphore.__init__(self, *args, **kwargs)
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self._initial_value = self.counter
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def release(self):
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if self.counter >= self._initial_value:
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raise self._OVER_RELEASE_ERROR("Semaphore released too many times")
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Semaphore.release(self)
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# By building the semaphore with Cython under PyPy, we get
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# atomic operations (specifically, exiting/releasing), at the
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# cost of some speed (one trivial semaphore micro-benchmark put the pure-python version
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# at around 1s and the compiled version at around 4s). Some clever subclassing
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# and having only the bare minimum be in cython might help reduce that penalty.
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# NOTE: You must use version 0.23.4 or later to avoid a memory leak.
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# https://mail.python.org/pipermail/cython-devel/2015-October/004571.html
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# However, that's all for naught on up to and including PyPy 4.0.1 which
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# have some serious crashing bugs with GC interacting with cython.
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# It hasn't been tested since then, and PURE_PYTHON is assumed to be true
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# for PyPy in all cases anyway, so this does nothing.
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from gevent._util import import_c_accel
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import_c_accel(globals(), 'gevent.__semaphore')
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