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# -*- coding: utf-8 -*-
"""
kombu.async.semaphore
=====================
Semaphores and concurrency primitives.
"""
from __future__ import absolute_import
from collections import deque
__all__ = ['DummyLock', 'LaxBoundedSemaphore']
class LaxBoundedSemaphore(object):
"""Asynchronous Bounded Semaphore.
Lax means that the value will stay within the specified
range even if released more times than it was acquired.
Example:
>>> from future import print_statement as printf
# ^ ignore: just fooling stupid pyflakes
>>> x = LaxBoundedSemaphore(2)
>>> x.acquire(printf, 'HELLO 1')
HELLO 1
>>> x.acquire(printf, 'HELLO 2')
HELLO 2
>>> x.acquire(printf, 'HELLO 3')
>>> x._waiters # private, do not access directly
[print, ('HELLO 3', )]
>>> x.release()
HELLO 3
"""
def __init__(self, value):
self.initial_value = self.value = value
self._waiting = deque()
self._add_waiter = self._waiting.append
self._pop_waiter = self._waiting.popleft
def acquire(self, callback, *partial_args):
"""Acquire semaphore, applying ``callback`` if
the resource is available.
:param callback: The callback to apply.
:param \*partial_args: partial arguments to callback.
"""
value = self.value
if value <= 0:
self._add_waiter((callback, partial_args))
return False
else:
self.value = max(value - 1, 0)
callback(*partial_args)
return True
def release(self):
"""Release semaphore.
If there are any waiters this will apply the first waiter
that is waiting for the resource (FIFO order).
"""
self.value = min(self.value + 1, self.initial_value)
try:
waiter, args = self._pop_waiter()
except IndexError:
pass
else:
waiter(*args)
def grow(self, n=1):
"""Change the size of the semaphore to accept more users."""
self.initial_value += n
self.value += n
[self.release() for _ in range(n)]
def shrink(self, n=1):
"""Change the size of the semaphore to accept less users."""
self.initial_value = max(self.initial_value - n, 0)
self.value = max(self.value - n, 0)
def clear(self):
"""Reset the semaphore, which also wipes out any waiting callbacks."""
self._waiting.clear()
self.value = self.initial_value
def __repr__(self):
return '<{0} at {1:#x} value:{2} waiting:{3}>'.format(
self.__class__.__name__, id(self), self.value, len(self._waiting),
)
class DummyLock(object):
"""Pretending to be a lock."""
def __enter__(self):
return self
def __exit__(self, *exc_info):
pass
|
