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# -*- coding: utf-8 -*-
# Copyright (C) 2014 Yahoo! Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
import threading
from oslo_utils import timeutils
class Latch(object):
"""A class that ensures N-arrivals occur before unblocking.
TODO(harlowja): replace with http://bugs.python.org/issue8777 when we no
longer have to support python 2.6 or 2.7 and we can only support 3.2 or
later.
"""
def __init__(self, count):
count = int(count)
if count <= 0:
raise ValueError("Count must be greater than zero")
self._count = count
self._cond = threading.Condition()
@property
def needed(self):
"""Returns how many decrements are needed before latch is released."""
return max(0, self._count)
def countdown(self):
"""Decrements the internal counter due to an arrival."""
with self._cond:
self._count -= 1
if self._count <= 0:
self._cond.notify_all()
def wait(self, timeout=None):
"""Waits until the latch is released.
:param timeout: wait until the timeout expires
:type timeout: number
:returns: true if the latch has been released before the
timeout expires otherwise false
:rtype: boolean
"""
watch = timeutils.StopWatch(duration=timeout)
watch.start()
with self._cond:
while self._count > 0:
if watch.expired():
return False
else:
self._cond.wait(watch.leftover(return_none=True))
return True
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