97e6bb162c
This adds comments that associate the classes we have for threading usage to upstream bugs in python where similar features are being created (and potentially supported upstream). When we are able to reduce the number of supported python versions we can/should try to remove our implementations and move to the ones that may showup in the python standard library instead. Change-Id: I7b58380aeb57a58fa3b3c424c9f39de30f44f0e9
75 lines
2.4 KiB
Python
75 lines
2.4 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright (C) 2014 Yahoo! Inc. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import threading
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from taskflow.types import timing as tt
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class Latch(object):
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"""A class that ensures N-arrivals occur before unblocking.
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TODO(harlowja): replace with http://bugs.python.org/issue8777 when we no
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longer have to support python 2.6 or 2.7 and we can only support 3.2 or
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later.
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"""
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def __init__(self, count):
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count = int(count)
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if count <= 0:
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raise ValueError("Count must be greater than zero")
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self._count = count
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self._cond = threading.Condition()
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@property
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def needed(self):
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"""Returns how many decrements are needed before latch is released."""
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return max(0, self._count)
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def countdown(self):
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"""Decrements the internal counter due to an arrival."""
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self._cond.acquire()
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try:
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self._count -= 1
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if self._count <= 0:
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self._cond.notify_all()
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finally:
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self._cond.release()
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def wait(self, timeout=None):
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"""Waits until the latch is released.
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NOTE(harlowja): if a timeout is provided this function will wait
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until that timeout expires, if the latch has been released before the
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timeout expires then this will return True, otherwise it will
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return False.
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"""
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w = None
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if timeout is not None:
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w = tt.StopWatch(timeout).start()
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self._cond.acquire()
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try:
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while self._count > 0:
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if w is not None:
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if w.expired():
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return False
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else:
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timeout = w.leftover()
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self._cond.wait(timeout)
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return True
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finally:
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self._cond.release()
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