Revision 162c1c1f
b/lib/locking.py | ||
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# Copyright (C) 2006, 2007 Google Inc. |
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# |
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# This program is free software; you can redistribute it and/or modify |
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# it under the terms of the GNU General Public License as published by |
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# the Free Software Foundation; either version 2 of the License, or |
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# (at your option) any later version. |
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# |
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# This program is distributed in the hope that it will be useful, but |
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# WITHOUT ANY WARRANTY; without even the implied warranty of |
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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# General Public License for more details. |
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# |
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# You should have received a copy of the GNU General Public License |
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# along with this program; if not, write to the Free Software |
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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# 02110-1301, USA. |
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"""Module implementing the Ganeti locking code.""" |
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# pylint: disable-msg=W0613,W0201 |
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import threading |
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class SharedLock: |
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"""Implements a shared lock. |
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Multiple threads can acquire the lock in a shared way, calling |
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acquire_shared(). In order to acquire the lock in an exclusive way threads |
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can call acquire_exclusive(). |
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The lock prevents starvation but does not guarantee that threads will acquire |
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the shared lock in the order they queued for it, just that they will |
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eventually do so. |
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""" |
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def __init__(self): |
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"""Construct a new Shared Lock""" |
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# we have two conditions, c_shr and c_exc, sharing the same lock. |
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self.__lock = threading.Lock() |
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self.__turn_shr = threading.Condition(self.__lock) |
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self.__turn_exc = threading.Condition(self.__lock) |
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# current lock holders |
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self.__shr = set() |
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self.__exc = None |
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# lock waiters |
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self.__nwait_exc = 0 |
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self.__nwait_shr = 0 |
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def __is_sharer(self): |
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"""Is the current thread sharing the lock at this time?""" |
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return threading.currentThread() in self.__shr |
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def __is_exclusive(self): |
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"""Is the current thread holding the lock exclusively at this time?""" |
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return threading.currentThread() == self.__exc |
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def __is_owned(self, shared=-1): |
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"""Is the current thread somehow owning the lock at this time? |
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This is a private version of the function, which presumes you're holding |
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the internal lock. |
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""" |
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if shared < 0: |
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return self.__is_sharer() or self.__is_exclusive() |
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elif shared: |
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return self.__is_sharer() |
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else: |
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return self.__is_exclusive() |
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def _is_owned(self, shared=-1): |
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"""Is the current thread somehow owning the lock at this time? |
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Args: |
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shared: |
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< 0: check for any type of ownership (default) |
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0: check for exclusive ownership |
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> 0: check for shared ownership |
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""" |
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self.__lock.acquire() |
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try: |
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result = self.__is_owned(shared) |
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finally: |
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self.__lock.release() |
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return result |
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def acquire(self, blocking=1, shared=0): |
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"""Acquire a shared lock. |
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Args: |
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shared: whether to acquire in shared mode. By default an exclusive lock |
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will be acquired. |
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blocking: whether to block while trying to acquire or to operate in try-lock mode. |
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this locking mode is not supported yet. |
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""" |
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if not blocking: |
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# We don't have non-blocking mode for now |
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raise NotImplementedError |
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self.__lock.acquire() |
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try: |
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# We cannot acquire the lock if we already have it |
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assert not self.__is_owned(), "double acquire() on a non-recursive lock" |
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if shared: |
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self.__nwait_shr += 1 |
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try: |
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# If there is an exclusive holder waiting we have to wait. We'll |
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# only do this once, though, when we start waiting for the lock. Then |
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# we'll just wait while there are no exclusive holders. |
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if self.__nwait_exc > 0: |
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# TODO: if !blocking... |
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self.__turn_shr.wait() |
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while self.__exc is not None: |
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# TODO: if !blocking... |
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self.__turn_shr.wait() |
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self.__shr.add(threading.currentThread()) |
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finally: |
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self.__nwait_shr -= 1 |
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else: |
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self.__nwait_exc += 1 |
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try: |
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# This is to save ourselves from a nasty race condition that could |
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# theoretically make the sharers starve. |
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if self.__nwait_shr > 0 or self.__nwait_exc > 1: |
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# TODO: if !blocking... |
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self.__turn_exc.wait() |
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while len(self.__shr) > 0 or self.__exc is not None: |
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# TODO: if !blocking... |
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self.__turn_exc.wait() |
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self.__exc = threading.currentThread() |
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finally: |
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self.__nwait_exc -= 1 |
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finally: |
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self.__lock.release() |
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return True |
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def release(self): |
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"""Release a Shared Lock. |
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You must have acquired the lock, either in shared or in exclusive mode, |
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before calling this function. |
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""" |
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self.__lock.acquire() |
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try: |
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# Autodetect release type |
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if self.__is_exclusive(): |
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self.__exc = None |
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# An exclusive holder has just had the lock, time to put it in shared |
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# mode if there are shared holders waiting. Otherwise wake up the next |
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# exclusive holder. |
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if self.__nwait_shr > 0: |
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self.__turn_shr.notifyAll() |
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elif self.__nwait_exc > 0: |
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self.__turn_exc.notify() |
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elif self.__is_sharer(): |
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self.__shr.remove(threading.currentThread()) |
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# If there are shared holders waiting there *must* be an exclusive holder |
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# waiting as well; otherwise what were they waiting for? |
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assert (self.__nwait_shr == 0 or self.__nwait_exc > 0, |
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"Lock sharers waiting while no exclusive is queueing") |
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# If there are no more shared holders and some exclusive holders are |
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# waiting let's wake one up. |
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if len(self.__shr) == 0 and self.__nwait_exc > 0: |
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self.__turn_exc.notify() |
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else: |
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assert False, "Cannot release non-owned lock" |
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finally: |
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self.__lock.release() |
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b/test/Makefile.am | ||
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ganeti.config_unittest.py \ |
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ganeti.hooks_unittest.py \ |
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ganeti.utils_unittest.py \ |
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ganeti.bdev_unittest.py |
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ganeti.bdev_unittest.py \ |
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ganeti.locking_unittest.py |
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TESTS_ENVIRONMENT = PYTHONPATH=.:$(top_builddir) |
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b/test/ganeti.locking_unittest.py | ||
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#!/usr/bin/python |
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# |
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# Copyright (C) 2006, 2007 Google Inc. |
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# |
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# This program is free software; you can redistribute it and/or modify |
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# it under the terms of the GNU General Public License as published by |
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# the Free Software Foundation; either version 2 of the License, or |
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# (at your option) any later version. |
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# |
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# This program is distributed in the hope that it will be useful, but |
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# WITHOUT ANY WARRANTY; without even the implied warranty of |
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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# General Public License for more details. |
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# |
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# You should have received a copy of the GNU General Public License |
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# along with this program; if not, write to the Free Software |
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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# 0.0510-1301, USA. |
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"""Script for unittesting the locking module""" |
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import os |
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import unittest |
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import time |
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import Queue |
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from ganeti import locking |
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from threading import Thread |
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class TestSharedLock(unittest.TestCase): |
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"""Shared lock tests""" |
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def setUp(self): |
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self.sl = locking.SharedLock() |
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# helper threads use the 'done' queue to tell the master they finished. |
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self.done = Queue.Queue(0) |
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def testSequenceAndOwnership(self): |
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self.assert_(not self.sl._is_owned()) |
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self.sl.acquire(shared=1) |
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self.assert_(self.sl._is_owned()) |
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self.assert_(self.sl._is_owned(shared=1)) |
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self.assert_(not self.sl._is_owned(shared=0)) |
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self.sl.release() |
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self.assert_(not self.sl._is_owned()) |
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self.sl.acquire() |
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self.assert_(self.sl._is_owned()) |
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self.assert_(not self.sl._is_owned(shared=1)) |
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self.assert_(self.sl._is_owned(shared=0)) |
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self.sl.release() |
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self.assert_(not self.sl._is_owned()) |
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self.sl.acquire(shared=1) |
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self.assert_(self.sl._is_owned()) |
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self.assert_(self.sl._is_owned(shared=1)) |
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self.assert_(not self.sl._is_owned(shared=0)) |
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self.sl.release() |
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self.assert_(not self.sl._is_owned()) |
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def testBooleanValue(self): |
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# semaphores are supposed to return a true value on a successful acquire |
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self.assert_(self.sl.acquire(shared=1)) |
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self.sl.release() |
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self.assert_(self.sl.acquire()) |
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self.sl.release() |
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def testDoubleLockingStoE(self): |
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self.sl.acquire(shared=1) |
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self.assertRaises(AssertionError, self.sl.acquire) |
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def testDoubleLockingEtoS(self): |
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self.sl.acquire() |
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self.assertRaises(AssertionError, self.sl.acquire, shared=1) |
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def testDoubleLockingStoS(self): |
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self.sl.acquire(shared=1) |
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self.assertRaises(AssertionError, self.sl.acquire, shared=1) |
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def testDoubleLockingEtoE(self): |
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self.sl.acquire() |
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self.assertRaises(AssertionError, self.sl.acquire) |
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# helper functions: called in a separate thread they acquire the lock, send |
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# their identifier on the done queue, then release it. |
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def _doItSharer(self): |
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self.sl.acquire(shared=1) |
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self.done.put('SHR') |
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self.sl.release() |
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def _doItExclusive(self): |
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self.sl.acquire() |
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self.done.put('EXC') |
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self.sl.release() |
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def testSharersCanCoexist(self): |
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self.sl.acquire(shared=1) |
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Thread(target=self._doItSharer).start() |
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self.assert_(self.done.get(True, 1)) |
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self.sl.release() |
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def testExclusiveBlocksExclusive(self): |
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self.sl.acquire() |
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Thread(target=self._doItExclusive).start() |
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# give it a bit of time to check that it's not actually doing anything |
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self.assertRaises(Queue.Empty, self.done.get, True, 0.2) |
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self.sl.release() |
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self.assert_(self.done.get(True, 1)) |
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def testExclusiveBlocksSharer(self): |
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self.sl.acquire() |
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Thread(target=self._doItSharer).start() |
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time.sleep(0.05) |
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self.assertRaises(Queue.Empty, self.done.get, True, 0.2) |
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self.sl.release() |
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self.assert_(self.done.get(True, 1)) |
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def testSharerBlocksExclusive(self): |
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self.sl.acquire(shared=1) |
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Thread(target=self._doItExclusive).start() |
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time.sleep(0.05) |
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self.assertRaises(Queue.Empty, self.done.get, True, 0.2) |
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self.sl.release() |
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self.assert_(self.done.get(True, 1)) |
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def testWaitingExclusiveBlocksSharer(self): |
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self.sl.acquire(shared=1) |
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# the lock is acquired in shared mode... |
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Thread(target=self._doItExclusive).start() |
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# ...but now an exclusive is waiting... |
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time.sleep(0.05) |
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Thread(target=self._doItSharer).start() |
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# ...so the sharer should be blocked as well |
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self.assertRaises(Queue.Empty, self.done.get, True, 0.2) |
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self.sl.release() |
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# The exclusive passed before |
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self.assertEqual(self.done.get(True, 1), 'EXC') |
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self.assertEqual(self.done.get(True, 1), 'SHR') |
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def testWaitingSharerBlocksExclusive(self): |
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self.sl.acquire() |
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# the lock is acquired in exclusive mode... |
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Thread(target=self._doItSharer).start() |
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# ...but now a sharer is waiting... |
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time.sleep(0.05) |
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Thread(target=self._doItExclusive).start() |
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# ...the exclusive is waiting too... |
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self.assertRaises(Queue.Empty, self.done.get, True, 0.2) |
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self.sl.release() |
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# The sharer passed before |
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self.assertEqual(self.done.get(True, 1), 'SHR') |
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self.assertEqual(self.done.get(True, 1), 'EXC') |
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if __name__ == '__main__': |
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unittest.main() |
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#suite = unittest.TestLoader().loadTestsFromTestCase(TestSharedLock) |
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#unittest.TextTestRunner(verbosity=2).run(suite) |
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