root / lib / locking.py @ 936f3c59
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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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# Disable "Invalid name ..." message
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# pylint: disable-msg=C0103
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"""Module implementing the Ganeti locking code."""
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import os |
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import select |
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import threading |
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import time |
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import errno |
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from ganeti import errors |
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from ganeti import utils |
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def ssynchronized(lock, shared=0): |
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"""Shared Synchronization decorator.
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Calls the function holding the given lock, either in exclusive or shared
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mode. It requires the passed lock to be a SharedLock (or support its
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semantics).
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"""
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def wrap(fn): |
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def sync_function(*args, **kwargs): |
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lock.acquire(shared=shared) |
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try:
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return fn(*args, **kwargs)
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finally:
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lock.release() |
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return sync_function
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return wrap
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class RunningTimeout(object): |
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"""Class to calculate remaining timeout when doing several operations.
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"""
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__slots__ = [ |
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"_allow_negative",
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"_start_time",
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"_time_fn",
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"_timeout",
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] |
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def __init__(self, timeout, allow_negative, _time_fn=time.time): |
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"""Initializes this class.
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@type timeout: float
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@param timeout: Timeout duration
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@type allow_negative: bool
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@param allow_negative: Whether to return values below zero
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@param _time_fn: Time function for unittests
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"""
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object.__init__(self) |
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if timeout is not None and timeout < 0.0: |
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raise ValueError("Timeout must not be negative") |
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self._timeout = timeout
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self._allow_negative = allow_negative
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self._time_fn = _time_fn
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self._start_time = None |
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def Remaining(self): |
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"""Returns the remaining timeout.
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"""
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if self._timeout is None: |
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return None |
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# Get start time on first calculation
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if self._start_time is None: |
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self._start_time = self._time_fn() |
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# Calculate remaining time
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remaining_timeout = self._start_time + self._timeout - self._time_fn() |
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if not self._allow_negative: |
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# Ensure timeout is always >= 0
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return max(0.0, remaining_timeout) |
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return remaining_timeout
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class _SingleNotifyPipeConditionWaiter(object): |
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"""Helper class for SingleNotifyPipeCondition
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"""
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__slots__ = [ |
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"_fd",
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"_poller",
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] |
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def __init__(self, poller, fd): |
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"""Constructor for _SingleNotifyPipeConditionWaiter
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@type poller: select.poll
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@param poller: Poller object
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@type fd: int
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@param fd: File descriptor to wait for
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"""
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object.__init__(self) |
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self._poller = poller
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self._fd = fd
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def __call__(self, timeout): |
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"""Wait for something to happen on the pipe.
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@type timeout: float or None
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@param timeout: Timeout for waiting (can be None)
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"""
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running_timeout = RunningTimeout(timeout, True)
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while True: |
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remaining_time = running_timeout.Remaining() |
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if remaining_time is not None and remaining_time < 0.0: |
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break
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try:
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result = self._poller.poll(remaining_time)
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except EnvironmentError, err: |
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if err.errno != errno.EINTR:
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raise
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result = None
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# Check whether we were notified
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if result and result[0][0] == self._fd: |
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break
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class _BaseCondition(object): |
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"""Base class containing common code for conditions.
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Some of this code is taken from python's threading module.
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"""
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__slots__ = [ |
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"_lock",
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"acquire",
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"release",
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] |
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def __init__(self, lock): |
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"""Constructor for _BaseCondition.
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@type lock: threading.Lock
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@param lock: condition base lock
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"""
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object.__init__(self) |
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# Recursive locks are not supported
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assert not hasattr(lock, "_acquire_restore") |
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assert not hasattr(lock, "_release_save") |
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self._lock = lock
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# Export the lock's acquire() and release() methods
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self.acquire = lock.acquire
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self.release = lock.release
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def _is_owned(self): |
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"""Check whether lock is owned by current thread.
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"""
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if self._lock.acquire(0): |
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self._lock.release()
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return False |
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return True |
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def _check_owned(self): |
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"""Raise an exception if the current thread doesn't own the lock.
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"""
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if not self._is_owned(): |
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raise RuntimeError("cannot work with un-aquired lock") |
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class SingleNotifyPipeCondition(_BaseCondition): |
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"""Condition which can only be notified once.
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This condition class uses pipes and poll, internally, to be able to wait for
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notification with a timeout, without resorting to polling. It is almost
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compatible with Python's threading.Condition, with the following differences:
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- notifyAll can only be called once, and no wait can happen after that
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- notify is not supported, only notifyAll
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"""
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__slots__ = _BaseCondition.__slots__ + [ |
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"_poller",
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"_read_fd",
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"_write_fd",
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"_nwaiters",
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"_notified",
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] |
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_waiter_class = _SingleNotifyPipeConditionWaiter |
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def __init__(self, lock): |
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"""Constructor for SingleNotifyPipeCondition
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"""
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_BaseCondition.__init__(self, lock)
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self._nwaiters = 0 |
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self._notified = False |
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self._read_fd = None |
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self._write_fd = None |
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self._poller = None |
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def _check_unnotified(self): |
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"""Throws an exception if already notified.
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"""
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if self._notified: |
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raise RuntimeError("cannot use already notified condition") |
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def _Cleanup(self): |
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"""Cleanup open file descriptors, if any.
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"""
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if self._read_fd is not None: |
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os.close(self._read_fd)
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self._read_fd = None |
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if self._write_fd is not None: |
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os.close(self._write_fd)
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self._write_fd = None |
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self._poller = None |
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def wait(self, timeout=None): |
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"""Wait for a notification.
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@type timeout: float or None
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@param timeout: Waiting timeout (can be None)
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"""
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self._check_owned()
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self._check_unnotified()
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self._nwaiters += 1 |
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try:
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if self._poller is None: |
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(self._read_fd, self._write_fd) = os.pipe() |
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self._poller = select.poll()
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self._poller.register(self._read_fd, select.POLLHUP) |
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wait_fn = self._waiter_class(self._poller, self._read_fd) |
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self.release()
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try:
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# Wait for notification
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wait_fn(timeout) |
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finally:
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# Re-acquire lock
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self.acquire()
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finally:
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self._nwaiters -= 1 |
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if self._nwaiters == 0: |
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self._Cleanup()
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def notifyAll(self): |
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"""Close the writing side of the pipe to notify all waiters.
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"""
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self._check_owned()
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self._check_unnotified()
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self._notified = True |
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if self._write_fd is not None: |
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os.close(self._write_fd)
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self._write_fd = None |
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class PipeCondition(_BaseCondition): |
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"""Group-only non-polling condition with counters.
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This condition class uses pipes and poll, internally, to be able to wait for
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notification with a timeout, without resorting to polling. It is almost
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compatible with Python's threading.Condition, but only supports notifyAll and
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non-recursive locks. As an additional features it's able to report whether
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there are any waiting threads.
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"""
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__slots__ = _BaseCondition.__slots__ + [ |
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"_nwaiters",
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"_single_condition",
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] |
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_single_condition_class = SingleNotifyPipeCondition |
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def __init__(self, lock): |
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"""Initializes this class.
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"""
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_BaseCondition.__init__(self, lock)
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self._nwaiters = 0 |
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self._single_condition = self._single_condition_class(self._lock) |
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def wait(self, timeout=None): |
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"""Wait for a notification.
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@type timeout: float or None
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@param timeout: Waiting timeout (can be None)
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"""
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self._check_owned()
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# Keep local reference to the pipe. It could be replaced by another thread
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# notifying while we're waiting.
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my_condition = self._single_condition
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assert self._nwaiters >= 0 |
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self._nwaiters += 1 |
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try:
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my_condition.wait(timeout) |
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finally:
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assert self._nwaiters > 0 |
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self._nwaiters -= 1 |
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def notifyAll(self): |
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"""Notify all currently waiting threads.
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"""
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self._check_owned()
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self._single_condition.notifyAll()
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self._single_condition = self._single_condition_class(self._lock) |
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def has_waiting(self): |
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"""Returns whether there are active waiters.
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"""
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self._check_owned()
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return bool(self._nwaiters) |
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class _CountingCondition(object): |
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"""Wrapper for Python's built-in threading.Condition class.
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This wrapper keeps a count of active waiters. We can't access the internal
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"__waiters" attribute of threading.Condition because it's not thread-safe.
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"""
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__slots__ = [ |
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"_cond",
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"_nwaiters",
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] |
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def __init__(self, lock): |
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"""Initializes this class.
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"""
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object.__init__(self) |
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self._cond = threading.Condition(lock=lock)
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self._nwaiters = 0 |
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def notifyAll(self): |
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"""Notifies the condition.
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"""
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return self._cond.notifyAll() |
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def wait(self, timeout=None): |
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"""Waits for the condition to be notified.
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@type timeout: float or None
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@param timeout: Waiting timeout (can be None)
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"""
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assert self._nwaiters >= 0 |
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self._nwaiters += 1 |
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try:
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return self._cond.wait(timeout=timeout) |
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finally:
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self._nwaiters -= 1 |
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def has_waiting(self): |
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"""Returns whether there are active waiters.
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"""
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return bool(self._nwaiters) |
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class SharedLock(object): |
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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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__slots__ = [ |
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"__active_shr_c",
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"__inactive_shr_c",
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"__deleted",
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"__exc",
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"__lock",
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"__pending",
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"__shr",
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] |
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__condition_class = PipeCondition |
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def __init__(self): |
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"""Construct a new SharedLock.
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"""
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object.__init__(self) |
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# Internal lock
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self.__lock = threading.Lock()
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# Queue containing waiting acquires
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self.__pending = []
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# Active and inactive conditions for shared locks
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self.__active_shr_c = self.__condition_class(self.__lock) |
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self.__inactive_shr_c = self.__condition_class(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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# is this lock in the deleted state?
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self.__deleted = False |
457 |
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def __check_deleted(self): |
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"""Raises an exception if the lock has been deleted.
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"""
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462 |
if self.__deleted: |
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raise errors.LockError("Deleted lock") |
464 |
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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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"""
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return threading.currentThread() in self.__shr |
470 |
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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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"""
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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() |
486 |
elif shared:
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return self.__is_sharer() |
488 |
else:
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return self.__is_exclusive() |
490 |
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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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493 |
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494 |
@param shared:
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- < 0: check for any type of ownership (default)
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496 |
- 0: check for exclusive ownership
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497 |
- > 0: check for shared ownership
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498 |
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"""
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500 |
self.__lock.acquire()
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501 |
try:
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return self.__is_owned(shared=shared) |
503 |
finally:
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504 |
self.__lock.release()
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505 |
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def _count_pending(self): |
507 |
"""Returns the number of pending acquires.
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508 |
|
509 |
@rtype: int
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510 |
|
511 |
"""
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512 |
self.__lock.acquire()
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513 |
try:
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514 |
return len(self.__pending) |
515 |
finally:
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self.__lock.release()
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517 |
|
518 |
def __do_acquire(self, shared): |
519 |
"""Actually acquire the lock.
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520 |
|
521 |
"""
|
522 |
if shared:
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523 |
self.__shr.add(threading.currentThread())
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524 |
else:
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525 |
self.__exc = threading.currentThread()
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526 |
|
527 |
def __can_acquire(self, shared): |
528 |
"""Determine whether lock can be acquired.
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529 |
|
530 |
"""
|
531 |
if shared:
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532 |
return self.__exc is None |
533 |
else:
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return len(self.__shr) == 0 and self.__exc is None |
535 |
|
536 |
def __is_on_top(self, cond): |
537 |
"""Checks whether the passed condition is on top of the queue.
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538 |
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539 |
The caller must make sure the queue isn't empty.
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540 |
|
541 |
"""
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542 |
return self.__pending[0] == cond |
543 |
|
544 |
def __acquire_unlocked(self, shared, timeout): |
545 |
"""Acquire a shared lock.
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546 |
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547 |
@param shared: whether to acquire in shared mode; by default an
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548 |
exclusive lock will be acquired
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549 |
@param timeout: maximum waiting time before giving up
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550 |
|
551 |
"""
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552 |
self.__check_deleted()
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553 |
|
554 |
# 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" |
556 |
|
557 |
# Check whether someone else holds the lock or there are pending acquires.
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if not self.__pending and self.__can_acquire(shared): |
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# Apparently not, can acquire lock directly.
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560 |
self.__do_acquire(shared)
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return True |
562 |
|
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if shared:
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wait_condition = self.__active_shr_c
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565 |
|
566 |
# Check if we're not yet in the queue
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if wait_condition not in self.__pending: |
568 |
self.__pending.append(wait_condition)
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569 |
else:
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570 |
wait_condition = self.__condition_class(self.__lock) |
571 |
# Always add to queue
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572 |
self.__pending.append(wait_condition)
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573 |
|
574 |
try:
|
575 |
# Wait until we become the topmost acquire in the queue or the timeout
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576 |
# expires.
|
577 |
while not (self.__is_on_top(wait_condition) and |
578 |
self.__can_acquire(shared)):
|
579 |
# Wait for notification
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580 |
wait_condition.wait(timeout) |
581 |
self.__check_deleted()
|
582 |
|
583 |
# A lot of code assumes blocking acquires always succeed. Loop
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584 |
# internally for that case.
|
585 |
if timeout is not None: |
586 |
break
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587 |
|
588 |
if self.__is_on_top(wait_condition) and self.__can_acquire(shared): |
589 |
self.__do_acquire(shared)
|
590 |
return True |
591 |
finally:
|
592 |
# Remove condition from queue if there are no more waiters
|
593 |
if not wait_condition.has_waiting() and not self.__deleted: |
594 |
self.__pending.remove(wait_condition)
|
595 |
|
596 |
return False |
597 |
|
598 |
def acquire(self, shared=0, timeout=None, test_notify=None): |
599 |
"""Acquire a shared lock.
|
600 |
|
601 |
@type shared: int
|
602 |
@param shared: whether to acquire in shared mode; by default an
|
603 |
exclusive lock will be acquired
|
604 |
@type timeout: float
|
605 |
@param timeout: maximum waiting time before giving up
|
606 |
@type test_notify: callable or None
|
607 |
@param test_notify: Special callback function for unittesting
|
608 |
|
609 |
"""
|
610 |
self.__lock.acquire()
|
611 |
try:
|
612 |
# We already got the lock, notify now
|
613 |
if __debug__ and callable(test_notify): |
614 |
test_notify() |
615 |
|
616 |
return self.__acquire_unlocked(shared, timeout) |
617 |
finally:
|
618 |
self.__lock.release()
|
619 |
|
620 |
def release(self): |
621 |
"""Release a Shared Lock.
|
622 |
|
623 |
You must have acquired the lock, either in shared or in exclusive mode,
|
624 |
before calling this function.
|
625 |
|
626 |
"""
|
627 |
self.__lock.acquire()
|
628 |
try:
|
629 |
assert self.__is_exclusive() or self.__is_sharer(), \ |
630 |
"Cannot release non-owned lock"
|
631 |
|
632 |
# Autodetect release type
|
633 |
if self.__is_exclusive(): |
634 |
self.__exc = None |
635 |
else:
|
636 |
self.__shr.remove(threading.currentThread())
|
637 |
|
638 |
# Notify topmost condition in queue
|
639 |
if self.__pending: |
640 |
first_condition = self.__pending[0] |
641 |
first_condition.notifyAll() |
642 |
|
643 |
if first_condition == self.__active_shr_c: |
644 |
self.__active_shr_c = self.__inactive_shr_c |
645 |
self.__inactive_shr_c = first_condition
|
646 |
|
647 |
finally:
|
648 |
self.__lock.release()
|
649 |
|
650 |
def delete(self, timeout=None): |
651 |
"""Delete a Shared Lock.
|
652 |
|
653 |
This operation will declare the lock for removal. First the lock will be
|
654 |
acquired in exclusive mode if you don't already own it, then the lock
|
655 |
will be put in a state where any future and pending acquire() fail.
|
656 |
|
657 |
@type timeout: float
|
658 |
@param timeout: maximum waiting time before giving up
|
659 |
|
660 |
"""
|
661 |
self.__lock.acquire()
|
662 |
try:
|
663 |
assert not self.__is_sharer(), "Cannot delete() a lock while sharing it" |
664 |
|
665 |
self.__check_deleted()
|
666 |
|
667 |
# The caller is allowed to hold the lock exclusively already.
|
668 |
acquired = self.__is_exclusive()
|
669 |
|
670 |
if not acquired: |
671 |
acquired = self.__acquire_unlocked(0, timeout) |
672 |
|
673 |
assert self.__is_exclusive() and not self.__is_sharer(), \ |
674 |
"Lock wasn't acquired in exclusive mode"
|
675 |
|
676 |
if acquired:
|
677 |
self.__deleted = True |
678 |
self.__exc = None |
679 |
|
680 |
# Notify all acquires. They'll throw an error.
|
681 |
while self.__pending: |
682 |
self.__pending.pop().notifyAll()
|
683 |
|
684 |
return acquired
|
685 |
finally:
|
686 |
self.__lock.release()
|
687 |
|
688 |
|
689 |
# Whenever we want to acquire a full LockSet we pass None as the value
|
690 |
# to acquire. Hide this behind this nicely named constant.
|
691 |
ALL_SET = None
|
692 |
|
693 |
|
694 |
class _AcquireTimeout(Exception): |
695 |
"""Internal exception to abort an acquire on a timeout.
|
696 |
|
697 |
"""
|
698 |
|
699 |
|
700 |
class LockSet: |
701 |
"""Implements a set of locks.
|
702 |
|
703 |
This abstraction implements a set of shared locks for the same resource type,
|
704 |
distinguished by name. The user can lock a subset of the resources and the
|
705 |
LockSet will take care of acquiring the locks always in the same order, thus
|
706 |
preventing deadlock.
|
707 |
|
708 |
All the locks needed in the same set must be acquired together, though.
|
709 |
|
710 |
"""
|
711 |
def __init__(self, members=None): |
712 |
"""Constructs a new LockSet.
|
713 |
|
714 |
@param members: initial members of the set
|
715 |
|
716 |
"""
|
717 |
# Used internally to guarantee coherency.
|
718 |
self.__lock = SharedLock()
|
719 |
|
720 |
# The lockdict indexes the relationship name -> lock
|
721 |
# The order-of-locking is implied by the alphabetical order of names
|
722 |
self.__lockdict = {}
|
723 |
|
724 |
if members is not None: |
725 |
for name in members: |
726 |
self.__lockdict[name] = SharedLock()
|
727 |
|
728 |
# The owner dict contains the set of locks each thread owns. For
|
729 |
# performance each thread can access its own key without a global lock on
|
730 |
# this structure. It is paramount though that *no* other type of access is
|
731 |
# done to this structure (eg. no looping over its keys). *_owner helper
|
732 |
# function are defined to guarantee access is correct, but in general never
|
733 |
# do anything different than __owners[threading.currentThread()], or there
|
734 |
# will be trouble.
|
735 |
self.__owners = {}
|
736 |
|
737 |
def _is_owned(self): |
738 |
"""Is the current thread a current level owner?"""
|
739 |
return threading.currentThread() in self.__owners |
740 |
|
741 |
def _add_owned(self, name=None): |
742 |
"""Note the current thread owns the given lock"""
|
743 |
if name is None: |
744 |
if not self._is_owned(): |
745 |
self.__owners[threading.currentThread()] = set() |
746 |
else:
|
747 |
if self._is_owned(): |
748 |
self.__owners[threading.currentThread()].add(name)
|
749 |
else:
|
750 |
self.__owners[threading.currentThread()] = set([name]) |
751 |
|
752 |
def _del_owned(self, name=None): |
753 |
"""Note the current thread owns the given lock"""
|
754 |
|
755 |
assert not (name is None and self.__lock._is_owned()), \ |
756 |
"Cannot hold internal lock when deleting owner status"
|
757 |
|
758 |
if name is not None: |
759 |
self.__owners[threading.currentThread()].remove(name)
|
760 |
|
761 |
# Only remove the key if we don't hold the set-lock as well
|
762 |
if (not self.__lock._is_owned() and |
763 |
not self.__owners[threading.currentThread()]): |
764 |
del self.__owners[threading.currentThread()] |
765 |
|
766 |
def _list_owned(self): |
767 |
"""Get the set of resource names owned by the current thread"""
|
768 |
if self._is_owned(): |
769 |
return self.__owners[threading.currentThread()].copy() |
770 |
else:
|
771 |
return set() |
772 |
|
773 |
def _release_and_delete_owned(self): |
774 |
"""Release and delete all resources owned by the current thread"""
|
775 |
for lname in self._list_owned(): |
776 |
self.__lockdict[lname].release()
|
777 |
self._del_owned(name=lname)
|
778 |
|
779 |
def __names(self): |
780 |
"""Return the current set of names.
|
781 |
|
782 |
Only call this function while holding __lock and don't iterate on the
|
783 |
result after releasing the lock.
|
784 |
|
785 |
"""
|
786 |
return self.__lockdict.keys() |
787 |
|
788 |
def _names(self): |
789 |
"""Return a copy of the current set of elements.
|
790 |
|
791 |
Used only for debugging purposes.
|
792 |
|
793 |
"""
|
794 |
# If we don't already own the set-level lock acquired
|
795 |
# we'll get it and note we need to release it later.
|
796 |
release_lock = False
|
797 |
if not self.__lock._is_owned(): |
798 |
release_lock = True
|
799 |
self.__lock.acquire(shared=1) |
800 |
try:
|
801 |
result = self.__names()
|
802 |
finally:
|
803 |
if release_lock:
|
804 |
self.__lock.release()
|
805 |
return set(result) |
806 |
|
807 |
def acquire(self, names, timeout=None, shared=0, test_notify=None): |
808 |
"""Acquire a set of resource locks.
|
809 |
|
810 |
@param names: the names of the locks which shall be acquired
|
811 |
(special lock names, or instance/node names)
|
812 |
@param shared: whether to acquire in shared mode; by default an
|
813 |
exclusive lock will be acquired
|
814 |
@type timeout: float or None
|
815 |
@param timeout: Maximum time to acquire all locks
|
816 |
@type test_notify: callable or None
|
817 |
@param test_notify: Special callback function for unittesting
|
818 |
|
819 |
@return: Set of all locks successfully acquired or None in case of timeout
|
820 |
|
821 |
@raise errors.LockError: when any lock we try to acquire has
|
822 |
been deleted before we succeed. In this case none of the
|
823 |
locks requested will be acquired.
|
824 |
|
825 |
"""
|
826 |
assert timeout is None or timeout >= 0.0 |
827 |
|
828 |
# Check we don't already own locks at this level
|
829 |
assert not self._is_owned(), "Cannot acquire locks in the same set twice" |
830 |
|
831 |
# We need to keep track of how long we spent waiting for a lock. The
|
832 |
# timeout passed to this function is over all lock acquires.
|
833 |
running_timeout = RunningTimeout(timeout, False)
|
834 |
|
835 |
try:
|
836 |
if names is not None: |
837 |
# Support passing in a single resource to acquire rather than many
|
838 |
if isinstance(names, basestring): |
839 |
names = [names] |
840 |
else:
|
841 |
names = sorted(names)
|
842 |
|
843 |
return self.__acquire_inner(names, False, shared, |
844 |
running_timeout.Remaining, test_notify) |
845 |
|
846 |
else:
|
847 |
# If no names are given acquire the whole set by not letting new names
|
848 |
# being added before we release, and getting the current list of names.
|
849 |
# Some of them may then be deleted later, but we'll cope with this.
|
850 |
#
|
851 |
# We'd like to acquire this lock in a shared way, as it's nice if
|
852 |
# everybody else can use the instances at the same time. If are
|
853 |
# acquiring them exclusively though they won't be able to do this
|
854 |
# anyway, though, so we'll get the list lock exclusively as well in
|
855 |
# order to be able to do add() on the set while owning it.
|
856 |
if not self.__lock.acquire(shared=shared, |
857 |
timeout=running_timeout.Remaining()): |
858 |
raise _AcquireTimeout()
|
859 |
try:
|
860 |
# note we own the set-lock
|
861 |
self._add_owned()
|
862 |
|
863 |
return self.__acquire_inner(self.__names(), True, shared, |
864 |
running_timeout.Remaining, test_notify) |
865 |
except:
|
866 |
# We shouldn't have problems adding the lock to the owners list, but
|
867 |
# if we did we'll try to release this lock and re-raise exception.
|
868 |
# Of course something is going to be really wrong, after this.
|
869 |
self.__lock.release()
|
870 |
self._del_owned()
|
871 |
raise
|
872 |
|
873 |
except _AcquireTimeout:
|
874 |
return None |
875 |
|
876 |
def __acquire_inner(self, names, want_all, shared, timeout_fn, test_notify): |
877 |
"""Inner logic for acquiring a number of locks.
|
878 |
|
879 |
@param names: Names of the locks to be acquired
|
880 |
@param want_all: Whether all locks in the set should be acquired
|
881 |
@param shared: Whether to acquire in shared mode
|
882 |
@param timeout_fn: Function returning remaining timeout
|
883 |
@param test_notify: Special callback function for unittesting
|
884 |
|
885 |
"""
|
886 |
acquire_list = [] |
887 |
|
888 |
# First we look the locks up on __lockdict. We have no way of being sure
|
889 |
# they will still be there after, but this makes it a lot faster should
|
890 |
# just one of them be the already wrong
|
891 |
for lname in utils.UniqueSequence(names): |
892 |
try:
|
893 |
lock = self.__lockdict[lname] # raises KeyError if lock is not there |
894 |
acquire_list.append((lname, lock)) |
895 |
except KeyError: |
896 |
if want_all:
|
897 |
# We are acquiring all the set, it doesn't matter if this particular
|
898 |
# element is not there anymore.
|
899 |
continue
|
900 |
|
901 |
raise errors.LockError("Non-existing lock in set (%s)" % lname) |
902 |
|
903 |
# This will hold the locknames we effectively acquired.
|
904 |
acquired = set()
|
905 |
|
906 |
try:
|
907 |
# Now acquire_list contains a sorted list of resources and locks we
|
908 |
# want. In order to get them we loop on this (private) list and
|
909 |
# acquire() them. We gave no real guarantee they will still exist till
|
910 |
# this is done but .acquire() itself is safe and will alert us if the
|
911 |
# lock gets deleted.
|
912 |
for (lname, lock) in acquire_list: |
913 |
if __debug__ and callable(test_notify): |
914 |
test_notify_fn = lambda: test_notify(lname)
|
915 |
else:
|
916 |
test_notify_fn = None
|
917 |
|
918 |
timeout = timeout_fn() |
919 |
|
920 |
try:
|
921 |
# raises LockError if the lock was deleted
|
922 |
acq_success = lock.acquire(shared=shared, timeout=timeout, |
923 |
test_notify=test_notify_fn) |
924 |
except errors.LockError:
|
925 |
if want_all:
|
926 |
# We are acquiring all the set, it doesn't matter if this
|
927 |
# particular element is not there anymore.
|
928 |
continue
|
929 |
|
930 |
raise errors.LockError("Non-existing lock in set (%s)" % lname) |
931 |
|
932 |
if not acq_success: |
933 |
# Couldn't get lock or timeout occurred
|
934 |
if timeout is None: |
935 |
# This shouldn't happen as SharedLock.acquire(timeout=None) is
|
936 |
# blocking.
|
937 |
raise errors.LockError("Failed to get lock %s" % lname) |
938 |
|
939 |
raise _AcquireTimeout()
|
940 |
|
941 |
try:
|
942 |
# now the lock cannot be deleted, we have it!
|
943 |
self._add_owned(name=lname)
|
944 |
acquired.add(lname) |
945 |
|
946 |
except:
|
947 |
# We shouldn't have problems adding the lock to the owners list, but
|
948 |
# if we did we'll try to release this lock and re-raise exception.
|
949 |
# Of course something is going to be really wrong after this.
|
950 |
if lock._is_owned():
|
951 |
lock.release() |
952 |
raise
|
953 |
|
954 |
except:
|
955 |
# Release all owned locks
|
956 |
self._release_and_delete_owned()
|
957 |
raise
|
958 |
|
959 |
return acquired
|
960 |
|
961 |
def release(self, names=None): |
962 |
"""Release a set of resource locks, at the same level.
|
963 |
|
964 |
You must have acquired the locks, either in shared or in exclusive mode,
|
965 |
before releasing them.
|
966 |
|
967 |
@param names: the names of the locks which shall be released
|
968 |
(defaults to all the locks acquired at that level).
|
969 |
|
970 |
"""
|
971 |
assert self._is_owned(), "release() on lock set while not owner" |
972 |
|
973 |
# Support passing in a single resource to release rather than many
|
974 |
if isinstance(names, basestring): |
975 |
names = [names] |
976 |
|
977 |
if names is None: |
978 |
names = self._list_owned()
|
979 |
else:
|
980 |
names = set(names)
|
981 |
assert self._list_owned().issuperset(names), ( |
982 |
"release() on unheld resources %s" %
|
983 |
names.difference(self._list_owned()))
|
984 |
|
985 |
# First of all let's release the "all elements" lock, if set.
|
986 |
# After this 'add' can work again
|
987 |
if self.__lock._is_owned(): |
988 |
self.__lock.release()
|
989 |
self._del_owned()
|
990 |
|
991 |
for lockname in names: |
992 |
# If we are sure the lock doesn't leave __lockdict without being
|
993 |
# exclusively held we can do this...
|
994 |
self.__lockdict[lockname].release()
|
995 |
self._del_owned(name=lockname)
|
996 |
|
997 |
def add(self, names, acquired=0, shared=0): |
998 |
"""Add a new set of elements to the set
|
999 |
|
1000 |
@param names: names of the new elements to add
|
1001 |
@param acquired: pre-acquire the new resource?
|
1002 |
@param shared: is the pre-acquisition shared?
|
1003 |
|
1004 |
"""
|
1005 |
# Check we don't already own locks at this level
|
1006 |
assert not self._is_owned() or self.__lock._is_owned(shared=0), \ |
1007 |
"Cannot add locks if the set is only partially owned, or shared"
|
1008 |
|
1009 |
# Support passing in a single resource to add rather than many
|
1010 |
if isinstance(names, basestring): |
1011 |
names = [names] |
1012 |
|
1013 |
# If we don't already own the set-level lock acquired in an exclusive way
|
1014 |
# we'll get it and note we need to release it later.
|
1015 |
release_lock = False
|
1016 |
if not self.__lock._is_owned(): |
1017 |
release_lock = True
|
1018 |
self.__lock.acquire()
|
1019 |
|
1020 |
try:
|
1021 |
invalid_names = set(self.__names()).intersection(names) |
1022 |
if invalid_names:
|
1023 |
# This must be an explicit raise, not an assert, because assert is
|
1024 |
# turned off when using optimization, and this can happen because of
|
1025 |
# concurrency even if the user doesn't want it.
|
1026 |
raise errors.LockError("duplicate add() (%s)" % invalid_names) |
1027 |
|
1028 |
for lockname in names: |
1029 |
lock = SharedLock() |
1030 |
|
1031 |
if acquired:
|
1032 |
lock.acquire(shared=shared) |
1033 |
# now the lock cannot be deleted, we have it!
|
1034 |
try:
|
1035 |
self._add_owned(name=lockname)
|
1036 |
except:
|
1037 |
# We shouldn't have problems adding the lock to the owners list,
|
1038 |
# but if we did we'll try to release this lock and re-raise
|
1039 |
# exception. Of course something is going to be really wrong,
|
1040 |
# after this. On the other hand the lock hasn't been added to the
|
1041 |
# __lockdict yet so no other threads should be pending on it. This
|
1042 |
# release is just a safety measure.
|
1043 |
lock.release() |
1044 |
raise
|
1045 |
|
1046 |
self.__lockdict[lockname] = lock
|
1047 |
|
1048 |
finally:
|
1049 |
# Only release __lock if we were not holding it previously.
|
1050 |
if release_lock:
|
1051 |
self.__lock.release()
|
1052 |
|
1053 |
return True |
1054 |
|
1055 |
def remove(self, names): |
1056 |
"""Remove elements from the lock set.
|
1057 |
|
1058 |
You can either not hold anything in the lockset or already hold a superset
|
1059 |
of the elements you want to delete, exclusively.
|
1060 |
|
1061 |
@param names: names of the resource to remove.
|
1062 |
|
1063 |
@return: a list of locks which we removed; the list is always
|
1064 |
equal to the names list if we were holding all the locks
|
1065 |
exclusively
|
1066 |
|
1067 |
"""
|
1068 |
# Support passing in a single resource to remove rather than many
|
1069 |
if isinstance(names, basestring): |
1070 |
names = [names] |
1071 |
|
1072 |
# If we own any subset of this lock it must be a superset of what we want
|
1073 |
# to delete. The ownership must also be exclusive, but that will be checked
|
1074 |
# by the lock itself.
|
1075 |
assert not self._is_owned() or self._list_owned().issuperset(names), ( |
1076 |
"remove() on acquired lockset while not owning all elements")
|
1077 |
|
1078 |
removed = [] |
1079 |
|
1080 |
for lname in names: |
1081 |
# Calling delete() acquires the lock exclusively if we don't already own
|
1082 |
# it, and causes all pending and subsequent lock acquires to fail. It's
|
1083 |
# fine to call it out of order because delete() also implies release(),
|
1084 |
# and the assertion above guarantees that if we either already hold
|
1085 |
# everything we want to delete, or we hold none.
|
1086 |
try:
|
1087 |
self.__lockdict[lname].delete()
|
1088 |
removed.append(lname) |
1089 |
except (KeyError, errors.LockError): |
1090 |
# This cannot happen if we were already holding it, verify:
|
1091 |
assert not self._is_owned(), "remove failed while holding lockset" |
1092 |
else:
|
1093 |
# If no LockError was raised we are the ones who deleted the lock.
|
1094 |
# This means we can safely remove it from lockdict, as any further or
|
1095 |
# pending delete() or acquire() will fail (and nobody can have the lock
|
1096 |
# since before our call to delete()).
|
1097 |
#
|
1098 |
# This is done in an else clause because if the exception was thrown
|
1099 |
# it's the job of the one who actually deleted it.
|
1100 |
del self.__lockdict[lname] |
1101 |
# And let's remove it from our private list if we owned it.
|
1102 |
if self._is_owned(): |
1103 |
self._del_owned(name=lname)
|
1104 |
|
1105 |
return removed
|
1106 |
|
1107 |
|
1108 |
# Locking levels, must be acquired in increasing order.
|
1109 |
# Current rules are:
|
1110 |
# - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
|
1111 |
# acquired before performing any operation, either in shared or in exclusive
|
1112 |
# mode. acquiring the BGL in exclusive mode is discouraged and should be
|
1113 |
# avoided.
|
1114 |
# - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
|
1115 |
# If you need more than one node, or more than one instance, acquire them at
|
1116 |
# the same time.
|
1117 |
LEVEL_CLUSTER = 0
|
1118 |
LEVEL_INSTANCE = 1
|
1119 |
LEVEL_NODE = 2
|
1120 |
|
1121 |
LEVELS = [LEVEL_CLUSTER, |
1122 |
LEVEL_INSTANCE, |
1123 |
LEVEL_NODE] |
1124 |
|
1125 |
# Lock levels which are modifiable
|
1126 |
LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE] |
1127 |
|
1128 |
LEVEL_NAMES = { |
1129 |
LEVEL_CLUSTER: "cluster",
|
1130 |
LEVEL_INSTANCE: "instance",
|
1131 |
LEVEL_NODE: "node",
|
1132 |
} |
1133 |
|
1134 |
# Constant for the big ganeti lock
|
1135 |
BGL = 'BGL'
|
1136 |
|
1137 |
|
1138 |
class GanetiLockManager: |
1139 |
"""The Ganeti Locking Library
|
1140 |
|
1141 |
The purpose of this small library is to manage locking for ganeti clusters
|
1142 |
in a central place, while at the same time doing dynamic checks against
|
1143 |
possible deadlocks. It will also make it easier to transition to a different
|
1144 |
lock type should we migrate away from python threads.
|
1145 |
|
1146 |
"""
|
1147 |
_instance = None
|
1148 |
|
1149 |
def __init__(self, nodes=None, instances=None): |
1150 |
"""Constructs a new GanetiLockManager object.
|
1151 |
|
1152 |
There should be only a GanetiLockManager object at any time, so this
|
1153 |
function raises an error if this is not the case.
|
1154 |
|
1155 |
@param nodes: list of node names
|
1156 |
@param instances: list of instance names
|
1157 |
|
1158 |
"""
|
1159 |
assert self.__class__._instance is None, \ |
1160 |
"double GanetiLockManager instance"
|
1161 |
|
1162 |
self.__class__._instance = self |
1163 |
|
1164 |
# The keyring contains all the locks, at their level and in the correct
|
1165 |
# locking order.
|
1166 |
self.__keyring = {
|
1167 |
LEVEL_CLUSTER: LockSet([BGL]), |
1168 |
LEVEL_NODE: LockSet(nodes), |
1169 |
LEVEL_INSTANCE: LockSet(instances), |
1170 |
} |
1171 |
|
1172 |
def _names(self, level): |
1173 |
"""List the lock names at the given level.
|
1174 |
|
1175 |
This can be used for debugging/testing purposes.
|
1176 |
|
1177 |
@param level: the level whose list of locks to get
|
1178 |
|
1179 |
"""
|
1180 |
assert level in LEVELS, "Invalid locking level %s" % level |
1181 |
return self.__keyring[level]._names() |
1182 |
|
1183 |
def _is_owned(self, level): |
1184 |
"""Check whether we are owning locks at the given level
|
1185 |
|
1186 |
"""
|
1187 |
return self.__keyring[level]._is_owned() |
1188 |
|
1189 |
is_owned = _is_owned |
1190 |
|
1191 |
def _list_owned(self, level): |
1192 |
"""Get the set of owned locks at the given level
|
1193 |
|
1194 |
"""
|
1195 |
return self.__keyring[level]._list_owned() |
1196 |
|
1197 |
def _upper_owned(self, level): |
1198 |
"""Check that we don't own any lock at a level greater than the given one.
|
1199 |
|
1200 |
"""
|
1201 |
# This way of checking only works if LEVELS[i] = i, which we check for in
|
1202 |
# the test cases.
|
1203 |
return utils.any((self._is_owned(l) for l in LEVELS[level + 1:])) |
1204 |
|
1205 |
def _BGL_owned(self): |
1206 |
"""Check if the current thread owns the BGL.
|
1207 |
|
1208 |
Both an exclusive or a shared acquisition work.
|
1209 |
|
1210 |
"""
|
1211 |
return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned() |
1212 |
|
1213 |
def _contains_BGL(self, level, names): |
1214 |
"""Check if the level contains the BGL.
|
1215 |
|
1216 |
Check if acting on the given level and set of names will change
|
1217 |
the status of the Big Ganeti Lock.
|
1218 |
|
1219 |
"""
|
1220 |
return level == LEVEL_CLUSTER and (names is None or BGL in names) |
1221 |
|
1222 |
def acquire(self, level, names, timeout=None, shared=0): |
1223 |
"""Acquire a set of resource locks, at the same level.
|
1224 |
|
1225 |
@param level: the level at which the locks shall be acquired;
|
1226 |
it must be a member of LEVELS.
|
1227 |
@param names: the names of the locks which shall be acquired
|
1228 |
(special lock names, or instance/node names)
|
1229 |
@param shared: whether to acquire in shared mode; by default
|
1230 |
an exclusive lock will be acquired
|
1231 |
@type timeout: float
|
1232 |
@param timeout: Maximum time to acquire all locks
|
1233 |
|
1234 |
"""
|
1235 |
assert level in LEVELS, "Invalid locking level %s" % level |
1236 |
|
1237 |
# Check that we are either acquiring the Big Ganeti Lock or we already own
|
1238 |
# it. Some "legacy" opcodes need to be sure they are run non-concurrently
|
1239 |
# so even if we've migrated we need to at least share the BGL to be
|
1240 |
# compatible with them. Of course if we own the BGL exclusively there's no
|
1241 |
# point in acquiring any other lock, unless perhaps we are half way through
|
1242 |
# the migration of the current opcode.
|
1243 |
assert (self._contains_BGL(level, names) or self._BGL_owned()), ( |
1244 |
"You must own the Big Ganeti Lock before acquiring any other")
|
1245 |
|
1246 |
# Check we don't own locks at the same or upper levels.
|
1247 |
assert not self._upper_owned(level), ("Cannot acquire locks at a level" |
1248 |
" while owning some at a greater one")
|
1249 |
|
1250 |
# Acquire the locks in the set.
|
1251 |
return self.__keyring[level].acquire(names, shared=shared, timeout=timeout) |
1252 |
|
1253 |
def release(self, level, names=None): |
1254 |
"""Release a set of resource locks, at the same level.
|
1255 |
|
1256 |
You must have acquired the locks, either in shared or in exclusive
|
1257 |
mode, before releasing them.
|
1258 |
|
1259 |
@param level: the level at which the locks shall be released;
|
1260 |
it must be a member of LEVELS
|
1261 |
@param names: the names of the locks which shall be released
|
1262 |
(defaults to all the locks acquired at that level)
|
1263 |
|
1264 |
"""
|
1265 |
assert level in LEVELS, "Invalid locking level %s" % level |
1266 |
assert (not self._contains_BGL(level, names) or |
1267 |
not self._upper_owned(LEVEL_CLUSTER)), ( |
1268 |
"Cannot release the Big Ganeti Lock while holding something"
|
1269 |
" at upper levels (%r)" %
|
1270 |
(", ".join(["%s=%r" % (LEVEL_NAMES[i], self._list_owned(i)) |
1271 |
for i in self.__keyring.keys()]), )) |
1272 |
|
1273 |
# Release will complain if we don't own the locks already
|
1274 |
return self.__keyring[level].release(names) |
1275 |
|
1276 |
def add(self, level, names, acquired=0, shared=0): |
1277 |
"""Add locks at the specified level.
|
1278 |
|
1279 |
@param level: the level at which the locks shall be added;
|
1280 |
it must be a member of LEVELS_MOD.
|
1281 |
@param names: names of the locks to acquire
|
1282 |
@param acquired: whether to acquire the newly added locks
|
1283 |
@param shared: whether the acquisition will be shared
|
1284 |
|
1285 |
"""
|
1286 |
assert level in LEVELS_MOD, "Invalid or immutable level %s" % level |
1287 |
assert self._BGL_owned(), ("You must own the BGL before performing other" |
1288 |
" operations")
|
1289 |
assert not self._upper_owned(level), ("Cannot add locks at a level" |
1290 |
" while owning some at a greater one")
|
1291 |
return self.__keyring[level].add(names, acquired=acquired, shared=shared) |
1292 |
|
1293 |
def remove(self, level, names): |
1294 |
"""Remove locks from the specified level.
|
1295 |
|
1296 |
You must either already own the locks you are trying to remove
|
1297 |
exclusively or not own any lock at an upper level.
|
1298 |
|
1299 |
@param level: the level at which the locks shall be removed;
|
1300 |
it must be a member of LEVELS_MOD
|
1301 |
@param names: the names of the locks which shall be removed
|
1302 |
(special lock names, or instance/node names)
|
1303 |
|
1304 |
"""
|
1305 |
assert level in LEVELS_MOD, "Invalid or immutable level %s" % level |
1306 |
assert self._BGL_owned(), ("You must own the BGL before performing other" |
1307 |
" operations")
|
1308 |
# Check we either own the level or don't own anything from here
|
1309 |
# up. LockSet.remove() will check the case in which we don't own
|
1310 |
# all the needed resources, or we have a shared ownership.
|
1311 |
assert self._is_owned(level) or not self._upper_owned(level), ( |
1312 |
"Cannot remove locks at a level while not owning it or"
|
1313 |
" owning some at a greater one")
|
1314 |
return self.__keyring[level].remove(names) |