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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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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 _SingleActionPipeConditionWaiter(object): |
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"""Callable helper class for _SingleActionPipeCondition.
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"""
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__slots__ = [ |
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"_cond",
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"_fd",
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"_poller",
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] |
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def __init__(self, cond, poller, fd): |
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"""Initializes this class.
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@type cond: L{_SingleActionPipeCondition}
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@param cond: Parent condition
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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._cond = cond
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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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start_time = time.time() |
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remaining_time = timeout |
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while timeout is None or remaining_time > 0: |
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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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# Re-calculate timeout if necessary
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if timeout is not None: |
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remaining_time = start_time + timeout - time.time() |
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class _SingleActionPipeCondition(object): |
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"""Wrapper around a pipe for usage inside conditions.
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This class contains a POSIX pipe(2) and a poller to poll it. The pipe is
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always allocated when constructing the class. Extra care is taken to always
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close the file descriptors.
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An additional class, L{_SingleActionPipeConditionWaiter}, is used to wait for
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notifications.
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Warning: This class is designed to be used as the underlying component of a
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locking condition, but is not by itself thread safe, and needs to be
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protected by an external lock.
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"""
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__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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] |
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_waiter_class = _SingleActionPipeConditionWaiter |
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def __init__(self): |
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"""Initializes this class.
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"""
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object.__init__(self) |
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self._nwaiters = 0 |
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# Just assume the unpacking is successful, otherwise error handling gets
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# very complicated.
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(self._read_fd, self._write_fd) = os.pipe() |
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try:
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# The poller looks for closure of the write side
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poller = select.poll() |
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poller.register(self._read_fd, select.POLLHUP)
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self._poller = poller
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except:
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if self._read_fd is not None: |
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os.close(self._read_fd)
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if self._write_fd is not None: |
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os.close(self._write_fd)
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raise
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# There should be no code here anymore, otherwise the pipe file descriptors
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# may be not be cleaned up properly in case of errors.
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def StartWaiting(self): |
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"""Return function to wait for notification.
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@rtype: L{_SingleActionPipeConditionWaiter}
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@return: Function to wait for notification
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"""
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assert self._nwaiters >= 0 |
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if self._poller is None: |
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raise RuntimeError("Already cleaned up") |
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# Create waiter function and increase number of waiters
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wait_fn = self._waiter_class(self, self._poller, self._read_fd) |
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self._nwaiters += 1 |
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return wait_fn
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def DoneWaiting(self): |
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"""Decrement number of waiters and automatic cleanup.
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Must be called after waiting for a notification.
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@rtype: bool
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@return: Whether this was the last waiter
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"""
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assert self._nwaiters > 0 |
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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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return True |
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return False |
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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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if self._write_fd is None: |
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raise RuntimeError("Can only notify once") |
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os.close(self._write_fd)
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self._write_fd = None |
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def _Cleanup(self): |
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"""Close all file descriptors.
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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 __del__(self): |
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"""Called on object deletion.
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Ensure no file descriptors are left open.
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"""
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self._Cleanup()
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class _PipeCondition(object): |
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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__ = [ |
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"_lock",
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"_nwaiters",
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"_pipe",
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"acquire",
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"release",
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] |
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_pipe_class = _SingleActionPipeCondition |
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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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# 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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self._nwaiters = 0 |
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self._pipe = None |
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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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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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if not self._pipe: |
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self._pipe = self._pipe_class() |
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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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pipe = self._pipe
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assert self._nwaiters >= 0 |
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self._nwaiters += 1 |
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try:
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# Get function to wait on the pipe
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wait_fn = pipe.StartWaiting() |
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try:
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# Release lock while waiting
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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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# Destroy pipe if this was the last waiter and the current pipe is
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# still the same. The same pipe cannot be reused after cleanup.
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if pipe.DoneWaiting() and pipe == self._pipe: |
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self._pipe = None |
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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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# Notify and forget pipe. A new one will be created on the next call to
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# wait.
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if self._pipe is not None: |
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self._pipe.notifyAll()
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self._pipe = None |
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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: Timeout in seconds
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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 = _CountingCondition |
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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 |
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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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if self.__deleted: |
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raise errors.LockError("Deleted lock") |
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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 |
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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() |
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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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@param 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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return self.__is_owned(shared=shared) |
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finally:
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self.__lock.release()
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def _count_pending(self): |
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"""Returns the number of pending acquires.
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@rtype: int
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"""
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self.__lock.acquire()
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try:
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return len(self.__pending) |
494 |
finally:
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self.__lock.release()
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def __do_acquire(self, shared): |
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"""Actually acquire the lock.
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499 |
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"""
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501 |
if shared:
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self.__shr.add(threading.currentThread())
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else:
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self.__exc = threading.currentThread()
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def __can_acquire(self, shared): |
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"""Determine whether lock can be acquired.
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"""
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if shared:
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return self.__exc is None |
512 |
else:
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return len(self.__shr) == 0 and self.__exc is None |
514 |
|
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def __is_on_top(self, cond): |
516 |
"""Checks whether the passed condition is on top of the queue.
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517 |
|
518 |
The caller must make sure the queue isn't empty.
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519 |
|
520 |
"""
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521 |
return self.__pending[0] == cond |
522 |
|
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def __acquire_unlocked(self, shared=0, timeout=None): |
524 |
"""Acquire a shared lock.
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525 |
|
526 |
@param shared: whether to acquire in shared mode; by default an
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527 |
exclusive lock will be acquired
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528 |
@param timeout: maximum waiting time before giving up
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529 |
|
530 |
"""
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self.__check_deleted()
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|
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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" |
535 |
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# Check whether someone else holds the lock or there are pending acquires.
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537 |
if not self.__pending and self.__can_acquire(shared): |
538 |
# Apparently not, can acquire lock directly.
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self.__do_acquire(shared)
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return True |
541 |
|
542 |
if shared:
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wait_condition = self.__active_shr_c
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# Check if we're not yet in the queue
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if wait_condition not in self.__pending: |
547 |
self.__pending.append(wait_condition)
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else:
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wait_condition = self.__condition_class(self.__lock) |
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# Always add to queue
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self.__pending.append(wait_condition)
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try:
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# Wait until we become the topmost acquire in the queue or the timeout
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555 |
# expires.
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while not (self.__is_on_top(wait_condition) and |
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self.__can_acquire(shared)):
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# Wait for notification
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wait_condition.wait(timeout) |
560 |
self.__check_deleted()
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|
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# A lot of code assumes blocking acquires always succeed. Loop
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# internally for that case.
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if timeout is not None: |
565 |
break
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|
567 |
if self.__is_on_top(wait_condition) and self.__can_acquire(shared): |
568 |
self.__do_acquire(shared)
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569 |
return True |
570 |
finally:
|
571 |
# Remove condition from queue if there are no more waiters
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572 |
if not wait_condition.has_waiting() and not self.__deleted: |
573 |
self.__pending.remove(wait_condition)
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574 |
|
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return False |
576 |
|
577 |
def acquire(self, shared=0, timeout=None): |
578 |
"""Acquire a shared lock.
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579 |
|
580 |
@type shared: int
|
581 |
@param shared: whether to acquire in shared mode; by default an
|
582 |
exclusive lock will be acquired
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583 |
@type timeout: float
|
584 |
@param timeout: maximum waiting time before giving up
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585 |
|
586 |
"""
|
587 |
self.__lock.acquire()
|
588 |
try:
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589 |
return self.__acquire_unlocked(shared, timeout) |
590 |
finally:
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591 |
self.__lock.release()
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592 |
|
593 |
def release(self): |
594 |
"""Release a Shared Lock.
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595 |
|
596 |
You must have acquired the lock, either in shared or in exclusive mode,
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597 |
before calling this function.
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598 |
|
599 |
"""
|
600 |
self.__lock.acquire()
|
601 |
try:
|
602 |
assert self.__is_exclusive() or self.__is_sharer(), \ |
603 |
"Cannot release non-owned lock"
|
604 |
|
605 |
# Autodetect release type
|
606 |
if self.__is_exclusive(): |
607 |
self.__exc = None |
608 |
else:
|
609 |
self.__shr.remove(threading.currentThread())
|
610 |
|
611 |
# Notify topmost condition in queue
|
612 |
if self.__pending: |
613 |
first_condition = self.__pending[0] |
614 |
first_condition.notifyAll() |
615 |
|
616 |
if first_condition == self.__active_shr_c: |
617 |
self.__active_shr_c = self.__inactive_shr_c |
618 |
self.__inactive_shr_c = first_condition
|
619 |
|
620 |
finally:
|
621 |
self.__lock.release()
|
622 |
|
623 |
def delete(self, timeout=None): |
624 |
"""Delete a Shared Lock.
|
625 |
|
626 |
This operation will declare the lock for removal. First the lock will be
|
627 |
acquired in exclusive mode if you don't already own it, then the lock
|
628 |
will be put in a state where any future and pending acquire() fail.
|
629 |
|
630 |
@type timeout: float
|
631 |
@param timeout: maximum waiting time before giving up
|
632 |
|
633 |
"""
|
634 |
self.__lock.acquire()
|
635 |
try:
|
636 |
assert not self.__is_sharer(), "Cannot delete() a lock while sharing it" |
637 |
|
638 |
self.__check_deleted()
|
639 |
|
640 |
# The caller is allowed to hold the lock exclusively already.
|
641 |
acquired = self.__is_exclusive()
|
642 |
|
643 |
if not acquired: |
644 |
acquired = self.__acquire_unlocked(timeout)
|
645 |
|
646 |
if acquired:
|
647 |
self.__deleted = True |
648 |
self.__exc = None |
649 |
|
650 |
# Notify all acquires. They'll throw an error.
|
651 |
while self.__pending: |
652 |
self.__pending.pop().notifyAll()
|
653 |
|
654 |
return acquired
|
655 |
finally:
|
656 |
self.__lock.release()
|
657 |
|
658 |
|
659 |
# Whenever we want to acquire a full LockSet we pass None as the value
|
660 |
# to acquire. Hide this behind this nicely named constant.
|
661 |
ALL_SET = None
|
662 |
|
663 |
|
664 |
class LockSet: |
665 |
"""Implements a set of locks.
|
666 |
|
667 |
This abstraction implements a set of shared locks for the same resource type,
|
668 |
distinguished by name. The user can lock a subset of the resources and the
|
669 |
LockSet will take care of acquiring the locks always in the same order, thus
|
670 |
preventing deadlock.
|
671 |
|
672 |
All the locks needed in the same set must be acquired together, though.
|
673 |
|
674 |
"""
|
675 |
def __init__(self, members=None): |
676 |
"""Constructs a new LockSet.
|
677 |
|
678 |
@param members: initial members of the set
|
679 |
|
680 |
"""
|
681 |
# Used internally to guarantee coherency.
|
682 |
self.__lock = SharedLock()
|
683 |
|
684 |
# The lockdict indexes the relationship name -> lock
|
685 |
# The order-of-locking is implied by the alphabetical order of names
|
686 |
self.__lockdict = {}
|
687 |
|
688 |
if members is not None: |
689 |
for name in members: |
690 |
self.__lockdict[name] = SharedLock()
|
691 |
|
692 |
# The owner dict contains the set of locks each thread owns. For
|
693 |
# performance each thread can access its own key without a global lock on
|
694 |
# this structure. It is paramount though that *no* other type of access is
|
695 |
# done to this structure (eg. no looping over its keys). *_owner helper
|
696 |
# function are defined to guarantee access is correct, but in general never
|
697 |
# do anything different than __owners[threading.currentThread()], or there
|
698 |
# will be trouble.
|
699 |
self.__owners = {}
|
700 |
|
701 |
def _is_owned(self): |
702 |
"""Is the current thread a current level owner?"""
|
703 |
return threading.currentThread() in self.__owners |
704 |
|
705 |
def _add_owned(self, name=None): |
706 |
"""Note the current thread owns the given lock"""
|
707 |
if name is None: |
708 |
if not self._is_owned(): |
709 |
self.__owners[threading.currentThread()] = set() |
710 |
else:
|
711 |
if self._is_owned(): |
712 |
self.__owners[threading.currentThread()].add(name)
|
713 |
else:
|
714 |
self.__owners[threading.currentThread()] = set([name]) |
715 |
|
716 |
def _del_owned(self, name=None): |
717 |
"""Note the current thread owns the given lock"""
|
718 |
|
719 |
if name is not None: |
720 |
self.__owners[threading.currentThread()].remove(name)
|
721 |
|
722 |
# Only remove the key if we don't hold the set-lock as well
|
723 |
if (not self.__lock._is_owned() and |
724 |
not self.__owners[threading.currentThread()]): |
725 |
del self.__owners[threading.currentThread()] |
726 |
|
727 |
def _list_owned(self): |
728 |
"""Get the set of resource names owned by the current thread"""
|
729 |
if self._is_owned(): |
730 |
return self.__owners[threading.currentThread()].copy() |
731 |
else:
|
732 |
return set() |
733 |
|
734 |
def __names(self): |
735 |
"""Return the current set of names.
|
736 |
|
737 |
Only call this function while holding __lock and don't iterate on the
|
738 |
result after releasing the lock.
|
739 |
|
740 |
"""
|
741 |
return self.__lockdict.keys() |
742 |
|
743 |
def _names(self): |
744 |
"""Return a copy of the current set of elements.
|
745 |
|
746 |
Used only for debugging purposes.
|
747 |
|
748 |
"""
|
749 |
# If we don't already own the set-level lock acquired
|
750 |
# we'll get it and note we need to release it later.
|
751 |
release_lock = False
|
752 |
if not self.__lock._is_owned(): |
753 |
release_lock = True
|
754 |
self.__lock.acquire(shared=1) |
755 |
try:
|
756 |
result = self.__names()
|
757 |
finally:
|
758 |
if release_lock:
|
759 |
self.__lock.release()
|
760 |
return set(result) |
761 |
|
762 |
def acquire(self, names, blocking=1, shared=0): |
763 |
"""Acquire a set of resource locks.
|
764 |
|
765 |
@param names: the names of the locks which shall be acquired
|
766 |
(special lock names, or instance/node names)
|
767 |
@param shared: whether to acquire in shared mode; by default an
|
768 |
exclusive lock will be acquired
|
769 |
@param blocking: whether to block while trying to acquire or to
|
770 |
operate in try-lock mode (this locking mode is not supported yet)
|
771 |
|
772 |
@return: True when all the locks are successfully acquired
|
773 |
|
774 |
@raise errors.LockError: when any lock we try to acquire has
|
775 |
been deleted before we succeed. In this case none of the
|
776 |
locks requested will be acquired.
|
777 |
|
778 |
"""
|
779 |
if not blocking: |
780 |
# We don't have non-blocking mode for now
|
781 |
raise NotImplementedError |
782 |
|
783 |
# Check we don't already own locks at this level
|
784 |
assert not self._is_owned(), "Cannot acquire locks in the same set twice" |
785 |
|
786 |
if names is None: |
787 |
# If no names are given acquire the whole set by not letting new names
|
788 |
# being added before we release, and getting the current list of names.
|
789 |
# Some of them may then be deleted later, but we'll cope with this.
|
790 |
#
|
791 |
# We'd like to acquire this lock in a shared way, as it's nice if
|
792 |
# everybody else can use the instances at the same time. If are acquiring
|
793 |
# them exclusively though they won't be able to do this anyway, though,
|
794 |
# so we'll get the list lock exclusively as well in order to be able to
|
795 |
# do add() on the set while owning it.
|
796 |
self.__lock.acquire(shared=shared)
|
797 |
try:
|
798 |
# note we own the set-lock
|
799 |
self._add_owned()
|
800 |
names = self.__names()
|
801 |
except:
|
802 |
# We shouldn't have problems adding the lock to the owners list, but
|
803 |
# if we did we'll try to release this lock and re-raise exception.
|
804 |
# Of course something is going to be really wrong, after this.
|
805 |
self.__lock.release()
|
806 |
raise
|
807 |
|
808 |
try:
|
809 |
# Support passing in a single resource to acquire rather than many
|
810 |
if isinstance(names, basestring): |
811 |
names = [names] |
812 |
else:
|
813 |
names = sorted(names)
|
814 |
|
815 |
acquire_list = [] |
816 |
# First we look the locks up on __lockdict. We have no way of being sure
|
817 |
# they will still be there after, but this makes it a lot faster should
|
818 |
# just one of them be the already wrong
|
819 |
for lname in utils.UniqueSequence(names): |
820 |
try:
|
821 |
lock = self.__lockdict[lname] # raises KeyError if lock is not there |
822 |
acquire_list.append((lname, lock)) |
823 |
except (KeyError): |
824 |
if self.__lock._is_owned(): |
825 |
# We are acquiring all the set, it doesn't matter if this
|
826 |
# particular element is not there anymore.
|
827 |
continue
|
828 |
else:
|
829 |
raise errors.LockError('non-existing lock in set (%s)' % lname) |
830 |
|
831 |
# This will hold the locknames we effectively acquired.
|
832 |
acquired = set()
|
833 |
# Now acquire_list contains a sorted list of resources and locks we want.
|
834 |
# In order to get them we loop on this (private) list and acquire() them.
|
835 |
# We gave no real guarantee they will still exist till this is done but
|
836 |
# .acquire() itself is safe and will alert us if the lock gets deleted.
|
837 |
for (lname, lock) in acquire_list: |
838 |
try:
|
839 |
lock.acquire(shared=shared) # raises LockError if the lock is deleted
|
840 |
# now the lock cannot be deleted, we have it!
|
841 |
self._add_owned(name=lname)
|
842 |
acquired.add(lname) |
843 |
except (errors.LockError):
|
844 |
if self.__lock._is_owned(): |
845 |
# We are acquiring all the set, it doesn't matter if this
|
846 |
# particular element is not there anymore.
|
847 |
continue
|
848 |
else:
|
849 |
name_fail = lname |
850 |
for lname in self._list_owned(): |
851 |
self.__lockdict[lname].release()
|
852 |
self._del_owned(name=lname)
|
853 |
raise errors.LockError('non-existing lock in set (%s)' % name_fail) |
854 |
except:
|
855 |
# We shouldn't have problems adding the lock to the owners list, but
|
856 |
# if we did we'll try to release this lock and re-raise exception.
|
857 |
# Of course something is going to be really wrong, after this.
|
858 |
if lock._is_owned():
|
859 |
lock.release() |
860 |
raise
|
861 |
|
862 |
except:
|
863 |
# If something went wrong and we had the set-lock let's release it...
|
864 |
if self.__lock._is_owned(): |
865 |
self.__lock.release()
|
866 |
raise
|
867 |
|
868 |
return acquired
|
869 |
|
870 |
def release(self, names=None): |
871 |
"""Release a set of resource locks, at the same level.
|
872 |
|
873 |
You must have acquired the locks, either in shared or in exclusive mode,
|
874 |
before releasing them.
|
875 |
|
876 |
@param names: the names of the locks which shall be released
|
877 |
(defaults to all the locks acquired at that level).
|
878 |
|
879 |
"""
|
880 |
assert self._is_owned(), "release() on lock set while not owner" |
881 |
|
882 |
# Support passing in a single resource to release rather than many
|
883 |
if isinstance(names, basestring): |
884 |
names = [names] |
885 |
|
886 |
if names is None: |
887 |
names = self._list_owned()
|
888 |
else:
|
889 |
names = set(names)
|
890 |
assert self._list_owned().issuperset(names), ( |
891 |
"release() on unheld resources %s" %
|
892 |
names.difference(self._list_owned()))
|
893 |
|
894 |
# First of all let's release the "all elements" lock, if set.
|
895 |
# After this 'add' can work again
|
896 |
if self.__lock._is_owned(): |
897 |
self.__lock.release()
|
898 |
self._del_owned()
|
899 |
|
900 |
for lockname in names: |
901 |
# If we are sure the lock doesn't leave __lockdict without being
|
902 |
# exclusively held we can do this...
|
903 |
self.__lockdict[lockname].release()
|
904 |
self._del_owned(name=lockname)
|
905 |
|
906 |
def add(self, names, acquired=0, shared=0): |
907 |
"""Add a new set of elements to the set
|
908 |
|
909 |
@param names: names of the new elements to add
|
910 |
@param acquired: pre-acquire the new resource?
|
911 |
@param shared: is the pre-acquisition shared?
|
912 |
|
913 |
"""
|
914 |
# Check we don't already own locks at this level
|
915 |
assert not self._is_owned() or self.__lock._is_owned(shared=0), \ |
916 |
"Cannot add locks if the set is only partially owned, or shared"
|
917 |
|
918 |
# Support passing in a single resource to add rather than many
|
919 |
if isinstance(names, basestring): |
920 |
names = [names] |
921 |
|
922 |
# If we don't already own the set-level lock acquired in an exclusive way
|
923 |
# we'll get it and note we need to release it later.
|
924 |
release_lock = False
|
925 |
if not self.__lock._is_owned(): |
926 |
release_lock = True
|
927 |
self.__lock.acquire()
|
928 |
|
929 |
try:
|
930 |
invalid_names = set(self.__names()).intersection(names) |
931 |
if invalid_names:
|
932 |
# This must be an explicit raise, not an assert, because assert is
|
933 |
# turned off when using optimization, and this can happen because of
|
934 |
# concurrency even if the user doesn't want it.
|
935 |
raise errors.LockError("duplicate add() (%s)" % invalid_names) |
936 |
|
937 |
for lockname in names: |
938 |
lock = SharedLock() |
939 |
|
940 |
if acquired:
|
941 |
lock.acquire(shared=shared) |
942 |
# now the lock cannot be deleted, we have it!
|
943 |
try:
|
944 |
self._add_owned(name=lockname)
|
945 |
except:
|
946 |
# We shouldn't have problems adding the lock to the owners list,
|
947 |
# but if we did we'll try to release this lock and re-raise
|
948 |
# exception. Of course something is going to be really wrong,
|
949 |
# after this. On the other hand the lock hasn't been added to the
|
950 |
# __lockdict yet so no other threads should be pending on it. This
|
951 |
# release is just a safety measure.
|
952 |
lock.release() |
953 |
raise
|
954 |
|
955 |
self.__lockdict[lockname] = lock
|
956 |
|
957 |
finally:
|
958 |
# Only release __lock if we were not holding it previously.
|
959 |
if release_lock:
|
960 |
self.__lock.release()
|
961 |
|
962 |
return True |
963 |
|
964 |
def remove(self, names, blocking=1): |
965 |
"""Remove elements from the lock set.
|
966 |
|
967 |
You can either not hold anything in the lockset or already hold a superset
|
968 |
of the elements you want to delete, exclusively.
|
969 |
|
970 |
@param names: names of the resource to remove.
|
971 |
@param blocking: whether to block while trying to acquire or to
|
972 |
operate in try-lock mode (this locking mode is not supported
|
973 |
yet unless you are already holding exclusively the locks)
|
974 |
|
975 |
@return:: a list of locks which we removed; the list is always
|
976 |
equal to the names list if we were holding all the locks
|
977 |
exclusively
|
978 |
|
979 |
"""
|
980 |
if not blocking and not self._is_owned(): |
981 |
# We don't have non-blocking mode for now
|
982 |
raise NotImplementedError |
983 |
|
984 |
# Support passing in a single resource to remove rather than many
|
985 |
if isinstance(names, basestring): |
986 |
names = [names] |
987 |
|
988 |
# If we own any subset of this lock it must be a superset of what we want
|
989 |
# to delete. The ownership must also be exclusive, but that will be checked
|
990 |
# by the lock itself.
|
991 |
assert not self._is_owned() or self._list_owned().issuperset(names), ( |
992 |
"remove() on acquired lockset while not owning all elements")
|
993 |
|
994 |
removed = [] |
995 |
|
996 |
for lname in names: |
997 |
# Calling delete() acquires the lock exclusively if we don't already own
|
998 |
# it, and causes all pending and subsequent lock acquires to fail. It's
|
999 |
# fine to call it out of order because delete() also implies release(),
|
1000 |
# and the assertion above guarantees that if we either already hold
|
1001 |
# everything we want to delete, or we hold none.
|
1002 |
try:
|
1003 |
self.__lockdict[lname].delete()
|
1004 |
removed.append(lname) |
1005 |
except (KeyError, errors.LockError): |
1006 |
# This cannot happen if we were already holding it, verify:
|
1007 |
assert not self._is_owned(), "remove failed while holding lockset" |
1008 |
else:
|
1009 |
# If no LockError was raised we are the ones who deleted the lock.
|
1010 |
# This means we can safely remove it from lockdict, as any further or
|
1011 |
# pending delete() or acquire() will fail (and nobody can have the lock
|
1012 |
# since before our call to delete()).
|
1013 |
#
|
1014 |
# This is done in an else clause because if the exception was thrown
|
1015 |
# it's the job of the one who actually deleted it.
|
1016 |
del self.__lockdict[lname] |
1017 |
# And let's remove it from our private list if we owned it.
|
1018 |
if self._is_owned(): |
1019 |
self._del_owned(name=lname)
|
1020 |
|
1021 |
return removed
|
1022 |
|
1023 |
|
1024 |
# Locking levels, must be acquired in increasing order.
|
1025 |
# Current rules are:
|
1026 |
# - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
|
1027 |
# acquired before performing any operation, either in shared or in exclusive
|
1028 |
# mode. acquiring the BGL in exclusive mode is discouraged and should be
|
1029 |
# avoided.
|
1030 |
# - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
|
1031 |
# If you need more than one node, or more than one instance, acquire them at
|
1032 |
# the same time.
|
1033 |
LEVEL_CLUSTER = 0
|
1034 |
LEVEL_INSTANCE = 1
|
1035 |
LEVEL_NODE = 2
|
1036 |
|
1037 |
LEVELS = [LEVEL_CLUSTER, |
1038 |
LEVEL_INSTANCE, |
1039 |
LEVEL_NODE] |
1040 |
|
1041 |
# Lock levels which are modifiable
|
1042 |
LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE] |
1043 |
|
1044 |
LEVEL_NAMES = { |
1045 |
LEVEL_CLUSTER: "cluster",
|
1046 |
LEVEL_INSTANCE: "instance",
|
1047 |
LEVEL_NODE: "node",
|
1048 |
} |
1049 |
|
1050 |
# Constant for the big ganeti lock
|
1051 |
BGL = 'BGL'
|
1052 |
|
1053 |
|
1054 |
class GanetiLockManager: |
1055 |
"""The Ganeti Locking Library
|
1056 |
|
1057 |
The purpose of this small library is to manage locking for ganeti clusters
|
1058 |
in a central place, while at the same time doing dynamic checks against
|
1059 |
possible deadlocks. It will also make it easier to transition to a different
|
1060 |
lock type should we migrate away from python threads.
|
1061 |
|
1062 |
"""
|
1063 |
_instance = None
|
1064 |
|
1065 |
def __init__(self, nodes=None, instances=None): |
1066 |
"""Constructs a new GanetiLockManager object.
|
1067 |
|
1068 |
There should be only a GanetiLockManager object at any time, so this
|
1069 |
function raises an error if this is not the case.
|
1070 |
|
1071 |
@param nodes: list of node names
|
1072 |
@param instances: list of instance names
|
1073 |
|
1074 |
"""
|
1075 |
assert self.__class__._instance is None, \ |
1076 |
"double GanetiLockManager instance"
|
1077 |
|
1078 |
self.__class__._instance = self |
1079 |
|
1080 |
# The keyring contains all the locks, at their level and in the correct
|
1081 |
# locking order.
|
1082 |
self.__keyring = {
|
1083 |
LEVEL_CLUSTER: LockSet([BGL]), |
1084 |
LEVEL_NODE: LockSet(nodes), |
1085 |
LEVEL_INSTANCE: LockSet(instances), |
1086 |
} |
1087 |
|
1088 |
def _names(self, level): |
1089 |
"""List the lock names at the given level.
|
1090 |
|
1091 |
This can be used for debugging/testing purposes.
|
1092 |
|
1093 |
@param level: the level whose list of locks to get
|
1094 |
|
1095 |
"""
|
1096 |
assert level in LEVELS, "Invalid locking level %s" % level |
1097 |
return self.__keyring[level]._names() |
1098 |
|
1099 |
def _is_owned(self, level): |
1100 |
"""Check whether we are owning locks at the given level
|
1101 |
|
1102 |
"""
|
1103 |
return self.__keyring[level]._is_owned() |
1104 |
|
1105 |
is_owned = _is_owned |
1106 |
|
1107 |
def _list_owned(self, level): |
1108 |
"""Get the set of owned locks at the given level
|
1109 |
|
1110 |
"""
|
1111 |
return self.__keyring[level]._list_owned() |
1112 |
|
1113 |
def _upper_owned(self, level): |
1114 |
"""Check that we don't own any lock at a level greater than the given one.
|
1115 |
|
1116 |
"""
|
1117 |
# This way of checking only works if LEVELS[i] = i, which we check for in
|
1118 |
# the test cases.
|
1119 |
return utils.any((self._is_owned(l) for l in LEVELS[level + 1:])) |
1120 |
|
1121 |
def _BGL_owned(self): |
1122 |
"""Check if the current thread owns the BGL.
|
1123 |
|
1124 |
Both an exclusive or a shared acquisition work.
|
1125 |
|
1126 |
"""
|
1127 |
return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned() |
1128 |
|
1129 |
def _contains_BGL(self, level, names): |
1130 |
"""Check if the level contains the BGL.
|
1131 |
|
1132 |
Check if acting on the given level and set of names will change
|
1133 |
the status of the Big Ganeti Lock.
|
1134 |
|
1135 |
"""
|
1136 |
return level == LEVEL_CLUSTER and (names is None or BGL in names) |
1137 |
|
1138 |
def acquire(self, level, names, blocking=1, shared=0): |
1139 |
"""Acquire a set of resource locks, at the same level.
|
1140 |
|
1141 |
@param level: the level at which the locks shall be acquired;
|
1142 |
it must be a member of LEVELS.
|
1143 |
@param names: the names of the locks which shall be acquired
|
1144 |
(special lock names, or instance/node names)
|
1145 |
@param shared: whether to acquire in shared mode; by default
|
1146 |
an exclusive lock will be acquired
|
1147 |
@param blocking: whether to block while trying to acquire or to
|
1148 |
operate in try-lock mode (this locking mode is not supported yet)
|
1149 |
|
1150 |
"""
|
1151 |
assert level in LEVELS, "Invalid locking level %s" % level |
1152 |
|
1153 |
# Check that we are either acquiring the Big Ganeti Lock or we already own
|
1154 |
# it. Some "legacy" opcodes need to be sure they are run non-concurrently
|
1155 |
# so even if we've migrated we need to at least share the BGL to be
|
1156 |
# compatible with them. Of course if we own the BGL exclusively there's no
|
1157 |
# point in acquiring any other lock, unless perhaps we are half way through
|
1158 |
# the migration of the current opcode.
|
1159 |
assert (self._contains_BGL(level, names) or self._BGL_owned()), ( |
1160 |
"You must own the Big Ganeti Lock before acquiring any other")
|
1161 |
|
1162 |
# Check we don't own locks at the same or upper levels.
|
1163 |
assert not self._upper_owned(level), ("Cannot acquire locks at a level" |
1164 |
" while owning some at a greater one")
|
1165 |
|
1166 |
# Acquire the locks in the set.
|
1167 |
return self.__keyring[level].acquire(names, shared=shared, |
1168 |
blocking=blocking) |
1169 |
|
1170 |
def release(self, level, names=None): |
1171 |
"""Release a set of resource locks, at the same level.
|
1172 |
|
1173 |
You must have acquired the locks, either in shared or in exclusive
|
1174 |
mode, before releasing them.
|
1175 |
|
1176 |
@param level: the level at which the locks shall be released;
|
1177 |
it must be a member of LEVELS
|
1178 |
@param names: the names of the locks which shall be released
|
1179 |
(defaults to all the locks acquired at that level)
|
1180 |
|
1181 |
"""
|
1182 |
assert level in LEVELS, "Invalid locking level %s" % level |
1183 |
assert (not self._contains_BGL(level, names) or |
1184 |
not self._upper_owned(LEVEL_CLUSTER)), ( |
1185 |
"Cannot release the Big Ganeti Lock while holding something"
|
1186 |
" at upper levels")
|
1187 |
|
1188 |
# Release will complain if we don't own the locks already
|
1189 |
return self.__keyring[level].release(names) |
1190 |
|
1191 |
def add(self, level, names, acquired=0, shared=0): |
1192 |
"""Add locks at the specified level.
|
1193 |
|
1194 |
@param level: the level at which the locks shall be added;
|
1195 |
it must be a member of LEVELS_MOD.
|
1196 |
@param names: names of the locks to acquire
|
1197 |
@param acquired: whether to acquire the newly added locks
|
1198 |
@param shared: whether the acquisition will be shared
|
1199 |
|
1200 |
"""
|
1201 |
assert level in LEVELS_MOD, "Invalid or immutable level %s" % level |
1202 |
assert self._BGL_owned(), ("You must own the BGL before performing other" |
1203 |
" operations")
|
1204 |
assert not self._upper_owned(level), ("Cannot add locks at a level" |
1205 |
" while owning some at a greater one")
|
1206 |
return self.__keyring[level].add(names, acquired=acquired, shared=shared) |
1207 |
|
1208 |
def remove(self, level, names, blocking=1): |
1209 |
"""Remove locks from the specified level.
|
1210 |
|
1211 |
You must either already own the locks you are trying to remove
|
1212 |
exclusively or not own any lock at an upper level.
|
1213 |
|
1214 |
@param level: the level at which the locks shall be removed;
|
1215 |
it must be a member of LEVELS_MOD
|
1216 |
@param names: the names of the locks which shall be removed
|
1217 |
(special lock names, or instance/node names)
|
1218 |
@param blocking: whether to block while trying to operate in
|
1219 |
try-lock mode (this locking mode is not supported yet)
|
1220 |
|
1221 |
"""
|
1222 |
assert level in LEVELS_MOD, "Invalid or immutable level %s" % level |
1223 |
assert self._BGL_owned(), ("You must own the BGL before performing other" |
1224 |
" operations")
|
1225 |
# Check we either own the level or don't own anything from here
|
1226 |
# up. LockSet.remove() will check the case in which we don't own
|
1227 |
# all the needed resources, or we have a shared ownership.
|
1228 |
assert self._is_owned(level) or not self._upper_owned(level), ( |
1229 |
"Cannot remove locks at a level while not owning it or"
|
1230 |
" owning some at a greater one")
|
1231 |
return self.__keyring[level].remove(names, blocking=blocking) |