root / lib / locking.py @ 84e344d4
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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 threading |
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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 _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) |
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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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"""
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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 |
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else:
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return len(self.__shr) == 0 and self.__exc is None |
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def __is_on_top(self, cond): |
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"""Checks whether the passed condition is on top of the queue.
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The caller must make sure the queue isn't empty.
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"""
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return self.__pending[0] == cond |
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def __acquire_unlocked(self, shared=0, timeout=None): |
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"""Acquire a shared lock.
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@param shared: whether to acquire in shared mode; by default an
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exclusive lock will be acquired
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@param timeout: maximum waiting time before giving up
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"""
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self.__check_deleted()
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# We cannot acquire the lock if we already have it
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assert not self.__is_owned(), "double acquire() on a non-recursive lock" |
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# 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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self.__do_acquire(shared)
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return True |
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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: |
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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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# 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) |
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self.__check_deleted()
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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: |
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break
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if self.__is_on_top(wait_condition) and self.__can_acquire(shared): |
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self.__do_acquire(shared)
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return True |
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finally:
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# Remove condition from queue if there are no more waiters
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if not wait_condition.has_waiting() and not self.__deleted: |
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self.__pending.remove(wait_condition)
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return False |
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def acquire(self, shared=0, timeout=None): |
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"""Acquire a shared lock.
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@type shared: int
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@param shared: whether to acquire in shared mode; by default an
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exclusive lock will be acquired
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@type timeout: float
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@param timeout: maximum waiting time before giving up
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"""
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self.__lock.acquire()
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try:
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return self.__acquire_unlocked(shared, timeout) |
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finally:
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self.__lock.release()
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def release(self): |
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"""Release a Shared Lock.
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You must have acquired the lock, either in shared or in exclusive mode,
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before calling this function.
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"""
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self.__lock.acquire()
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try:
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assert self.__is_exclusive() or self.__is_sharer(), \ |
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"Cannot release non-owned lock"
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# Autodetect release type
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if self.__is_exclusive(): |
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self.__exc = None |
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else:
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self.__shr.remove(threading.currentThread())
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# Notify topmost condition in queue
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if self.__pending: |
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first_condition = self.__pending[0] |
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first_condition.notifyAll() |
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if first_condition == self.__active_shr_c: |
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self.__active_shr_c = self.__inactive_shr_c |
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self.__inactive_shr_c = first_condition
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finally:
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self.__lock.release()
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def delete(self, timeout=None): |
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"""Delete a Shared Lock.
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This operation will declare the lock for removal. First the lock will be
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acquired in exclusive mode if you don't already own it, then the lock
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will be put in a state where any future and pending acquire() fail.
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@type timeout: float
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@param timeout: maximum waiting time before giving up
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"""
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self.__lock.acquire()
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try:
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assert not self.__is_sharer(), "Cannot delete() a lock while sharing it" |
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self.__check_deleted()
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# The caller is allowed to hold the lock exclusively already.
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acquired = self.__is_exclusive()
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if not acquired: |
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acquired = self.__acquire_unlocked(timeout)
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if acquired:
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self.__deleted = True |
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self.__exc = None |
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# Notify all acquires. They'll throw an error.
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while self.__pending: |
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self.__pending.pop().notifyAll()
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return acquired
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finally:
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self.__lock.release()
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# Whenever we want to acquire a full LockSet we pass None as the value
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# to acquire. Hide this behind this nicely named constant.
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ALL_SET = None
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class LockSet: |
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"""Implements a set of locks.
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This abstraction implements a set of shared locks for the same resource type,
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distinguished by name. The user can lock a subset of the resources and the
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LockSet will take care of acquiring the locks always in the same order, thus
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preventing deadlock.
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All the locks needed in the same set must be acquired together, though.
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"""
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def __init__(self, members=None): |
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"""Constructs a new LockSet.
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@param members: initial members of the set
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"""
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# Used internally to guarantee coherency.
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self.__lock = SharedLock()
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# The lockdict indexes the relationship name -> lock
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# The order-of-locking is implied by the alphabetical order of names
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self.__lockdict = {}
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if members is not None: |
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for name in members: |
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self.__lockdict[name] = SharedLock()
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# The owner dict contains the set of locks each thread owns. For
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# performance each thread can access its own key without a global lock on
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# this structure. It is paramount though that *no* other type of access is
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# done to this structure (eg. no looping over its keys). *_owner helper
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# function are defined to guarantee access is correct, but in general never
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# do anything different than __owners[threading.currentThread()], or there
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# will be trouble.
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self.__owners = {}
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def _is_owned(self): |
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"""Is the current thread a current level owner?"""
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return threading.currentThread() in self.__owners |
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def _add_owned(self, name=None): |
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"""Note the current thread owns the given lock"""
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if name is None: |
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if not self._is_owned(): |
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self.__owners[threading.currentThread()] = set() |
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else:
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if self._is_owned(): |
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self.__owners[threading.currentThread()].add(name)
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else:
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self.__owners[threading.currentThread()] = set([name]) |
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def _del_owned(self, name=None): |
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"""Note the current thread owns the given lock"""
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if name is not None: |
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self.__owners[threading.currentThread()].remove(name)
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# Only remove the key if we don't hold the set-lock as well
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if (not self.__lock._is_owned() and |
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not self.__owners[threading.currentThread()]): |
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del self.__owners[threading.currentThread()] |
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def _list_owned(self): |
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"""Get the set of resource names owned by the current thread"""
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if self._is_owned(): |
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return self.__owners[threading.currentThread()].copy() |
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else:
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return set() |
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def __names(self): |
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"""Return the current set of names.
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Only call this function while holding __lock and don't iterate on the
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result after releasing the lock.
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"""
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return self.__lockdict.keys() |
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def _names(self): |
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"""Return a copy of the current set of elements.
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Used only for debugging purposes.
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"""
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# If we don't already own the set-level lock acquired
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# we'll get it and note we need to release it later.
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release_lock = False
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if not self.__lock._is_owned(): |
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release_lock = True
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self.__lock.acquire(shared=1) |
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try:
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result = self.__names()
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finally:
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if release_lock:
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self.__lock.release()
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return set(result) |
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def acquire(self, names, blocking=1, shared=0): |
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"""Acquire a set of resource locks.
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@param names: the names of the locks which shall be acquired
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(special lock names, or instance/node names)
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@param shared: whether to acquire in shared mode; by default an
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exclusive lock will be acquired
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@param blocking: whether to block while trying to acquire or to
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operate in try-lock mode (this locking mode is not supported yet)
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@return: True when all the locks are successfully acquired
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@raise errors.LockError: when any lock we try to acquire has
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been deleted before we succeed. In this case none of the
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locks requested will be acquired.
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"""
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if not blocking: |
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# We don't have non-blocking mode for now
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raise NotImplementedError |
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# Check we don't already own locks at this level
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assert not self._is_owned(), "Cannot acquire locks in the same set twice" |
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if names is None: |
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# If no names are given acquire the whole set by not letting new names
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# being added before we release, and getting the current list of names.
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# Some of them may then be deleted later, but we'll cope with this.
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#
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# We'd like to acquire this lock in a shared way, as it's nice if
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# everybody else can use the instances at the same time. If are acquiring
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# them exclusively though they won't be able to do this anyway, though,
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# so we'll get the list lock exclusively as well in order to be able to
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# do add() on the set while owning it.
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self.__lock.acquire(shared=shared)
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try:
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# note we own the set-lock
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self._add_owned()
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names = self.__names()
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except:
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# We shouldn't have problems adding the lock to the owners list, but
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# if we did we'll try to release this lock and re-raise exception.
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# Of course something is going to be really wrong, after this.
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self.__lock.release()
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raise
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try:
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# Support passing in a single resource to acquire rather than many
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if isinstance(names, basestring): |
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names = [names] |
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else:
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names = sorted(names)
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acquire_list = [] |
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# First we look the locks up on __lockdict. We have no way of being sure
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# they will still be there after, but this makes it a lot faster should
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# just one of them be the already wrong
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for lname in utils.UniqueSequence(names): |
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try:
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lock = self.__lockdict[lname] # raises KeyError if lock is not there |
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acquire_list.append((lname, lock)) |
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except (KeyError): |
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if self.__lock._is_owned(): |
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# We are acquiring all the set, it doesn't matter if this
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# particular element is not there anymore.
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continue
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else:
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raise errors.LockError('non-existing lock in set (%s)' % lname) |
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# This will hold the locknames we effectively acquired.
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acquired = set()
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# Now acquire_list contains a sorted list of resources and locks we want.
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# In order to get them we loop on this (private) list and acquire() them.
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# We gave no real guarantee they will still exist till this is done but
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# .acquire() itself is safe and will alert us if the lock gets deleted.
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for (lname, lock) in acquire_list: |
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try:
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lock.acquire(shared=shared) # raises LockError if the lock is deleted
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# now the lock cannot be deleted, we have it!
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self._add_owned(name=lname)
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acquired.add(lname) |
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except (errors.LockError):
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if self.__lock._is_owned(): |
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# We are acquiring all the set, it doesn't matter if this
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# particular element is not there anymore.
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continue
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else:
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name_fail = lname |
556 |
for lname in self._list_owned(): |
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self.__lockdict[lname].release()
|
558 |
self._del_owned(name=lname)
|
559 |
raise errors.LockError('non-existing lock in set (%s)' % name_fail) |
560 |
except:
|
561 |
# We shouldn't have problems adding the lock to the owners list, but
|
562 |
# if we did we'll try to release this lock and re-raise exception.
|
563 |
# Of course something is going to be really wrong, after this.
|
564 |
if lock._is_owned():
|
565 |
lock.release() |
566 |
raise
|
567 |
|
568 |
except:
|
569 |
# If something went wrong and we had the set-lock let's release it...
|
570 |
if self.__lock._is_owned(): |
571 |
self.__lock.release()
|
572 |
raise
|
573 |
|
574 |
return acquired
|
575 |
|
576 |
def release(self, names=None): |
577 |
"""Release a set of resource locks, at the same level.
|
578 |
|
579 |
You must have acquired the locks, either in shared or in exclusive mode,
|
580 |
before releasing them.
|
581 |
|
582 |
@param names: the names of the locks which shall be released
|
583 |
(defaults to all the locks acquired at that level).
|
584 |
|
585 |
"""
|
586 |
assert self._is_owned(), "release() on lock set while not owner" |
587 |
|
588 |
# Support passing in a single resource to release rather than many
|
589 |
if isinstance(names, basestring): |
590 |
names = [names] |
591 |
|
592 |
if names is None: |
593 |
names = self._list_owned()
|
594 |
else:
|
595 |
names = set(names)
|
596 |
assert self._list_owned().issuperset(names), ( |
597 |
"release() on unheld resources %s" %
|
598 |
names.difference(self._list_owned()))
|
599 |
|
600 |
# First of all let's release the "all elements" lock, if set.
|
601 |
# After this 'add' can work again
|
602 |
if self.__lock._is_owned(): |
603 |
self.__lock.release()
|
604 |
self._del_owned()
|
605 |
|
606 |
for lockname in names: |
607 |
# If we are sure the lock doesn't leave __lockdict without being
|
608 |
# exclusively held we can do this...
|
609 |
self.__lockdict[lockname].release()
|
610 |
self._del_owned(name=lockname)
|
611 |
|
612 |
def add(self, names, acquired=0, shared=0): |
613 |
"""Add a new set of elements to the set
|
614 |
|
615 |
@param names: names of the new elements to add
|
616 |
@param acquired: pre-acquire the new resource?
|
617 |
@param shared: is the pre-acquisition shared?
|
618 |
|
619 |
"""
|
620 |
# Check we don't already own locks at this level
|
621 |
assert not self._is_owned() or self.__lock._is_owned(shared=0), \ |
622 |
"Cannot add locks if the set is only partially owned, or shared"
|
623 |
|
624 |
# Support passing in a single resource to add rather than many
|
625 |
if isinstance(names, basestring): |
626 |
names = [names] |
627 |
|
628 |
# If we don't already own the set-level lock acquired in an exclusive way
|
629 |
# we'll get it and note we need to release it later.
|
630 |
release_lock = False
|
631 |
if not self.__lock._is_owned(): |
632 |
release_lock = True
|
633 |
self.__lock.acquire()
|
634 |
|
635 |
try:
|
636 |
invalid_names = set(self.__names()).intersection(names) |
637 |
if invalid_names:
|
638 |
# This must be an explicit raise, not an assert, because assert is
|
639 |
# turned off when using optimization, and this can happen because of
|
640 |
# concurrency even if the user doesn't want it.
|
641 |
raise errors.LockError("duplicate add() (%s)" % invalid_names) |
642 |
|
643 |
for lockname in names: |
644 |
lock = SharedLock() |
645 |
|
646 |
if acquired:
|
647 |
lock.acquire(shared=shared) |
648 |
# now the lock cannot be deleted, we have it!
|
649 |
try:
|
650 |
self._add_owned(name=lockname)
|
651 |
except:
|
652 |
# We shouldn't have problems adding the lock to the owners list,
|
653 |
# but if we did we'll try to release this lock and re-raise
|
654 |
# exception. Of course something is going to be really wrong,
|
655 |
# after this. On the other hand the lock hasn't been added to the
|
656 |
# __lockdict yet so no other threads should be pending on it. This
|
657 |
# release is just a safety measure.
|
658 |
lock.release() |
659 |
raise
|
660 |
|
661 |
self.__lockdict[lockname] = lock
|
662 |
|
663 |
finally:
|
664 |
# Only release __lock if we were not holding it previously.
|
665 |
if release_lock:
|
666 |
self.__lock.release()
|
667 |
|
668 |
return True |
669 |
|
670 |
def remove(self, names, blocking=1): |
671 |
"""Remove elements from the lock set.
|
672 |
|
673 |
You can either not hold anything in the lockset or already hold a superset
|
674 |
of the elements you want to delete, exclusively.
|
675 |
|
676 |
@param names: names of the resource to remove.
|
677 |
@param blocking: whether to block while trying to acquire or to
|
678 |
operate in try-lock mode (this locking mode is not supported
|
679 |
yet unless you are already holding exclusively the locks)
|
680 |
|
681 |
@return:: a list of locks which we removed; the list is always
|
682 |
equal to the names list if we were holding all the locks
|
683 |
exclusively
|
684 |
|
685 |
"""
|
686 |
if not blocking and not self._is_owned(): |
687 |
# We don't have non-blocking mode for now
|
688 |
raise NotImplementedError |
689 |
|
690 |
# Support passing in a single resource to remove rather than many
|
691 |
if isinstance(names, basestring): |
692 |
names = [names] |
693 |
|
694 |
# If we own any subset of this lock it must be a superset of what we want
|
695 |
# to delete. The ownership must also be exclusive, but that will be checked
|
696 |
# by the lock itself.
|
697 |
assert not self._is_owned() or self._list_owned().issuperset(names), ( |
698 |
"remove() on acquired lockset while not owning all elements")
|
699 |
|
700 |
removed = [] |
701 |
|
702 |
for lname in names: |
703 |
# Calling delete() acquires the lock exclusively if we don't already own
|
704 |
# it, and causes all pending and subsequent lock acquires to fail. It's
|
705 |
# fine to call it out of order because delete() also implies release(),
|
706 |
# and the assertion above guarantees that if we either already hold
|
707 |
# everything we want to delete, or we hold none.
|
708 |
try:
|
709 |
self.__lockdict[lname].delete()
|
710 |
removed.append(lname) |
711 |
except (KeyError, errors.LockError): |
712 |
# This cannot happen if we were already holding it, verify:
|
713 |
assert not self._is_owned(), "remove failed while holding lockset" |
714 |
else:
|
715 |
# If no LockError was raised we are the ones who deleted the lock.
|
716 |
# This means we can safely remove it from lockdict, as any further or
|
717 |
# pending delete() or acquire() will fail (and nobody can have the lock
|
718 |
# since before our call to delete()).
|
719 |
#
|
720 |
# This is done in an else clause because if the exception was thrown
|
721 |
# it's the job of the one who actually deleted it.
|
722 |
del self.__lockdict[lname] |
723 |
# And let's remove it from our private list if we owned it.
|
724 |
if self._is_owned(): |
725 |
self._del_owned(name=lname)
|
726 |
|
727 |
return removed
|
728 |
|
729 |
|
730 |
# Locking levels, must be acquired in increasing order.
|
731 |
# Current rules are:
|
732 |
# - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
|
733 |
# acquired before performing any operation, either in shared or in exclusive
|
734 |
# mode. acquiring the BGL in exclusive mode is discouraged and should be
|
735 |
# avoided.
|
736 |
# - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
|
737 |
# If you need more than one node, or more than one instance, acquire them at
|
738 |
# the same time.
|
739 |
LEVEL_CLUSTER = 0
|
740 |
LEVEL_INSTANCE = 1
|
741 |
LEVEL_NODE = 2
|
742 |
|
743 |
LEVELS = [LEVEL_CLUSTER, |
744 |
LEVEL_INSTANCE, |
745 |
LEVEL_NODE] |
746 |
|
747 |
# Lock levels which are modifiable
|
748 |
LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE] |
749 |
|
750 |
LEVEL_NAMES = { |
751 |
LEVEL_CLUSTER: "cluster",
|
752 |
LEVEL_INSTANCE: "instance",
|
753 |
LEVEL_NODE: "node",
|
754 |
} |
755 |
|
756 |
# Constant for the big ganeti lock
|
757 |
BGL = 'BGL'
|
758 |
|
759 |
|
760 |
class GanetiLockManager: |
761 |
"""The Ganeti Locking Library
|
762 |
|
763 |
The purpose of this small library is to manage locking for ganeti clusters
|
764 |
in a central place, while at the same time doing dynamic checks against
|
765 |
possible deadlocks. It will also make it easier to transition to a different
|
766 |
lock type should we migrate away from python threads.
|
767 |
|
768 |
"""
|
769 |
_instance = None
|
770 |
|
771 |
def __init__(self, nodes=None, instances=None): |
772 |
"""Constructs a new GanetiLockManager object.
|
773 |
|
774 |
There should be only a GanetiLockManager object at any time, so this
|
775 |
function raises an error if this is not the case.
|
776 |
|
777 |
@param nodes: list of node names
|
778 |
@param instances: list of instance names
|
779 |
|
780 |
"""
|
781 |
assert self.__class__._instance is None, \ |
782 |
"double GanetiLockManager instance"
|
783 |
|
784 |
self.__class__._instance = self |
785 |
|
786 |
# The keyring contains all the locks, at their level and in the correct
|
787 |
# locking order.
|
788 |
self.__keyring = {
|
789 |
LEVEL_CLUSTER: LockSet([BGL]), |
790 |
LEVEL_NODE: LockSet(nodes), |
791 |
LEVEL_INSTANCE: LockSet(instances), |
792 |
} |
793 |
|
794 |
def _names(self, level): |
795 |
"""List the lock names at the given level.
|
796 |
|
797 |
This can be used for debugging/testing purposes.
|
798 |
|
799 |
@param level: the level whose list of locks to get
|
800 |
|
801 |
"""
|
802 |
assert level in LEVELS, "Invalid locking level %s" % level |
803 |
return self.__keyring[level]._names() |
804 |
|
805 |
def _is_owned(self, level): |
806 |
"""Check whether we are owning locks at the given level
|
807 |
|
808 |
"""
|
809 |
return self.__keyring[level]._is_owned() |
810 |
|
811 |
is_owned = _is_owned |
812 |
|
813 |
def _list_owned(self, level): |
814 |
"""Get the set of owned locks at the given level
|
815 |
|
816 |
"""
|
817 |
return self.__keyring[level]._list_owned() |
818 |
|
819 |
def _upper_owned(self, level): |
820 |
"""Check that we don't own any lock at a level greater than the given one.
|
821 |
|
822 |
"""
|
823 |
# This way of checking only works if LEVELS[i] = i, which we check for in
|
824 |
# the test cases.
|
825 |
return utils.any((self._is_owned(l) for l in LEVELS[level + 1:])) |
826 |
|
827 |
def _BGL_owned(self): |
828 |
"""Check if the current thread owns the BGL.
|
829 |
|
830 |
Both an exclusive or a shared acquisition work.
|
831 |
|
832 |
"""
|
833 |
return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned() |
834 |
|
835 |
def _contains_BGL(self, level, names): |
836 |
"""Check if the level contains the BGL.
|
837 |
|
838 |
Check if acting on the given level and set of names will change
|
839 |
the status of the Big Ganeti Lock.
|
840 |
|
841 |
"""
|
842 |
return level == LEVEL_CLUSTER and (names is None or BGL in names) |
843 |
|
844 |
def acquire(self, level, names, blocking=1, shared=0): |
845 |
"""Acquire a set of resource locks, at the same level.
|
846 |
|
847 |
@param level: the level at which the locks shall be acquired;
|
848 |
it must be a member of LEVELS.
|
849 |
@param names: the names of the locks which shall be acquired
|
850 |
(special lock names, or instance/node names)
|
851 |
@param shared: whether to acquire in shared mode; by default
|
852 |
an exclusive lock will be acquired
|
853 |
@param blocking: whether to block while trying to acquire or to
|
854 |
operate in try-lock mode (this locking mode is not supported yet)
|
855 |
|
856 |
"""
|
857 |
assert level in LEVELS, "Invalid locking level %s" % level |
858 |
|
859 |
# Check that we are either acquiring the Big Ganeti Lock or we already own
|
860 |
# it. Some "legacy" opcodes need to be sure they are run non-concurrently
|
861 |
# so even if we've migrated we need to at least share the BGL to be
|
862 |
# compatible with them. Of course if we own the BGL exclusively there's no
|
863 |
# point in acquiring any other lock, unless perhaps we are half way through
|
864 |
# the migration of the current opcode.
|
865 |
assert (self._contains_BGL(level, names) or self._BGL_owned()), ( |
866 |
"You must own the Big Ganeti Lock before acquiring any other")
|
867 |
|
868 |
# Check we don't own locks at the same or upper levels.
|
869 |
assert not self._upper_owned(level), ("Cannot acquire locks at a level" |
870 |
" while owning some at a greater one")
|
871 |
|
872 |
# Acquire the locks in the set.
|
873 |
return self.__keyring[level].acquire(names, shared=shared, |
874 |
blocking=blocking) |
875 |
|
876 |
def release(self, level, names=None): |
877 |
"""Release a set of resource locks, at the same level.
|
878 |
|
879 |
You must have acquired the locks, either in shared or in exclusive
|
880 |
mode, before releasing them.
|
881 |
|
882 |
@param level: the level at which the locks shall be released;
|
883 |
it must be a member of LEVELS
|
884 |
@param names: the names of the locks which shall be released
|
885 |
(defaults to all the locks acquired at that level)
|
886 |
|
887 |
"""
|
888 |
assert level in LEVELS, "Invalid locking level %s" % level |
889 |
assert (not self._contains_BGL(level, names) or |
890 |
not self._upper_owned(LEVEL_CLUSTER)), ( |
891 |
"Cannot release the Big Ganeti Lock while holding something"
|
892 |
" at upper levels")
|
893 |
|
894 |
# Release will complain if we don't own the locks already
|
895 |
return self.__keyring[level].release(names) |
896 |
|
897 |
def add(self, level, names, acquired=0, shared=0): |
898 |
"""Add locks at the specified level.
|
899 |
|
900 |
@param level: the level at which the locks shall be added;
|
901 |
it must be a member of LEVELS_MOD.
|
902 |
@param names: names of the locks to acquire
|
903 |
@param acquired: whether to acquire the newly added locks
|
904 |
@param shared: whether the acquisition will be shared
|
905 |
|
906 |
"""
|
907 |
assert level in LEVELS_MOD, "Invalid or immutable level %s" % level |
908 |
assert self._BGL_owned(), ("You must own the BGL before performing other" |
909 |
" operations")
|
910 |
assert not self._upper_owned(level), ("Cannot add locks at a level" |
911 |
" while owning some at a greater one")
|
912 |
return self.__keyring[level].add(names, acquired=acquired, shared=shared) |
913 |
|
914 |
def remove(self, level, names, blocking=1): |
915 |
"""Remove locks from the specified level.
|
916 |
|
917 |
You must either already own the locks you are trying to remove
|
918 |
exclusively or not own any lock at an upper level.
|
919 |
|
920 |
@param level: the level at which the locks shall be removed;
|
921 |
it must be a member of LEVELS_MOD
|
922 |
@param names: the names of the locks which shall be removed
|
923 |
(special lock names, or instance/node names)
|
924 |
@param blocking: whether to block while trying to operate in
|
925 |
try-lock mode (this locking mode is not supported yet)
|
926 |
|
927 |
"""
|
928 |
assert level in LEVELS_MOD, "Invalid or immutable level %s" % level |
929 |
assert self._BGL_owned(), ("You must own the BGL before performing other" |
930 |
" operations")
|
931 |
# Check we either own the level or don't own anything from here
|
932 |
# up. LockSet.remove() will check the case in which we don't own
|
933 |
# all the needed resources, or we have a shared ownership.
|
934 |
assert self._is_owned(level) or not self._upper_owned(level), ( |
935 |
"Cannot remove locks at a level while not owning it or"
|
936 |
" owning some at a greater one")
|
937 |
return self.__keyring[level].remove(names, blocking=blocking) |