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# Copyright (C) 2006, 2007 Google Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301, USA.
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"""Module implementing the Ganeti locking code."""
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# pylint: disable-msg=W0212
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# W0212 since e.g. LockSet methods use (a lot) the internals of
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# SharedLock
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import threading |
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# Wouldn't it be better to define LockingError in the locking module?
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# Well, for now that's how the rest of the code does it...
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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 SharedLock: |
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"""Implements a shared lock.
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Multiple threads can acquire the lock in a shared way, calling
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acquire_shared(). In order to acquire the lock in an exclusive way threads
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can call acquire_exclusive().
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The lock prevents starvation but does not guarantee that threads will acquire
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the shared lock in the order they queued for it, just that they will
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eventually do so.
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"""
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def __init__(self): |
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"""Construct a new SharedLock"""
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# we have two conditions, c_shr and c_exc, sharing the same lock.
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self.__lock = threading.Lock()
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self.__turn_shr = threading.Condition(self.__lock) |
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self.__turn_exc = threading.Condition(self.__lock) |
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# current lock holders
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self.__shr = set() |
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self.__exc = None |
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# lock waiters
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self.__nwait_exc = 0 |
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self.__nwait_shr = 0 |
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self.__npass_shr = 0 |
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# is this lock in the deleted state?
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self.__deleted = False |
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def __is_sharer(self): |
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"""Is the current thread sharing the lock at this time?"""
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return threading.currentThread() in self.__shr |
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def __is_exclusive(self): |
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"""Is the current thread holding the lock exclusively at this time?"""
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return threading.currentThread() == self.__exc |
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def __is_owned(self, shared=-1): |
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"""Is the current thread somehow owning the lock at this time?
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This is a private version of the function, which presumes you're holding
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the internal lock.
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"""
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if shared < 0: |
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return self.__is_sharer() or self.__is_exclusive() |
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elif shared:
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return self.__is_sharer() |
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else:
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return self.__is_exclusive() |
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def _is_owned(self, shared=-1): |
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"""Is the current thread somehow owning the lock at this time?
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@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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result = self.__is_owned(shared=shared)
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finally:
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self.__lock.release()
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return result
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def __wait(self, c): |
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"""Wait on the given condition, and raise an exception if the current lock
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is declared deleted in the meantime.
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@param c: the condition to wait on
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"""
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c.wait() |
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if self.__deleted: |
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raise errors.LockError('deleted lock') |
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def __exclusive_acquire(self): |
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"""Acquire the lock exclusively.
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This is a private function that presumes you are already holding the
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internal lock. It's defined separately to avoid code duplication between
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acquire() and delete()
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"""
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self.__nwait_exc += 1 |
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try:
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# This is to save ourselves from a nasty race condition that could
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# theoretically make the sharers starve.
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if self.__nwait_shr > 0 or self.__nwait_exc > 1: |
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self.__wait(self.__turn_exc) |
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while len(self.__shr) > 0 or self.__exc is not None: |
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self.__wait(self.__turn_exc) |
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self.__exc = threading.currentThread()
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finally:
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self.__nwait_exc -= 1 |
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assert self.__npass_shr == 0, "SharedLock: internal fairness violation" |
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def acquire(self, blocking=1, shared=0): |
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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 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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"""
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if not blocking: |
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# We don't have non-blocking mode for now
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raise NotImplementedError |
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self.__lock.acquire()
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try:
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if self.__deleted: |
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raise errors.LockError('deleted lock') |
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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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assert self.__npass_shr >= 0, "Internal fairness condition weirdness" |
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if shared:
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self.__nwait_shr += 1 |
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try:
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wait = False
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# If there is an exclusive holder waiting we have to wait.
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# We'll only do this once, though, when we start waiting for
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# the lock. Then we'll just wait while there are no
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# exclusive holders.
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if self.__nwait_exc > 0: |
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# TODO: if !blocking...
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wait = True
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self.__wait(self.__turn_shr) |
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while self.__exc is not None: |
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wait = True
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# TODO: if !blocking...
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self.__wait(self.__turn_shr) |
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self.__shr.add(threading.currentThread())
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# If we were waiting note that we passed
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if wait:
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self.__npass_shr -= 1 |
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finally:
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self.__nwait_shr -= 1 |
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assert self.__npass_shr >= 0, "Internal fairness condition weirdness" |
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else:
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# TODO: if !blocking...
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# (or modify __exclusive_acquire for non-blocking mode)
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self.__exclusive_acquire()
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finally:
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self.__lock.release()
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return True |
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def release(self): |
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"""Release a Shared Lock.
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You must have acquired the lock, either in shared or in exclusive mode,
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before calling this function.
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"""
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self.__lock.acquire()
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try:
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assert self.__npass_shr >= 0, "Internal fairness condition weirdness" |
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# Autodetect release type
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if self.__is_exclusive(): |
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self.__exc = None |
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# An exclusive holder has just had the lock, time to put it in shared
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# mode if there are shared holders waiting. Otherwise wake up the next
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# exclusive holder.
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if self.__nwait_shr > 0: |
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# Make sure at least the ones which were blocked pass.
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self.__npass_shr = self.__nwait_shr |
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self.__turn_shr.notifyAll()
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elif self.__nwait_exc > 0: |
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self.__turn_exc.notify()
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elif self.__is_sharer(): |
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self.__shr.remove(threading.currentThread())
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# If there are shared holders waiting (and not just scheduled to pass)
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# there *must* be an exclusive holder waiting as well; otherwise what
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# were they waiting for?
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assert (self.__nwait_exc > 0 or |
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self.__npass_shr == self.__nwait_shr), \ |
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"Lock sharers waiting while no exclusive is queueing"
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# If there are no more shared holders either in or scheduled to pass,
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# and some exclusive holders are waiting let's wake one up.
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if (len(self.__shr) == 0 and |
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self.__nwait_exc > 0 and |
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not self.__npass_shr > 0): |
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self.__turn_exc.notify()
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else:
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assert False, "Cannot release non-owned lock" |
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finally:
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self.__lock.release()
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def delete(self, blocking=1): |
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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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@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
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yet unless you are already holding exclusively the lock.
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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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if self.__deleted: |
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raise errors.LockError('deleted lock') |
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if not self.__is_exclusive(): |
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if not blocking: |
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# We don't have non-blocking mode for now
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raise NotImplementedError |
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self.__exclusive_acquire()
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self.__deleted = True |
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self.__exc = None |
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# Wake up everybody, they will fail acquiring the lock and
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# raise an exception instead.
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self.__turn_exc.notifyAll()
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self.__turn_shr.notifyAll()
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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)) |
467 |
except (KeyError): |
468 |
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) |
474 |
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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) |
487 |
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 |
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for lname in self._list_owned(): |
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self.__lockdict[lname].release()
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self._del_owned(name=lname)
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raise errors.LockError('non-existing lock in set (%s)' % name_fail) |
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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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if lock._is_owned():
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lock.release() |
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raise
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|
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except:
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# If something went wrong and we had the set-lock let's release it...
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if self.__lock._is_owned(): |
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self.__lock.release()
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raise
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|
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return acquired
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|
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def release(self, names=None): |
515 |
"""Release a set of resource locks, at the same level.
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|
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You must have acquired the locks, either in shared or in exclusive mode,
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before releasing them.
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|
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@param names: the names of the locks which shall be released
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(defaults to all the locks acquired at that level).
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|
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"""
|
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assert self._is_owned(), "release() on lock set while not owner" |
525 |
|
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# Support passing in a single resource to release rather than many
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527 |
if isinstance(names, basestring): |
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names = [names] |
529 |
|
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if names is None: |
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names = self._list_owned()
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else:
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533 |
names = set(names)
|
534 |
assert self._list_owned().issuperset(names), ( |
535 |
"release() on unheld resources %s" %
|
536 |
names.difference(self._list_owned()))
|
537 |
|
538 |
# First of all let's release the "all elements" lock, if set.
|
539 |
# After this 'add' can work again
|
540 |
if self.__lock._is_owned(): |
541 |
self.__lock.release()
|
542 |
self._del_owned()
|
543 |
|
544 |
for lockname in names: |
545 |
# If we are sure the lock doesn't leave __lockdict without being
|
546 |
# exclusively held we can do this...
|
547 |
self.__lockdict[lockname].release()
|
548 |
self._del_owned(name=lockname)
|
549 |
|
550 |
def add(self, names, acquired=0, shared=0): |
551 |
"""Add a new set of elements to the set
|
552 |
|
553 |
@param names: names of the new elements to add
|
554 |
@param acquired: pre-acquire the new resource?
|
555 |
@param shared: is the pre-acquisition shared?
|
556 |
|
557 |
"""
|
558 |
# Check we don't already own locks at this level
|
559 |
assert not self._is_owned() or self.__lock._is_owned(shared=0), \ |
560 |
"Cannot add locks if the set is only partially owned, or shared"
|
561 |
|
562 |
# Support passing in a single resource to add rather than many
|
563 |
if isinstance(names, basestring): |
564 |
names = [names] |
565 |
|
566 |
# If we don't already own the set-level lock acquired in an exclusive way
|
567 |
# we'll get it and note we need to release it later.
|
568 |
release_lock = False
|
569 |
if not self.__lock._is_owned(): |
570 |
release_lock = True
|
571 |
self.__lock.acquire()
|
572 |
|
573 |
try:
|
574 |
invalid_names = set(self.__names()).intersection(names) |
575 |
if invalid_names:
|
576 |
# This must be an explicit raise, not an assert, because assert is
|
577 |
# turned off when using optimization, and this can happen because of
|
578 |
# concurrency even if the user doesn't want it.
|
579 |
raise errors.LockError("duplicate add() (%s)" % invalid_names) |
580 |
|
581 |
for lockname in names: |
582 |
lock = SharedLock() |
583 |
|
584 |
if acquired:
|
585 |
lock.acquire(shared=shared) |
586 |
# now the lock cannot be deleted, we have it!
|
587 |
try:
|
588 |
self._add_owned(name=lockname)
|
589 |
except:
|
590 |
# We shouldn't have problems adding the lock to the owners list,
|
591 |
# but if we did we'll try to release this lock and re-raise
|
592 |
# exception. Of course something is going to be really wrong,
|
593 |
# after this. On the other hand the lock hasn't been added to the
|
594 |
# __lockdict yet so no other threads should be pending on it. This
|
595 |
# release is just a safety measure.
|
596 |
lock.release() |
597 |
raise
|
598 |
|
599 |
self.__lockdict[lockname] = lock
|
600 |
|
601 |
finally:
|
602 |
# Only release __lock if we were not holding it previously.
|
603 |
if release_lock:
|
604 |
self.__lock.release()
|
605 |
|
606 |
return True |
607 |
|
608 |
def remove(self, names, blocking=1): |
609 |
"""Remove elements from the lock set.
|
610 |
|
611 |
You can either not hold anything in the lockset or already hold a superset
|
612 |
of the elements you want to delete, exclusively.
|
613 |
|
614 |
@param names: names of the resource to remove.
|
615 |
@param blocking: whether to block while trying to acquire or to
|
616 |
operate in try-lock mode (this locking mode is not supported
|
617 |
yet unless you are already holding exclusively the locks)
|
618 |
|
619 |
@return:: a list of locks which we removed; the list is always
|
620 |
equal to the names list if we were holding all the locks
|
621 |
exclusively
|
622 |
|
623 |
"""
|
624 |
if not blocking and not self._is_owned(): |
625 |
# We don't have non-blocking mode for now
|
626 |
raise NotImplementedError |
627 |
|
628 |
# Support passing in a single resource to remove rather than many
|
629 |
if isinstance(names, basestring): |
630 |
names = [names] |
631 |
|
632 |
# If we own any subset of this lock it must be a superset of what we want
|
633 |
# to delete. The ownership must also be exclusive, but that will be checked
|
634 |
# by the lock itself.
|
635 |
assert not self._is_owned() or self._list_owned().issuperset(names), ( |
636 |
"remove() on acquired lockset while not owning all elements")
|
637 |
|
638 |
removed = [] |
639 |
|
640 |
for lname in names: |
641 |
# Calling delete() acquires the lock exclusively if we don't already own
|
642 |
# it, and causes all pending and subsequent lock acquires to fail. It's
|
643 |
# fine to call it out of order because delete() also implies release(),
|
644 |
# and the assertion above guarantees that if we either already hold
|
645 |
# everything we want to delete, or we hold none.
|
646 |
try:
|
647 |
self.__lockdict[lname].delete()
|
648 |
removed.append(lname) |
649 |
except (KeyError, errors.LockError): |
650 |
# This cannot happen if we were already holding it, verify:
|
651 |
assert not self._is_owned(), "remove failed while holding lockset" |
652 |
else:
|
653 |
# If no LockError was raised we are the ones who deleted the lock.
|
654 |
# This means we can safely remove it from lockdict, as any further or
|
655 |
# pending delete() or acquire() will fail (and nobody can have the lock
|
656 |
# since before our call to delete()).
|
657 |
#
|
658 |
# This is done in an else clause because if the exception was thrown
|
659 |
# it's the job of the one who actually deleted it.
|
660 |
del self.__lockdict[lname] |
661 |
# And let's remove it from our private list if we owned it.
|
662 |
if self._is_owned(): |
663 |
self._del_owned(name=lname)
|
664 |
|
665 |
return removed
|
666 |
|
667 |
|
668 |
# Locking levels, must be acquired in increasing order.
|
669 |
# Current rules are:
|
670 |
# - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
|
671 |
# acquired before performing any operation, either in shared or in exclusive
|
672 |
# mode. acquiring the BGL in exclusive mode is discouraged and should be
|
673 |
# avoided.
|
674 |
# - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
|
675 |
# If you need more than one node, or more than one instance, acquire them at
|
676 |
# the same time.
|
677 |
LEVEL_CLUSTER = 0
|
678 |
LEVEL_INSTANCE = 1
|
679 |
LEVEL_NODE = 2
|
680 |
|
681 |
LEVELS = [LEVEL_CLUSTER, |
682 |
LEVEL_INSTANCE, |
683 |
LEVEL_NODE] |
684 |
|
685 |
# Lock levels which are modifiable
|
686 |
LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE] |
687 |
|
688 |
# Constant for the big ganeti lock
|
689 |
BGL = 'BGL'
|
690 |
|
691 |
|
692 |
class GanetiLockManager: |
693 |
"""The Ganeti Locking Library
|
694 |
|
695 |
The purpose of this small library is to manage locking for ganeti clusters
|
696 |
in a central place, while at the same time doing dynamic checks against
|
697 |
possible deadlocks. It will also make it easier to transition to a different
|
698 |
lock type should we migrate away from python threads.
|
699 |
|
700 |
"""
|
701 |
_instance = None
|
702 |
|
703 |
def __init__(self, nodes=None, instances=None): |
704 |
"""Constructs a new GanetiLockManager object.
|
705 |
|
706 |
There should be only a GanetiLockManager object at any time, so this
|
707 |
function raises an error if this is not the case.
|
708 |
|
709 |
@param nodes: list of node names
|
710 |
@param instances: list of instance names
|
711 |
|
712 |
"""
|
713 |
assert self.__class__._instance is None, \ |
714 |
"double GanetiLockManager instance"
|
715 |
|
716 |
self.__class__._instance = self |
717 |
|
718 |
# The keyring contains all the locks, at their level and in the correct
|
719 |
# locking order.
|
720 |
self.__keyring = {
|
721 |
LEVEL_CLUSTER: LockSet([BGL]), |
722 |
LEVEL_NODE: LockSet(nodes), |
723 |
LEVEL_INSTANCE: LockSet(instances), |
724 |
} |
725 |
|
726 |
def _names(self, level): |
727 |
"""List the lock names at the given level.
|
728 |
|
729 |
This can be used for debugging/testing purposes.
|
730 |
|
731 |
@param level: the level whose list of locks to get
|
732 |
|
733 |
"""
|
734 |
assert level in LEVELS, "Invalid locking level %s" % level |
735 |
return self.__keyring[level]._names() |
736 |
|
737 |
def _is_owned(self, level): |
738 |
"""Check whether we are owning locks at the given level
|
739 |
|
740 |
"""
|
741 |
return self.__keyring[level]._is_owned() |
742 |
|
743 |
is_owned = _is_owned |
744 |
|
745 |
def _list_owned(self, level): |
746 |
"""Get the set of owned locks at the given level
|
747 |
|
748 |
"""
|
749 |
return self.__keyring[level]._list_owned() |
750 |
|
751 |
def _upper_owned(self, level): |
752 |
"""Check that we don't own any lock at a level greater than the given one.
|
753 |
|
754 |
"""
|
755 |
# This way of checking only works if LEVELS[i] = i, which we check for in
|
756 |
# the test cases.
|
757 |
return utils.any((self._is_owned(l) for l in LEVELS[level + 1:])) |
758 |
|
759 |
def _BGL_owned(self): # pylint: disable-msg=C0103 |
760 |
"""Check if the current thread owns the BGL.
|
761 |
|
762 |
Both an exclusive or a shared acquisition work.
|
763 |
|
764 |
"""
|
765 |
return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned() |
766 |
|
767 |
@staticmethod
|
768 |
def _contains_BGL(level, names): # pylint: disable-msg=C0103 |
769 |
"""Check if the level contains the BGL.
|
770 |
|
771 |
Check if acting on the given level and set of names will change
|
772 |
the status of the Big Ganeti Lock.
|
773 |
|
774 |
"""
|
775 |
return level == LEVEL_CLUSTER and (names is None or BGL in names) |
776 |
|
777 |
def acquire(self, level, names, blocking=1, shared=0): |
778 |
"""Acquire a set of resource locks, at the same level.
|
779 |
|
780 |
@param level: the level at which the locks shall be acquired;
|
781 |
it must be a member of LEVELS.
|
782 |
@param names: the names of the locks which shall be acquired
|
783 |
(special lock names, or instance/node names)
|
784 |
@param shared: whether to acquire in shared mode; by default
|
785 |
an exclusive lock will be acquired
|
786 |
@param blocking: whether to block while trying to acquire or to
|
787 |
operate in try-lock mode (this locking mode is not supported yet)
|
788 |
|
789 |
"""
|
790 |
assert level in LEVELS, "Invalid locking level %s" % level |
791 |
|
792 |
# Check that we are either acquiring the Big Ganeti Lock or we already own
|
793 |
# it. Some "legacy" opcodes need to be sure they are run non-concurrently
|
794 |
# so even if we've migrated we need to at least share the BGL to be
|
795 |
# compatible with them. Of course if we own the BGL exclusively there's no
|
796 |
# point in acquiring any other lock, unless perhaps we are half way through
|
797 |
# the migration of the current opcode.
|
798 |
assert (self._contains_BGL(level, names) or self._BGL_owned()), ( |
799 |
"You must own the Big Ganeti Lock before acquiring any other")
|
800 |
|
801 |
# Check we don't own locks at the same or upper levels.
|
802 |
assert not self._upper_owned(level), ("Cannot acquire locks at a level" |
803 |
" while owning some at a greater one")
|
804 |
|
805 |
# Acquire the locks in the set.
|
806 |
return self.__keyring[level].acquire(names, shared=shared, |
807 |
blocking=blocking) |
808 |
|
809 |
def release(self, level, names=None): |
810 |
"""Release a set of resource locks, at the same level.
|
811 |
|
812 |
You must have acquired the locks, either in shared or in exclusive
|
813 |
mode, before releasing them.
|
814 |
|
815 |
@param level: the level at which the locks shall be released;
|
816 |
it must be a member of LEVELS
|
817 |
@param names: the names of the locks which shall be released
|
818 |
(defaults to all the locks acquired at that level)
|
819 |
|
820 |
"""
|
821 |
assert level in LEVELS, "Invalid locking level %s" % level |
822 |
assert (not self._contains_BGL(level, names) or |
823 |
not self._upper_owned(LEVEL_CLUSTER)), ( |
824 |
"Cannot release the Big Ganeti Lock while holding something"
|
825 |
" at upper levels")
|
826 |
|
827 |
# Release will complain if we don't own the locks already
|
828 |
return self.__keyring[level].release(names) |
829 |
|
830 |
def add(self, level, names, acquired=0, shared=0): |
831 |
"""Add locks at the specified level.
|
832 |
|
833 |
@param level: the level at which the locks shall be added;
|
834 |
it must be a member of LEVELS_MOD.
|
835 |
@param names: names of the locks to acquire
|
836 |
@param acquired: whether to acquire the newly added locks
|
837 |
@param shared: whether the acquisition will be shared
|
838 |
|
839 |
"""
|
840 |
assert level in LEVELS_MOD, "Invalid or immutable level %s" % level |
841 |
assert self._BGL_owned(), ("You must own the BGL before performing other" |
842 |
" operations")
|
843 |
assert not self._upper_owned(level), ("Cannot add locks at a level" |
844 |
" while owning some at a greater one")
|
845 |
return self.__keyring[level].add(names, acquired=acquired, shared=shared) |
846 |
|
847 |
def remove(self, level, names, blocking=1): |
848 |
"""Remove locks from the specified level.
|
849 |
|
850 |
You must either already own the locks you are trying to remove
|
851 |
exclusively or not own any lock at an upper level.
|
852 |
|
853 |
@param level: the level at which the locks shall be removed;
|
854 |
it must be a member of LEVELS_MOD
|
855 |
@param names: the names of the locks which shall be removed
|
856 |
(special lock names, or instance/node names)
|
857 |
@param blocking: whether to block while trying to operate in
|
858 |
try-lock mode (this locking mode is not supported yet)
|
859 |
|
860 |
"""
|
861 |
assert level in LEVELS_MOD, "Invalid or immutable level %s" % level |
862 |
assert self._BGL_owned(), ("You must own the BGL before performing other" |
863 |
" operations")
|
864 |
# Check we either own the level or don't own anything from here
|
865 |
# up. LockSet.remove() will check the case in which we don't own
|
866 |
# all the needed resources, or we have a shared ownership.
|
867 |
assert self._is_owned(level) or not self._upper_owned(level), ( |
868 |
"Cannot remove locks at a level while not owning it or"
|
869 |
" owning some at a greater one")
|
870 |
return self.__keyring[level].remove(names, blocking=blocking) |