4 # Copyright (C) 2006, 2007, 2008, 2009, 2010 Google Inc.
6 # This program is free software; you can redistribute it and/or modify
7 # it under the terms of the GNU General Public License as published by
8 # the Free Software Foundation; either version 2 of the License, or
9 # (at your option) any later version.
11 # This program is distributed in the hope that it will be useful, but
12 # WITHOUT ANY WARRANTY; without even the implied warranty of
13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 # General Public License for more details.
16 # You should have received a copy of the GNU General Public License
17 # along with this program; if not, write to the Free Software
18 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
21 """Module implementing the Ganeti locking code."""
23 # pylint: disable-msg=W0212
25 # W0212 since e.g. LockSet methods use (a lot) the internals of
38 from ganeti import errors
39 from ganeti import utils
40 from ganeti import compat
41 from ganeti import query
44 _EXCLUSIVE_TEXT = "exclusive"
45 _SHARED_TEXT = "shared"
46 _DELETED_TEXT = "deleted"
51 def ssynchronized(mylock, shared=0):
52 """Shared Synchronization decorator.
54 Calls the function holding the given lock, either in exclusive or shared
55 mode. It requires the passed lock to be a SharedLock (or support its
58 @type mylock: lockable object or string
59 @param mylock: lock to acquire or class member name of the lock to acquire
63 def sync_function(*args, **kwargs):
64 if isinstance(mylock, basestring):
65 assert args, "cannot ssynchronize on non-class method: self not found"
67 lock = getattr(args[0], mylock)
70 lock.acquire(shared=shared)
72 return fn(*args, **kwargs)
79 class _SingleNotifyPipeConditionWaiter(object):
80 """Helper class for SingleNotifyPipeCondition
88 def __init__(self, poller, fd):
89 """Constructor for _SingleNotifyPipeConditionWaiter
91 @type poller: select.poll
92 @param poller: Poller object
94 @param fd: File descriptor to wait for
101 def __call__(self, timeout):
102 """Wait for something to happen on the pipe.
104 @type timeout: float or None
105 @param timeout: Timeout for waiting (can be None)
108 running_timeout = utils.RunningTimeout(timeout, True)
111 remaining_time = running_timeout.Remaining()
113 if remaining_time is not None:
114 if remaining_time < 0.0:
117 # Our calculation uses seconds, poll() wants milliseconds
118 remaining_time *= 1000
121 result = self._poller.poll(remaining_time)
122 except EnvironmentError, err:
123 if err.errno != errno.EINTR:
127 # Check whether we were notified
128 if result and result[0][0] == self._fd:
132 class _BaseCondition(object):
133 """Base class containing common code for conditions.
135 Some of this code is taken from python's threading module.
147 def __init__(self, lock):
148 """Constructor for _BaseCondition.
150 @type lock: threading.Lock
151 @param lock: condition base lock
154 object.__init__(self)
157 self._release_save = lock._release_save
158 except AttributeError:
159 self._release_save = self._base_release_save
161 self._acquire_restore = lock._acquire_restore
162 except AttributeError:
163 self._acquire_restore = self._base_acquire_restore
165 self._is_owned = lock._is_owned
166 except AttributeError:
167 self._is_owned = self._base_is_owned
171 # Export the lock's acquire() and release() methods
172 self.acquire = lock.acquire
173 self.release = lock.release
175 def _base_is_owned(self):
176 """Check whether lock is owned by current thread.
179 if self._lock.acquire(0):
184 def _base_release_save(self):
187 def _base_acquire_restore(self, _):
190 def _check_owned(self):
191 """Raise an exception if the current thread doesn't own the lock.
194 if not self._is_owned():
195 raise RuntimeError("cannot work with un-aquired lock")
198 class SingleNotifyPipeCondition(_BaseCondition):
199 """Condition which can only be notified once.
201 This condition class uses pipes and poll, internally, to be able to wait for
202 notification with a timeout, without resorting to polling. It is almost
203 compatible with Python's threading.Condition, with the following differences:
204 - notifyAll can only be called once, and no wait can happen after that
205 - notify is not supported, only notifyAll
217 _waiter_class = _SingleNotifyPipeConditionWaiter
219 def __init__(self, lock):
220 """Constructor for SingleNotifyPipeCondition
223 _BaseCondition.__init__(self, lock)
225 self._notified = False
227 self._write_fd = None
230 def _check_unnotified(self):
231 """Throws an exception if already notified.
235 raise RuntimeError("cannot use already notified condition")
238 """Cleanup open file descriptors, if any.
241 if self._read_fd is not None:
242 os.close(self._read_fd)
245 if self._write_fd is not None:
246 os.close(self._write_fd)
247 self._write_fd = None
250 def wait(self, timeout):
251 """Wait for a notification.
253 @type timeout: float or None
254 @param timeout: Waiting timeout (can be None)
258 self._check_unnotified()
262 if self._poller is None:
263 (self._read_fd, self._write_fd) = os.pipe()
264 self._poller = select.poll()
265 self._poller.register(self._read_fd, select.POLLHUP)
267 wait_fn = self._waiter_class(self._poller, self._read_fd)
268 state = self._release_save()
270 # Wait for notification
274 self._acquire_restore(state)
277 if self._nwaiters == 0:
280 def notifyAll(self): # pylint: disable-msg=C0103
281 """Close the writing side of the pipe to notify all waiters.
285 self._check_unnotified()
286 self._notified = True
287 if self._write_fd is not None:
288 os.close(self._write_fd)
289 self._write_fd = None
292 class PipeCondition(_BaseCondition):
293 """Group-only non-polling condition with counters.
295 This condition class uses pipes and poll, internally, to be able to wait for
296 notification with a timeout, without resorting to polling. It is almost
297 compatible with Python's threading.Condition, but only supports notifyAll and
298 non-recursive locks. As an additional features it's able to report whether
299 there are any waiting threads.
307 _single_condition_class = SingleNotifyPipeCondition
309 def __init__(self, lock):
310 """Initializes this class.
313 _BaseCondition.__init__(self, lock)
314 self._waiters = set()
315 self._single_condition = self._single_condition_class(self._lock)
317 def wait(self, timeout):
318 """Wait for a notification.
320 @type timeout: float or None
321 @param timeout: Waiting timeout (can be None)
326 # Keep local reference to the pipe. It could be replaced by another thread
327 # notifying while we're waiting.
328 cond = self._single_condition
330 self._waiters.add(threading.currentThread())
335 self._waiters.remove(threading.currentThread())
337 def notifyAll(self): # pylint: disable-msg=C0103
338 """Notify all currently waiting threads.
342 self._single_condition.notifyAll()
343 self._single_condition = self._single_condition_class(self._lock)
345 def get_waiting(self):
346 """Returns a list of all waiting threads.
353 def has_waiting(self):
354 """Returns whether there are active waiters.
359 return bool(self._waiters)
362 class _PipeConditionWithMode(PipeCondition):
367 def __init__(self, lock, shared):
368 """Initializes this class.
372 PipeCondition.__init__(self, lock)
375 class SharedLock(object):
376 """Implements a shared lock.
378 Multiple threads can acquire the lock in a shared way by calling
379 C{acquire(shared=1)}. In order to acquire the lock in an exclusive way
380 threads can call C{acquire(shared=0)}.
382 Notes on data structures: C{__pending} contains a priority queue (heapq) of
383 all pending acquires: C{[(priority1: prioqueue1), (priority2: prioqueue2),
384 ...]}. Each per-priority queue contains a normal in-order list of conditions
385 to be notified when the lock can be acquired. Shared locks are grouped
386 together by priority and the condition for them is stored in
387 C{__pending_shared} if it already exists. C{__pending_by_prio} keeps
388 references for the per-priority queues indexed by priority for faster access.
391 @ivar name: the name of the lock
406 __condition_class = _PipeConditionWithMode
408 def __init__(self, name, monitor=None):
409 """Construct a new SharedLock.
411 @param name: the name of the lock
412 @type monitor: L{LockMonitor}
413 @param monitor: Lock monitor with which to register
416 object.__init__(self)
421 self.__lock = threading.Lock()
423 # Queue containing waiting acquires
425 self.__pending_by_prio = {}
426 self.__pending_shared = {}
428 # Current lock holders
432 # is this lock in the deleted state?
433 self.__deleted = False
435 # Register with lock monitor
437 logging.debug("Adding lock %s to monitor", name)
438 monitor.RegisterLock(self)
440 def GetLockInfo(self, requested):
441 """Retrieves information for querying locks.
444 @param requested: Requested information, see C{query.LQ_*}
447 self.__lock.acquire()
449 # Note: to avoid unintentional race conditions, no references to
450 # modifiable objects should be returned unless they were created in this
455 if query.LQ_MODE in requested:
458 assert not (self.__exc or self.__shr)
460 mode = _EXCLUSIVE_TEXT
464 # Current owner(s) are wanted
465 if query.LQ_OWNER in requested:
472 assert not self.__deleted
473 owner_names = [i.getName() for i in owner]
475 # Pending acquires are wanted
476 if query.LQ_PENDING in requested:
479 # Sorting instead of copying and using heaq functions for simplicity
480 for (_, prioqueue) in sorted(self.__pending):
481 for cond in prioqueue:
483 pendmode = _SHARED_TEXT
485 pendmode = _EXCLUSIVE_TEXT
487 # List of names will be sorted in L{query._GetLockPending}
488 pending.append((pendmode, [i.getName()
489 for i in cond.get_waiting()]))
493 return [(self.name, mode, owner_names, pending)]
495 self.__lock.release()
497 def __check_deleted(self):
498 """Raises an exception if the lock has been deleted.
502 raise errors.LockError("Deleted lock %s" % self.name)
504 def __is_sharer(self):
505 """Is the current thread sharing the lock at this time?
508 return threading.currentThread() in self.__shr
510 def __is_exclusive(self):
511 """Is the current thread holding the lock exclusively at this time?
514 return threading.currentThread() == self.__exc
516 def __is_owned(self, shared=-1):
517 """Is the current thread somehow owning the lock at this time?
519 This is a private version of the function, which presumes you're holding
524 return self.__is_sharer() or self.__is_exclusive()
526 return self.__is_sharer()
528 return self.__is_exclusive()
530 def _is_owned(self, shared=-1):
531 """Is the current thread somehow owning the lock at this time?
534 - < 0: check for any type of ownership (default)
535 - 0: check for exclusive ownership
536 - > 0: check for shared ownership
539 self.__lock.acquire()
541 return self.__is_owned(shared=shared)
543 self.__lock.release()
547 def _count_pending(self):
548 """Returns the number of pending acquires.
553 self.__lock.acquire()
555 return sum(len(prioqueue) for (_, prioqueue) in self.__pending)
557 self.__lock.release()
559 def _check_empty(self):
560 """Checks whether there are any pending acquires.
565 self.__lock.acquire()
567 # Order is important: __find_first_pending_queue modifies __pending
568 (_, prioqueue) = self.__find_first_pending_queue()
570 return not (prioqueue or
572 self.__pending_by_prio or
573 self.__pending_shared)
575 self.__lock.release()
577 def __do_acquire(self, shared):
578 """Actually acquire the lock.
582 self.__shr.add(threading.currentThread())
584 self.__exc = threading.currentThread()
586 def __can_acquire(self, shared):
587 """Determine whether lock can be acquired.
591 return self.__exc is None
593 return len(self.__shr) == 0 and self.__exc is None
595 def __find_first_pending_queue(self):
596 """Tries to find the topmost queued entry with pending acquires.
598 Removes empty entries while going through the list.
601 while self.__pending:
602 (priority, prioqueue) = self.__pending[0]
605 return (priority, prioqueue)
608 heapq.heappop(self.__pending)
609 del self.__pending_by_prio[priority]
610 assert priority not in self.__pending_shared
614 def __is_on_top(self, cond):
615 """Checks whether the passed condition is on top of the queue.
617 The caller must make sure the queue isn't empty.
620 (_, prioqueue) = self.__find_first_pending_queue()
622 return cond == prioqueue[0]
624 def __acquire_unlocked(self, shared, timeout, priority):
625 """Acquire a shared lock.
627 @param shared: whether to acquire in shared mode; by default an
628 exclusive lock will be acquired
629 @param timeout: maximum waiting time before giving up
630 @type priority: integer
631 @param priority: Priority for acquiring lock
634 self.__check_deleted()
636 # We cannot acquire the lock if we already have it
637 assert not self.__is_owned(), ("double acquire() on a non-recursive lock"
640 # Remove empty entries from queue
641 self.__find_first_pending_queue()
643 # Check whether someone else holds the lock or there are pending acquires.
644 if not self.__pending and self.__can_acquire(shared):
645 # Apparently not, can acquire lock directly.
646 self.__do_acquire(shared)
649 prioqueue = self.__pending_by_prio.get(priority, None)
652 # Try to re-use condition for shared acquire
653 wait_condition = self.__pending_shared.get(priority, None)
654 assert (wait_condition is None or
655 (wait_condition.shared and wait_condition in prioqueue))
657 wait_condition = None
659 if wait_condition is None:
660 if prioqueue is None:
661 assert priority not in self.__pending_by_prio
664 heapq.heappush(self.__pending, (priority, prioqueue))
665 self.__pending_by_prio[priority] = prioqueue
667 wait_condition = self.__condition_class(self.__lock, shared)
668 prioqueue.append(wait_condition)
671 # Keep reference for further shared acquires on same priority. This is
672 # better than trying to find it in the list of pending acquires.
673 assert priority not in self.__pending_shared
674 self.__pending_shared[priority] = wait_condition
677 # Wait until we become the topmost acquire in the queue or the timeout
679 # TODO: Decrease timeout with spurious notifications
680 while not (self.__is_on_top(wait_condition) and
681 self.__can_acquire(shared)):
682 # Wait for notification
683 wait_condition.wait(timeout)
684 self.__check_deleted()
686 # A lot of code assumes blocking acquires always succeed. Loop
687 # internally for that case.
688 if timeout is not None:
691 if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
692 self.__do_acquire(shared)
695 # Remove condition from queue if there are no more waiters
696 if not wait_condition.has_waiting():
697 prioqueue.remove(wait_condition)
698 if wait_condition.shared:
699 # Remove from list of shared acquires if it wasn't while releasing
700 # (e.g. on lock deletion)
701 self.__pending_shared.pop(priority, None)
705 def acquire(self, shared=0, timeout=None, priority=None,
707 """Acquire a shared lock.
709 @type shared: integer (0/1) used as a boolean
710 @param shared: whether to acquire in shared mode; by default an
711 exclusive lock will be acquired
713 @param timeout: maximum waiting time before giving up
714 @type priority: integer
715 @param priority: Priority for acquiring lock
716 @type test_notify: callable or None
717 @param test_notify: Special callback function for unittesting
721 priority = _DEFAULT_PRIORITY
723 self.__lock.acquire()
725 # We already got the lock, notify now
726 if __debug__ and callable(test_notify):
729 return self.__acquire_unlocked(shared, timeout, priority)
731 self.__lock.release()
734 """Changes the lock mode from exclusive to shared.
736 Pending acquires in shared mode on the same priority will go ahead.
739 self.__lock.acquire()
741 assert self.__is_owned(), "Lock must be owned"
743 if self.__is_exclusive():
744 # Do nothing if the lock is already acquired in shared mode
748 # Important: pending shared acquires should only jump ahead if there
749 # was a transition from exclusive to shared, otherwise an owner of a
750 # shared lock can keep calling this function to push incoming shared
752 (priority, prioqueue) = self.__find_first_pending_queue()
754 # Is there a pending shared acquire on this priority?
755 cond = self.__pending_shared.pop(priority, None)
758 assert cond in prioqueue
760 # Ensure shared acquire is on top of queue
761 if len(prioqueue) > 1:
762 prioqueue.remove(cond)
763 prioqueue.insert(0, cond)
768 assert not self.__is_exclusive()
769 assert self.__is_sharer()
773 self.__lock.release()
776 """Release a Shared Lock.
778 You must have acquired the lock, either in shared or in exclusive mode,
779 before calling this function.
782 self.__lock.acquire()
784 assert self.__is_exclusive() or self.__is_sharer(), \
785 "Cannot release non-owned lock"
787 # Autodetect release type
788 if self.__is_exclusive():
791 self.__shr.remove(threading.currentThread())
793 # Notify topmost condition in queue
794 (priority, prioqueue) = self.__find_first_pending_queue()
799 # Prevent further shared acquires from sneaking in while waiters are
801 self.__pending_shared.pop(priority, None)
804 self.__lock.release()
806 def delete(self, timeout=None, priority=None):
807 """Delete a Shared Lock.
809 This operation will declare the lock for removal. First the lock will be
810 acquired in exclusive mode if you don't already own it, then the lock
811 will be put in a state where any future and pending acquire() fail.
814 @param timeout: maximum waiting time before giving up
815 @type priority: integer
816 @param priority: Priority for acquiring lock
820 priority = _DEFAULT_PRIORITY
822 self.__lock.acquire()
824 assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"
826 self.__check_deleted()
828 # The caller is allowed to hold the lock exclusively already.
829 acquired = self.__is_exclusive()
832 acquired = self.__acquire_unlocked(0, timeout, priority)
834 assert self.__is_exclusive() and not self.__is_sharer(), \
835 "Lock wasn't acquired in exclusive mode"
838 self.__deleted = True
841 assert not (self.__exc or self.__shr), "Found owner during deletion"
843 # Notify all acquires. They'll throw an error.
844 for (_, prioqueue) in self.__pending:
845 for cond in prioqueue:
848 assert self.__deleted
852 self.__lock.release()
854 def _release_save(self):
855 shared = self.__is_sharer()
859 def _acquire_restore(self, shared):
860 self.acquire(shared=shared)
863 # Whenever we want to acquire a full LockSet we pass None as the value
864 # to acquire. Hide this behind this nicely named constant.
868 class _AcquireTimeout(Exception):
869 """Internal exception to abort an acquire on a timeout.
875 """Implements a set of locks.
877 This abstraction implements a set of shared locks for the same resource type,
878 distinguished by name. The user can lock a subset of the resources and the
879 LockSet will take care of acquiring the locks always in the same order, thus
882 All the locks needed in the same set must be acquired together, though.
885 @ivar name: the name of the lockset
888 def __init__(self, members, name, monitor=None):
889 """Constructs a new LockSet.
891 @type members: list of strings
892 @param members: initial members of the set
893 @type monitor: L{LockMonitor}
894 @param monitor: Lock monitor with which to register member locks
897 assert members is not None, "members parameter is not a list"
901 self.__monitor = monitor
903 # Used internally to guarantee coherency
904 self.__lock = SharedLock(self._GetLockName("[lockset]"), monitor=monitor)
906 # The lockdict indexes the relationship name -> lock
907 # The order-of-locking is implied by the alphabetical order of names
910 for mname in members:
911 self.__lockdict[mname] = SharedLock(self._GetLockName(mname),
914 # The owner dict contains the set of locks each thread owns. For
915 # performance each thread can access its own key without a global lock on
916 # this structure. It is paramount though that *no* other type of access is
917 # done to this structure (eg. no looping over its keys). *_owner helper
918 # function are defined to guarantee access is correct, but in general never
919 # do anything different than __owners[threading.currentThread()], or there
923 def _GetLockName(self, mname):
924 """Returns the name for a member lock.
927 return "%s/%s" % (self.name, mname)
930 """Returns the lockset-internal lock.
935 def _get_lockdict(self):
936 """Returns the lockset-internal lock dictionary.
938 Accessing this structure is only safe in single-thread usage or when the
939 lockset-internal lock is held.
942 return self.__lockdict
945 """Is the current thread a current level owner?"""
946 return threading.currentThread() in self.__owners
948 def _add_owned(self, name=None):
949 """Note the current thread owns the given lock"""
951 if not self._is_owned():
952 self.__owners[threading.currentThread()] = set()
955 self.__owners[threading.currentThread()].add(name)
957 self.__owners[threading.currentThread()] = set([name])
959 def _del_owned(self, name=None):
960 """Note the current thread owns the given lock"""
962 assert not (name is None and self.__lock._is_owned()), \
963 "Cannot hold internal lock when deleting owner status"
966 self.__owners[threading.currentThread()].remove(name)
968 # Only remove the key if we don't hold the set-lock as well
969 if (not self.__lock._is_owned() and
970 not self.__owners[threading.currentThread()]):
971 del self.__owners[threading.currentThread()]
973 def _list_owned(self):
974 """Get the set of resource names owned by the current thread"""
976 return self.__owners[threading.currentThread()].copy()
980 def _release_and_delete_owned(self):
981 """Release and delete all resources owned by the current thread"""
982 for lname in self._list_owned():
983 lock = self.__lockdict[lname]
986 self._del_owned(name=lname)
989 """Return the current set of names.
991 Only call this function while holding __lock and don't iterate on the
992 result after releasing the lock.
995 return self.__lockdict.keys()
998 """Return a copy of the current set of elements.
1000 Used only for debugging purposes.
1003 # If we don't already own the set-level lock acquired
1004 # we'll get it and note we need to release it later.
1005 release_lock = False
1006 if not self.__lock._is_owned():
1008 self.__lock.acquire(shared=1)
1010 result = self.__names()
1013 self.__lock.release()
1016 def acquire(self, names, timeout=None, shared=0, priority=None,
1018 """Acquire a set of resource locks.
1020 @type names: list of strings (or string)
1021 @param names: the names of the locks which shall be acquired
1022 (special lock names, or instance/node names)
1023 @type shared: integer (0/1) used as a boolean
1024 @param shared: whether to acquire in shared mode; by default an
1025 exclusive lock will be acquired
1026 @type timeout: float or None
1027 @param timeout: Maximum time to acquire all locks
1028 @type priority: integer
1029 @param priority: Priority for acquiring locks
1030 @type test_notify: callable or None
1031 @param test_notify: Special callback function for unittesting
1033 @return: Set of all locks successfully acquired or None in case of timeout
1035 @raise errors.LockError: when any lock we try to acquire has
1036 been deleted before we succeed. In this case none of the
1037 locks requested will be acquired.
1040 assert timeout is None or timeout >= 0.0
1042 # Check we don't already own locks at this level
1043 assert not self._is_owned(), ("Cannot acquire locks in the same set twice"
1044 " (lockset %s)" % self.name)
1046 if priority is None:
1047 priority = _DEFAULT_PRIORITY
1049 # We need to keep track of how long we spent waiting for a lock. The
1050 # timeout passed to this function is over all lock acquires.
1051 running_timeout = utils.RunningTimeout(timeout, False)
1054 if names is not None:
1055 # Support passing in a single resource to acquire rather than many
1056 if isinstance(names, basestring):
1059 return self.__acquire_inner(names, False, shared, priority,
1060 running_timeout.Remaining, test_notify)
1063 # If no names are given acquire the whole set by not letting new names
1064 # being added before we release, and getting the current list of names.
1065 # Some of them may then be deleted later, but we'll cope with this.
1067 # We'd like to acquire this lock in a shared way, as it's nice if
1068 # everybody else can use the instances at the same time. If we are
1069 # acquiring them exclusively though they won't be able to do this
1070 # anyway, though, so we'll get the list lock exclusively as well in
1071 # order to be able to do add() on the set while owning it.
1072 if not self.__lock.acquire(shared=shared, priority=priority,
1073 timeout=running_timeout.Remaining()):
1074 raise _AcquireTimeout()
1076 # note we own the set-lock
1079 return self.__acquire_inner(self.__names(), True, shared, priority,
1080 running_timeout.Remaining, test_notify)
1082 # We shouldn't have problems adding the lock to the owners list, but
1083 # if we did we'll try to release this lock and re-raise exception.
1084 # Of course something is going to be really wrong, after this.
1085 self.__lock.release()
1089 except _AcquireTimeout:
1092 def __acquire_inner(self, names, want_all, shared, priority,
1093 timeout_fn, test_notify):
1094 """Inner logic for acquiring a number of locks.
1096 @param names: Names of the locks to be acquired
1097 @param want_all: Whether all locks in the set should be acquired
1098 @param shared: Whether to acquire in shared mode
1099 @param timeout_fn: Function returning remaining timeout
1100 @param priority: Priority for acquiring locks
1101 @param test_notify: Special callback function for unittesting
1106 # First we look the locks up on __lockdict. We have no way of being sure
1107 # they will still be there after, but this makes it a lot faster should
1108 # just one of them be the already wrong. Using a sorted sequence to prevent
1110 for lname in sorted(utils.UniqueSequence(names)):
1112 lock = self.__lockdict[lname] # raises KeyError if lock is not there
1115 # We are acquiring all the set, it doesn't matter if this particular
1116 # element is not there anymore.
1119 raise errors.LockError("Non-existing lock %s in set %s (it may have"
1120 " been removed)" % (lname, self.name))
1122 acquire_list.append((lname, lock))
1124 # This will hold the locknames we effectively acquired.
1128 # Now acquire_list contains a sorted list of resources and locks we
1129 # want. In order to get them we loop on this (private) list and
1130 # acquire() them. We gave no real guarantee they will still exist till
1131 # this is done but .acquire() itself is safe and will alert us if the
1132 # lock gets deleted.
1133 for (lname, lock) in acquire_list:
1134 if __debug__ and callable(test_notify):
1135 test_notify_fn = lambda: test_notify(lname)
1137 test_notify_fn = None
1139 timeout = timeout_fn()
1142 # raises LockError if the lock was deleted
1143 acq_success = lock.acquire(shared=shared, timeout=timeout,
1145 test_notify=test_notify_fn)
1146 except errors.LockError:
1148 # We are acquiring all the set, it doesn't matter if this
1149 # particular element is not there anymore.
1152 raise errors.LockError("Non-existing lock %s in set %s (it may"
1153 " have been removed)" % (lname, self.name))
1156 # Couldn't get lock or timeout occurred
1158 # This shouldn't happen as SharedLock.acquire(timeout=None) is
1160 raise errors.LockError("Failed to get lock %s (set %s)" %
1163 raise _AcquireTimeout()
1166 # now the lock cannot be deleted, we have it!
1167 self._add_owned(name=lname)
1171 # We shouldn't have problems adding the lock to the owners list, but
1172 # if we did we'll try to release this lock and re-raise exception.
1173 # Of course something is going to be really wrong after this.
1174 if lock._is_owned():
1179 # Release all owned locks
1180 self._release_and_delete_owned()
1185 def downgrade(self, names=None):
1186 """Downgrade a set of resource locks from exclusive to shared mode.
1188 The locks must have been acquired in exclusive mode.
1191 assert self._is_owned(), ("downgrade on lockset %s while not owning any"
1192 " lock" % self.name)
1194 # Support passing in a single resource to downgrade rather than many
1195 if isinstance(names, basestring):
1198 owned = self._list_owned()
1204 assert owned.issuperset(names), \
1205 ("downgrade() on unheld resources %s (set %s)" %
1206 (names.difference(owned), self.name))
1208 for lockname in names:
1209 self.__lockdict[lockname].downgrade()
1211 # Do we own the lockset in exclusive mode?
1212 if self.__lock._is_owned(shared=0):
1213 # Have all locks been downgraded?
1214 if not compat.any(lock._is_owned(shared=0)
1215 for lock in self.__lockdict.values()):
1216 self.__lock.downgrade()
1217 assert self.__lock._is_owned(shared=1)
1221 def release(self, names=None):
1222 """Release a set of resource locks, at the same level.
1224 You must have acquired the locks, either in shared or in exclusive mode,
1225 before releasing them.
1227 @type names: list of strings, or None
1228 @param names: the names of the locks which shall be released
1229 (defaults to all the locks acquired at that level).
1232 assert self._is_owned(), ("release() on lock set %s while not owner" %
1235 # Support passing in a single resource to release rather than many
1236 if isinstance(names, basestring):
1240 names = self._list_owned()
1243 assert self._list_owned().issuperset(names), (
1244 "release() on unheld resources %s (set %s)" %
1245 (names.difference(self._list_owned()), self.name))
1247 # First of all let's release the "all elements" lock, if set.
1248 # After this 'add' can work again
1249 if self.__lock._is_owned():
1250 self.__lock.release()
1253 for lockname in names:
1254 # If we are sure the lock doesn't leave __lockdict without being
1255 # exclusively held we can do this...
1256 self.__lockdict[lockname].release()
1257 self._del_owned(name=lockname)
1259 def add(self, names, acquired=0, shared=0):
1260 """Add a new set of elements to the set
1262 @type names: list of strings
1263 @param names: names of the new elements to add
1264 @type acquired: integer (0/1) used as a boolean
1265 @param acquired: pre-acquire the new resource?
1266 @type shared: integer (0/1) used as a boolean
1267 @param shared: is the pre-acquisition shared?
1270 # Check we don't already own locks at this level
1271 assert not self._is_owned() or self.__lock._is_owned(shared=0), \
1272 ("Cannot add locks if the set %s is only partially owned, or shared" %
1275 # Support passing in a single resource to add rather than many
1276 if isinstance(names, basestring):
1279 # If we don't already own the set-level lock acquired in an exclusive way
1280 # we'll get it and note we need to release it later.
1281 release_lock = False
1282 if not self.__lock._is_owned():
1284 self.__lock.acquire()
1287 invalid_names = set(self.__names()).intersection(names)
1289 # This must be an explicit raise, not an assert, because assert is
1290 # turned off when using optimization, and this can happen because of
1291 # concurrency even if the user doesn't want it.
1292 raise errors.LockError("duplicate add(%s) on lockset %s" %
1293 (invalid_names, self.name))
1295 for lockname in names:
1296 lock = SharedLock(self._GetLockName(lockname), monitor=self.__monitor)
1299 # No need for priority or timeout here as this lock has just been
1301 lock.acquire(shared=shared)
1302 # now the lock cannot be deleted, we have it!
1304 self._add_owned(name=lockname)
1306 # We shouldn't have problems adding the lock to the owners list,
1307 # but if we did we'll try to release this lock and re-raise
1308 # exception. Of course something is going to be really wrong,
1309 # after this. On the other hand the lock hasn't been added to the
1310 # __lockdict yet so no other threads should be pending on it. This
1311 # release is just a safety measure.
1315 self.__lockdict[lockname] = lock
1318 # Only release __lock if we were not holding it previously.
1320 self.__lock.release()
1324 def remove(self, names):
1325 """Remove elements from the lock set.
1327 You can either not hold anything in the lockset or already hold a superset
1328 of the elements you want to delete, exclusively.
1330 @type names: list of strings
1331 @param names: names of the resource to remove.
1333 @return: a list of locks which we removed; the list is always
1334 equal to the names list if we were holding all the locks
1338 # Support passing in a single resource to remove rather than many
1339 if isinstance(names, basestring):
1342 # If we own any subset of this lock it must be a superset of what we want
1343 # to delete. The ownership must also be exclusive, but that will be checked
1344 # by the lock itself.
1345 assert not self._is_owned() or self._list_owned().issuperset(names), (
1346 "remove() on acquired lockset %s while not owning all elements" %
1352 # Calling delete() acquires the lock exclusively if we don't already own
1353 # it, and causes all pending and subsequent lock acquires to fail. It's
1354 # fine to call it out of order because delete() also implies release(),
1355 # and the assertion above guarantees that if we either already hold
1356 # everything we want to delete, or we hold none.
1358 self.__lockdict[lname].delete()
1359 removed.append(lname)
1360 except (KeyError, errors.LockError):
1361 # This cannot happen if we were already holding it, verify:
1362 assert not self._is_owned(), ("remove failed while holding lockset %s"
1365 # If no LockError was raised we are the ones who deleted the lock.
1366 # This means we can safely remove it from lockdict, as any further or
1367 # pending delete() or acquire() will fail (and nobody can have the lock
1368 # since before our call to delete()).
1370 # This is done in an else clause because if the exception was thrown
1371 # it's the job of the one who actually deleted it.
1372 del self.__lockdict[lname]
1373 # And let's remove it from our private list if we owned it.
1374 if self._is_owned():
1375 self._del_owned(name=lname)
1380 # Locking levels, must be acquired in increasing order.
1381 # Current rules are:
1382 # - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
1383 # acquired before performing any operation, either in shared or in exclusive
1384 # mode. acquiring the BGL in exclusive mode is discouraged and should be
1386 # - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
1387 # If you need more than one node, or more than one instance, acquire them at
1394 LEVELS = [LEVEL_CLUSTER,
1399 # Lock levels which are modifiable
1400 LEVELS_MOD = [LEVEL_NODE, LEVEL_NODEGROUP, LEVEL_INSTANCE]
1403 LEVEL_CLUSTER: "cluster",
1404 LEVEL_INSTANCE: "instance",
1405 LEVEL_NODEGROUP: "nodegroup",
1409 # Constant for the big ganeti lock
1413 class GanetiLockManager:
1414 """The Ganeti Locking Library
1416 The purpose of this small library is to manage locking for ganeti clusters
1417 in a central place, while at the same time doing dynamic checks against
1418 possible deadlocks. It will also make it easier to transition to a different
1419 lock type should we migrate away from python threads.
1424 def __init__(self, nodes, nodegroups, instances):
1425 """Constructs a new GanetiLockManager object.
1427 There should be only a GanetiLockManager object at any time, so this
1428 function raises an error if this is not the case.
1430 @param nodes: list of node names
1431 @param nodegroups: list of nodegroup uuids
1432 @param instances: list of instance names
1435 assert self.__class__._instance is None, \
1436 "double GanetiLockManager instance"
1438 self.__class__._instance = self
1440 self._monitor = LockMonitor()
1442 # The keyring contains all the locks, at their level and in the correct
1445 LEVEL_CLUSTER: LockSet([BGL], "BGL", monitor=self._monitor),
1446 LEVEL_NODE: LockSet(nodes, "nodes", monitor=self._monitor),
1447 LEVEL_NODEGROUP: LockSet(nodegroups, "nodegroups", monitor=self._monitor),
1448 LEVEL_INSTANCE: LockSet(instances, "instances",
1449 monitor=self._monitor),
1452 def AddToLockMonitor(self, provider):
1453 """Registers a new lock with the monitor.
1455 See L{LockMonitor.RegisterLock}.
1458 return self._monitor.RegisterLock(provider)
1460 def QueryLocks(self, fields):
1461 """Queries information from all locks.
1463 See L{LockMonitor.QueryLocks}.
1466 return self._monitor.QueryLocks(fields)
1468 def OldStyleQueryLocks(self, fields):
1469 """Queries information from all locks, returning old-style data.
1471 See L{LockMonitor.OldStyleQueryLocks}.
1474 return self._monitor.OldStyleQueryLocks(fields)
1476 def _names(self, level):
1477 """List the lock names at the given level.
1479 This can be used for debugging/testing purposes.
1481 @param level: the level whose list of locks to get
1484 assert level in LEVELS, "Invalid locking level %s" % level
1485 return self.__keyring[level]._names()
1487 def _is_owned(self, level):
1488 """Check whether we are owning locks at the given level
1491 return self.__keyring[level]._is_owned()
1493 is_owned = _is_owned
1495 def _list_owned(self, level):
1496 """Get the set of owned locks at the given level
1499 return self.__keyring[level]._list_owned()
1501 list_owned = _list_owned
1503 def _upper_owned(self, level):
1504 """Check that we don't own any lock at a level greater than the given one.
1507 # This way of checking only works if LEVELS[i] = i, which we check for in
1509 return compat.any((self._is_owned(l) for l in LEVELS[level + 1:]))
1511 def _BGL_owned(self): # pylint: disable-msg=C0103
1512 """Check if the current thread owns the BGL.
1514 Both an exclusive or a shared acquisition work.
1517 return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned()
1520 def _contains_BGL(level, names): # pylint: disable-msg=C0103
1521 """Check if the level contains the BGL.
1523 Check if acting on the given level and set of names will change
1524 the status of the Big Ganeti Lock.
1527 return level == LEVEL_CLUSTER and (names is None or BGL in names)
1529 def acquire(self, level, names, timeout=None, shared=0, priority=None):
1530 """Acquire a set of resource locks, at the same level.
1532 @type level: member of locking.LEVELS
1533 @param level: the level at which the locks shall be acquired
1534 @type names: list of strings (or string)
1535 @param names: the names of the locks which shall be acquired
1536 (special lock names, or instance/node names)
1537 @type shared: integer (0/1) used as a boolean
1538 @param shared: whether to acquire in shared mode; by default
1539 an exclusive lock will be acquired
1540 @type timeout: float
1541 @param timeout: Maximum time to acquire all locks
1542 @type priority: integer
1543 @param priority: Priority for acquiring lock
1546 assert level in LEVELS, "Invalid locking level %s" % level
1548 # Check that we are either acquiring the Big Ganeti Lock or we already own
1549 # it. Some "legacy" opcodes need to be sure they are run non-concurrently
1550 # so even if we've migrated we need to at least share the BGL to be
1551 # compatible with them. Of course if we own the BGL exclusively there's no
1552 # point in acquiring any other lock, unless perhaps we are half way through
1553 # the migration of the current opcode.
1554 assert (self._contains_BGL(level, names) or self._BGL_owned()), (
1555 "You must own the Big Ganeti Lock before acquiring any other")
1557 # Check we don't own locks at the same or upper levels.
1558 assert not self._upper_owned(level), ("Cannot acquire locks at a level"
1559 " while owning some at a greater one")
1561 # Acquire the locks in the set.
1562 return self.__keyring[level].acquire(names, shared=shared, timeout=timeout,
1565 def downgrade(self, level, names=None):
1566 """Downgrade a set of resource locks from exclusive to shared mode.
1568 You must have acquired the locks in exclusive mode.
1570 @type level: member of locking.LEVELS
1571 @param level: the level at which the locks shall be downgraded
1572 @type names: list of strings, or None
1573 @param names: the names of the locks which shall be downgraded
1574 (defaults to all the locks acquired at the level)
1577 assert level in LEVELS, "Invalid locking level %s" % level
1579 return self.__keyring[level].downgrade(names=names)
1581 def release(self, level, names=None):
1582 """Release a set of resource locks, at the same level.
1584 You must have acquired the locks, either in shared or in exclusive
1585 mode, before releasing them.
1587 @type level: member of locking.LEVELS
1588 @param level: the level at which the locks shall be released
1589 @type names: list of strings, or None
1590 @param names: the names of the locks which shall be released
1591 (defaults to all the locks acquired at that level)
1594 assert level in LEVELS, "Invalid locking level %s" % level
1595 assert (not self._contains_BGL(level, names) or
1596 not self._upper_owned(LEVEL_CLUSTER)), (
1597 "Cannot release the Big Ganeti Lock while holding something"
1598 " at upper levels (%r)" %
1599 (utils.CommaJoin(["%s=%r" % (LEVEL_NAMES[i], self._list_owned(i))
1600 for i in self.__keyring.keys()]), ))
1602 # Release will complain if we don't own the locks already
1603 return self.__keyring[level].release(names)
1605 def add(self, level, names, acquired=0, shared=0):
1606 """Add locks at the specified level.
1608 @type level: member of locking.LEVELS_MOD
1609 @param level: the level at which the locks shall be added
1610 @type names: list of strings
1611 @param names: names of the locks to acquire
1612 @type acquired: integer (0/1) used as a boolean
1613 @param acquired: whether to acquire the newly added locks
1614 @type shared: integer (0/1) used as a boolean
1615 @param shared: whether the acquisition will be shared
1618 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1619 assert self._BGL_owned(), ("You must own the BGL before performing other"
1621 assert not self._upper_owned(level), ("Cannot add locks at a level"
1622 " while owning some at a greater one")
1623 return self.__keyring[level].add(names, acquired=acquired, shared=shared)
1625 def remove(self, level, names):
1626 """Remove locks from the specified level.
1628 You must either already own the locks you are trying to remove
1629 exclusively or not own any lock at an upper level.
1631 @type level: member of locking.LEVELS_MOD
1632 @param level: the level at which the locks shall be removed
1633 @type names: list of strings
1634 @param names: the names of the locks which shall be removed
1635 (special lock names, or instance/node names)
1638 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1639 assert self._BGL_owned(), ("You must own the BGL before performing other"
1641 # Check we either own the level or don't own anything from here
1642 # up. LockSet.remove() will check the case in which we don't own
1643 # all the needed resources, or we have a shared ownership.
1644 assert self._is_owned(level) or not self._upper_owned(level), (
1645 "Cannot remove locks at a level while not owning it or"
1646 " owning some at a greater one")
1647 return self.__keyring[level].remove(names)
1650 def _MonitorSortKey((item, idx, num)):
1651 """Sorting key function.
1653 Sort by name, registration order and then order of information. This provides
1654 a stable sort order over different providers, even if they return the same
1658 (name, _, _, _) = item
1660 return (utils.NiceSortKey(name), num, idx)
1663 class LockMonitor(object):
1664 _LOCK_ATTR = "_lock"
1667 """Initializes this class.
1670 self._lock = SharedLock("LockMonitor")
1672 # Counter for stable sorting
1673 self._counter = itertools.count(0)
1675 # Tracked locks. Weak references are used to avoid issues with circular
1676 # references and deletion.
1677 self._locks = weakref.WeakKeyDictionary()
1679 @ssynchronized(_LOCK_ATTR)
1680 def RegisterLock(self, provider):
1681 """Registers a new lock.
1683 @param provider: Object with a callable method named C{GetLockInfo}, taking
1684 a single C{set} containing the requested information items
1685 @note: It would be nicer to only receive the function generating the
1686 requested information but, as it turns out, weak references to bound
1687 methods (e.g. C{self.GetLockInfo}) are tricky; there are several
1688 workarounds, but none of the ones I found works properly in combination
1689 with a standard C{WeakKeyDictionary}
1692 assert provider not in self._locks, "Duplicate registration"
1694 # There used to be a check for duplicate names here. As it turned out, when
1695 # a lock is re-created with the same name in a very short timeframe, the
1696 # previous instance might not yet be removed from the weakref dictionary.
1697 # By keeping track of the order of incoming registrations, a stable sort
1698 # ordering can still be guaranteed.
1700 self._locks[provider] = self._counter.next()
1702 def _GetLockInfo(self, requested):
1703 """Get information from all locks.
1706 # Must hold lock while getting consistent list of tracked items
1707 self._lock.acquire(shared=1)
1709 items = self._locks.items()
1711 self._lock.release()
1713 return [(info, idx, num)
1714 for (provider, num) in items
1715 for (idx, info) in enumerate(provider.GetLockInfo(requested))]
1717 def _Query(self, fields):
1718 """Queries information from all locks.
1720 @type fields: list of strings
1721 @param fields: List of fields to return
1724 qobj = query.Query(query.LOCK_FIELDS, fields)
1726 # Get all data with internal lock held and then sort by name and incoming
1728 lockinfo = sorted(self._GetLockInfo(qobj.RequestedData()),
1729 key=_MonitorSortKey)
1731 # Extract lock information and build query data
1732 return (qobj, query.LockQueryData(map(operator.itemgetter(0), lockinfo)))
1734 def QueryLocks(self, fields):
1735 """Queries information from all locks.
1737 @type fields: list of strings
1738 @param fields: List of fields to return
1741 (qobj, ctx) = self._Query(fields)
1743 # Prepare query response
1744 return query.GetQueryResponse(qobj, ctx)
1746 def OldStyleQueryLocks(self, fields):
1747 """Queries information from all locks, returning old-style data.
1749 @type fields: list of strings
1750 @param fields: List of fields to return
1753 (qobj, ctx) = self._Query(fields)
1755 return qobj.OldStyleQuery(ctx)