4 # Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 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=W0212
25 # W0212 since e.g. LockSet methods use (a lot) the internals of
37 from ganeti import errors
38 from ganeti import utils
39 from ganeti import compat
40 from ganeti import query
43 _EXCLUSIVE_TEXT = "exclusive"
44 _SHARED_TEXT = "shared"
45 _DELETED_TEXT = "deleted"
50 def ssynchronized(mylock, shared=0):
51 """Shared Synchronization decorator.
53 Calls the function holding the given lock, either in exclusive or shared
54 mode. It requires the passed lock to be a SharedLock (or support its
57 @type mylock: lockable object or string
58 @param mylock: lock to acquire or class member name of the lock to acquire
62 def sync_function(*args, **kwargs):
63 if isinstance(mylock, basestring):
64 assert args, "cannot ssynchronize on non-class method: self not found"
66 lock = getattr(args[0], mylock)
69 lock.acquire(shared=shared)
71 return fn(*args, **kwargs)
78 class _SingleNotifyPipeConditionWaiter(object):
79 """Helper class for SingleNotifyPipeCondition
87 def __init__(self, poller, fd):
88 """Constructor for _SingleNotifyPipeConditionWaiter
90 @type poller: select.poll
91 @param poller: Poller object
93 @param fd: File descriptor to wait for
100 def __call__(self, timeout):
101 """Wait for something to happen on the pipe.
103 @type timeout: float or None
104 @param timeout: Timeout for waiting (can be None)
107 running_timeout = utils.RunningTimeout(timeout, True)
110 remaining_time = running_timeout.Remaining()
112 if remaining_time is not None:
113 if remaining_time < 0.0:
116 # Our calculation uses seconds, poll() wants milliseconds
117 remaining_time *= 1000
120 result = self._poller.poll(remaining_time)
121 except EnvironmentError, err:
122 if err.errno != errno.EINTR:
126 # Check whether we were notified
127 if result and result[0][0] == self._fd:
131 class _BaseCondition(object):
132 """Base class containing common code for conditions.
134 Some of this code is taken from python's threading module.
146 def __init__(self, lock):
147 """Constructor for _BaseCondition.
149 @type lock: threading.Lock
150 @param lock: condition base lock
153 object.__init__(self)
156 self._release_save = lock._release_save
157 except AttributeError:
158 self._release_save = self._base_release_save
160 self._acquire_restore = lock._acquire_restore
161 except AttributeError:
162 self._acquire_restore = self._base_acquire_restore
164 self._is_owned = lock.is_owned
165 except AttributeError:
166 self._is_owned = self._base_is_owned
170 # Export the lock's acquire() and release() methods
171 self.acquire = lock.acquire
172 self.release = lock.release
174 def _base_is_owned(self):
175 """Check whether lock is owned by current thread.
178 if self._lock.acquire(0):
183 def _base_release_save(self):
186 def _base_acquire_restore(self, _):
189 def _check_owned(self):
190 """Raise an exception if the current thread doesn't own the lock.
193 if not self._is_owned():
194 raise RuntimeError("cannot work with un-aquired lock")
197 class SingleNotifyPipeCondition(_BaseCondition):
198 """Condition which can only be notified once.
200 This condition class uses pipes and poll, internally, to be able to wait for
201 notification with a timeout, without resorting to polling. It is almost
202 compatible with Python's threading.Condition, with the following differences:
203 - notifyAll can only be called once, and no wait can happen after that
204 - notify is not supported, only notifyAll
216 _waiter_class = _SingleNotifyPipeConditionWaiter
218 def __init__(self, lock):
219 """Constructor for SingleNotifyPipeCondition
222 _BaseCondition.__init__(self, lock)
224 self._notified = False
226 self._write_fd = None
229 def _check_unnotified(self):
230 """Throws an exception if already notified.
234 raise RuntimeError("cannot use already notified condition")
237 """Cleanup open file descriptors, if any.
240 if self._read_fd is not None:
241 os.close(self._read_fd)
244 if self._write_fd is not None:
245 os.close(self._write_fd)
246 self._write_fd = None
249 def wait(self, timeout):
250 """Wait for a notification.
252 @type timeout: float or None
253 @param timeout: Waiting timeout (can be None)
257 self._check_unnotified()
261 if self._poller is None:
262 (self._read_fd, self._write_fd) = os.pipe()
263 self._poller = select.poll()
264 self._poller.register(self._read_fd, select.POLLHUP)
266 wait_fn = self._waiter_class(self._poller, self._read_fd)
267 state = self._release_save()
269 # Wait for notification
273 self._acquire_restore(state)
276 if self._nwaiters == 0:
279 def notifyAll(self): # pylint: disable=C0103
280 """Close the writing side of the pipe to notify all waiters.
284 self._check_unnotified()
285 self._notified = True
286 if self._write_fd is not None:
287 os.close(self._write_fd)
288 self._write_fd = None
291 class PipeCondition(_BaseCondition):
292 """Group-only non-polling condition with counters.
294 This condition class uses pipes and poll, internally, to be able to wait for
295 notification with a timeout, without resorting to polling. It is almost
296 compatible with Python's threading.Condition, but only supports notifyAll and
297 non-recursive locks. As an additional features it's able to report whether
298 there are any waiting threads.
306 _single_condition_class = SingleNotifyPipeCondition
308 def __init__(self, lock):
309 """Initializes this class.
312 _BaseCondition.__init__(self, lock)
313 self._waiters = set()
314 self._single_condition = self._single_condition_class(self._lock)
316 def wait(self, timeout):
317 """Wait for a notification.
319 @type timeout: float or None
320 @param timeout: Waiting timeout (can be None)
325 # Keep local reference to the pipe. It could be replaced by another thread
326 # notifying while we're waiting.
327 cond = self._single_condition
329 self._waiters.add(threading.currentThread())
334 self._waiters.remove(threading.currentThread())
336 def notifyAll(self): # pylint: disable=C0103
337 """Notify all currently waiting threads.
341 self._single_condition.notifyAll()
342 self._single_condition = self._single_condition_class(self._lock)
344 def get_waiting(self):
345 """Returns a list of all waiting threads.
352 def has_waiting(self):
353 """Returns whether there are active waiters.
358 return bool(self._waiters)
361 class _PipeConditionWithMode(PipeCondition):
366 def __init__(self, lock, shared):
367 """Initializes this class.
371 PipeCondition.__init__(self, lock)
374 class SharedLock(object):
375 """Implements a shared lock.
377 Multiple threads can acquire the lock in a shared way by calling
378 C{acquire(shared=1)}. In order to acquire the lock in an exclusive way
379 threads can call C{acquire(shared=0)}.
381 Notes on data structures: C{__pending} contains a priority queue (heapq) of
382 all pending acquires: C{[(priority1: prioqueue1), (priority2: prioqueue2),
383 ...]}. Each per-priority queue contains a normal in-order list of conditions
384 to be notified when the lock can be acquired. Shared locks are grouped
385 together by priority and the condition for them is stored in
386 C{__pending_shared} if it already exists. C{__pending_by_prio} keeps
387 references for the per-priority queues indexed by priority for faster access.
390 @ivar name: the name of the lock
405 __condition_class = _PipeConditionWithMode
407 def __init__(self, name, monitor=None):
408 """Construct a new SharedLock.
410 @param name: the name of the lock
411 @type monitor: L{LockMonitor}
412 @param monitor: Lock monitor with which to register
415 object.__init__(self)
420 self.__lock = threading.Lock()
422 # Queue containing waiting acquires
424 self.__pending_by_prio = {}
425 self.__pending_shared = {}
427 # Current lock holders
431 # is this lock in the deleted state?
432 self.__deleted = False
434 # Register with lock monitor
436 logging.debug("Adding lock %s to monitor", name)
437 monitor.RegisterLock(self)
439 def GetLockInfo(self, requested):
440 """Retrieves information for querying locks.
443 @param requested: Requested information, see C{query.LQ_*}
446 self.__lock.acquire()
448 # Note: to avoid unintentional race conditions, no references to
449 # modifiable objects should be returned unless they were created in this
454 if query.LQ_MODE in requested:
457 assert not (self.__exc or self.__shr)
459 mode = _EXCLUSIVE_TEXT
463 # Current owner(s) are wanted
464 if query.LQ_OWNER in requested:
471 assert not self.__deleted
472 owner_names = [i.getName() for i in owner]
474 # Pending acquires are wanted
475 if query.LQ_PENDING in requested:
478 # Sorting instead of copying and using heaq functions for simplicity
479 for (_, prioqueue) in sorted(self.__pending):
480 for cond in prioqueue:
482 pendmode = _SHARED_TEXT
484 pendmode = _EXCLUSIVE_TEXT
486 # List of names will be sorted in L{query._GetLockPending}
487 pending.append((pendmode, [i.getName()
488 for i in cond.get_waiting()]))
492 return [(self.name, mode, owner_names, pending)]
494 self.__lock.release()
496 def __check_deleted(self):
497 """Raises an exception if the lock has been deleted.
501 raise errors.LockError("Deleted lock %s" % self.name)
503 def __is_sharer(self):
504 """Is the current thread sharing the lock at this time?
507 return threading.currentThread() in self.__shr
509 def __is_exclusive(self):
510 """Is the current thread holding the lock exclusively at this time?
513 return threading.currentThread() == self.__exc
515 def __is_owned(self, shared=-1):
516 """Is the current thread somehow owning the lock at this time?
518 This is a private version of the function, which presumes you're holding
523 return self.__is_sharer() or self.__is_exclusive()
525 return self.__is_sharer()
527 return self.__is_exclusive()
529 def is_owned(self, shared=-1):
530 """Is the current thread somehow owning the lock at this time?
533 - < 0: check for any type of ownership (default)
534 - 0: check for exclusive ownership
535 - > 0: check for shared ownership
538 self.__lock.acquire()
540 return self.__is_owned(shared=shared)
542 self.__lock.release()
544 #: Necessary to remain compatible with threading.Condition, which tries to
545 #: retrieve a locks' "_is_owned" attribute
548 def _count_pending(self):
549 """Returns the number of pending acquires.
554 self.__lock.acquire()
556 return sum(len(prioqueue) for (_, prioqueue) in self.__pending)
558 self.__lock.release()
560 def _check_empty(self):
561 """Checks whether there are any pending acquires.
566 self.__lock.acquire()
568 # Order is important: __find_first_pending_queue modifies __pending
569 (_, prioqueue) = self.__find_first_pending_queue()
571 return not (prioqueue or
573 self.__pending_by_prio or
574 self.__pending_shared)
576 self.__lock.release()
578 def __do_acquire(self, shared):
579 """Actually acquire the lock.
583 self.__shr.add(threading.currentThread())
585 self.__exc = threading.currentThread()
587 def __can_acquire(self, shared):
588 """Determine whether lock can be acquired.
592 return self.__exc is None
594 return len(self.__shr) == 0 and self.__exc is None
596 def __find_first_pending_queue(self):
597 """Tries to find the topmost queued entry with pending acquires.
599 Removes empty entries while going through the list.
602 while self.__pending:
603 (priority, prioqueue) = self.__pending[0]
606 return (priority, prioqueue)
609 heapq.heappop(self.__pending)
610 del self.__pending_by_prio[priority]
611 assert priority not in self.__pending_shared
615 def __is_on_top(self, cond):
616 """Checks whether the passed condition is on top of the queue.
618 The caller must make sure the queue isn't empty.
621 (_, prioqueue) = self.__find_first_pending_queue()
623 return cond == prioqueue[0]
625 def __acquire_unlocked(self, shared, timeout, priority):
626 """Acquire a shared lock.
628 @param shared: whether to acquire in shared mode; by default an
629 exclusive lock will be acquired
630 @param timeout: maximum waiting time before giving up
631 @type priority: integer
632 @param priority: Priority for acquiring lock
635 self.__check_deleted()
637 # We cannot acquire the lock if we already have it
638 assert not self.__is_owned(), ("double acquire() on a non-recursive lock"
641 # Remove empty entries from queue
642 self.__find_first_pending_queue()
644 # Check whether someone else holds the lock or there are pending acquires.
645 if not self.__pending and self.__can_acquire(shared):
646 # Apparently not, can acquire lock directly.
647 self.__do_acquire(shared)
650 prioqueue = self.__pending_by_prio.get(priority, None)
653 # Try to re-use condition for shared acquire
654 wait_condition = self.__pending_shared.get(priority, None)
655 assert (wait_condition is None or
656 (wait_condition.shared and wait_condition in prioqueue))
658 wait_condition = None
660 if wait_condition is None:
661 if prioqueue is None:
662 assert priority not in self.__pending_by_prio
665 heapq.heappush(self.__pending, (priority, prioqueue))
666 self.__pending_by_prio[priority] = prioqueue
668 wait_condition = self.__condition_class(self.__lock, shared)
669 prioqueue.append(wait_condition)
672 # Keep reference for further shared acquires on same priority. This is
673 # better than trying to find it in the list of pending acquires.
674 assert priority not in self.__pending_shared
675 self.__pending_shared[priority] = wait_condition
678 # Wait until we become the topmost acquire in the queue or the timeout
680 # TODO: Decrease timeout with spurious notifications
681 while not (self.__is_on_top(wait_condition) and
682 self.__can_acquire(shared)):
683 # Wait for notification
684 wait_condition.wait(timeout)
685 self.__check_deleted()
687 # A lot of code assumes blocking acquires always succeed. Loop
688 # internally for that case.
689 if timeout is not None:
692 if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
693 self.__do_acquire(shared)
696 # Remove condition from queue if there are no more waiters
697 if not wait_condition.has_waiting():
698 prioqueue.remove(wait_condition)
699 if wait_condition.shared:
700 # Remove from list of shared acquires if it wasn't while releasing
701 # (e.g. on lock deletion)
702 self.__pending_shared.pop(priority, None)
706 def acquire(self, shared=0, timeout=None, priority=None,
708 """Acquire a shared lock.
710 @type shared: integer (0/1) used as a boolean
711 @param shared: whether to acquire in shared mode; by default an
712 exclusive lock will be acquired
714 @param timeout: maximum waiting time before giving up
715 @type priority: integer
716 @param priority: Priority for acquiring lock
717 @type test_notify: callable or None
718 @param test_notify: Special callback function for unittesting
722 priority = _DEFAULT_PRIORITY
724 self.__lock.acquire()
726 # We already got the lock, notify now
727 if __debug__ and callable(test_notify):
730 return self.__acquire_unlocked(shared, timeout, priority)
732 self.__lock.release()
735 """Changes the lock mode from exclusive to shared.
737 Pending acquires in shared mode on the same priority will go ahead.
740 self.__lock.acquire()
742 assert self.__is_owned(), "Lock must be owned"
744 if self.__is_exclusive():
745 # Do nothing if the lock is already acquired in shared mode
749 # Important: pending shared acquires should only jump ahead if there
750 # was a transition from exclusive to shared, otherwise an owner of a
751 # shared lock can keep calling this function to push incoming shared
753 (priority, prioqueue) = self.__find_first_pending_queue()
755 # Is there a pending shared acquire on this priority?
756 cond = self.__pending_shared.pop(priority, None)
759 assert cond in prioqueue
761 # Ensure shared acquire is on top of queue
762 if len(prioqueue) > 1:
763 prioqueue.remove(cond)
764 prioqueue.insert(0, cond)
769 assert not self.__is_exclusive()
770 assert self.__is_sharer()
774 self.__lock.release()
777 """Release a Shared Lock.
779 You must have acquired the lock, either in shared or in exclusive mode,
780 before calling this function.
783 self.__lock.acquire()
785 assert self.__is_exclusive() or self.__is_sharer(), \
786 "Cannot release non-owned lock"
788 # Autodetect release type
789 if self.__is_exclusive():
792 self.__shr.remove(threading.currentThread())
794 # Notify topmost condition in queue
795 (priority, prioqueue) = self.__find_first_pending_queue()
800 # Prevent further shared acquires from sneaking in while waiters are
802 self.__pending_shared.pop(priority, None)
805 self.__lock.release()
807 def delete(self, timeout=None, priority=None):
808 """Delete a Shared Lock.
810 This operation will declare the lock for removal. First the lock will be
811 acquired in exclusive mode if you don't already own it, then the lock
812 will be put in a state where any future and pending acquire() fail.
815 @param timeout: maximum waiting time before giving up
816 @type priority: integer
817 @param priority: Priority for acquiring lock
821 priority = _DEFAULT_PRIORITY
823 self.__lock.acquire()
825 assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"
827 self.__check_deleted()
829 # The caller is allowed to hold the lock exclusively already.
830 acquired = self.__is_exclusive()
833 acquired = self.__acquire_unlocked(0, timeout, priority)
835 assert self.__is_exclusive() and not self.__is_sharer(), \
836 "Lock wasn't acquired in exclusive mode"
839 self.__deleted = True
842 assert not (self.__exc or self.__shr), "Found owner during deletion"
844 # Notify all acquires. They'll throw an error.
845 for (_, prioqueue) in self.__pending:
846 for cond in prioqueue:
849 assert self.__deleted
853 self.__lock.release()
855 def _release_save(self):
856 shared = self.__is_sharer()
860 def _acquire_restore(self, shared):
861 self.acquire(shared=shared)
864 # Whenever we want to acquire a full LockSet we pass None as the value
865 # to acquire. Hide this behind this nicely named constant.
869 class _AcquireTimeout(Exception):
870 """Internal exception to abort an acquire on a timeout.
876 """Implements a set of locks.
878 This abstraction implements a set of shared locks for the same resource type,
879 distinguished by name. The user can lock a subset of the resources and the
880 LockSet will take care of acquiring the locks always in the same order, thus
883 All the locks needed in the same set must be acquired together, though.
886 @ivar name: the name of the lockset
889 def __init__(self, members, name, monitor=None):
890 """Constructs a new LockSet.
892 @type members: list of strings
893 @param members: initial members of the set
894 @type monitor: L{LockMonitor}
895 @param monitor: Lock monitor with which to register member locks
898 assert members is not None, "members parameter is not a list"
902 self.__monitor = monitor
904 # Used internally to guarantee coherency
905 self.__lock = SharedLock(self._GetLockName("[lockset]"), monitor=monitor)
907 # The lockdict indexes the relationship name -> lock
908 # The order-of-locking is implied by the alphabetical order of names
911 for mname in members:
912 self.__lockdict[mname] = SharedLock(self._GetLockName(mname),
915 # The owner dict contains the set of locks each thread owns. For
916 # performance each thread can access its own key without a global lock on
917 # this structure. It is paramount though that *no* other type of access is
918 # done to this structure (eg. no looping over its keys). *_owner helper
919 # function are defined to guarantee access is correct, but in general never
920 # do anything different than __owners[threading.currentThread()], or there
924 def _GetLockName(self, mname):
925 """Returns the name for a member lock.
928 return "%s/%s" % (self.name, mname)
931 """Returns the lockset-internal lock.
936 def _get_lockdict(self):
937 """Returns the lockset-internal lock dictionary.
939 Accessing this structure is only safe in single-thread usage or when the
940 lockset-internal lock is held.
943 return self.__lockdict
946 """Is the current thread a current level owner?
948 @note: Use L{check_owned} to check if a specific lock is held
951 return threading.currentThread() in self.__owners
953 def check_owned(self, names, shared=-1):
954 """Check if locks are owned in a specific mode.
956 @type names: sequence or string
957 @param names: Lock names (or a single lock name)
958 @param shared: See L{SharedLock.is_owned}
960 @note: Use L{is_owned} to check if the current thread holds I{any} lock and
961 L{list_owned} to get the names of all owned locks
964 if isinstance(names, basestring):
967 # Avoid check if no locks are owned anyway
968 if names and self.is_owned():
971 # Gather references to all locks (in case they're deleted in the meantime)
974 lock = self.__lockdict[lname]
976 raise errors.LockError("Non-existing lock '%s' in set '%s' (it may"
977 " have been removed)" % (lname, self.name))
979 candidates.append(lock)
981 return compat.all(lock.is_owned(shared=shared) for lock in candidates)
985 def _add_owned(self, name=None):
986 """Note the current thread owns the given lock"""
988 if not self.is_owned():
989 self.__owners[threading.currentThread()] = set()
992 self.__owners[threading.currentThread()].add(name)
994 self.__owners[threading.currentThread()] = set([name])
996 def _del_owned(self, name=None):
997 """Note the current thread owns the given lock"""
999 assert not (name is None and self.__lock.is_owned()), \
1000 "Cannot hold internal lock when deleting owner status"
1002 if name is not None:
1003 self.__owners[threading.currentThread()].remove(name)
1005 # Only remove the key if we don't hold the set-lock as well
1006 if (not self.__lock.is_owned() and
1007 not self.__owners[threading.currentThread()]):
1008 del self.__owners[threading.currentThread()]
1010 def list_owned(self):
1011 """Get the set of resource names owned by the current thread"""
1013 return self.__owners[threading.currentThread()].copy()
1017 def _release_and_delete_owned(self):
1018 """Release and delete all resources owned by the current thread"""
1019 for lname in self.list_owned():
1020 lock = self.__lockdict[lname]
1023 self._del_owned(name=lname)
1026 """Return the current set of names.
1028 Only call this function while holding __lock and don't iterate on the
1029 result after releasing the lock.
1032 return self.__lockdict.keys()
1035 """Return a copy of the current set of elements.
1037 Used only for debugging purposes.
1040 # If we don't already own the set-level lock acquired
1041 # we'll get it and note we need to release it later.
1042 release_lock = False
1043 if not self.__lock.is_owned():
1045 self.__lock.acquire(shared=1)
1047 result = self.__names()
1050 self.__lock.release()
1053 def acquire(self, names, timeout=None, shared=0, priority=None,
1055 """Acquire a set of resource locks.
1057 @type names: list of strings (or string)
1058 @param names: the names of the locks which shall be acquired
1059 (special lock names, or instance/node names)
1060 @type shared: integer (0/1) used as a boolean
1061 @param shared: whether to acquire in shared mode; by default an
1062 exclusive lock will be acquired
1063 @type timeout: float or None
1064 @param timeout: Maximum time to acquire all locks
1065 @type priority: integer
1066 @param priority: Priority for acquiring locks
1067 @type test_notify: callable or None
1068 @param test_notify: Special callback function for unittesting
1070 @return: Set of all locks successfully acquired or None in case of timeout
1072 @raise errors.LockError: when any lock we try to acquire has
1073 been deleted before we succeed. In this case none of the
1074 locks requested will be acquired.
1077 assert timeout is None or timeout >= 0.0
1079 # Check we don't already own locks at this level
1080 assert not self.is_owned(), ("Cannot acquire locks in the same set twice"
1081 " (lockset %s)" % self.name)
1083 if priority is None:
1084 priority = _DEFAULT_PRIORITY
1086 # We need to keep track of how long we spent waiting for a lock. The
1087 # timeout passed to this function is over all lock acquires.
1088 running_timeout = utils.RunningTimeout(timeout, False)
1091 if names is not None:
1092 # Support passing in a single resource to acquire rather than many
1093 if isinstance(names, basestring):
1096 return self.__acquire_inner(names, False, shared, priority,
1097 running_timeout.Remaining, test_notify)
1100 # If no names are given acquire the whole set by not letting new names
1101 # being added before we release, and getting the current list of names.
1102 # Some of them may then be deleted later, but we'll cope with this.
1104 # We'd like to acquire this lock in a shared way, as it's nice if
1105 # everybody else can use the instances at the same time. If we are
1106 # acquiring them exclusively though they won't be able to do this
1107 # anyway, though, so we'll get the list lock exclusively as well in
1108 # order to be able to do add() on the set while owning it.
1109 if not self.__lock.acquire(shared=shared, priority=priority,
1110 timeout=running_timeout.Remaining()):
1111 raise _AcquireTimeout()
1113 # note we own the set-lock
1116 return self.__acquire_inner(self.__names(), True, shared, priority,
1117 running_timeout.Remaining, test_notify)
1119 # We shouldn't have problems adding the lock to the owners list, but
1120 # if we did we'll try to release this lock and re-raise exception.
1121 # Of course something is going to be really wrong, after this.
1122 self.__lock.release()
1126 except _AcquireTimeout:
1129 def __acquire_inner(self, names, want_all, shared, priority,
1130 timeout_fn, test_notify):
1131 """Inner logic for acquiring a number of locks.
1133 @param names: Names of the locks to be acquired
1134 @param want_all: Whether all locks in the set should be acquired
1135 @param shared: Whether to acquire in shared mode
1136 @param timeout_fn: Function returning remaining timeout
1137 @param priority: Priority for acquiring locks
1138 @param test_notify: Special callback function for unittesting
1143 # First we look the locks up on __lockdict. We have no way of being sure
1144 # they will still be there after, but this makes it a lot faster should
1145 # just one of them be the already wrong. Using a sorted sequence to prevent
1147 for lname in sorted(utils.UniqueSequence(names)):
1149 lock = self.__lockdict[lname] # raises KeyError if lock is not there
1152 # We are acquiring all the set, it doesn't matter if this particular
1153 # element is not there anymore.
1156 raise errors.LockError("Non-existing lock %s in set %s (it may have"
1157 " been removed)" % (lname, self.name))
1159 acquire_list.append((lname, lock))
1161 # This will hold the locknames we effectively acquired.
1165 # Now acquire_list contains a sorted list of resources and locks we
1166 # want. In order to get them we loop on this (private) list and
1167 # acquire() them. We gave no real guarantee they will still exist till
1168 # this is done but .acquire() itself is safe and will alert us if the
1169 # lock gets deleted.
1170 for (lname, lock) in acquire_list:
1171 if __debug__ and callable(test_notify):
1172 test_notify_fn = lambda: test_notify(lname)
1174 test_notify_fn = None
1176 timeout = timeout_fn()
1179 # raises LockError if the lock was deleted
1180 acq_success = lock.acquire(shared=shared, timeout=timeout,
1182 test_notify=test_notify_fn)
1183 except errors.LockError:
1185 # We are acquiring all the set, it doesn't matter if this
1186 # particular element is not there anymore.
1189 raise errors.LockError("Non-existing lock %s in set %s (it may"
1190 " have been removed)" % (lname, self.name))
1193 # Couldn't get lock or timeout occurred
1195 # This shouldn't happen as SharedLock.acquire(timeout=None) is
1197 raise errors.LockError("Failed to get lock %s (set %s)" %
1200 raise _AcquireTimeout()
1203 # now the lock cannot be deleted, we have it!
1204 self._add_owned(name=lname)
1208 # We shouldn't have problems adding the lock to the owners list, but
1209 # if we did we'll try to release this lock and re-raise exception.
1210 # Of course something is going to be really wrong after this.
1216 # Release all owned locks
1217 self._release_and_delete_owned()
1222 def downgrade(self, names=None):
1223 """Downgrade a set of resource locks from exclusive to shared mode.
1225 The locks must have been acquired in exclusive mode.
1228 assert self.is_owned(), ("downgrade on lockset %s while not owning any"
1229 " lock" % self.name)
1231 # Support passing in a single resource to downgrade rather than many
1232 if isinstance(names, basestring):
1235 owned = self.list_owned()
1241 assert owned.issuperset(names), \
1242 ("downgrade() on unheld resources %s (set %s)" %
1243 (names.difference(owned), self.name))
1245 for lockname in names:
1246 self.__lockdict[lockname].downgrade()
1248 # Do we own the lockset in exclusive mode?
1249 if self.__lock.is_owned(shared=0):
1250 # Have all locks been downgraded?
1251 if not compat.any(lock.is_owned(shared=0)
1252 for lock in self.__lockdict.values()):
1253 self.__lock.downgrade()
1254 assert self.__lock.is_owned(shared=1)
1258 def release(self, names=None):
1259 """Release a set of resource locks, at the same level.
1261 You must have acquired the locks, either in shared or in exclusive mode,
1262 before releasing them.
1264 @type names: list of strings, or None
1265 @param names: the names of the locks which shall be released
1266 (defaults to all the locks acquired at that level).
1269 assert self.is_owned(), ("release() on lock set %s while not owner" %
1272 # Support passing in a single resource to release rather than many
1273 if isinstance(names, basestring):
1277 names = self.list_owned()
1280 assert self.list_owned().issuperset(names), (
1281 "release() on unheld resources %s (set %s)" %
1282 (names.difference(self.list_owned()), self.name))
1284 # First of all let's release the "all elements" lock, if set.
1285 # After this 'add' can work again
1286 if self.__lock.is_owned():
1287 self.__lock.release()
1290 for lockname in names:
1291 # If we are sure the lock doesn't leave __lockdict without being
1292 # exclusively held we can do this...
1293 self.__lockdict[lockname].release()
1294 self._del_owned(name=lockname)
1296 def add(self, names, acquired=0, shared=0):
1297 """Add a new set of elements to the set
1299 @type names: list of strings
1300 @param names: names of the new elements to add
1301 @type acquired: integer (0/1) used as a boolean
1302 @param acquired: pre-acquire the new resource?
1303 @type shared: integer (0/1) used as a boolean
1304 @param shared: is the pre-acquisition shared?
1307 # Check we don't already own locks at this level
1308 assert not self.is_owned() or self.__lock.is_owned(shared=0), \
1309 ("Cannot add locks if the set %s is only partially owned, or shared" %
1312 # Support passing in a single resource to add rather than many
1313 if isinstance(names, basestring):
1316 # If we don't already own the set-level lock acquired in an exclusive way
1317 # we'll get it and note we need to release it later.
1318 release_lock = False
1319 if not self.__lock.is_owned():
1321 self.__lock.acquire()
1324 invalid_names = set(self.__names()).intersection(names)
1326 # This must be an explicit raise, not an assert, because assert is
1327 # turned off when using optimization, and this can happen because of
1328 # concurrency even if the user doesn't want it.
1329 raise errors.LockError("duplicate add(%s) on lockset %s" %
1330 (invalid_names, self.name))
1332 for lockname in names:
1333 lock = SharedLock(self._GetLockName(lockname), monitor=self.__monitor)
1336 # No need for priority or timeout here as this lock has just been
1338 lock.acquire(shared=shared)
1339 # now the lock cannot be deleted, we have it!
1341 self._add_owned(name=lockname)
1343 # We shouldn't have problems adding the lock to the owners list,
1344 # but if we did we'll try to release this lock and re-raise
1345 # exception. Of course something is going to be really wrong,
1346 # after this. On the other hand the lock hasn't been added to the
1347 # __lockdict yet so no other threads should be pending on it. This
1348 # release is just a safety measure.
1352 self.__lockdict[lockname] = lock
1355 # Only release __lock if we were not holding it previously.
1357 self.__lock.release()
1361 def remove(self, names):
1362 """Remove elements from the lock set.
1364 You can either not hold anything in the lockset or already hold a superset
1365 of the elements you want to delete, exclusively.
1367 @type names: list of strings
1368 @param names: names of the resource to remove.
1370 @return: a list of locks which we removed; the list is always
1371 equal to the names list if we were holding all the locks
1375 # Support passing in a single resource to remove rather than many
1376 if isinstance(names, basestring):
1379 # If we own any subset of this lock it must be a superset of what we want
1380 # to delete. The ownership must also be exclusive, but that will be checked
1381 # by the lock itself.
1382 assert not self.is_owned() or self.list_owned().issuperset(names), (
1383 "remove() on acquired lockset %s while not owning all elements" %
1389 # Calling delete() acquires the lock exclusively if we don't already own
1390 # it, and causes all pending and subsequent lock acquires to fail. It's
1391 # fine to call it out of order because delete() also implies release(),
1392 # and the assertion above guarantees that if we either already hold
1393 # everything we want to delete, or we hold none.
1395 self.__lockdict[lname].delete()
1396 removed.append(lname)
1397 except (KeyError, errors.LockError):
1398 # This cannot happen if we were already holding it, verify:
1399 assert not self.is_owned(), ("remove failed while holding lockset %s" %
1402 # If no LockError was raised we are the ones who deleted the lock.
1403 # This means we can safely remove it from lockdict, as any further or
1404 # pending delete() or acquire() will fail (and nobody can have the lock
1405 # since before our call to delete()).
1407 # This is done in an else clause because if the exception was thrown
1408 # it's the job of the one who actually deleted it.
1409 del self.__lockdict[lname]
1410 # And let's remove it from our private list if we owned it.
1412 self._del_owned(name=lname)
1417 # Locking levels, must be acquired in increasing order.
1418 # Current rules are:
1419 # - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
1420 # acquired before performing any operation, either in shared or in exclusive
1421 # mode. acquiring the BGL in exclusive mode is discouraged and should be
1423 # - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
1424 # If you need more than one node, or more than one instance, acquire them at
1440 # Lock levels which are modifiable
1441 LEVELS_MOD = frozenset([
1448 #: Lock level names (make sure to use singular form)
1450 LEVEL_CLUSTER: "cluster",
1451 LEVEL_INSTANCE: "instance",
1452 LEVEL_NODEGROUP: "nodegroup",
1454 LEVEL_NODE_RES: "node-res",
1457 # Constant for the big ganeti lock
1461 class GanetiLockManager:
1462 """The Ganeti Locking Library
1464 The purpose of this small library is to manage locking for ganeti clusters
1465 in a central place, while at the same time doing dynamic checks against
1466 possible deadlocks. It will also make it easier to transition to a different
1467 lock type should we migrate away from python threads.
1472 def __init__(self, nodes, nodegroups, instances):
1473 """Constructs a new GanetiLockManager object.
1475 There should be only a GanetiLockManager object at any time, so this
1476 function raises an error if this is not the case.
1478 @param nodes: list of node names
1479 @param nodegroups: list of nodegroup uuids
1480 @param instances: list of instance names
1483 assert self.__class__._instance is None, \
1484 "double GanetiLockManager instance"
1486 self.__class__._instance = self
1488 self._monitor = LockMonitor()
1490 # The keyring contains all the locks, at their level and in the correct
1493 LEVEL_CLUSTER: LockSet([BGL], "cluster", monitor=self._monitor),
1494 LEVEL_NODE: LockSet(nodes, "node", monitor=self._monitor),
1495 LEVEL_NODE_RES: LockSet(nodes, "node-res", monitor=self._monitor),
1496 LEVEL_NODEGROUP: LockSet(nodegroups, "nodegroup", monitor=self._monitor),
1497 LEVEL_INSTANCE: LockSet(instances, "instance",
1498 monitor=self._monitor),
1501 assert compat.all(ls.name == LEVEL_NAMES[level]
1502 for (level, ls) in self.__keyring.items())
1504 def AddToLockMonitor(self, provider):
1505 """Registers a new lock with the monitor.
1507 See L{LockMonitor.RegisterLock}.
1510 return self._monitor.RegisterLock(provider)
1512 def QueryLocks(self, fields):
1513 """Queries information from all locks.
1515 See L{LockMonitor.QueryLocks}.
1518 return self._monitor.QueryLocks(fields)
1520 def OldStyleQueryLocks(self, fields):
1521 """Queries information from all locks, returning old-style data.
1523 See L{LockMonitor.OldStyleQueryLocks}.
1526 return self._monitor.OldStyleQueryLocks(fields)
1528 def _names(self, level):
1529 """List the lock names at the given level.
1531 This can be used for debugging/testing purposes.
1533 @param level: the level whose list of locks to get
1536 assert level in LEVELS, "Invalid locking level %s" % level
1537 return self.__keyring[level]._names()
1539 def is_owned(self, level):
1540 """Check whether we are owning locks at the given level
1543 return self.__keyring[level].is_owned()
1545 def list_owned(self, level):
1546 """Get the set of owned locks at the given level
1549 return self.__keyring[level].list_owned()
1551 def check_owned(self, level, names, shared=-1):
1552 """Check if locks at a certain level are owned in a specific mode.
1554 @see: L{LockSet.check_owned}
1557 return self.__keyring[level].check_owned(names, shared=shared)
1559 def _upper_owned(self, level):
1560 """Check that we don't own any lock at a level greater than the given one.
1563 # This way of checking only works if LEVELS[i] = i, which we check for in
1565 return compat.any((self.is_owned(l) for l in LEVELS[level + 1:]))
1567 def _BGL_owned(self): # pylint: disable=C0103
1568 """Check if the current thread owns the BGL.
1570 Both an exclusive or a shared acquisition work.
1573 return BGL in self.__keyring[LEVEL_CLUSTER].list_owned()
1576 def _contains_BGL(level, names): # pylint: disable=C0103
1577 """Check if the level contains the BGL.
1579 Check if acting on the given level and set of names will change
1580 the status of the Big Ganeti Lock.
1583 return level == LEVEL_CLUSTER and (names is None or BGL in names)
1585 def acquire(self, level, names, timeout=None, shared=0, priority=None):
1586 """Acquire a set of resource locks, at the same level.
1588 @type level: member of locking.LEVELS
1589 @param level: the level at which the locks shall be acquired
1590 @type names: list of strings (or string)
1591 @param names: the names of the locks which shall be acquired
1592 (special lock names, or instance/node names)
1593 @type shared: integer (0/1) used as a boolean
1594 @param shared: whether to acquire in shared mode; by default
1595 an exclusive lock will be acquired
1596 @type timeout: float
1597 @param timeout: Maximum time to acquire all locks
1598 @type priority: integer
1599 @param priority: Priority for acquiring lock
1602 assert level in LEVELS, "Invalid locking level %s" % level
1604 # Check that we are either acquiring the Big Ganeti Lock or we already own
1605 # it. Some "legacy" opcodes need to be sure they are run non-concurrently
1606 # so even if we've migrated we need to at least share the BGL to be
1607 # compatible with them. Of course if we own the BGL exclusively there's no
1608 # point in acquiring any other lock, unless perhaps we are half way through
1609 # the migration of the current opcode.
1610 assert (self._contains_BGL(level, names) or self._BGL_owned()), (
1611 "You must own the Big Ganeti Lock before acquiring any other")
1613 # Check we don't own locks at the same or upper levels.
1614 assert not self._upper_owned(level), ("Cannot acquire locks at a level"
1615 " while owning some at a greater one")
1617 # Acquire the locks in the set.
1618 return self.__keyring[level].acquire(names, shared=shared, timeout=timeout,
1621 def downgrade(self, level, names=None):
1622 """Downgrade a set of resource locks from exclusive to shared mode.
1624 You must have acquired the locks in exclusive mode.
1626 @type level: member of locking.LEVELS
1627 @param level: the level at which the locks shall be downgraded
1628 @type names: list of strings, or None
1629 @param names: the names of the locks which shall be downgraded
1630 (defaults to all the locks acquired at the level)
1633 assert level in LEVELS, "Invalid locking level %s" % level
1635 return self.__keyring[level].downgrade(names=names)
1637 def release(self, level, names=None):
1638 """Release a set of resource locks, at the same level.
1640 You must have acquired the locks, either in shared or in exclusive
1641 mode, before releasing them.
1643 @type level: member of locking.LEVELS
1644 @param level: the level at which the locks shall be released
1645 @type names: list of strings, or None
1646 @param names: the names of the locks which shall be released
1647 (defaults to all the locks acquired at that level)
1650 assert level in LEVELS, "Invalid locking level %s" % level
1651 assert (not self._contains_BGL(level, names) or
1652 not self._upper_owned(LEVEL_CLUSTER)), (
1653 "Cannot release the Big Ganeti Lock while holding something"
1654 " at upper levels (%r)" %
1655 (utils.CommaJoin(["%s=%r" % (LEVEL_NAMES[i], self.list_owned(i))
1656 for i in self.__keyring.keys()]), ))
1658 # Release will complain if we don't own the locks already
1659 return self.__keyring[level].release(names)
1661 def add(self, level, names, acquired=0, shared=0):
1662 """Add locks at the specified level.
1664 @type level: member of locking.LEVELS_MOD
1665 @param level: the level at which the locks shall be added
1666 @type names: list of strings
1667 @param names: names of the locks to acquire
1668 @type acquired: integer (0/1) used as a boolean
1669 @param acquired: whether to acquire the newly added locks
1670 @type shared: integer (0/1) used as a boolean
1671 @param shared: whether the acquisition will be shared
1674 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1675 assert self._BGL_owned(), ("You must own the BGL before performing other"
1677 assert not self._upper_owned(level), ("Cannot add locks at a level"
1678 " while owning some at a greater one")
1679 return self.__keyring[level].add(names, acquired=acquired, shared=shared)
1681 def remove(self, level, names):
1682 """Remove locks from the specified level.
1684 You must either already own the locks you are trying to remove
1685 exclusively or not own any lock at an upper level.
1687 @type level: member of locking.LEVELS_MOD
1688 @param level: the level at which the locks shall be removed
1689 @type names: list of strings
1690 @param names: the names of the locks which shall be removed
1691 (special lock names, or instance/node names)
1694 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1695 assert self._BGL_owned(), ("You must own the BGL before performing other"
1697 # Check we either own the level or don't own anything from here
1698 # up. LockSet.remove() will check the case in which we don't own
1699 # all the needed resources, or we have a shared ownership.
1700 assert self.is_owned(level) or not self._upper_owned(level), (
1701 "Cannot remove locks at a level while not owning it or"
1702 " owning some at a greater one")
1703 return self.__keyring[level].remove(names)
1706 def _MonitorSortKey((item, idx, num)):
1707 """Sorting key function.
1709 Sort by name, registration order and then order of information. This provides
1710 a stable sort order over different providers, even if they return the same
1714 (name, _, _, _) = item
1716 return (utils.NiceSortKey(name), num, idx)
1719 class LockMonitor(object):
1720 _LOCK_ATTR = "_lock"
1723 """Initializes this class.
1726 self._lock = SharedLock("LockMonitor")
1728 # Counter for stable sorting
1729 self._counter = itertools.count(0)
1731 # Tracked locks. Weak references are used to avoid issues with circular
1732 # references and deletion.
1733 self._locks = weakref.WeakKeyDictionary()
1735 @ssynchronized(_LOCK_ATTR)
1736 def RegisterLock(self, provider):
1737 """Registers a new lock.
1739 @param provider: Object with a callable method named C{GetLockInfo}, taking
1740 a single C{set} containing the requested information items
1741 @note: It would be nicer to only receive the function generating the
1742 requested information but, as it turns out, weak references to bound
1743 methods (e.g. C{self.GetLockInfo}) are tricky; there are several
1744 workarounds, but none of the ones I found works properly in combination
1745 with a standard C{WeakKeyDictionary}
1748 assert provider not in self._locks, "Duplicate registration"
1750 # There used to be a check for duplicate names here. As it turned out, when
1751 # a lock is re-created with the same name in a very short timeframe, the
1752 # previous instance might not yet be removed from the weakref dictionary.
1753 # By keeping track of the order of incoming registrations, a stable sort
1754 # ordering can still be guaranteed.
1756 self._locks[provider] = self._counter.next()
1758 def _GetLockInfo(self, requested):
1759 """Get information from all locks.
1762 # Must hold lock while getting consistent list of tracked items
1763 self._lock.acquire(shared=1)
1765 items = self._locks.items()
1767 self._lock.release()
1769 return [(info, idx, num)
1770 for (provider, num) in items
1771 for (idx, info) in enumerate(provider.GetLockInfo(requested))]
1773 def _Query(self, fields):
1774 """Queries information from all locks.
1776 @type fields: list of strings
1777 @param fields: List of fields to return
1780 qobj = query.Query(query.LOCK_FIELDS, fields)
1782 # Get all data with internal lock held and then sort by name and incoming
1784 lockinfo = sorted(self._GetLockInfo(qobj.RequestedData()),
1785 key=_MonitorSortKey)
1787 # Extract lock information and build query data
1788 return (qobj, query.LockQueryData(map(compat.fst, lockinfo)))
1790 def QueryLocks(self, fields):
1791 """Queries information from all locks.
1793 @type fields: list of strings
1794 @param fields: List of fields to return
1797 (qobj, ctx) = self._Query(fields)
1799 # Prepare query response
1800 return query.GetQueryResponse(qobj, ctx)
1802 def OldStyleQueryLocks(self, fields):
1803 """Queries information from all locks, returning old-style data.
1805 @type fields: list of strings
1806 @param fields: List of fields to return
1809 (qobj, ctx) = self._Query(fields)
1811 return qobj.OldStyleQuery(ctx)