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
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=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=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 return ("<%s.%s waiters=%s at %#x>" %
363 (self.__class__.__module__, self.__class__.__name__,
364 self._waiters, id(self)))
367 class _PipeConditionWithMode(PipeCondition):
372 def __init__(self, lock, shared):
373 """Initializes this class.
377 PipeCondition.__init__(self, lock)
380 class SharedLock(object):
381 """Implements a shared lock.
383 Multiple threads can acquire the lock in a shared way by calling
384 C{acquire(shared=1)}. In order to acquire the lock in an exclusive way
385 threads can call C{acquire(shared=0)}.
387 Notes on data structures: C{__pending} contains a priority queue (heapq) of
388 all pending acquires: C{[(priority1: prioqueue1), (priority2: prioqueue2),
389 ...]}. Each per-priority queue contains a normal in-order list of conditions
390 to be notified when the lock can be acquired. Shared locks are grouped
391 together by priority and the condition for them is stored in
392 C{__pending_shared} if it already exists. C{__pending_by_prio} keeps
393 references for the per-priority queues indexed by priority for faster access.
396 @ivar name: the name of the lock
412 __condition_class = _PipeConditionWithMode
414 def __init__(self, name, monitor=None, _time_fn=time.time):
415 """Construct a new SharedLock.
417 @param name: the name of the lock
418 @type monitor: L{LockMonitor}
419 @param monitor: Lock monitor with which to register
422 object.__init__(self)
426 # Used for unittesting
427 self.__time_fn = _time_fn
430 self.__lock = threading.Lock()
432 # Queue containing waiting acquires
434 self.__pending_by_prio = {}
435 self.__pending_shared = {}
437 # Current lock holders
441 # is this lock in the deleted state?
442 self.__deleted = False
444 # Register with lock monitor
446 logging.debug("Adding lock %s to monitor", name)
447 monitor.RegisterLock(self)
450 return ("<%s.%s name=%s at %#x>" %
451 (self.__class__.__module__, self.__class__.__name__,
452 self.name, id(self)))
454 def GetLockInfo(self, requested):
455 """Retrieves information for querying locks.
458 @param requested: Requested information, see C{query.LQ_*}
461 self.__lock.acquire()
463 # Note: to avoid unintentional race conditions, no references to
464 # modifiable objects should be returned unless they were created in this
469 if query.LQ_MODE in requested:
472 assert not (self.__exc or self.__shr)
474 mode = _EXCLUSIVE_TEXT
478 # Current owner(s) are wanted
479 if query.LQ_OWNER in requested:
486 assert not self.__deleted
487 owner_names = [i.getName() for i in owner]
489 # Pending acquires are wanted
490 if query.LQ_PENDING in requested:
493 # Sorting instead of copying and using heaq functions for simplicity
494 for (_, prioqueue) in sorted(self.__pending):
495 for cond in prioqueue:
497 pendmode = _SHARED_TEXT
499 pendmode = _EXCLUSIVE_TEXT
501 # List of names will be sorted in L{query._GetLockPending}
502 pending.append((pendmode, [i.getName()
503 for i in cond.get_waiting()]))
507 return [(self.name, mode, owner_names, pending)]
509 self.__lock.release()
511 def __check_deleted(self):
512 """Raises an exception if the lock has been deleted.
516 raise errors.LockError("Deleted lock %s" % self.name)
518 def __is_sharer(self):
519 """Is the current thread sharing the lock at this time?
522 return threading.currentThread() in self.__shr
524 def __is_exclusive(self):
525 """Is the current thread holding the lock exclusively at this time?
528 return threading.currentThread() == self.__exc
530 def __is_owned(self, shared=-1):
531 """Is the current thread somehow owning the lock at this time?
533 This is a private version of the function, which presumes you're holding
538 return self.__is_sharer() or self.__is_exclusive()
540 return self.__is_sharer()
542 return self.__is_exclusive()
544 def is_owned(self, shared=-1):
545 """Is the current thread somehow owning the lock at this time?
548 - < 0: check for any type of ownership (default)
549 - 0: check for exclusive ownership
550 - > 0: check for shared ownership
553 self.__lock.acquire()
555 return self.__is_owned(shared=shared)
557 self.__lock.release()
559 #: Necessary to remain compatible with threading.Condition, which tries to
560 #: retrieve a locks' "_is_owned" attribute
563 def _count_pending(self):
564 """Returns the number of pending acquires.
569 self.__lock.acquire()
571 return sum(len(prioqueue) for (_, prioqueue) in self.__pending)
573 self.__lock.release()
575 def _check_empty(self):
576 """Checks whether there are any pending acquires.
581 self.__lock.acquire()
583 # Order is important: __find_first_pending_queue modifies __pending
584 (_, prioqueue) = self.__find_first_pending_queue()
586 return not (prioqueue or
588 self.__pending_by_prio or
589 self.__pending_shared)
591 self.__lock.release()
593 def __do_acquire(self, shared):
594 """Actually acquire the lock.
598 self.__shr.add(threading.currentThread())
600 self.__exc = threading.currentThread()
602 def __can_acquire(self, shared):
603 """Determine whether lock can be acquired.
607 return self.__exc is None
609 return len(self.__shr) == 0 and self.__exc is None
611 def __find_first_pending_queue(self):
612 """Tries to find the topmost queued entry with pending acquires.
614 Removes empty entries while going through the list.
617 while self.__pending:
618 (priority, prioqueue) = self.__pending[0]
621 return (priority, prioqueue)
624 heapq.heappop(self.__pending)
625 del self.__pending_by_prio[priority]
626 assert priority not in self.__pending_shared
630 def __is_on_top(self, cond):
631 """Checks whether the passed condition is on top of the queue.
633 The caller must make sure the queue isn't empty.
636 (_, prioqueue) = self.__find_first_pending_queue()
638 return cond == prioqueue[0]
640 def __acquire_unlocked(self, shared, timeout, priority):
641 """Acquire a shared lock.
643 @param shared: whether to acquire in shared mode; by default an
644 exclusive lock will be acquired
645 @param timeout: maximum waiting time before giving up
646 @type priority: integer
647 @param priority: Priority for acquiring lock
650 self.__check_deleted()
652 # We cannot acquire the lock if we already have it
653 assert not self.__is_owned(), ("double acquire() on a non-recursive lock"
656 # Remove empty entries from queue
657 self.__find_first_pending_queue()
659 # Check whether someone else holds the lock or there are pending acquires.
660 if not self.__pending and self.__can_acquire(shared):
661 # Apparently not, can acquire lock directly.
662 self.__do_acquire(shared)
665 prioqueue = self.__pending_by_prio.get(priority, None)
668 # Try to re-use condition for shared acquire
669 wait_condition = self.__pending_shared.get(priority, None)
670 assert (wait_condition is None or
671 (wait_condition.shared and wait_condition in prioqueue))
673 wait_condition = None
675 if wait_condition is None:
676 if prioqueue is None:
677 assert priority not in self.__pending_by_prio
680 heapq.heappush(self.__pending, (priority, prioqueue))
681 self.__pending_by_prio[priority] = prioqueue
683 wait_condition = self.__condition_class(self.__lock, shared)
684 prioqueue.append(wait_condition)
687 # Keep reference for further shared acquires on same priority. This is
688 # better than trying to find it in the list of pending acquires.
689 assert priority not in self.__pending_shared
690 self.__pending_shared[priority] = wait_condition
692 wait_start = self.__time_fn()
696 # Wait until we become the topmost acquire in the queue or the timeout
699 if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
700 self.__do_acquire(shared)
704 # A lot of code assumes blocking acquires always succeed, therefore we
705 # can never return False for a blocking acquire
706 if (timeout is not None and
707 utils.TimeoutExpired(wait_start, timeout, _time_fn=self.__time_fn)):
710 # Wait for notification
711 wait_condition.wait(timeout)
712 self.__check_deleted()
714 # Remove condition from queue if there are no more waiters
715 if not wait_condition.has_waiting():
716 prioqueue.remove(wait_condition)
717 if wait_condition.shared:
718 # Remove from list of shared acquires if it wasn't while releasing
719 # (e.g. on lock deletion)
720 self.__pending_shared.pop(priority, None)
724 def acquire(self, shared=0, timeout=None, priority=None,
726 """Acquire a shared lock.
728 @type shared: integer (0/1) used as a boolean
729 @param shared: whether to acquire in shared mode; by default an
730 exclusive lock will be acquired
732 @param timeout: maximum waiting time before giving up
733 @type priority: integer
734 @param priority: Priority for acquiring lock
735 @type test_notify: callable or None
736 @param test_notify: Special callback function for unittesting
740 priority = _DEFAULT_PRIORITY
742 self.__lock.acquire()
744 # We already got the lock, notify now
745 if __debug__ and callable(test_notify):
748 return self.__acquire_unlocked(shared, timeout, priority)
750 self.__lock.release()
753 """Changes the lock mode from exclusive to shared.
755 Pending acquires in shared mode on the same priority will go ahead.
758 self.__lock.acquire()
760 assert self.__is_owned(), "Lock must be owned"
762 if self.__is_exclusive():
763 # Do nothing if the lock is already acquired in shared mode
767 # Important: pending shared acquires should only jump ahead if there
768 # was a transition from exclusive to shared, otherwise an owner of a
769 # shared lock can keep calling this function to push incoming shared
771 (priority, prioqueue) = self.__find_first_pending_queue()
773 # Is there a pending shared acquire on this priority?
774 cond = self.__pending_shared.pop(priority, None)
777 assert cond in prioqueue
779 # Ensure shared acquire is on top of queue
780 if len(prioqueue) > 1:
781 prioqueue.remove(cond)
782 prioqueue.insert(0, cond)
787 assert not self.__is_exclusive()
788 assert self.__is_sharer()
792 self.__lock.release()
795 """Release a Shared Lock.
797 You must have acquired the lock, either in shared or in exclusive mode,
798 before calling this function.
801 self.__lock.acquire()
803 assert self.__is_exclusive() or self.__is_sharer(), \
804 "Cannot release non-owned lock"
806 # Autodetect release type
807 if self.__is_exclusive():
811 self.__shr.remove(threading.currentThread())
812 notify = not self.__shr
814 # Notify topmost condition in queue if there are no owners left (for
817 self.__notify_topmost()
819 self.__lock.release()
821 def __notify_topmost(self):
822 """Notifies topmost condition in queue of pending acquires.
825 (priority, prioqueue) = self.__find_first_pending_queue()
830 # Prevent further shared acquires from sneaking in while waiters are
832 self.__pending_shared.pop(priority, None)
834 def _notify_topmost(self):
835 """Exported version of L{__notify_topmost}.
838 self.__lock.acquire()
840 return self.__notify_topmost()
842 self.__lock.release()
844 def delete(self, timeout=None, priority=None):
845 """Delete a Shared Lock.
847 This operation will declare the lock for removal. First the lock will be
848 acquired in exclusive mode if you don't already own it, then the lock
849 will be put in a state where any future and pending acquire() fail.
852 @param timeout: maximum waiting time before giving up
853 @type priority: integer
854 @param priority: Priority for acquiring lock
858 priority = _DEFAULT_PRIORITY
860 self.__lock.acquire()
862 assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"
864 self.__check_deleted()
866 # The caller is allowed to hold the lock exclusively already.
867 acquired = self.__is_exclusive()
870 acquired = self.__acquire_unlocked(0, timeout, priority)
873 assert self.__is_exclusive() and not self.__is_sharer(), \
874 "Lock wasn't acquired in exclusive mode"
876 self.__deleted = True
879 assert not (self.__exc or self.__shr), "Found owner during deletion"
881 # Notify all acquires. They'll throw an error.
882 for (_, prioqueue) in self.__pending:
883 for cond in prioqueue:
886 assert self.__deleted
890 self.__lock.release()
892 def _release_save(self):
893 shared = self.__is_sharer()
897 def _acquire_restore(self, shared):
898 self.acquire(shared=shared)
901 # Whenever we want to acquire a full LockSet we pass None as the value
902 # to acquire. Hide this behind this nicely named constant.
906 class _AcquireTimeout(Exception):
907 """Internal exception to abort an acquire on a timeout.
913 """Implements a set of locks.
915 This abstraction implements a set of shared locks for the same resource type,
916 distinguished by name. The user can lock a subset of the resources and the
917 LockSet will take care of acquiring the locks always in the same order, thus
920 All the locks needed in the same set must be acquired together, though.
923 @ivar name: the name of the lockset
926 def __init__(self, members, name, monitor=None):
927 """Constructs a new LockSet.
929 @type members: list of strings
930 @param members: initial members of the set
931 @type monitor: L{LockMonitor}
932 @param monitor: Lock monitor with which to register member locks
935 assert members is not None, "members parameter is not a list"
939 self.__monitor = monitor
941 # Used internally to guarantee coherency
942 self.__lock = SharedLock(self._GetLockName("[lockset]"), monitor=monitor)
944 # The lockdict indexes the relationship name -> lock
945 # The order-of-locking is implied by the alphabetical order of names
948 for mname in members:
949 self.__lockdict[mname] = SharedLock(self._GetLockName(mname),
952 # The owner dict contains the set of locks each thread owns. For
953 # performance each thread can access its own key without a global lock on
954 # this structure. It is paramount though that *no* other type of access is
955 # done to this structure (eg. no looping over its keys). *_owner helper
956 # function are defined to guarantee access is correct, but in general never
957 # do anything different than __owners[threading.currentThread()], or there
961 def _GetLockName(self, mname):
962 """Returns the name for a member lock.
965 return "%s/%s" % (self.name, mname)
968 """Returns the lockset-internal lock.
973 def _get_lockdict(self):
974 """Returns the lockset-internal lock dictionary.
976 Accessing this structure is only safe in single-thread usage or when the
977 lockset-internal lock is held.
980 return self.__lockdict
983 """Is the current thread a current level owner?
985 @note: Use L{check_owned} to check if a specific lock is held
988 return threading.currentThread() in self.__owners
990 def check_owned(self, names, shared=-1):
991 """Check if locks are owned in a specific mode.
993 @type names: sequence or string
994 @param names: Lock names (or a single lock name)
995 @param shared: See L{SharedLock.is_owned}
997 @note: Use L{is_owned} to check if the current thread holds I{any} lock and
998 L{list_owned} to get the names of all owned locks
1001 if isinstance(names, basestring):
1004 # Avoid check if no locks are owned anyway
1005 if names and self.is_owned():
1008 # Gather references to all locks (in case they're deleted in the meantime)
1011 lock = self.__lockdict[lname]
1013 raise errors.LockError("Non-existing lock '%s' in set '%s' (it may"
1014 " have been removed)" % (lname, self.name))
1016 candidates.append(lock)
1018 return compat.all(lock.is_owned(shared=shared) for lock in candidates)
1022 def _add_owned(self, name=None):
1023 """Note the current thread owns the given lock"""
1025 if not self.is_owned():
1026 self.__owners[threading.currentThread()] = set()
1029 self.__owners[threading.currentThread()].add(name)
1031 self.__owners[threading.currentThread()] = set([name])
1033 def _del_owned(self, name=None):
1034 """Note the current thread owns the given lock"""
1036 assert not (name is None and self.__lock.is_owned()), \
1037 "Cannot hold internal lock when deleting owner status"
1039 if name is not None:
1040 self.__owners[threading.currentThread()].remove(name)
1042 # Only remove the key if we don't hold the set-lock as well
1043 if (not self.__lock.is_owned() and
1044 not self.__owners[threading.currentThread()]):
1045 del self.__owners[threading.currentThread()]
1047 def list_owned(self):
1048 """Get the set of resource names owned by the current thread"""
1050 return self.__owners[threading.currentThread()].copy()
1054 def _release_and_delete_owned(self):
1055 """Release and delete all resources owned by the current thread"""
1056 for lname in self.list_owned():
1057 lock = self.__lockdict[lname]
1060 self._del_owned(name=lname)
1063 """Return the current set of names.
1065 Only call this function while holding __lock and don't iterate on the
1066 result after releasing the lock.
1069 return self.__lockdict.keys()
1072 """Return a copy of the current set of elements.
1074 Used only for debugging purposes.
1077 # If we don't already own the set-level lock acquired
1078 # we'll get it and note we need to release it later.
1079 release_lock = False
1080 if not self.__lock.is_owned():
1082 self.__lock.acquire(shared=1)
1084 result = self.__names()
1087 self.__lock.release()
1090 def acquire(self, names, timeout=None, shared=0, priority=None,
1092 """Acquire a set of resource locks.
1094 @type names: list of strings (or string)
1095 @param names: the names of the locks which shall be acquired
1096 (special lock names, or instance/node names)
1097 @type shared: integer (0/1) used as a boolean
1098 @param shared: whether to acquire in shared mode; by default an
1099 exclusive lock will be acquired
1100 @type timeout: float or None
1101 @param timeout: Maximum time to acquire all locks
1102 @type priority: integer
1103 @param priority: Priority for acquiring locks
1104 @type test_notify: callable or None
1105 @param test_notify: Special callback function for unittesting
1107 @return: Set of all locks successfully acquired or None in case of timeout
1109 @raise errors.LockError: when any lock we try to acquire has
1110 been deleted before we succeed. In this case none of the
1111 locks requested will be acquired.
1114 assert timeout is None or timeout >= 0.0
1116 # Check we don't already own locks at this level
1117 assert not self.is_owned(), ("Cannot acquire locks in the same set twice"
1118 " (lockset %s)" % self.name)
1120 if priority is None:
1121 priority = _DEFAULT_PRIORITY
1123 # We need to keep track of how long we spent waiting for a lock. The
1124 # timeout passed to this function is over all lock acquires.
1125 running_timeout = utils.RunningTimeout(timeout, False)
1128 if names is not None:
1129 # Support passing in a single resource to acquire rather than many
1130 if isinstance(names, basestring):
1133 return self.__acquire_inner(names, False, shared, priority,
1134 running_timeout.Remaining, test_notify)
1137 # If no names are given acquire the whole set by not letting new names
1138 # being added before we release, and getting the current list of names.
1139 # Some of them may then be deleted later, but we'll cope with this.
1141 # We'd like to acquire this lock in a shared way, as it's nice if
1142 # everybody else can use the instances at the same time. If we are
1143 # acquiring them exclusively though they won't be able to do this
1144 # anyway, though, so we'll get the list lock exclusively as well in
1145 # order to be able to do add() on the set while owning it.
1146 if not self.__lock.acquire(shared=shared, priority=priority,
1147 timeout=running_timeout.Remaining()):
1148 raise _AcquireTimeout()
1150 # note we own the set-lock
1153 return self.__acquire_inner(self.__names(), True, shared, priority,
1154 running_timeout.Remaining, test_notify)
1156 # We shouldn't have problems adding the lock to the owners list, but
1157 # if we did we'll try to release this lock and re-raise exception.
1158 # Of course something is going to be really wrong, after this.
1159 self.__lock.release()
1163 except _AcquireTimeout:
1166 def __acquire_inner(self, names, want_all, shared, priority,
1167 timeout_fn, test_notify):
1168 """Inner logic for acquiring a number of locks.
1170 @param names: Names of the locks to be acquired
1171 @param want_all: Whether all locks in the set should be acquired
1172 @param shared: Whether to acquire in shared mode
1173 @param timeout_fn: Function returning remaining timeout
1174 @param priority: Priority for acquiring locks
1175 @param test_notify: Special callback function for unittesting
1180 # First we look the locks up on __lockdict. We have no way of being sure
1181 # they will still be there after, but this makes it a lot faster should
1182 # just one of them be the already wrong. Using a sorted sequence to prevent
1184 for lname in sorted(utils.UniqueSequence(names)):
1186 lock = self.__lockdict[lname] # raises KeyError if lock is not there
1189 # We are acquiring all the set, it doesn't matter if this particular
1190 # element is not there anymore.
1193 raise errors.LockError("Non-existing lock %s in set %s (it may have"
1194 " been removed)" % (lname, self.name))
1196 acquire_list.append((lname, lock))
1198 # This will hold the locknames we effectively acquired.
1202 # Now acquire_list contains a sorted list of resources and locks we
1203 # want. In order to get them we loop on this (private) list and
1204 # acquire() them. We gave no real guarantee they will still exist till
1205 # this is done but .acquire() itself is safe and will alert us if the
1206 # lock gets deleted.
1207 for (lname, lock) in acquire_list:
1208 if __debug__ and callable(test_notify):
1209 test_notify_fn = lambda: test_notify(lname)
1211 test_notify_fn = None
1213 timeout = timeout_fn()
1216 # raises LockError if the lock was deleted
1217 acq_success = lock.acquire(shared=shared, timeout=timeout,
1219 test_notify=test_notify_fn)
1220 except errors.LockError:
1222 # We are acquiring all the set, it doesn't matter if this
1223 # particular element is not there anymore.
1226 raise errors.LockError("Non-existing lock %s in set %s (it may"
1227 " have been removed)" % (lname, self.name))
1230 # Couldn't get lock or timeout occurred
1232 # This shouldn't happen as SharedLock.acquire(timeout=None) is
1234 raise errors.LockError("Failed to get lock %s (set %s)" %
1237 raise _AcquireTimeout()
1240 # now the lock cannot be deleted, we have it!
1241 self._add_owned(name=lname)
1245 # We shouldn't have problems adding the lock to the owners list, but
1246 # if we did we'll try to release this lock and re-raise exception.
1247 # Of course something is going to be really wrong after this.
1253 # Release all owned locks
1254 self._release_and_delete_owned()
1259 def downgrade(self, names=None):
1260 """Downgrade a set of resource locks from exclusive to shared mode.
1262 The locks must have been acquired in exclusive mode.
1265 assert self.is_owned(), ("downgrade on lockset %s while not owning any"
1266 " lock" % self.name)
1268 # Support passing in a single resource to downgrade rather than many
1269 if isinstance(names, basestring):
1272 owned = self.list_owned()
1278 assert owned.issuperset(names), \
1279 ("downgrade() on unheld resources %s (set %s)" %
1280 (names.difference(owned), self.name))
1282 for lockname in names:
1283 self.__lockdict[lockname].downgrade()
1285 # Do we own the lockset in exclusive mode?
1286 if self.__lock.is_owned(shared=0):
1287 # Have all locks been downgraded?
1288 if not compat.any(lock.is_owned(shared=0)
1289 for lock in self.__lockdict.values()):
1290 self.__lock.downgrade()
1291 assert self.__lock.is_owned(shared=1)
1295 def release(self, names=None):
1296 """Release a set of resource locks, at the same level.
1298 You must have acquired the locks, either in shared or in exclusive mode,
1299 before releasing them.
1301 @type names: list of strings, or None
1302 @param names: the names of the locks which shall be released
1303 (defaults to all the locks acquired at that level).
1306 assert self.is_owned(), ("release() on lock set %s while not owner" %
1309 # Support passing in a single resource to release rather than many
1310 if isinstance(names, basestring):
1314 names = self.list_owned()
1317 assert self.list_owned().issuperset(names), (
1318 "release() on unheld resources %s (set %s)" %
1319 (names.difference(self.list_owned()), self.name))
1321 # First of all let's release the "all elements" lock, if set.
1322 # After this 'add' can work again
1323 if self.__lock.is_owned():
1324 self.__lock.release()
1327 for lockname in names:
1328 # If we are sure the lock doesn't leave __lockdict without being
1329 # exclusively held we can do this...
1330 self.__lockdict[lockname].release()
1331 self._del_owned(name=lockname)
1333 def add(self, names, acquired=0, shared=0):
1334 """Add a new set of elements to the set
1336 @type names: list of strings
1337 @param names: names of the new elements to add
1338 @type acquired: integer (0/1) used as a boolean
1339 @param acquired: pre-acquire the new resource?
1340 @type shared: integer (0/1) used as a boolean
1341 @param shared: is the pre-acquisition shared?
1344 # Check we don't already own locks at this level
1345 assert not self.is_owned() or self.__lock.is_owned(shared=0), \
1346 ("Cannot add locks if the set %s is only partially owned, or shared" %
1349 # Support passing in a single resource to add rather than many
1350 if isinstance(names, basestring):
1353 # If we don't already own the set-level lock acquired in an exclusive way
1354 # we'll get it and note we need to release it later.
1355 release_lock = False
1356 if not self.__lock.is_owned():
1358 self.__lock.acquire()
1361 invalid_names = set(self.__names()).intersection(names)
1363 # This must be an explicit raise, not an assert, because assert is
1364 # turned off when using optimization, and this can happen because of
1365 # concurrency even if the user doesn't want it.
1366 raise errors.LockError("duplicate add(%s) on lockset %s" %
1367 (invalid_names, self.name))
1369 for lockname in names:
1370 lock = SharedLock(self._GetLockName(lockname), monitor=self.__monitor)
1373 # No need for priority or timeout here as this lock has just been
1375 lock.acquire(shared=shared)
1376 # now the lock cannot be deleted, we have it!
1378 self._add_owned(name=lockname)
1380 # We shouldn't have problems adding the lock to the owners list,
1381 # but if we did we'll try to release this lock and re-raise
1382 # exception. Of course something is going to be really wrong,
1383 # after this. On the other hand the lock hasn't been added to the
1384 # __lockdict yet so no other threads should be pending on it. This
1385 # release is just a safety measure.
1389 self.__lockdict[lockname] = lock
1392 # Only release __lock if we were not holding it previously.
1394 self.__lock.release()
1398 def remove(self, names):
1399 """Remove elements from the lock set.
1401 You can either not hold anything in the lockset or already hold a superset
1402 of the elements you want to delete, exclusively.
1404 @type names: list of strings
1405 @param names: names of the resource to remove.
1407 @return: a list of locks which we removed; the list is always
1408 equal to the names list if we were holding all the locks
1412 # Support passing in a single resource to remove rather than many
1413 if isinstance(names, basestring):
1416 # If we own any subset of this lock it must be a superset of what we want
1417 # to delete. The ownership must also be exclusive, but that will be checked
1418 # by the lock itself.
1419 assert not self.is_owned() or self.list_owned().issuperset(names), (
1420 "remove() on acquired lockset %s while not owning all elements" %
1426 # Calling delete() acquires the lock exclusively if we don't already own
1427 # it, and causes all pending and subsequent lock acquires to fail. It's
1428 # fine to call it out of order because delete() also implies release(),
1429 # and the assertion above guarantees that if we either already hold
1430 # everything we want to delete, or we hold none.
1432 self.__lockdict[lname].delete()
1433 removed.append(lname)
1434 except (KeyError, errors.LockError):
1435 # This cannot happen if we were already holding it, verify:
1436 assert not self.is_owned(), ("remove failed while holding lockset %s" %
1439 # If no LockError was raised we are the ones who deleted the lock.
1440 # This means we can safely remove it from lockdict, as any further or
1441 # pending delete() or acquire() will fail (and nobody can have the lock
1442 # since before our call to delete()).
1444 # This is done in an else clause because if the exception was thrown
1445 # it's the job of the one who actually deleted it.
1446 del self.__lockdict[lname]
1447 # And let's remove it from our private list if we owned it.
1449 self._del_owned(name=lname)
1454 # Locking levels, must be acquired in increasing order.
1455 # Current rules are:
1456 # - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
1457 # acquired before performing any operation, either in shared or in exclusive
1458 # mode. acquiring the BGL in exclusive mode is discouraged and should be
1460 # - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
1461 # If you need more than one node, or more than one instance, acquire them at
1477 # Lock levels which are modifiable
1478 LEVELS_MOD = frozenset([
1485 #: Lock level names (make sure to use singular form)
1487 LEVEL_CLUSTER: "cluster",
1488 LEVEL_INSTANCE: "instance",
1489 LEVEL_NODEGROUP: "nodegroup",
1491 LEVEL_NODE_RES: "node-res",
1494 # Constant for the big ganeti lock
1498 class GanetiLockManager:
1499 """The Ganeti Locking Library
1501 The purpose of this small library is to manage locking for ganeti clusters
1502 in a central place, while at the same time doing dynamic checks against
1503 possible deadlocks. It will also make it easier to transition to a different
1504 lock type should we migrate away from python threads.
1509 def __init__(self, nodes, nodegroups, instances):
1510 """Constructs a new GanetiLockManager object.
1512 There should be only a GanetiLockManager object at any time, so this
1513 function raises an error if this is not the case.
1515 @param nodes: list of node names
1516 @param nodegroups: list of nodegroup uuids
1517 @param instances: list of instance names
1520 assert self.__class__._instance is None, \
1521 "double GanetiLockManager instance"
1523 self.__class__._instance = self
1525 self._monitor = LockMonitor()
1527 # The keyring contains all the locks, at their level and in the correct
1530 LEVEL_CLUSTER: LockSet([BGL], "cluster", monitor=self._monitor),
1531 LEVEL_NODE: LockSet(nodes, "node", monitor=self._monitor),
1532 LEVEL_NODE_RES: LockSet(nodes, "node-res", monitor=self._monitor),
1533 LEVEL_NODEGROUP: LockSet(nodegroups, "nodegroup", monitor=self._monitor),
1534 LEVEL_INSTANCE: LockSet(instances, "instance",
1535 monitor=self._monitor),
1538 assert compat.all(ls.name == LEVEL_NAMES[level]
1539 for (level, ls) in self.__keyring.items())
1541 def AddToLockMonitor(self, provider):
1542 """Registers a new lock with the monitor.
1544 See L{LockMonitor.RegisterLock}.
1547 return self._monitor.RegisterLock(provider)
1549 def QueryLocks(self, fields):
1550 """Queries information from all locks.
1552 See L{LockMonitor.QueryLocks}.
1555 return self._monitor.QueryLocks(fields)
1557 def _names(self, level):
1558 """List the lock names at the given level.
1560 This can be used for debugging/testing purposes.
1562 @param level: the level whose list of locks to get
1565 assert level in LEVELS, "Invalid locking level %s" % level
1566 return self.__keyring[level]._names()
1568 def is_owned(self, level):
1569 """Check whether we are owning locks at the given level
1572 return self.__keyring[level].is_owned()
1574 def list_owned(self, level):
1575 """Get the set of owned locks at the given level
1578 return self.__keyring[level].list_owned()
1580 def check_owned(self, level, names, shared=-1):
1581 """Check if locks at a certain level are owned in a specific mode.
1583 @see: L{LockSet.check_owned}
1586 return self.__keyring[level].check_owned(names, shared=shared)
1588 def _upper_owned(self, level):
1589 """Check that we don't own any lock at a level greater than the given one.
1592 # This way of checking only works if LEVELS[i] = i, which we check for in
1594 return compat.any((self.is_owned(l) for l in LEVELS[level + 1:]))
1596 def _BGL_owned(self): # pylint: disable=C0103
1597 """Check if the current thread owns the BGL.
1599 Both an exclusive or a shared acquisition work.
1602 return BGL in self.__keyring[LEVEL_CLUSTER].list_owned()
1605 def _contains_BGL(level, names): # pylint: disable=C0103
1606 """Check if the level contains the BGL.
1608 Check if acting on the given level and set of names will change
1609 the status of the Big Ganeti Lock.
1612 return level == LEVEL_CLUSTER and (names is None or BGL in names)
1614 def acquire(self, level, names, timeout=None, shared=0, priority=None):
1615 """Acquire a set of resource locks, at the same level.
1617 @type level: member of locking.LEVELS
1618 @param level: the level at which the locks shall be acquired
1619 @type names: list of strings (or string)
1620 @param names: the names of the locks which shall be acquired
1621 (special lock names, or instance/node names)
1622 @type shared: integer (0/1) used as a boolean
1623 @param shared: whether to acquire in shared mode; by default
1624 an exclusive lock will be acquired
1625 @type timeout: float
1626 @param timeout: Maximum time to acquire all locks
1627 @type priority: integer
1628 @param priority: Priority for acquiring lock
1631 assert level in LEVELS, "Invalid locking level %s" % level
1633 # Check that we are either acquiring the Big Ganeti Lock or we already own
1634 # it. Some "legacy" opcodes need to be sure they are run non-concurrently
1635 # so even if we've migrated we need to at least share the BGL to be
1636 # compatible with them. Of course if we own the BGL exclusively there's no
1637 # point in acquiring any other lock, unless perhaps we are half way through
1638 # the migration of the current opcode.
1639 assert (self._contains_BGL(level, names) or self._BGL_owned()), (
1640 "You must own the Big Ganeti Lock before acquiring any other")
1642 # Check we don't own locks at the same or upper levels.
1643 assert not self._upper_owned(level), ("Cannot acquire locks at a level"
1644 " while owning some at a greater one")
1646 # Acquire the locks in the set.
1647 return self.__keyring[level].acquire(names, shared=shared, timeout=timeout,
1650 def downgrade(self, level, names=None):
1651 """Downgrade a set of resource locks from exclusive to shared mode.
1653 You must have acquired the locks in exclusive mode.
1655 @type level: member of locking.LEVELS
1656 @param level: the level at which the locks shall be downgraded
1657 @type names: list of strings, or None
1658 @param names: the names of the locks which shall be downgraded
1659 (defaults to all the locks acquired at the level)
1662 assert level in LEVELS, "Invalid locking level %s" % level
1664 return self.__keyring[level].downgrade(names=names)
1666 def release(self, level, names=None):
1667 """Release a set of resource locks, at the same level.
1669 You must have acquired the locks, either in shared or in exclusive
1670 mode, before releasing them.
1672 @type level: member of locking.LEVELS
1673 @param level: the level at which the locks shall be released
1674 @type names: list of strings, or None
1675 @param names: the names of the locks which shall be released
1676 (defaults to all the locks acquired at that level)
1679 assert level in LEVELS, "Invalid locking level %s" % level
1680 assert (not self._contains_BGL(level, names) or
1681 not self._upper_owned(LEVEL_CLUSTER)), (
1682 "Cannot release the Big Ganeti Lock while holding something"
1683 " at upper levels (%r)" %
1684 (utils.CommaJoin(["%s=%r" % (LEVEL_NAMES[i], self.list_owned(i))
1685 for i in self.__keyring.keys()]), ))
1687 # Release will complain if we don't own the locks already
1688 return self.__keyring[level].release(names)
1690 def add(self, level, names, acquired=0, shared=0):
1691 """Add locks at the specified level.
1693 @type level: member of locking.LEVELS_MOD
1694 @param level: the level at which the locks shall be added
1695 @type names: list of strings
1696 @param names: names of the locks to acquire
1697 @type acquired: integer (0/1) used as a boolean
1698 @param acquired: whether to acquire the newly added locks
1699 @type shared: integer (0/1) used as a boolean
1700 @param shared: whether the acquisition will be shared
1703 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1704 assert self._BGL_owned(), ("You must own the BGL before performing other"
1706 assert not self._upper_owned(level), ("Cannot add locks at a level"
1707 " while owning some at a greater one")
1708 return self.__keyring[level].add(names, acquired=acquired, shared=shared)
1710 def remove(self, level, names):
1711 """Remove locks from the specified level.
1713 You must either already own the locks you are trying to remove
1714 exclusively or not own any lock at an upper level.
1716 @type level: member of locking.LEVELS_MOD
1717 @param level: the level at which the locks shall be removed
1718 @type names: list of strings
1719 @param names: the names of the locks which shall be removed
1720 (special lock names, or instance/node names)
1723 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1724 assert self._BGL_owned(), ("You must own the BGL before performing other"
1726 # Check we either own the level or don't own anything from here
1727 # up. LockSet.remove() will check the case in which we don't own
1728 # all the needed resources, or we have a shared ownership.
1729 assert self.is_owned(level) or not self._upper_owned(level), (
1730 "Cannot remove locks at a level while not owning it or"
1731 " owning some at a greater one")
1732 return self.__keyring[level].remove(names)
1735 def _MonitorSortKey((item, idx, num)):
1736 """Sorting key function.
1738 Sort by name, registration order and then order of information. This provides
1739 a stable sort order over different providers, even if they return the same
1743 (name, _, _, _) = item
1745 return (utils.NiceSortKey(name), num, idx)
1748 class LockMonitor(object):
1749 _LOCK_ATTR = "_lock"
1752 """Initializes this class.
1755 self._lock = SharedLock("LockMonitor")
1757 # Counter for stable sorting
1758 self._counter = itertools.count(0)
1760 # Tracked locks. Weak references are used to avoid issues with circular
1761 # references and deletion.
1762 self._locks = weakref.WeakKeyDictionary()
1764 @ssynchronized(_LOCK_ATTR)
1765 def RegisterLock(self, provider):
1766 """Registers a new lock.
1768 @param provider: Object with a callable method named C{GetLockInfo}, taking
1769 a single C{set} containing the requested information items
1770 @note: It would be nicer to only receive the function generating the
1771 requested information but, as it turns out, weak references to bound
1772 methods (e.g. C{self.GetLockInfo}) are tricky; there are several
1773 workarounds, but none of the ones I found works properly in combination
1774 with a standard C{WeakKeyDictionary}
1777 assert provider not in self._locks, "Duplicate registration"
1779 # There used to be a check for duplicate names here. As it turned out, when
1780 # a lock is re-created with the same name in a very short timeframe, the
1781 # previous instance might not yet be removed from the weakref dictionary.
1782 # By keeping track of the order of incoming registrations, a stable sort
1783 # ordering can still be guaranteed.
1785 self._locks[provider] = self._counter.next()
1787 def _GetLockInfo(self, requested):
1788 """Get information from all locks.
1791 # Must hold lock while getting consistent list of tracked items
1792 self._lock.acquire(shared=1)
1794 items = self._locks.items()
1796 self._lock.release()
1798 return [(info, idx, num)
1799 for (provider, num) in items
1800 for (idx, info) in enumerate(provider.GetLockInfo(requested))]
1802 def _Query(self, fields):
1803 """Queries information from all locks.
1805 @type fields: list of strings
1806 @param fields: List of fields to return
1809 qobj = query.Query(query.LOCK_FIELDS, fields)
1811 # Get all data with internal lock held and then sort by name and incoming
1813 lockinfo = sorted(self._GetLockInfo(qobj.RequestedData()),
1814 key=_MonitorSortKey)
1816 # Extract lock information and build query data
1817 return (qobj, query.LockQueryData(map(compat.fst, lockinfo)))
1819 def QueryLocks(self, fields):
1820 """Queries information from all locks.
1822 @type fields: list of strings
1823 @param fields: List of fields to return
1826 (qobj, ctx) = self._Query(fields)
1828 # Prepare query response
1829 return query.GetQueryResponse(qobj, ctx)