4 # Copyright (C) 2006, 2007 Google Inc.
6 # This program is free software; you can redistribute it and/or modify
7 # it under the terms of the GNU General Public License as published by
8 # the Free Software Foundation; either version 2 of the License, or
9 # (at your option) any later version.
11 # This program is distributed in the hope that it will be useful, but
12 # WITHOUT ANY WARRANTY; without even the implied warranty of
13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 # General Public License for more details.
16 # You should have received a copy of the GNU General Public License
17 # along with this program; if not, write to the Free Software
18 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
21 """Module implementing the Ganeti locking code."""
23 # pylint: disable-msg=W0212
25 # W0212 since e.g. LockSet methods use (a lot) the internals of
34 from ganeti import errors
35 from ganeti import utils
36 from ganeti import compat
39 def ssynchronized(lock, shared=0):
40 """Shared Synchronization decorator.
42 Calls the function holding the given lock, either in exclusive or shared
43 mode. It requires the passed lock to be a SharedLock (or support its
48 def sync_function(*args, **kwargs):
49 lock.acquire(shared=shared)
51 return fn(*args, **kwargs)
58 class RunningTimeout(object):
59 """Class to calculate remaining timeout when doing several operations.
69 def __init__(self, timeout, allow_negative, _time_fn=time.time):
70 """Initializes this class.
73 @param timeout: Timeout duration
74 @type allow_negative: bool
75 @param allow_negative: Whether to return values below zero
76 @param _time_fn: Time function for unittests
81 if timeout is not None and timeout < 0.0:
82 raise ValueError("Timeout must not be negative")
84 self._timeout = timeout
85 self._allow_negative = allow_negative
86 self._time_fn = _time_fn
88 self._start_time = None
91 """Returns the remaining timeout.
94 if self._timeout is None:
97 # Get start time on first calculation
98 if self._start_time is None:
99 self._start_time = self._time_fn()
101 # Calculate remaining time
102 remaining_timeout = self._start_time + self._timeout - self._time_fn()
104 if not self._allow_negative:
105 # Ensure timeout is always >= 0
106 return max(0.0, remaining_timeout)
108 return remaining_timeout
111 class _SingleNotifyPipeConditionWaiter(object):
112 """Helper class for SingleNotifyPipeCondition
120 def __init__(self, poller, fd):
121 """Constructor for _SingleNotifyPipeConditionWaiter
123 @type poller: select.poll
124 @param poller: Poller object
126 @param fd: File descriptor to wait for
129 object.__init__(self)
130 self._poller = poller
133 def __call__(self, timeout):
134 """Wait for something to happen on the pipe.
136 @type timeout: float or None
137 @param timeout: Timeout for waiting (can be None)
140 running_timeout = RunningTimeout(timeout, True)
143 remaining_time = running_timeout.Remaining()
145 if remaining_time is not None:
146 if remaining_time < 0.0:
149 # Our calculation uses seconds, poll() wants milliseconds
150 remaining_time *= 1000
153 result = self._poller.poll(remaining_time)
154 except EnvironmentError, err:
155 if err.errno != errno.EINTR:
159 # Check whether we were notified
160 if result and result[0][0] == self._fd:
164 class _BaseCondition(object):
165 """Base class containing common code for conditions.
167 Some of this code is taken from python's threading module.
179 def __init__(self, lock):
180 """Constructor for _BaseCondition.
182 @type lock: threading.Lock
183 @param lock: condition base lock
186 object.__init__(self)
189 self._release_save = lock._release_save
190 except AttributeError:
191 self._release_save = self._base_release_save
193 self._acquire_restore = lock._acquire_restore
194 except AttributeError:
195 self._acquire_restore = self._base_acquire_restore
197 self._is_owned = lock._is_owned
198 except AttributeError:
199 self._is_owned = self._base_is_owned
203 # Export the lock's acquire() and release() methods
204 self.acquire = lock.acquire
205 self.release = lock.release
207 def _base_is_owned(self):
208 """Check whether lock is owned by current thread.
211 if self._lock.acquire(0):
216 def _base_release_save(self):
219 def _base_acquire_restore(self, _):
222 def _check_owned(self):
223 """Raise an exception if the current thread doesn't own the lock.
226 if not self._is_owned():
227 raise RuntimeError("cannot work with un-aquired lock")
230 class SingleNotifyPipeCondition(_BaseCondition):
231 """Condition which can only be notified once.
233 This condition class uses pipes and poll, internally, to be able to wait for
234 notification with a timeout, without resorting to polling. It is almost
235 compatible with Python's threading.Condition, with the following differences:
236 - notifyAll can only be called once, and no wait can happen after that
237 - notify is not supported, only notifyAll
249 _waiter_class = _SingleNotifyPipeConditionWaiter
251 def __init__(self, lock):
252 """Constructor for SingleNotifyPipeCondition
255 _BaseCondition.__init__(self, lock)
257 self._notified = False
259 self._write_fd = None
262 def _check_unnotified(self):
263 """Throws an exception if already notified.
267 raise RuntimeError("cannot use already notified condition")
270 """Cleanup open file descriptors, if any.
273 if self._read_fd is not None:
274 os.close(self._read_fd)
277 if self._write_fd is not None:
278 os.close(self._write_fd)
279 self._write_fd = None
282 def wait(self, timeout=None):
283 """Wait for a notification.
285 @type timeout: float or None
286 @param timeout: Waiting timeout (can be None)
290 self._check_unnotified()
294 if self._poller is None:
295 (self._read_fd, self._write_fd) = os.pipe()
296 self._poller = select.poll()
297 self._poller.register(self._read_fd, select.POLLHUP)
299 wait_fn = self._waiter_class(self._poller, self._read_fd)
300 state = self._release_save()
302 # Wait for notification
306 self._acquire_restore(state)
309 if self._nwaiters == 0:
312 def notifyAll(self): # pylint: disable-msg=C0103
313 """Close the writing side of the pipe to notify all waiters.
317 self._check_unnotified()
318 self._notified = True
319 if self._write_fd is not None:
320 os.close(self._write_fd)
321 self._write_fd = None
324 class PipeCondition(_BaseCondition):
325 """Group-only non-polling condition with counters.
327 This condition class uses pipes and poll, internally, to be able to wait for
328 notification with a timeout, without resorting to polling. It is almost
329 compatible with Python's threading.Condition, but only supports notifyAll and
330 non-recursive locks. As an additional features it's able to report whether
331 there are any waiting threads.
339 _single_condition_class = SingleNotifyPipeCondition
341 def __init__(self, lock):
342 """Initializes this class.
345 _BaseCondition.__init__(self, lock)
347 self._single_condition = self._single_condition_class(self._lock)
349 def wait(self, timeout=None):
350 """Wait for a notification.
352 @type timeout: float or None
353 @param timeout: Waiting timeout (can be None)
358 # Keep local reference to the pipe. It could be replaced by another thread
359 # notifying while we're waiting.
360 my_condition = self._single_condition
362 assert self._nwaiters >= 0
365 my_condition.wait(timeout)
367 assert self._nwaiters > 0
370 def notifyAll(self): # pylint: disable-msg=C0103
371 """Notify all currently waiting threads.
375 self._single_condition.notifyAll()
376 self._single_condition = self._single_condition_class(self._lock)
378 def has_waiting(self):
379 """Returns whether there are active waiters.
384 return bool(self._nwaiters)
387 class SharedLock(object):
388 """Implements a shared lock.
390 Multiple threads can acquire the lock in a shared way, calling
391 acquire_shared(). In order to acquire the lock in an exclusive way threads
392 can call acquire_exclusive().
394 The lock prevents starvation but does not guarantee that threads will acquire
395 the shared lock in the order they queued for it, just that they will
409 __condition_class = PipeCondition
412 """Construct a new SharedLock.
415 object.__init__(self)
418 self.__lock = threading.Lock()
420 # Queue containing waiting acquires
423 # Active and inactive conditions for shared locks
424 self.__active_shr_c = self.__condition_class(self.__lock)
425 self.__inactive_shr_c = self.__condition_class(self.__lock)
427 # Current lock holders
431 # is this lock in the deleted state?
432 self.__deleted = False
434 def __check_deleted(self):
435 """Raises an exception if the lock has been deleted.
439 raise errors.LockError("Deleted lock")
441 def __is_sharer(self):
442 """Is the current thread sharing the lock at this time?
445 return threading.currentThread() in self.__shr
447 def __is_exclusive(self):
448 """Is the current thread holding the lock exclusively at this time?
451 return threading.currentThread() == self.__exc
453 def __is_owned(self, shared=-1):
454 """Is the current thread somehow owning the lock at this time?
456 This is a private version of the function, which presumes you're holding
461 return self.__is_sharer() or self.__is_exclusive()
463 return self.__is_sharer()
465 return self.__is_exclusive()
467 def _is_owned(self, shared=-1):
468 """Is the current thread somehow owning the lock at this time?
471 - < 0: check for any type of ownership (default)
472 - 0: check for exclusive ownership
473 - > 0: check for shared ownership
476 self.__lock.acquire()
478 return self.__is_owned(shared=shared)
480 self.__lock.release()
482 def _count_pending(self):
483 """Returns the number of pending acquires.
488 self.__lock.acquire()
490 return len(self.__pending)
492 self.__lock.release()
494 def __do_acquire(self, shared):
495 """Actually acquire the lock.
499 self.__shr.add(threading.currentThread())
501 self.__exc = threading.currentThread()
503 def __can_acquire(self, shared):
504 """Determine whether lock can be acquired.
508 return self.__exc is None
510 return len(self.__shr) == 0 and self.__exc is None
512 def __is_on_top(self, cond):
513 """Checks whether the passed condition is on top of the queue.
515 The caller must make sure the queue isn't empty.
518 return self.__pending[0] == cond
520 def __acquire_unlocked(self, shared, timeout):
521 """Acquire a shared lock.
523 @param shared: whether to acquire in shared mode; by default an
524 exclusive lock will be acquired
525 @param timeout: maximum waiting time before giving up
528 self.__check_deleted()
530 # We cannot acquire the lock if we already have it
531 assert not self.__is_owned(), "double acquire() on a non-recursive lock"
533 # Check whether someone else holds the lock or there are pending acquires.
534 if not self.__pending and self.__can_acquire(shared):
535 # Apparently not, can acquire lock directly.
536 self.__do_acquire(shared)
540 wait_condition = self.__active_shr_c
542 # Check if we're not yet in the queue
543 if wait_condition not in self.__pending:
544 self.__pending.append(wait_condition)
546 wait_condition = self.__condition_class(self.__lock)
547 # Always add to queue
548 self.__pending.append(wait_condition)
551 # Wait until we become the topmost acquire in the queue or the timeout
553 while not (self.__is_on_top(wait_condition) and
554 self.__can_acquire(shared)):
555 # Wait for notification
556 wait_condition.wait(timeout)
557 self.__check_deleted()
559 # A lot of code assumes blocking acquires always succeed. Loop
560 # internally for that case.
561 if timeout is not None:
564 if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
565 self.__do_acquire(shared)
568 # Remove condition from queue if there are no more waiters
569 if not wait_condition.has_waiting() and not self.__deleted:
570 self.__pending.remove(wait_condition)
574 def acquire(self, shared=0, timeout=None, test_notify=None):
575 """Acquire a shared lock.
577 @type shared: integer (0/1) used as a boolean
578 @param shared: whether to acquire in shared mode; by default an
579 exclusive lock will be acquired
581 @param timeout: maximum waiting time before giving up
582 @type test_notify: callable or None
583 @param test_notify: Special callback function for unittesting
586 self.__lock.acquire()
588 # We already got the lock, notify now
589 if __debug__ and callable(test_notify):
592 return self.__acquire_unlocked(shared, timeout)
594 self.__lock.release()
597 """Release a Shared Lock.
599 You must have acquired the lock, either in shared or in exclusive mode,
600 before calling this function.
603 self.__lock.acquire()
605 assert self.__is_exclusive() or self.__is_sharer(), \
606 "Cannot release non-owned lock"
608 # Autodetect release type
609 if self.__is_exclusive():
612 self.__shr.remove(threading.currentThread())
614 # Notify topmost condition in queue
616 first_condition = self.__pending[0]
617 first_condition.notifyAll()
619 if first_condition == self.__active_shr_c:
620 self.__active_shr_c = self.__inactive_shr_c
621 self.__inactive_shr_c = first_condition
624 self.__lock.release()
626 def delete(self, timeout=None):
627 """Delete a Shared Lock.
629 This operation will declare the lock for removal. First the lock will be
630 acquired in exclusive mode if you don't already own it, then the lock
631 will be put in a state where any future and pending acquire() fail.
634 @param timeout: maximum waiting time before giving up
637 self.__lock.acquire()
639 assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"
641 self.__check_deleted()
643 # The caller is allowed to hold the lock exclusively already.
644 acquired = self.__is_exclusive()
647 acquired = self.__acquire_unlocked(0, timeout)
649 assert self.__is_exclusive() and not self.__is_sharer(), \
650 "Lock wasn't acquired in exclusive mode"
653 self.__deleted = True
656 # Notify all acquires. They'll throw an error.
657 while self.__pending:
658 self.__pending.pop().notifyAll()
662 self.__lock.release()
664 def _release_save(self):
665 shared = self.__is_sharer()
669 def _acquire_restore(self, shared):
670 self.acquire(shared=shared)
673 # Whenever we want to acquire a full LockSet we pass None as the value
674 # to acquire. Hide this behind this nicely named constant.
678 class _AcquireTimeout(Exception):
679 """Internal exception to abort an acquire on a timeout.
685 """Implements a set of locks.
687 This abstraction implements a set of shared locks for the same resource type,
688 distinguished by name. The user can lock a subset of the resources and the
689 LockSet will take care of acquiring the locks always in the same order, thus
692 All the locks needed in the same set must be acquired together, though.
695 def __init__(self, members=None):
696 """Constructs a new LockSet.
698 @type members: list of strings
699 @param members: initial members of the set
702 # Used internally to guarantee coherency.
703 self.__lock = SharedLock()
705 # The lockdict indexes the relationship name -> lock
706 # The order-of-locking is implied by the alphabetical order of names
709 if members is not None:
711 self.__lockdict[name] = SharedLock()
713 # The owner dict contains the set of locks each thread owns. For
714 # performance each thread can access its own key without a global lock on
715 # this structure. It is paramount though that *no* other type of access is
716 # done to this structure (eg. no looping over its keys). *_owner helper
717 # function are defined to guarantee access is correct, but in general never
718 # do anything different than __owners[threading.currentThread()], or there
723 """Is the current thread a current level owner?"""
724 return threading.currentThread() in self.__owners
726 def _add_owned(self, name=None):
727 """Note the current thread owns the given lock"""
729 if not self._is_owned():
730 self.__owners[threading.currentThread()] = set()
733 self.__owners[threading.currentThread()].add(name)
735 self.__owners[threading.currentThread()] = set([name])
737 def _del_owned(self, name=None):
738 """Note the current thread owns the given lock"""
740 assert not (name is None and self.__lock._is_owned()), \
741 "Cannot hold internal lock when deleting owner status"
744 self.__owners[threading.currentThread()].remove(name)
746 # Only remove the key if we don't hold the set-lock as well
747 if (not self.__lock._is_owned() and
748 not self.__owners[threading.currentThread()]):
749 del self.__owners[threading.currentThread()]
751 def _list_owned(self):
752 """Get the set of resource names owned by the current thread"""
754 return self.__owners[threading.currentThread()].copy()
758 def _release_and_delete_owned(self):
759 """Release and delete all resources owned by the current thread"""
760 for lname in self._list_owned():
761 lock = self.__lockdict[lname]
764 self._del_owned(name=lname)
767 """Return the current set of names.
769 Only call this function while holding __lock and don't iterate on the
770 result after releasing the lock.
773 return self.__lockdict.keys()
776 """Return a copy of the current set of elements.
778 Used only for debugging purposes.
781 # If we don't already own the set-level lock acquired
782 # we'll get it and note we need to release it later.
784 if not self.__lock._is_owned():
786 self.__lock.acquire(shared=1)
788 result = self.__names()
791 self.__lock.release()
794 def acquire(self, names, timeout=None, shared=0, test_notify=None):
795 """Acquire a set of resource locks.
797 @type names: list of strings (or string)
798 @param names: the names of the locks which shall be acquired
799 (special lock names, or instance/node names)
800 @type shared: integer (0/1) used as a boolean
801 @param shared: whether to acquire in shared mode; by default an
802 exclusive lock will be acquired
803 @type timeout: float or None
804 @param timeout: Maximum time to acquire all locks
805 @type test_notify: callable or None
806 @param test_notify: Special callback function for unittesting
808 @return: Set of all locks successfully acquired or None in case of timeout
810 @raise errors.LockError: when any lock we try to acquire has
811 been deleted before we succeed. In this case none of the
812 locks requested will be acquired.
815 assert timeout is None or timeout >= 0.0
817 # Check we don't already own locks at this level
818 assert not self._is_owned(), "Cannot acquire locks in the same set twice"
820 # We need to keep track of how long we spent waiting for a lock. The
821 # timeout passed to this function is over all lock acquires.
822 running_timeout = RunningTimeout(timeout, False)
825 if names is not None:
826 # Support passing in a single resource to acquire rather than many
827 if isinstance(names, basestring):
830 return self.__acquire_inner(names, False, shared,
831 running_timeout.Remaining, test_notify)
834 # If no names are given acquire the whole set by not letting new names
835 # being added before we release, and getting the current list of names.
836 # Some of them may then be deleted later, but we'll cope with this.
838 # We'd like to acquire this lock in a shared way, as it's nice if
839 # everybody else can use the instances at the same time. If are
840 # acquiring them exclusively though they won't be able to do this
841 # anyway, though, so we'll get the list lock exclusively as well in
842 # order to be able to do add() on the set while owning it.
843 if not self.__lock.acquire(shared=shared,
844 timeout=running_timeout.Remaining()):
845 raise _AcquireTimeout()
847 # note we own the set-lock
850 return self.__acquire_inner(self.__names(), True, shared,
851 running_timeout.Remaining, test_notify)
853 # We shouldn't have problems adding the lock to the owners list, but
854 # if we did we'll try to release this lock and re-raise exception.
855 # Of course something is going to be really wrong, after this.
856 self.__lock.release()
860 except _AcquireTimeout:
863 def __acquire_inner(self, names, want_all, shared, timeout_fn, test_notify):
864 """Inner logic for acquiring a number of locks.
866 @param names: Names of the locks to be acquired
867 @param want_all: Whether all locks in the set should be acquired
868 @param shared: Whether to acquire in shared mode
869 @param timeout_fn: Function returning remaining timeout
870 @param test_notify: Special callback function for unittesting
875 # First we look the locks up on __lockdict. We have no way of being sure
876 # they will still be there after, but this makes it a lot faster should
877 # just one of them be the already wrong. Using a sorted sequence to prevent
879 for lname in sorted(utils.UniqueSequence(names)):
881 lock = self.__lockdict[lname] # raises KeyError if lock is not there
884 # We are acquiring all the set, it doesn't matter if this particular
885 # element is not there anymore.
888 raise errors.LockError("Non-existing lock in set (%s)" % lname)
890 acquire_list.append((lname, lock))
892 # This will hold the locknames we effectively acquired.
896 # Now acquire_list contains a sorted list of resources and locks we
897 # want. In order to get them we loop on this (private) list and
898 # acquire() them. We gave no real guarantee they will still exist till
899 # this is done but .acquire() itself is safe and will alert us if the
901 for (lname, lock) in acquire_list:
902 if __debug__ and callable(test_notify):
903 test_notify_fn = lambda: test_notify(lname)
905 test_notify_fn = None
907 timeout = timeout_fn()
910 # raises LockError if the lock was deleted
911 acq_success = lock.acquire(shared=shared, timeout=timeout,
912 test_notify=test_notify_fn)
913 except errors.LockError:
915 # We are acquiring all the set, it doesn't matter if this
916 # particular element is not there anymore.
919 raise errors.LockError("Non-existing lock in set (%s)" % lname)
922 # Couldn't get lock or timeout occurred
924 # This shouldn't happen as SharedLock.acquire(timeout=None) is
926 raise errors.LockError("Failed to get lock %s" % lname)
928 raise _AcquireTimeout()
931 # now the lock cannot be deleted, we have it!
932 self._add_owned(name=lname)
936 # We shouldn't have problems adding the lock to the owners list, but
937 # if we did we'll try to release this lock and re-raise exception.
938 # Of course something is going to be really wrong after this.
944 # Release all owned locks
945 self._release_and_delete_owned()
950 def release(self, names=None):
951 """Release a set of resource locks, at the same level.
953 You must have acquired the locks, either in shared or in exclusive mode,
954 before releasing them.
956 @type names: list of strings, or None
957 @param names: the names of the locks which shall be released
958 (defaults to all the locks acquired at that level).
961 assert self._is_owned(), "release() on lock set while not owner"
963 # Support passing in a single resource to release rather than many
964 if isinstance(names, basestring):
968 names = self._list_owned()
971 assert self._list_owned().issuperset(names), (
972 "release() on unheld resources %s" %
973 names.difference(self._list_owned()))
975 # First of all let's release the "all elements" lock, if set.
976 # After this 'add' can work again
977 if self.__lock._is_owned():
978 self.__lock.release()
981 for lockname in names:
982 # If we are sure the lock doesn't leave __lockdict without being
983 # exclusively held we can do this...
984 self.__lockdict[lockname].release()
985 self._del_owned(name=lockname)
987 def add(self, names, acquired=0, shared=0):
988 """Add a new set of elements to the set
990 @type names: list of strings
991 @param names: names of the new elements to add
992 @type acquired: integer (0/1) used as a boolean
993 @param acquired: pre-acquire the new resource?
994 @type shared: integer (0/1) used as a boolean
995 @param shared: is the pre-acquisition shared?
998 # Check we don't already own locks at this level
999 assert not self._is_owned() or self.__lock._is_owned(shared=0), \
1000 "Cannot add locks if the set is only partially owned, or shared"
1002 # Support passing in a single resource to add rather than many
1003 if isinstance(names, basestring):
1006 # If we don't already own the set-level lock acquired in an exclusive way
1007 # we'll get it and note we need to release it later.
1008 release_lock = False
1009 if not self.__lock._is_owned():
1011 self.__lock.acquire()
1014 invalid_names = set(self.__names()).intersection(names)
1016 # This must be an explicit raise, not an assert, because assert is
1017 # turned off when using optimization, and this can happen because of
1018 # concurrency even if the user doesn't want it.
1019 raise errors.LockError("duplicate add() (%s)" % invalid_names)
1021 for lockname in names:
1025 lock.acquire(shared=shared)
1026 # now the lock cannot be deleted, we have it!
1028 self._add_owned(name=lockname)
1030 # We shouldn't have problems adding the lock to the owners list,
1031 # but if we did we'll try to release this lock and re-raise
1032 # exception. Of course something is going to be really wrong,
1033 # after this. On the other hand the lock hasn't been added to the
1034 # __lockdict yet so no other threads should be pending on it. This
1035 # release is just a safety measure.
1039 self.__lockdict[lockname] = lock
1042 # Only release __lock if we were not holding it previously.
1044 self.__lock.release()
1048 def remove(self, names):
1049 """Remove elements from the lock set.
1051 You can either not hold anything in the lockset or already hold a superset
1052 of the elements you want to delete, exclusively.
1054 @type names: list of strings
1055 @param names: names of the resource to remove.
1057 @return: a list of locks which we removed; the list is always
1058 equal to the names list if we were holding all the locks
1062 # Support passing in a single resource to remove rather than many
1063 if isinstance(names, basestring):
1066 # If we own any subset of this lock it must be a superset of what we want
1067 # to delete. The ownership must also be exclusive, but that will be checked
1068 # by the lock itself.
1069 assert not self._is_owned() or self._list_owned().issuperset(names), (
1070 "remove() on acquired lockset while not owning all elements")
1075 # Calling delete() acquires the lock exclusively if we don't already own
1076 # it, and causes all pending and subsequent lock acquires to fail. It's
1077 # fine to call it out of order because delete() also implies release(),
1078 # and the assertion above guarantees that if we either already hold
1079 # everything we want to delete, or we hold none.
1081 self.__lockdict[lname].delete()
1082 removed.append(lname)
1083 except (KeyError, errors.LockError):
1084 # This cannot happen if we were already holding it, verify:
1085 assert not self._is_owned(), "remove failed while holding lockset"
1087 # If no LockError was raised we are the ones who deleted the lock.
1088 # This means we can safely remove it from lockdict, as any further or
1089 # pending delete() or acquire() will fail (and nobody can have the lock
1090 # since before our call to delete()).
1092 # This is done in an else clause because if the exception was thrown
1093 # it's the job of the one who actually deleted it.
1094 del self.__lockdict[lname]
1095 # And let's remove it from our private list if we owned it.
1096 if self._is_owned():
1097 self._del_owned(name=lname)
1102 # Locking levels, must be acquired in increasing order.
1103 # Current rules are:
1104 # - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
1105 # acquired before performing any operation, either in shared or in exclusive
1106 # mode. acquiring the BGL in exclusive mode is discouraged and should be
1108 # - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
1109 # If you need more than one node, or more than one instance, acquire them at
1115 LEVELS = [LEVEL_CLUSTER,
1119 # Lock levels which are modifiable
1120 LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE]
1123 LEVEL_CLUSTER: "cluster",
1124 LEVEL_INSTANCE: "instance",
1128 # Constant for the big ganeti lock
1132 class GanetiLockManager:
1133 """The Ganeti Locking Library
1135 The purpose of this small library is to manage locking for ganeti clusters
1136 in a central place, while at the same time doing dynamic checks against
1137 possible deadlocks. It will also make it easier to transition to a different
1138 lock type should we migrate away from python threads.
1143 def __init__(self, nodes=None, instances=None):
1144 """Constructs a new GanetiLockManager object.
1146 There should be only a GanetiLockManager object at any time, so this
1147 function raises an error if this is not the case.
1149 @param nodes: list of node names
1150 @param instances: list of instance names
1153 assert self.__class__._instance is None, \
1154 "double GanetiLockManager instance"
1156 self.__class__._instance = self
1158 # The keyring contains all the locks, at their level and in the correct
1161 LEVEL_CLUSTER: LockSet([BGL]),
1162 LEVEL_NODE: LockSet(nodes),
1163 LEVEL_INSTANCE: LockSet(instances),
1166 def _names(self, level):
1167 """List the lock names at the given level.
1169 This can be used for debugging/testing purposes.
1171 @param level: the level whose list of locks to get
1174 assert level in LEVELS, "Invalid locking level %s" % level
1175 return self.__keyring[level]._names()
1177 def _is_owned(self, level):
1178 """Check whether we are owning locks at the given level
1181 return self.__keyring[level]._is_owned()
1183 is_owned = _is_owned
1185 def _list_owned(self, level):
1186 """Get the set of owned locks at the given level
1189 return self.__keyring[level]._list_owned()
1191 def _upper_owned(self, level):
1192 """Check that we don't own any lock at a level greater than the given one.
1195 # This way of checking only works if LEVELS[i] = i, which we check for in
1197 return compat.any((self._is_owned(l) for l in LEVELS[level + 1:]))
1199 def _BGL_owned(self): # pylint: disable-msg=C0103
1200 """Check if the current thread owns the BGL.
1202 Both an exclusive or a shared acquisition work.
1205 return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned()
1208 def _contains_BGL(level, names): # pylint: disable-msg=C0103
1209 """Check if the level contains the BGL.
1211 Check if acting on the given level and set of names will change
1212 the status of the Big Ganeti Lock.
1215 return level == LEVEL_CLUSTER and (names is None or BGL in names)
1217 def acquire(self, level, names, timeout=None, shared=0):
1218 """Acquire a set of resource locks, at the same level.
1220 @type level: member of locking.LEVELS
1221 @param level: the level at which the locks shall be acquired
1222 @type names: list of strings (or string)
1223 @param names: the names of the locks which shall be acquired
1224 (special lock names, or instance/node names)
1225 @type shared: integer (0/1) used as a boolean
1226 @param shared: whether to acquire in shared mode; by default
1227 an exclusive lock will be acquired
1228 @type timeout: float
1229 @param timeout: Maximum time to acquire all locks
1232 assert level in LEVELS, "Invalid locking level %s" % level
1234 # Check that we are either acquiring the Big Ganeti Lock or we already own
1235 # it. Some "legacy" opcodes need to be sure they are run non-concurrently
1236 # so even if we've migrated we need to at least share the BGL to be
1237 # compatible with them. Of course if we own the BGL exclusively there's no
1238 # point in acquiring any other lock, unless perhaps we are half way through
1239 # the migration of the current opcode.
1240 assert (self._contains_BGL(level, names) or self._BGL_owned()), (
1241 "You must own the Big Ganeti Lock before acquiring any other")
1243 # Check we don't own locks at the same or upper levels.
1244 assert not self._upper_owned(level), ("Cannot acquire locks at a level"
1245 " while owning some at a greater one")
1247 # Acquire the locks in the set.
1248 return self.__keyring[level].acquire(names, shared=shared, timeout=timeout)
1250 def release(self, level, names=None):
1251 """Release a set of resource locks, at the same level.
1253 You must have acquired the locks, either in shared or in exclusive
1254 mode, before releasing them.
1256 @type level: member of locking.LEVELS
1257 @param level: the level at which the locks shall be released
1258 @type names: list of strings, or None
1259 @param names: the names of the locks which shall be released
1260 (defaults to all the locks acquired at that level)
1263 assert level in LEVELS, "Invalid locking level %s" % level
1264 assert (not self._contains_BGL(level, names) or
1265 not self._upper_owned(LEVEL_CLUSTER)), (
1266 "Cannot release the Big Ganeti Lock while holding something"
1267 " at upper levels (%r)" %
1268 (utils.CommaJoin(["%s=%r" % (LEVEL_NAMES[i], self._list_owned(i))
1269 for i in self.__keyring.keys()]), ))
1271 # Release will complain if we don't own the locks already
1272 return self.__keyring[level].release(names)
1274 def add(self, level, names, acquired=0, shared=0):
1275 """Add locks at the specified level.
1277 @type level: member of locking.LEVELS_MOD
1278 @param level: the level at which the locks shall be added
1279 @type names: list of strings
1280 @param names: names of the locks to acquire
1281 @type acquired: integer (0/1) used as a boolean
1282 @param acquired: whether to acquire the newly added locks
1283 @type shared: integer (0/1) used as a boolean
1284 @param shared: whether the acquisition will be shared
1287 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1288 assert self._BGL_owned(), ("You must own the BGL before performing other"
1290 assert not self._upper_owned(level), ("Cannot add locks at a level"
1291 " while owning some at a greater one")
1292 return self.__keyring[level].add(names, acquired=acquired, shared=shared)
1294 def remove(self, level, names):
1295 """Remove locks from the specified level.
1297 You must either already own the locks you are trying to remove
1298 exclusively or not own any lock at an upper level.
1300 @type level: member of locking.LEVELS_MOD
1301 @param level: the level at which the locks shall be removed
1302 @type names: list of strings
1303 @param names: the names of the locks which shall be removed
1304 (special lock names, or instance/node names)
1307 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1308 assert self._BGL_owned(), ("You must own the BGL before performing other"
1310 # Check we either own the level or don't own anything from here
1311 # up. LockSet.remove() will check the case in which we don't own
1312 # all the needed resources, or we have a shared ownership.
1313 assert self._is_owned(level) or not self._upper_owned(level), (
1314 "Cannot remove locks at a level while not owning it or"
1315 " owning some at a greater one")
1316 return self.__keyring[level].remove(names)