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
38 def ssynchronized(lock, shared=0):
39 """Shared Synchronization decorator.
41 Calls the function holding the given lock, either in exclusive or shared
42 mode. It requires the passed lock to be a SharedLock (or support its
47 def sync_function(*args, **kwargs):
48 lock.acquire(shared=shared)
50 return fn(*args, **kwargs)
57 class RunningTimeout(object):
58 """Class to calculate remaining timeout when doing several operations.
68 def __init__(self, timeout, allow_negative, _time_fn=time.time):
69 """Initializes this class.
72 @param timeout: Timeout duration
73 @type allow_negative: bool
74 @param allow_negative: Whether to return values below zero
75 @param _time_fn: Time function for unittests
80 if timeout is not None and timeout < 0.0:
81 raise ValueError("Timeout must not be negative")
83 self._timeout = timeout
84 self._allow_negative = allow_negative
85 self._time_fn = _time_fn
87 self._start_time = None
90 """Returns the remaining timeout.
93 if self._timeout is None:
96 # Get start time on first calculation
97 if self._start_time is None:
98 self._start_time = self._time_fn()
100 # Calculate remaining time
101 remaining_timeout = self._start_time + self._timeout - self._time_fn()
103 if not self._allow_negative:
104 # Ensure timeout is always >= 0
105 return max(0.0, remaining_timeout)
107 return remaining_timeout
110 class _SingleNotifyPipeConditionWaiter(object):
111 """Helper class for SingleNotifyPipeCondition
119 def __init__(self, poller, fd):
120 """Constructor for _SingleNotifyPipeConditionWaiter
122 @type poller: select.poll
123 @param poller: Poller object
125 @param fd: File descriptor to wait for
128 object.__init__(self)
129 self._poller = poller
132 def __call__(self, timeout):
133 """Wait for something to happen on the pipe.
135 @type timeout: float or None
136 @param timeout: Timeout for waiting (can be None)
139 running_timeout = RunningTimeout(timeout, True)
142 remaining_time = running_timeout.Remaining()
144 if remaining_time is not None and remaining_time < 0.0:
148 result = self._poller.poll(remaining_time)
149 except EnvironmentError, err:
150 if err.errno != errno.EINTR:
154 # Check whether we were notified
155 if result and result[0][0] == self._fd:
159 class _BaseCondition(object):
160 """Base class containing common code for conditions.
162 Some of this code is taken from python's threading module.
171 def __init__(self, lock):
172 """Constructor for _BaseCondition.
174 @type lock: threading.Lock
175 @param lock: condition base lock
178 object.__init__(self)
180 # Recursive locks are not supported
181 assert not hasattr(lock, "_acquire_restore")
182 assert not hasattr(lock, "_release_save")
186 # Export the lock's acquire() and release() methods
187 self.acquire = lock.acquire
188 self.release = lock.release
191 """Check whether lock is owned by current thread.
194 if self._lock.acquire(0):
200 def _check_owned(self):
201 """Raise an exception if the current thread doesn't own the lock.
204 if not self._is_owned():
205 raise RuntimeError("cannot work with un-aquired lock")
208 class SingleNotifyPipeCondition(_BaseCondition):
209 """Condition which can only be notified once.
211 This condition class uses pipes and poll, internally, to be able to wait for
212 notification with a timeout, without resorting to polling. It is almost
213 compatible with Python's threading.Condition, with the following differences:
214 - notifyAll can only be called once, and no wait can happen after that
215 - notify is not supported, only notifyAll
227 _waiter_class = _SingleNotifyPipeConditionWaiter
229 def __init__(self, lock):
230 """Constructor for SingleNotifyPipeCondition
233 _BaseCondition.__init__(self, lock)
235 self._notified = False
237 self._write_fd = None
240 def _check_unnotified(self):
241 """Throws an exception if already notified.
245 raise RuntimeError("cannot use already notified condition")
248 """Cleanup open file descriptors, if any.
251 if self._read_fd is not None:
252 os.close(self._read_fd)
255 if self._write_fd is not None:
256 os.close(self._write_fd)
257 self._write_fd = None
260 def wait(self, timeout=None):
261 """Wait for a notification.
263 @type timeout: float or None
264 @param timeout: Waiting timeout (can be None)
268 self._check_unnotified()
272 if self._poller is None:
273 (self._read_fd, self._write_fd) = os.pipe()
274 self._poller = select.poll()
275 self._poller.register(self._read_fd, select.POLLHUP)
277 wait_fn = self._waiter_class(self._poller, self._read_fd)
280 # Wait for notification
287 if self._nwaiters == 0:
290 def notifyAll(self): # pylint: disable-msg=C0103
291 """Close the writing side of the pipe to notify all waiters.
295 self._check_unnotified()
296 self._notified = True
297 if self._write_fd is not None:
298 os.close(self._write_fd)
299 self._write_fd = None
302 class PipeCondition(_BaseCondition):
303 """Group-only non-polling condition with counters.
305 This condition class uses pipes and poll, internally, to be able to wait for
306 notification with a timeout, without resorting to polling. It is almost
307 compatible with Python's threading.Condition, but only supports notifyAll and
308 non-recursive locks. As an additional features it's able to report whether
309 there are any waiting threads.
317 _single_condition_class = SingleNotifyPipeCondition
319 def __init__(self, lock):
320 """Initializes this class.
323 _BaseCondition.__init__(self, lock)
325 self._single_condition = self._single_condition_class(self._lock)
327 def wait(self, timeout=None):
328 """Wait for a notification.
330 @type timeout: float or None
331 @param timeout: Waiting timeout (can be None)
336 # Keep local reference to the pipe. It could be replaced by another thread
337 # notifying while we're waiting.
338 my_condition = self._single_condition
340 assert self._nwaiters >= 0
343 my_condition.wait(timeout)
345 assert self._nwaiters > 0
348 def notifyAll(self): # pylint: disable-msg=C0103
349 """Notify all currently waiting threads.
353 self._single_condition.notifyAll()
354 self._single_condition = self._single_condition_class(self._lock)
356 def has_waiting(self):
357 """Returns whether there are active waiters.
362 return bool(self._nwaiters)
365 class _CountingCondition(object):
366 """Wrapper for Python's built-in threading.Condition class.
368 This wrapper keeps a count of active waiters. We can't access the internal
369 "__waiters" attribute of threading.Condition because it's not thread-safe.
377 def __init__(self, lock):
378 """Initializes this class.
381 object.__init__(self)
382 self._cond = threading.Condition(lock=lock)
385 def notifyAll(self): # pylint: disable-msg=C0103
386 """Notifies the condition.
389 return self._cond.notifyAll()
391 def wait(self, timeout=None):
392 """Waits for the condition to be notified.
394 @type timeout: float or None
395 @param timeout: Waiting timeout (can be None)
398 assert self._nwaiters >= 0
402 return self._cond.wait(timeout=timeout)
406 def has_waiting(self):
407 """Returns whether there are active waiters.
410 return bool(self._nwaiters)
413 class SharedLock(object):
414 """Implements a shared lock.
416 Multiple threads can acquire the lock in a shared way, calling
417 acquire_shared(). In order to acquire the lock in an exclusive way threads
418 can call acquire_exclusive().
420 The lock prevents starvation but does not guarantee that threads will acquire
421 the shared lock in the order they queued for it, just that they will
435 __condition_class = PipeCondition
438 """Construct a new SharedLock.
441 object.__init__(self)
444 self.__lock = threading.Lock()
446 # Queue containing waiting acquires
449 # Active and inactive conditions for shared locks
450 self.__active_shr_c = self.__condition_class(self.__lock)
451 self.__inactive_shr_c = self.__condition_class(self.__lock)
453 # Current lock holders
457 # is this lock in the deleted state?
458 self.__deleted = False
460 def __check_deleted(self):
461 """Raises an exception if the lock has been deleted.
465 raise errors.LockError("Deleted lock")
467 def __is_sharer(self):
468 """Is the current thread sharing the lock at this time?
471 return threading.currentThread() in self.__shr
473 def __is_exclusive(self):
474 """Is the current thread holding the lock exclusively at this time?
477 return threading.currentThread() == self.__exc
479 def __is_owned(self, shared=-1):
480 """Is the current thread somehow owning the lock at this time?
482 This is a private version of the function, which presumes you're holding
487 return self.__is_sharer() or self.__is_exclusive()
489 return self.__is_sharer()
491 return self.__is_exclusive()
493 def _is_owned(self, shared=-1):
494 """Is the current thread somehow owning the lock at this time?
497 - < 0: check for any type of ownership (default)
498 - 0: check for exclusive ownership
499 - > 0: check for shared ownership
502 self.__lock.acquire()
504 return self.__is_owned(shared=shared)
506 self.__lock.release()
508 def _count_pending(self):
509 """Returns the number of pending acquires.
514 self.__lock.acquire()
516 return len(self.__pending)
518 self.__lock.release()
520 def __do_acquire(self, shared):
521 """Actually acquire the lock.
525 self.__shr.add(threading.currentThread())
527 self.__exc = threading.currentThread()
529 def __can_acquire(self, shared):
530 """Determine whether lock can be acquired.
534 return self.__exc is None
536 return len(self.__shr) == 0 and self.__exc is None
538 def __is_on_top(self, cond):
539 """Checks whether the passed condition is on top of the queue.
541 The caller must make sure the queue isn't empty.
544 return self.__pending[0] == cond
546 def __acquire_unlocked(self, shared, timeout):
547 """Acquire a shared lock.
549 @param shared: whether to acquire in shared mode; by default an
550 exclusive lock will be acquired
551 @param timeout: maximum waiting time before giving up
554 self.__check_deleted()
556 # We cannot acquire the lock if we already have it
557 assert not self.__is_owned(), "double acquire() on a non-recursive lock"
559 # Check whether someone else holds the lock or there are pending acquires.
560 if not self.__pending and self.__can_acquire(shared):
561 # Apparently not, can acquire lock directly.
562 self.__do_acquire(shared)
566 wait_condition = self.__active_shr_c
568 # Check if we're not yet in the queue
569 if wait_condition not in self.__pending:
570 self.__pending.append(wait_condition)
572 wait_condition = self.__condition_class(self.__lock)
573 # Always add to queue
574 self.__pending.append(wait_condition)
577 # Wait until we become the topmost acquire in the queue or the timeout
579 while not (self.__is_on_top(wait_condition) and
580 self.__can_acquire(shared)):
581 # Wait for notification
582 wait_condition.wait(timeout)
583 self.__check_deleted()
585 # A lot of code assumes blocking acquires always succeed. Loop
586 # internally for that case.
587 if timeout is not None:
590 if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
591 self.__do_acquire(shared)
594 # Remove condition from queue if there are no more waiters
595 if not wait_condition.has_waiting() and not self.__deleted:
596 self.__pending.remove(wait_condition)
600 def acquire(self, shared=0, timeout=None, test_notify=None):
601 """Acquire a shared lock.
603 @type shared: integer (0/1) used as a boolean
604 @param shared: whether to acquire in shared mode; by default an
605 exclusive lock will be acquired
607 @param timeout: maximum waiting time before giving up
608 @type test_notify: callable or None
609 @param test_notify: Special callback function for unittesting
612 self.__lock.acquire()
614 # We already got the lock, notify now
615 if __debug__ and callable(test_notify):
618 return self.__acquire_unlocked(shared, timeout)
620 self.__lock.release()
623 """Release a Shared Lock.
625 You must have acquired the lock, either in shared or in exclusive mode,
626 before calling this function.
629 self.__lock.acquire()
631 assert self.__is_exclusive() or self.__is_sharer(), \
632 "Cannot release non-owned lock"
634 # Autodetect release type
635 if self.__is_exclusive():
638 self.__shr.remove(threading.currentThread())
640 # Notify topmost condition in queue
642 first_condition = self.__pending[0]
643 first_condition.notifyAll()
645 if first_condition == self.__active_shr_c:
646 self.__active_shr_c = self.__inactive_shr_c
647 self.__inactive_shr_c = first_condition
650 self.__lock.release()
652 def delete(self, timeout=None):
653 """Delete a Shared Lock.
655 This operation will declare the lock for removal. First the lock will be
656 acquired in exclusive mode if you don't already own it, then the lock
657 will be put in a state where any future and pending acquire() fail.
660 @param timeout: maximum waiting time before giving up
663 self.__lock.acquire()
665 assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"
667 self.__check_deleted()
669 # The caller is allowed to hold the lock exclusively already.
670 acquired = self.__is_exclusive()
673 acquired = self.__acquire_unlocked(0, timeout)
675 assert self.__is_exclusive() and not self.__is_sharer(), \
676 "Lock wasn't acquired in exclusive mode"
679 self.__deleted = True
682 # Notify all acquires. They'll throw an error.
683 while self.__pending:
684 self.__pending.pop().notifyAll()
688 self.__lock.release()
691 # Whenever we want to acquire a full LockSet we pass None as the value
692 # to acquire. Hide this behind this nicely named constant.
696 class _AcquireTimeout(Exception):
697 """Internal exception to abort an acquire on a timeout.
703 """Implements a set of locks.
705 This abstraction implements a set of shared locks for the same resource type,
706 distinguished by name. The user can lock a subset of the resources and the
707 LockSet will take care of acquiring the locks always in the same order, thus
710 All the locks needed in the same set must be acquired together, though.
713 def __init__(self, members=None):
714 """Constructs a new LockSet.
716 @type members: list of strings
717 @param members: initial members of the set
720 # Used internally to guarantee coherency.
721 self.__lock = SharedLock()
723 # The lockdict indexes the relationship name -> lock
724 # The order-of-locking is implied by the alphabetical order of names
727 if members is not None:
729 self.__lockdict[name] = SharedLock()
731 # The owner dict contains the set of locks each thread owns. For
732 # performance each thread can access its own key without a global lock on
733 # this structure. It is paramount though that *no* other type of access is
734 # done to this structure (eg. no looping over its keys). *_owner helper
735 # function are defined to guarantee access is correct, but in general never
736 # do anything different than __owners[threading.currentThread()], or there
741 """Is the current thread a current level owner?"""
742 return threading.currentThread() in self.__owners
744 def _add_owned(self, name=None):
745 """Note the current thread owns the given lock"""
747 if not self._is_owned():
748 self.__owners[threading.currentThread()] = set()
751 self.__owners[threading.currentThread()].add(name)
753 self.__owners[threading.currentThread()] = set([name])
755 def _del_owned(self, name=None):
756 """Note the current thread owns the given lock"""
758 assert not (name is None and self.__lock._is_owned()), \
759 "Cannot hold internal lock when deleting owner status"
762 self.__owners[threading.currentThread()].remove(name)
764 # Only remove the key if we don't hold the set-lock as well
765 if (not self.__lock._is_owned() and
766 not self.__owners[threading.currentThread()]):
767 del self.__owners[threading.currentThread()]
769 def _list_owned(self):
770 """Get the set of resource names owned by the current thread"""
772 return self.__owners[threading.currentThread()].copy()
776 def _release_and_delete_owned(self):
777 """Release and delete all resources owned by the current thread"""
778 for lname in self._list_owned():
779 lock = self.__lockdict[lname]
782 self._del_owned(name=lname)
785 """Return the current set of names.
787 Only call this function while holding __lock and don't iterate on the
788 result after releasing the lock.
791 return self.__lockdict.keys()
794 """Return a copy of the current set of elements.
796 Used only for debugging purposes.
799 # If we don't already own the set-level lock acquired
800 # we'll get it and note we need to release it later.
802 if not self.__lock._is_owned():
804 self.__lock.acquire(shared=1)
806 result = self.__names()
809 self.__lock.release()
812 def acquire(self, names, timeout=None, shared=0, test_notify=None):
813 """Acquire a set of resource locks.
815 @type names: list of strings (or string)
816 @param names: the names of the locks which shall be acquired
817 (special lock names, or instance/node names)
818 @type shared: integer (0/1) used as a boolean
819 @param shared: whether to acquire in shared mode; by default an
820 exclusive lock will be acquired
821 @type timeout: float or None
822 @param timeout: Maximum time to acquire all locks
823 @type test_notify: callable or None
824 @param test_notify: Special callback function for unittesting
826 @return: Set of all locks successfully acquired or None in case of timeout
828 @raise errors.LockError: when any lock we try to acquire has
829 been deleted before we succeed. In this case none of the
830 locks requested will be acquired.
833 assert timeout is None or timeout >= 0.0
835 # Check we don't already own locks at this level
836 assert not self._is_owned(), "Cannot acquire locks in the same set twice"
838 # We need to keep track of how long we spent waiting for a lock. The
839 # timeout passed to this function is over all lock acquires.
840 running_timeout = RunningTimeout(timeout, False)
843 if names is not None:
844 # Support passing in a single resource to acquire rather than many
845 if isinstance(names, basestring):
848 return self.__acquire_inner(names, False, shared,
849 running_timeout.Remaining, test_notify)
852 # If no names are given acquire the whole set by not letting new names
853 # being added before we release, and getting the current list of names.
854 # Some of them may then be deleted later, but we'll cope with this.
856 # We'd like to acquire this lock in a shared way, as it's nice if
857 # everybody else can use the instances at the same time. If are
858 # acquiring them exclusively though they won't be able to do this
859 # anyway, though, so we'll get the list lock exclusively as well in
860 # order to be able to do add() on the set while owning it.
861 if not self.__lock.acquire(shared=shared,
862 timeout=running_timeout.Remaining()):
863 raise _AcquireTimeout()
865 # note we own the set-lock
868 return self.__acquire_inner(self.__names(), True, shared,
869 running_timeout.Remaining, test_notify)
871 # We shouldn't have problems adding the lock to the owners list, but
872 # if we did we'll try to release this lock and re-raise exception.
873 # Of course something is going to be really wrong, after this.
874 self.__lock.release()
878 except _AcquireTimeout:
881 def __acquire_inner(self, names, want_all, shared, timeout_fn, test_notify):
882 """Inner logic for acquiring a number of locks.
884 @param names: Names of the locks to be acquired
885 @param want_all: Whether all locks in the set should be acquired
886 @param shared: Whether to acquire in shared mode
887 @param timeout_fn: Function returning remaining timeout
888 @param test_notify: Special callback function for unittesting
893 # First we look the locks up on __lockdict. We have no way of being sure
894 # they will still be there after, but this makes it a lot faster should
895 # just one of them be the already wrong. Using a sorted sequence to prevent
897 for lname in sorted(utils.UniqueSequence(names)):
899 lock = self.__lockdict[lname] # raises KeyError if lock is not there
902 # We are acquiring all the set, it doesn't matter if this particular
903 # element is not there anymore.
906 raise errors.LockError("Non-existing lock in set (%s)" % lname)
908 acquire_list.append((lname, lock))
910 # This will hold the locknames we effectively acquired.
914 # Now acquire_list contains a sorted list of resources and locks we
915 # want. In order to get them we loop on this (private) list and
916 # acquire() them. We gave no real guarantee they will still exist till
917 # this is done but .acquire() itself is safe and will alert us if the
919 for (lname, lock) in acquire_list:
920 if __debug__ and callable(test_notify):
921 test_notify_fn = lambda: test_notify(lname)
923 test_notify_fn = None
925 timeout = timeout_fn()
928 # raises LockError if the lock was deleted
929 acq_success = lock.acquire(shared=shared, timeout=timeout,
930 test_notify=test_notify_fn)
931 except errors.LockError:
933 # We are acquiring all the set, it doesn't matter if this
934 # particular element is not there anymore.
937 raise errors.LockError("Non-existing lock in set (%s)" % lname)
940 # Couldn't get lock or timeout occurred
942 # This shouldn't happen as SharedLock.acquire(timeout=None) is
944 raise errors.LockError("Failed to get lock %s" % lname)
946 raise _AcquireTimeout()
949 # now the lock cannot be deleted, we have it!
950 self._add_owned(name=lname)
954 # We shouldn't have problems adding the lock to the owners list, but
955 # if we did we'll try to release this lock and re-raise exception.
956 # Of course something is going to be really wrong after this.
962 # Release all owned locks
963 self._release_and_delete_owned()
968 def release(self, names=None):
969 """Release a set of resource locks, at the same level.
971 You must have acquired the locks, either in shared or in exclusive mode,
972 before releasing them.
974 @type names: list of strings, or None
975 @param names: the names of the locks which shall be released
976 (defaults to all the locks acquired at that level).
979 assert self._is_owned(), "release() on lock set while not owner"
981 # Support passing in a single resource to release rather than many
982 if isinstance(names, basestring):
986 names = self._list_owned()
989 assert self._list_owned().issuperset(names), (
990 "release() on unheld resources %s" %
991 names.difference(self._list_owned()))
993 # First of all let's release the "all elements" lock, if set.
994 # After this 'add' can work again
995 if self.__lock._is_owned():
996 self.__lock.release()
999 for lockname in names:
1000 # If we are sure the lock doesn't leave __lockdict without being
1001 # exclusively held we can do this...
1002 self.__lockdict[lockname].release()
1003 self._del_owned(name=lockname)
1005 def add(self, names, acquired=0, shared=0):
1006 """Add a new set of elements to the set
1008 @type names: list of strings
1009 @param names: names of the new elements to add
1010 @type acquired: integer (0/1) used as a boolean
1011 @param acquired: pre-acquire the new resource?
1012 @type shared: integer (0/1) used as a boolean
1013 @param shared: is the pre-acquisition shared?
1016 # Check we don't already own locks at this level
1017 assert not self._is_owned() or self.__lock._is_owned(shared=0), \
1018 "Cannot add locks if the set is only partially owned, or shared"
1020 # Support passing in a single resource to add rather than many
1021 if isinstance(names, basestring):
1024 # If we don't already own the set-level lock acquired in an exclusive way
1025 # we'll get it and note we need to release it later.
1026 release_lock = False
1027 if not self.__lock._is_owned():
1029 self.__lock.acquire()
1032 invalid_names = set(self.__names()).intersection(names)
1034 # This must be an explicit raise, not an assert, because assert is
1035 # turned off when using optimization, and this can happen because of
1036 # concurrency even if the user doesn't want it.
1037 raise errors.LockError("duplicate add() (%s)" % invalid_names)
1039 for lockname in names:
1043 lock.acquire(shared=shared)
1044 # now the lock cannot be deleted, we have it!
1046 self._add_owned(name=lockname)
1048 # We shouldn't have problems adding the lock to the owners list,
1049 # but if we did we'll try to release this lock and re-raise
1050 # exception. Of course something is going to be really wrong,
1051 # after this. On the other hand the lock hasn't been added to the
1052 # __lockdict yet so no other threads should be pending on it. This
1053 # release is just a safety measure.
1057 self.__lockdict[lockname] = lock
1060 # Only release __lock if we were not holding it previously.
1062 self.__lock.release()
1066 def remove(self, names):
1067 """Remove elements from the lock set.
1069 You can either not hold anything in the lockset or already hold a superset
1070 of the elements you want to delete, exclusively.
1072 @type names: list of strings
1073 @param names: names of the resource to remove.
1075 @return: a list of locks which we removed; the list is always
1076 equal to the names list if we were holding all the locks
1080 # Support passing in a single resource to remove rather than many
1081 if isinstance(names, basestring):
1084 # If we own any subset of this lock it must be a superset of what we want
1085 # to delete. The ownership must also be exclusive, but that will be checked
1086 # by the lock itself.
1087 assert not self._is_owned() or self._list_owned().issuperset(names), (
1088 "remove() on acquired lockset while not owning all elements")
1093 # Calling delete() acquires the lock exclusively if we don't already own
1094 # it, and causes all pending and subsequent lock acquires to fail. It's
1095 # fine to call it out of order because delete() also implies release(),
1096 # and the assertion above guarantees that if we either already hold
1097 # everything we want to delete, or we hold none.
1099 self.__lockdict[lname].delete()
1100 removed.append(lname)
1101 except (KeyError, errors.LockError):
1102 # This cannot happen if we were already holding it, verify:
1103 assert not self._is_owned(), "remove failed while holding lockset"
1105 # If no LockError was raised we are the ones who deleted the lock.
1106 # This means we can safely remove it from lockdict, as any further or
1107 # pending delete() or acquire() will fail (and nobody can have the lock
1108 # since before our call to delete()).
1110 # This is done in an else clause because if the exception was thrown
1111 # it's the job of the one who actually deleted it.
1112 del self.__lockdict[lname]
1113 # And let's remove it from our private list if we owned it.
1114 if self._is_owned():
1115 self._del_owned(name=lname)
1120 # Locking levels, must be acquired in increasing order.
1121 # Current rules are:
1122 # - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
1123 # acquired before performing any operation, either in shared or in exclusive
1124 # mode. acquiring the BGL in exclusive mode is discouraged and should be
1126 # - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
1127 # If you need more than one node, or more than one instance, acquire them at
1133 LEVELS = [LEVEL_CLUSTER,
1137 # Lock levels which are modifiable
1138 LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE]
1141 LEVEL_CLUSTER: "cluster",
1142 LEVEL_INSTANCE: "instance",
1146 # Constant for the big ganeti lock
1150 class GanetiLockManager:
1151 """The Ganeti Locking Library
1153 The purpose of this small library is to manage locking for ganeti clusters
1154 in a central place, while at the same time doing dynamic checks against
1155 possible deadlocks. It will also make it easier to transition to a different
1156 lock type should we migrate away from python threads.
1161 def __init__(self, nodes=None, instances=None):
1162 """Constructs a new GanetiLockManager object.
1164 There should be only a GanetiLockManager object at any time, so this
1165 function raises an error if this is not the case.
1167 @param nodes: list of node names
1168 @param instances: list of instance names
1171 assert self.__class__._instance is None, \
1172 "double GanetiLockManager instance"
1174 self.__class__._instance = self
1176 # The keyring contains all the locks, at their level and in the correct
1179 LEVEL_CLUSTER: LockSet([BGL]),
1180 LEVEL_NODE: LockSet(nodes),
1181 LEVEL_INSTANCE: LockSet(instances),
1184 def _names(self, level):
1185 """List the lock names at the given level.
1187 This can be used for debugging/testing purposes.
1189 @param level: the level whose list of locks to get
1192 assert level in LEVELS, "Invalid locking level %s" % level
1193 return self.__keyring[level]._names()
1195 def _is_owned(self, level):
1196 """Check whether we are owning locks at the given level
1199 return self.__keyring[level]._is_owned()
1201 is_owned = _is_owned
1203 def _list_owned(self, level):
1204 """Get the set of owned locks at the given level
1207 return self.__keyring[level]._list_owned()
1209 def _upper_owned(self, level):
1210 """Check that we don't own any lock at a level greater than the given one.
1213 # This way of checking only works if LEVELS[i] = i, which we check for in
1215 return utils.any((self._is_owned(l) for l in LEVELS[level + 1:]))
1217 def _BGL_owned(self): # pylint: disable-msg=C0103
1218 """Check if the current thread owns the BGL.
1220 Both an exclusive or a shared acquisition work.
1223 return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned()
1226 def _contains_BGL(level, names): # pylint: disable-msg=C0103
1227 """Check if the level contains the BGL.
1229 Check if acting on the given level and set of names will change
1230 the status of the Big Ganeti Lock.
1233 return level == LEVEL_CLUSTER and (names is None or BGL in names)
1235 def acquire(self, level, names, timeout=None, shared=0):
1236 """Acquire a set of resource locks, at the same level.
1238 @type level: member of locking.LEVELS
1239 @param level: the level at which the locks shall be acquired
1240 @type names: list of strings (or string)
1241 @param names: the names of the locks which shall be acquired
1242 (special lock names, or instance/node names)
1243 @type shared: integer (0/1) used as a boolean
1244 @param shared: whether to acquire in shared mode; by default
1245 an exclusive lock will be acquired
1246 @type timeout: float
1247 @param timeout: Maximum time to acquire all locks
1250 assert level in LEVELS, "Invalid locking level %s" % level
1252 # Check that we are either acquiring the Big Ganeti Lock or we already own
1253 # it. Some "legacy" opcodes need to be sure they are run non-concurrently
1254 # so even if we've migrated we need to at least share the BGL to be
1255 # compatible with them. Of course if we own the BGL exclusively there's no
1256 # point in acquiring any other lock, unless perhaps we are half way through
1257 # the migration of the current opcode.
1258 assert (self._contains_BGL(level, names) or self._BGL_owned()), (
1259 "You must own the Big Ganeti Lock before acquiring any other")
1261 # Check we don't own locks at the same or upper levels.
1262 assert not self._upper_owned(level), ("Cannot acquire locks at a level"
1263 " while owning some at a greater one")
1265 # Acquire the locks in the set.
1266 return self.__keyring[level].acquire(names, shared=shared, timeout=timeout)
1268 def release(self, level, names=None):
1269 """Release a set of resource locks, at the same level.
1271 You must have acquired the locks, either in shared or in exclusive
1272 mode, before releasing them.
1274 @type level: member of locking.LEVELS
1275 @param level: the level at which the locks shall be released
1276 @type names: list of strings, or None
1277 @param names: the names of the locks which shall be released
1278 (defaults to all the locks acquired at that level)
1281 assert level in LEVELS, "Invalid locking level %s" % level
1282 assert (not self._contains_BGL(level, names) or
1283 not self._upper_owned(LEVEL_CLUSTER)), (
1284 "Cannot release the Big Ganeti Lock while holding something"
1285 " at upper levels (%r)" %
1286 (utils.CommaJoin(["%s=%r" % (LEVEL_NAMES[i], self._list_owned(i))
1287 for i in self.__keyring.keys()]), ))
1289 # Release will complain if we don't own the locks already
1290 return self.__keyring[level].release(names)
1292 def add(self, level, names, acquired=0, shared=0):
1293 """Add locks at the specified level.
1295 @type level: member of locking.LEVELS_MOD
1296 @param level: the level at which the locks shall be added
1297 @type names: list of strings
1298 @param names: names of the locks to acquire
1299 @type acquired: integer (0/1) used as a boolean
1300 @param acquired: whether to acquire the newly added locks
1301 @type shared: integer (0/1) used as a boolean
1302 @param shared: whether the acquisition will be shared
1305 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1306 assert self._BGL_owned(), ("You must own the BGL before performing other"
1308 assert not self._upper_owned(level), ("Cannot add locks at a level"
1309 " while owning some at a greater one")
1310 return self.__keyring[level].add(names, acquired=acquired, shared=shared)
1312 def remove(self, level, names):
1313 """Remove locks from the specified level.
1315 You must either already own the locks you are trying to remove
1316 exclusively or not own any lock at an upper level.
1318 @type level: member of locking.LEVELS_MOD
1319 @param level: the level at which the locks shall be removed
1320 @type names: list of strings
1321 @param names: the names of the locks which shall be removed
1322 (special lock names, or instance/node names)
1325 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1326 assert self._BGL_owned(), ("You must own the BGL before performing other"
1328 # Check we either own the level or don't own anything from here
1329 # up. LockSet.remove() will check the case in which we don't own
1330 # all the needed resources, or we have a shared ownership.
1331 assert self._is_owned(level) or not self._upper_owned(level), (
1332 "Cannot remove locks at a level while not owning it or"
1333 " owning some at a greater one")
1334 return self.__keyring[level].remove(names)