Documentation for the NODE_RES level
[ganeti-github.git] / lib / locking.py
1 #
2 #
3
4 # Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Google Inc.
5 #
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.
10 #
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.
15 #
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
19 # 02110-1301, USA.
20
21 """Module implementing the Ganeti locking code."""
22
23 # pylint: disable=W0212
24
25 # W0212 since e.g. LockSet methods use (a lot) the internals of
26 # SharedLock
27
28 import os
29 import select
30 import threading
31 import errno
32 import weakref
33 import logging
34 import heapq
35 import itertools
36 import time
37
38 from ganeti import errors
39 from ganeti import utils
40 from ganeti import compat
41 from ganeti import query
42
43
44 _EXCLUSIVE_TEXT = "exclusive"
45 _SHARED_TEXT = "shared"
46 _DELETED_TEXT = "deleted"
47
48 _DEFAULT_PRIORITY = 0
49
50
51 def ssynchronized(mylock, shared=0):
52 """Shared Synchronization decorator.
53
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
56 semantics).
57
58 @type mylock: lockable object or string
59 @param mylock: lock to acquire or class member name of the lock to acquire
60
61 """
62 def wrap(fn):
63 def sync_function(*args, **kwargs):
64 if isinstance(mylock, basestring):
65 assert args, "cannot ssynchronize on non-class method: self not found"
66 # args[0] is "self"
67 lock = getattr(args[0], mylock)
68 else:
69 lock = mylock
70 lock.acquire(shared=shared)
71 try:
72 return fn(*args, **kwargs)
73 finally:
74 lock.release()
75 return sync_function
76 return wrap
77
78
79 class _SingleNotifyPipeConditionWaiter(object):
80 """Helper class for SingleNotifyPipeCondition
81
82 """
83 __slots__ = [
84 "_fd",
85 "_poller",
86 ]
87
88 def __init__(self, poller, fd):
89 """Constructor for _SingleNotifyPipeConditionWaiter
90
91 @type poller: select.poll
92 @param poller: Poller object
93 @type fd: int
94 @param fd: File descriptor to wait for
95
96 """
97 object.__init__(self)
98 self._poller = poller
99 self._fd = fd
100
101 def __call__(self, timeout):
102 """Wait for something to happen on the pipe.
103
104 @type timeout: float or None
105 @param timeout: Timeout for waiting (can be None)
106
107 """
108 running_timeout = utils.RunningTimeout(timeout, True)
109
110 while True:
111 remaining_time = running_timeout.Remaining()
112
113 if remaining_time is not None:
114 if remaining_time < 0.0:
115 break
116
117 # Our calculation uses seconds, poll() wants milliseconds
118 remaining_time *= 1000
119
120 try:
121 result = self._poller.poll(remaining_time)
122 except EnvironmentError, err:
123 if err.errno != errno.EINTR:
124 raise
125 result = None
126
127 # Check whether we were notified
128 if result and result[0][0] == self._fd:
129 break
130
131
132 class _BaseCondition(object):
133 """Base class containing common code for conditions.
134
135 Some of this code is taken from python's threading module.
136
137 """
138 __slots__ = [
139 "_lock",
140 "acquire",
141 "release",
142 "_is_owned",
143 "_acquire_restore",
144 "_release_save",
145 ]
146
147 def __init__(self, lock):
148 """Constructor for _BaseCondition.
149
150 @type lock: threading.Lock
151 @param lock: condition base lock
152
153 """
154 object.__init__(self)
155
156 try:
157 self._release_save = lock._release_save
158 except AttributeError:
159 self._release_save = self._base_release_save
160 try:
161 self._acquire_restore = lock._acquire_restore
162 except AttributeError:
163 self._acquire_restore = self._base_acquire_restore
164 try:
165 self._is_owned = lock.is_owned
166 except AttributeError:
167 self._is_owned = self._base_is_owned
168
169 self._lock = lock
170
171 # Export the lock's acquire() and release() methods
172 self.acquire = lock.acquire
173 self.release = lock.release
174
175 def _base_is_owned(self):
176 """Check whether lock is owned by current thread.
177
178 """
179 if self._lock.acquire(0):
180 self._lock.release()
181 return False
182 return True
183
184 def _base_release_save(self):
185 self._lock.release()
186
187 def _base_acquire_restore(self, _):
188 self._lock.acquire()
189
190 def _check_owned(self):
191 """Raise an exception if the current thread doesn't own the lock.
192
193 """
194 if not self._is_owned():
195 raise RuntimeError("cannot work with un-aquired lock")
196
197
198 class SingleNotifyPipeCondition(_BaseCondition):
199 """Condition which can only be notified once.
200
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
206
207 """
208
209 __slots__ = [
210 "_poller",
211 "_read_fd",
212 "_write_fd",
213 "_nwaiters",
214 "_notified",
215 ]
216
217 _waiter_class = _SingleNotifyPipeConditionWaiter
218
219 def __init__(self, lock):
220 """Constructor for SingleNotifyPipeCondition
221
222 """
223 _BaseCondition.__init__(self, lock)
224 self._nwaiters = 0
225 self._notified = False
226 self._read_fd = None
227 self._write_fd = None
228 self._poller = None
229
230 def _check_unnotified(self):
231 """Throws an exception if already notified.
232
233 """
234 if self._notified:
235 raise RuntimeError("cannot use already notified condition")
236
237 def _Cleanup(self):
238 """Cleanup open file descriptors, if any.
239
240 """
241 if self._read_fd is not None:
242 os.close(self._read_fd)
243 self._read_fd = None
244
245 if self._write_fd is not None:
246 os.close(self._write_fd)
247 self._write_fd = None
248 self._poller = None
249
250 def wait(self, timeout):
251 """Wait for a notification.
252
253 @type timeout: float or None
254 @param timeout: Waiting timeout (can be None)
255
256 """
257 self._check_owned()
258 self._check_unnotified()
259
260 self._nwaiters += 1
261 try:
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)
266
267 wait_fn = self._waiter_class(self._poller, self._read_fd)
268 state = self._release_save()
269 try:
270 # Wait for notification
271 wait_fn(timeout)
272 finally:
273 # Re-acquire lock
274 self._acquire_restore(state)
275 finally:
276 self._nwaiters -= 1
277 if self._nwaiters == 0:
278 self._Cleanup()
279
280 def notifyAll(self): # pylint: disable=C0103
281 """Close the writing side of the pipe to notify all waiters.
282
283 """
284 self._check_owned()
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
290
291
292 class PipeCondition(_BaseCondition):
293 """Group-only non-polling condition with counters.
294
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.
300
301 """
302 __slots__ = [
303 "_waiters",
304 "_single_condition",
305 ]
306
307 _single_condition_class = SingleNotifyPipeCondition
308
309 def __init__(self, lock):
310 """Initializes this class.
311
312 """
313 _BaseCondition.__init__(self, lock)
314 self._waiters = set()
315 self._single_condition = self._single_condition_class(self._lock)
316
317 def wait(self, timeout):
318 """Wait for a notification.
319
320 @type timeout: float or None
321 @param timeout: Waiting timeout (can be None)
322
323 """
324 self._check_owned()
325
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
329
330 self._waiters.add(threading.currentThread())
331 try:
332 cond.wait(timeout)
333 finally:
334 self._check_owned()
335 self._waiters.remove(threading.currentThread())
336
337 def notifyAll(self): # pylint: disable=C0103
338 """Notify all currently waiting threads.
339
340 """
341 self._check_owned()
342 self._single_condition.notifyAll()
343 self._single_condition = self._single_condition_class(self._lock)
344
345 def get_waiting(self):
346 """Returns a list of all waiting threads.
347
348 """
349 self._check_owned()
350
351 return self._waiters
352
353 def has_waiting(self):
354 """Returns whether there are active waiters.
355
356 """
357 self._check_owned()
358
359 return bool(self._waiters)
360
361 def __repr__(self):
362 return ("<%s.%s waiters=%s at %#x>" %
363 (self.__class__.__module__, self.__class__.__name__,
364 self._waiters, id(self)))
365
366
367 class _PipeConditionWithMode(PipeCondition):
368 __slots__ = [
369 "shared",
370 ]
371
372 def __init__(self, lock, shared):
373 """Initializes this class.
374
375 """
376 self.shared = shared
377 PipeCondition.__init__(self, lock)
378
379
380 class SharedLock(object):
381 """Implements a shared lock.
382
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)}.
386
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.
394
395 @type name: string
396 @ivar name: the name of the lock
397
398 """
399 __slots__ = [
400 "__weakref__",
401 "__deleted",
402 "__exc",
403 "__lock",
404 "__pending",
405 "__pending_by_prio",
406 "__pending_shared",
407 "__shr",
408 "__time_fn",
409 "name",
410 ]
411
412 __condition_class = _PipeConditionWithMode
413
414 def __init__(self, name, monitor=None, _time_fn=time.time):
415 """Construct a new SharedLock.
416
417 @param name: the name of the lock
418 @type monitor: L{LockMonitor}
419 @param monitor: Lock monitor with which to register
420
421 """
422 object.__init__(self)
423
424 self.name = name
425
426 # Used for unittesting
427 self.__time_fn = _time_fn
428
429 # Internal lock
430 self.__lock = threading.Lock()
431
432 # Queue containing waiting acquires
433 self.__pending = []
434 self.__pending_by_prio = {}
435 self.__pending_shared = {}
436
437 # Current lock holders
438 self.__shr = set()
439 self.__exc = None
440
441 # is this lock in the deleted state?
442 self.__deleted = False
443
444 # Register with lock monitor
445 if monitor:
446 logging.debug("Adding lock %s to monitor", name)
447 monitor.RegisterLock(self)
448
449 def __repr__(self):
450 return ("<%s.%s name=%s at %#x>" %
451 (self.__class__.__module__, self.__class__.__name__,
452 self.name, id(self)))
453
454 def GetLockInfo(self, requested):
455 """Retrieves information for querying locks.
456
457 @type requested: set
458 @param requested: Requested information, see C{query.LQ_*}
459
460 """
461 self.__lock.acquire()
462 try:
463 # Note: to avoid unintentional race conditions, no references to
464 # modifiable objects should be returned unless they were created in this
465 # function.
466 mode = None
467 owner_names = None
468
469 if query.LQ_MODE in requested:
470 if self.__deleted:
471 mode = _DELETED_TEXT
472 assert not (self.__exc or self.__shr)
473 elif self.__exc:
474 mode = _EXCLUSIVE_TEXT
475 elif self.__shr:
476 mode = _SHARED_TEXT
477
478 # Current owner(s) are wanted
479 if query.LQ_OWNER in requested:
480 if self.__exc:
481 owner = [self.__exc]
482 else:
483 owner = self.__shr
484
485 if owner:
486 assert not self.__deleted
487 owner_names = [i.getName() for i in owner]
488
489 # Pending acquires are wanted
490 if query.LQ_PENDING in requested:
491 pending = []
492
493 # Sorting instead of copying and using heaq functions for simplicity
494 for (_, prioqueue) in sorted(self.__pending):
495 for cond in prioqueue:
496 if cond.shared:
497 pendmode = _SHARED_TEXT
498 else:
499 pendmode = _EXCLUSIVE_TEXT
500
501 # List of names will be sorted in L{query._GetLockPending}
502 pending.append((pendmode, [i.getName()
503 for i in cond.get_waiting()]))
504 else:
505 pending = None
506
507 return [(self.name, mode, owner_names, pending)]
508 finally:
509 self.__lock.release()
510
511 def __check_deleted(self):
512 """Raises an exception if the lock has been deleted.
513
514 """
515 if self.__deleted:
516 raise errors.LockError("Deleted lock %s" % self.name)
517
518 def __is_sharer(self):
519 """Is the current thread sharing the lock at this time?
520
521 """
522 return threading.currentThread() in self.__shr
523
524 def __is_exclusive(self):
525 """Is the current thread holding the lock exclusively at this time?
526
527 """
528 return threading.currentThread() == self.__exc
529
530 def __is_owned(self, shared=-1):
531 """Is the current thread somehow owning the lock at this time?
532
533 This is a private version of the function, which presumes you're holding
534 the internal lock.
535
536 """
537 if shared < 0:
538 return self.__is_sharer() or self.__is_exclusive()
539 elif shared:
540 return self.__is_sharer()
541 else:
542 return self.__is_exclusive()
543
544 def is_owned(self, shared=-1):
545 """Is the current thread somehow owning the lock at this time?
546
547 @param shared:
548 - < 0: check for any type of ownership (default)
549 - 0: check for exclusive ownership
550 - > 0: check for shared ownership
551
552 """
553 self.__lock.acquire()
554 try:
555 return self.__is_owned(shared=shared)
556 finally:
557 self.__lock.release()
558
559 #: Necessary to remain compatible with threading.Condition, which tries to
560 #: retrieve a locks' "_is_owned" attribute
561 _is_owned = is_owned
562
563 def _count_pending(self):
564 """Returns the number of pending acquires.
565
566 @rtype: int
567
568 """
569 self.__lock.acquire()
570 try:
571 return sum(len(prioqueue) for (_, prioqueue) in self.__pending)
572 finally:
573 self.__lock.release()
574
575 def _check_empty(self):
576 """Checks whether there are any pending acquires.
577
578 @rtype: bool
579
580 """
581 self.__lock.acquire()
582 try:
583 # Order is important: __find_first_pending_queue modifies __pending
584 (_, prioqueue) = self.__find_first_pending_queue()
585
586 return not (prioqueue or
587 self.__pending or
588 self.__pending_by_prio or
589 self.__pending_shared)
590 finally:
591 self.__lock.release()
592
593 def __do_acquire(self, shared):
594 """Actually acquire the lock.
595
596 """
597 if shared:
598 self.__shr.add(threading.currentThread())
599 else:
600 self.__exc = threading.currentThread()
601
602 def __can_acquire(self, shared):
603 """Determine whether lock can be acquired.
604
605 """
606 if shared:
607 return self.__exc is None
608 else:
609 return len(self.__shr) == 0 and self.__exc is None
610
611 def __find_first_pending_queue(self):
612 """Tries to find the topmost queued entry with pending acquires.
613
614 Removes empty entries while going through the list.
615
616 """
617 while self.__pending:
618 (priority, prioqueue) = self.__pending[0]
619
620 if prioqueue:
621 return (priority, prioqueue)
622
623 # Remove empty queue
624 heapq.heappop(self.__pending)
625 del self.__pending_by_prio[priority]
626 assert priority not in self.__pending_shared
627
628 return (None, None)
629
630 def __is_on_top(self, cond):
631 """Checks whether the passed condition is on top of the queue.
632
633 The caller must make sure the queue isn't empty.
634
635 """
636 (_, prioqueue) = self.__find_first_pending_queue()
637
638 return cond == prioqueue[0]
639
640 def __acquire_unlocked(self, shared, timeout, priority):
641 """Acquire a shared lock.
642
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
648
649 """
650 self.__check_deleted()
651
652 # We cannot acquire the lock if we already have it
653 assert not self.__is_owned(), ("double acquire() on a non-recursive lock"
654 " %s" % self.name)
655
656 # Remove empty entries from queue
657 self.__find_first_pending_queue()
658
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)
663 return True
664
665 prioqueue = self.__pending_by_prio.get(priority, None)
666
667 if shared:
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))
672 else:
673 wait_condition = None
674
675 if wait_condition is None:
676 if prioqueue is None:
677 assert priority not in self.__pending_by_prio
678
679 prioqueue = []
680 heapq.heappush(self.__pending, (priority, prioqueue))
681 self.__pending_by_prio[priority] = prioqueue
682
683 wait_condition = self.__condition_class(self.__lock, shared)
684 prioqueue.append(wait_condition)
685
686 if shared:
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
691
692 wait_start = self.__time_fn()
693 acquired = False
694
695 try:
696 # Wait until we become the topmost acquire in the queue or the timeout
697 # expires.
698 while True:
699 if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
700 self.__do_acquire(shared)
701 acquired = True
702 break
703
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)):
708 break
709
710 # Wait for notification
711 wait_condition.wait(timeout)
712 self.__check_deleted()
713 finally:
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)
721
722 return acquired
723
724 def acquire(self, shared=0, timeout=None, priority=None,
725 test_notify=None):
726 """Acquire a shared lock.
727
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
731 @type timeout: float
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
737
738 """
739 if priority is None:
740 priority = _DEFAULT_PRIORITY
741
742 self.__lock.acquire()
743 try:
744 # We already got the lock, notify now
745 if __debug__ and callable(test_notify):
746 test_notify()
747
748 return self.__acquire_unlocked(shared, timeout, priority)
749 finally:
750 self.__lock.release()
751
752 def downgrade(self):
753 """Changes the lock mode from exclusive to shared.
754
755 Pending acquires in shared mode on the same priority will go ahead.
756
757 """
758 self.__lock.acquire()
759 try:
760 assert self.__is_owned(), "Lock must be owned"
761
762 if self.__is_exclusive():
763 # Do nothing if the lock is already acquired in shared mode
764 self.__exc = None
765 self.__do_acquire(1)
766
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
770 # acquires
771 (priority, prioqueue) = self.__find_first_pending_queue()
772 if prioqueue:
773 # Is there a pending shared acquire on this priority?
774 cond = self.__pending_shared.pop(priority, None)
775 if cond:
776 assert cond.shared
777 assert cond in prioqueue
778
779 # Ensure shared acquire is on top of queue
780 if len(prioqueue) > 1:
781 prioqueue.remove(cond)
782 prioqueue.insert(0, cond)
783
784 # Notify
785 cond.notifyAll()
786
787 assert not self.__is_exclusive()
788 assert self.__is_sharer()
789
790 return True
791 finally:
792 self.__lock.release()
793
794 def release(self):
795 """Release a Shared Lock.
796
797 You must have acquired the lock, either in shared or in exclusive mode,
798 before calling this function.
799
800 """
801 self.__lock.acquire()
802 try:
803 assert self.__is_exclusive() or self.__is_sharer(), \
804 "Cannot release non-owned lock"
805
806 # Autodetect release type
807 if self.__is_exclusive():
808 self.__exc = None
809 notify = True
810 else:
811 self.__shr.remove(threading.currentThread())
812 notify = not self.__shr
813
814 # Notify topmost condition in queue if there are no owners left (for
815 # shared locks)
816 if notify:
817 self.__notify_topmost()
818 finally:
819 self.__lock.release()
820
821 def __notify_topmost(self):
822 """Notifies topmost condition in queue of pending acquires.
823
824 """
825 (priority, prioqueue) = self.__find_first_pending_queue()
826 if prioqueue:
827 cond = prioqueue[0]
828 cond.notifyAll()
829 if cond.shared:
830 # Prevent further shared acquires from sneaking in while waiters are
831 # notified
832 self.__pending_shared.pop(priority, None)
833
834 def _notify_topmost(self):
835 """Exported version of L{__notify_topmost}.
836
837 """
838 self.__lock.acquire()
839 try:
840 return self.__notify_topmost()
841 finally:
842 self.__lock.release()
843
844 def delete(self, timeout=None, priority=None):
845 """Delete a Shared Lock.
846
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.
850
851 @type timeout: float
852 @param timeout: maximum waiting time before giving up
853 @type priority: integer
854 @param priority: Priority for acquiring lock
855
856 """
857 if priority is None:
858 priority = _DEFAULT_PRIORITY
859
860 self.__lock.acquire()
861 try:
862 assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"
863
864 self.__check_deleted()
865
866 # The caller is allowed to hold the lock exclusively already.
867 acquired = self.__is_exclusive()
868
869 if not acquired:
870 acquired = self.__acquire_unlocked(0, timeout, priority)
871
872 if acquired:
873 assert self.__is_exclusive() and not self.__is_sharer(), \
874 "Lock wasn't acquired in exclusive mode"
875
876 self.__deleted = True
877 self.__exc = None
878
879 assert not (self.__exc or self.__shr), "Found owner during deletion"
880
881 # Notify all acquires. They'll throw an error.
882 for (_, prioqueue) in self.__pending:
883 for cond in prioqueue:
884 cond.notifyAll()
885
886 assert self.__deleted
887
888 return acquired
889 finally:
890 self.__lock.release()
891
892 def _release_save(self):
893 shared = self.__is_sharer()
894 self.release()
895 return shared
896
897 def _acquire_restore(self, shared):
898 self.acquire(shared=shared)
899
900
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.
903 ALL_SET = None
904
905
906 class _AcquireTimeout(Exception):
907 """Internal exception to abort an acquire on a timeout.
908
909 """
910
911
912 class LockSet:
913 """Implements a set of locks.
914
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
918 preventing deadlock.
919
920 All the locks needed in the same set must be acquired together, though.
921
922 @type name: string
923 @ivar name: the name of the lockset
924
925 """
926 def __init__(self, members, name, monitor=None):
927 """Constructs a new LockSet.
928
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
933
934 """
935 assert members is not None, "members parameter is not a list"
936 self.name = name
937
938 # Lock monitor
939 self.__monitor = monitor
940
941 # Used internally to guarantee coherency
942 self.__lock = SharedLock(self._GetLockName("[lockset]"), monitor=monitor)
943
944 # The lockdict indexes the relationship name -> lock
945 # The order-of-locking is implied by the alphabetical order of names
946 self.__lockdict = {}
947
948 for mname in members:
949 self.__lockdict[mname] = SharedLock(self._GetLockName(mname),
950 monitor=monitor)
951
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
958 # will be trouble.
959 self.__owners = {}
960
961 def _GetLockName(self, mname):
962 """Returns the name for a member lock.
963
964 """
965 return "%s/%s" % (self.name, mname)
966
967 def _get_lock(self):
968 """Returns the lockset-internal lock.
969
970 """
971 return self.__lock
972
973 def _get_lockdict(self):
974 """Returns the lockset-internal lock dictionary.
975
976 Accessing this structure is only safe in single-thread usage or when the
977 lockset-internal lock is held.
978
979 """
980 return self.__lockdict
981
982 def is_owned(self):
983 """Is the current thread a current level owner?
984
985 @note: Use L{check_owned} to check if a specific lock is held
986
987 """
988 return threading.currentThread() in self.__owners
989
990 def check_owned(self, names, shared=-1):
991 """Check if locks are owned in a specific mode.
992
993 @type names: sequence or string
994 @param names: Lock names (or a single lock name)
995 @param shared: See L{SharedLock.is_owned}
996 @rtype: bool
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
999
1000 """
1001 if isinstance(names, basestring):
1002 names = [names]
1003
1004 # Avoid check if no locks are owned anyway
1005 if names and self.is_owned():
1006 candidates = []
1007
1008 # Gather references to all locks (in case they're deleted in the meantime)
1009 for lname in names:
1010 try:
1011 lock = self.__lockdict[lname]
1012 except KeyError:
1013 raise errors.LockError("Non-existing lock '%s' in set '%s' (it may"
1014 " have been removed)" % (lname, self.name))
1015 else:
1016 candidates.append(lock)
1017
1018 return compat.all(lock.is_owned(shared=shared) for lock in candidates)
1019 else:
1020 return False
1021
1022 def _add_owned(self, name=None):
1023 """Note the current thread owns the given lock"""
1024 if name is None:
1025 if not self.is_owned():
1026 self.__owners[threading.currentThread()] = set()
1027 else:
1028 if self.is_owned():
1029 self.__owners[threading.currentThread()].add(name)
1030 else:
1031 self.__owners[threading.currentThread()] = set([name])
1032
1033 def _del_owned(self, name=None):
1034 """Note the current thread owns the given lock"""
1035
1036 assert not (name is None and self.__lock.is_owned()), \
1037 "Cannot hold internal lock when deleting owner status"
1038
1039 if name is not None:
1040 self.__owners[threading.currentThread()].remove(name)
1041
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()]
1046
1047 def list_owned(self):
1048 """Get the set of resource names owned by the current thread"""
1049 if self.is_owned():
1050 return self.__owners[threading.currentThread()].copy()
1051 else:
1052 return set()
1053
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]
1058 if lock.is_owned():
1059 lock.release()
1060 self._del_owned(name=lname)
1061
1062 def __names(self):
1063 """Return the current set of names.
1064
1065 Only call this function while holding __lock and don't iterate on the
1066 result after releasing the lock.
1067
1068 """
1069 return self.__lockdict.keys()
1070
1071 def _names(self):
1072 """Return a copy of the current set of elements.
1073
1074 Used only for debugging purposes.
1075
1076 """
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():
1081 release_lock = True
1082 self.__lock.acquire(shared=1)
1083 try:
1084 result = self.__names()
1085 finally:
1086 if release_lock:
1087 self.__lock.release()
1088 return set(result)
1089
1090 def acquire(self, names, timeout=None, shared=0, priority=None,
1091 test_notify=None):
1092 """Acquire a set of resource locks.
1093
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
1106
1107 @return: Set of all locks successfully acquired or None in case of timeout
1108
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.
1112
1113 """
1114 assert timeout is None or timeout >= 0.0
1115
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)
1119
1120 if priority is None:
1121 priority = _DEFAULT_PRIORITY
1122
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)
1126
1127 try:
1128 if names is not None:
1129 # Support passing in a single resource to acquire rather than many
1130 if isinstance(names, basestring):
1131 names = [names]
1132
1133 return self.__acquire_inner(names, False, shared, priority,
1134 running_timeout.Remaining, test_notify)
1135
1136 else:
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.
1140 #
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()
1149 try:
1150 # note we own the set-lock
1151 self._add_owned()
1152
1153 return self.__acquire_inner(self.__names(), True, shared, priority,
1154 running_timeout.Remaining, test_notify)
1155 except:
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()
1160 self._del_owned()
1161 raise
1162
1163 except _AcquireTimeout:
1164 return None
1165
1166 def __acquire_inner(self, names, want_all, shared, priority,
1167 timeout_fn, test_notify):
1168 """Inner logic for acquiring a number of locks.
1169
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
1176
1177 """
1178 acquire_list = []
1179
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
1183 # deadlocks.
1184 for lname in sorted(utils.UniqueSequence(names)):
1185 try:
1186 lock = self.__lockdict[lname] # raises KeyError if lock is not there
1187 except KeyError:
1188 if want_all:
1189 # We are acquiring all the set, it doesn't matter if this particular
1190 # element is not there anymore.
1191 continue
1192
1193 raise errors.LockError("Non-existing lock %s in set %s (it may have"
1194 " been removed)" % (lname, self.name))
1195
1196 acquire_list.append((lname, lock))
1197
1198 # This will hold the locknames we effectively acquired.
1199 acquired = set()
1200
1201 try:
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)
1210 else:
1211 test_notify_fn = None
1212
1213 timeout = timeout_fn()
1214
1215 try:
1216 # raises LockError if the lock was deleted
1217 acq_success = lock.acquire(shared=shared, timeout=timeout,
1218 priority=priority,
1219 test_notify=test_notify_fn)
1220 except errors.LockError:
1221 if want_all:
1222 # We are acquiring all the set, it doesn't matter if this
1223 # particular element is not there anymore.
1224 continue
1225
1226 raise errors.LockError("Non-existing lock %s in set %s (it may"
1227 " have been removed)" % (lname, self.name))
1228
1229 if not acq_success:
1230 # Couldn't get lock or timeout occurred
1231 if timeout is None:
1232 # This shouldn't happen as SharedLock.acquire(timeout=None) is
1233 # blocking.
1234 raise errors.LockError("Failed to get lock %s (set %s)" %
1235 (lname, self.name))
1236
1237 raise _AcquireTimeout()
1238
1239 try:
1240 # now the lock cannot be deleted, we have it!
1241 self._add_owned(name=lname)
1242 acquired.add(lname)
1243
1244 except:
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.
1248 if lock.is_owned():
1249 lock.release()
1250 raise
1251
1252 except:
1253 # Release all owned locks
1254 self._release_and_delete_owned()
1255 raise
1256
1257 return acquired
1258
1259 def downgrade(self, names=None):
1260 """Downgrade a set of resource locks from exclusive to shared mode.
1261
1262 The locks must have been acquired in exclusive mode.
1263
1264 """
1265 assert self.is_owned(), ("downgrade on lockset %s while not owning any"
1266 " lock" % self.name)
1267
1268 # Support passing in a single resource to downgrade rather than many
1269 if isinstance(names, basestring):
1270 names = [names]
1271
1272 owned = self.list_owned()
1273
1274 if names is None:
1275 names = owned
1276 else:
1277 names = set(names)
1278 assert owned.issuperset(names), \
1279 ("downgrade() on unheld resources %s (set %s)" %
1280 (names.difference(owned), self.name))
1281
1282 for lockname in names:
1283 self.__lockdict[lockname].downgrade()
1284
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)
1292
1293 return True
1294
1295 def release(self, names=None):
1296 """Release a set of resource locks, at the same level.
1297
1298 You must have acquired the locks, either in shared or in exclusive mode,
1299 before releasing them.
1300
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).
1304
1305 """
1306 assert self.is_owned(), ("release() on lock set %s while not owner" %
1307 self.name)
1308
1309 # Support passing in a single resource to release rather than many
1310 if isinstance(names, basestring):
1311 names = [names]
1312
1313 if names is None:
1314 names = self.list_owned()
1315 else:
1316 names = set(names)
1317 assert self.list_owned().issuperset(names), (
1318 "release() on unheld resources %s (set %s)" %
1319 (names.difference(self.list_owned()), self.name))
1320
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()
1325 self._del_owned()
1326
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)
1332
1333 def add(self, names, acquired=0, shared=0):
1334 """Add a new set of elements to the set
1335
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?
1342
1343 """
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" %
1347 self.name)
1348
1349 # Support passing in a single resource to add rather than many
1350 if isinstance(names, basestring):
1351 names = [names]
1352
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():
1357 release_lock = True
1358 self.__lock.acquire()
1359
1360 try:
1361 invalid_names = set(self.__names()).intersection(names)
1362 if invalid_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))
1368
1369 for lockname in names:
1370 lock = SharedLock(self._GetLockName(lockname), monitor=self.__monitor)
1371
1372 if acquired:
1373 # No need for priority or timeout here as this lock has just been
1374 # created
1375 lock.acquire(shared=shared)
1376 # now the lock cannot be deleted, we have it!
1377 try:
1378 self._add_owned(name=lockname)
1379 except:
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.
1386 lock.release()
1387 raise
1388
1389 self.__lockdict[lockname] = lock
1390
1391 finally:
1392 # Only release __lock if we were not holding it previously.
1393 if release_lock:
1394 self.__lock.release()
1395
1396 return True
1397
1398 def remove(self, names):
1399 """Remove elements from the lock set.
1400
1401 You can either not hold anything in the lockset or already hold a superset
1402 of the elements you want to delete, exclusively.
1403
1404 @type names: list of strings
1405 @param names: names of the resource to remove.
1406
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
1409 exclusively
1410
1411 """
1412 # Support passing in a single resource to remove rather than many
1413 if isinstance(names, basestring):
1414 names = [names]
1415
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" %
1421 self.name)
1422
1423 removed = []
1424
1425 for lname in names:
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.
1431 try:
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" %
1437 self.name)
1438 else:
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()).
1443 #
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.
1448 if self.is_owned():
1449 self._del_owned(name=lname)
1450
1451 return removed
1452
1453
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
1459 # avoided.
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
1462 # the same time.
1463 LEVEL_CLUSTER = 0
1464 LEVEL_INSTANCE = 1
1465 LEVEL_NODEGROUP = 2
1466 LEVEL_NODE = 3
1467 #: Level for node resources, used for operations with possibly high impact on
1468 #: the node's disks.
1469 LEVEL_NODE_RES = 4
1470
1471 LEVELS = [
1472 LEVEL_CLUSTER,
1473 LEVEL_INSTANCE,
1474 LEVEL_NODEGROUP,
1475 LEVEL_NODE,
1476 LEVEL_NODE_RES,
1477 ]
1478
1479 # Lock levels which are modifiable
1480 LEVELS_MOD = frozenset([
1481 LEVEL_NODE_RES,
1482 LEVEL_NODE,
1483 LEVEL_NODEGROUP,
1484 LEVEL_INSTANCE,
1485 ])
1486
1487 #: Lock level names (make sure to use singular form)
1488 LEVEL_NAMES = {
1489 LEVEL_CLUSTER: "cluster",
1490 LEVEL_INSTANCE: "instance",
1491 LEVEL_NODEGROUP: "nodegroup",
1492 LEVEL_NODE: "node",
1493 LEVEL_NODE_RES: "node-res",
1494 }
1495
1496 # Constant for the big ganeti lock
1497 BGL = "BGL"
1498
1499
1500 class GanetiLockManager:
1501 """The Ganeti Locking Library
1502
1503 The purpose of this small library is to manage locking for ganeti clusters
1504 in a central place, while at the same time doing dynamic checks against
1505 possible deadlocks. It will also make it easier to transition to a different
1506 lock type should we migrate away from python threads.
1507
1508 """
1509 _instance = None
1510
1511 def __init__(self, nodes, nodegroups, instances):
1512 """Constructs a new GanetiLockManager object.
1513
1514 There should be only a GanetiLockManager object at any time, so this
1515 function raises an error if this is not the case.
1516
1517 @param nodes: list of node names
1518 @param nodegroups: list of nodegroup uuids
1519 @param instances: list of instance names
1520
1521 """
1522 assert self.__class__._instance is None, \
1523 "double GanetiLockManager instance"
1524
1525 self.__class__._instance = self
1526
1527 self._monitor = LockMonitor()
1528
1529 # The keyring contains all the locks, at their level and in the correct
1530 # locking order.
1531 self.__keyring = {
1532 LEVEL_CLUSTER: LockSet([BGL], "cluster", monitor=self._monitor),
1533 LEVEL_NODE: LockSet(nodes, "node", monitor=self._monitor),
1534 LEVEL_NODE_RES: LockSet(nodes, "node-res", monitor=self._monitor),
1535 LEVEL_NODEGROUP: LockSet(nodegroups, "nodegroup", monitor=self._monitor),
1536 LEVEL_INSTANCE: LockSet(instances, "instance",
1537 monitor=self._monitor),
1538 }
1539
1540 assert compat.all(ls.name == LEVEL_NAMES[level]
1541 for (level, ls) in self.__keyring.items())
1542
1543 def AddToLockMonitor(self, provider):
1544 """Registers a new lock with the monitor.
1545
1546 See L{LockMonitor.RegisterLock}.
1547
1548 """
1549 return self._monitor.RegisterLock(provider)
1550
1551 def QueryLocks(self, fields):
1552 """Queries information from all locks.
1553
1554 See L{LockMonitor.QueryLocks}.
1555
1556 """
1557 return self._monitor.QueryLocks(fields)
1558
1559 def _names(self, level):
1560 """List the lock names at the given level.
1561
1562 This can be used for debugging/testing purposes.
1563
1564 @param level: the level whose list of locks to get
1565
1566 """
1567 assert level in LEVELS, "Invalid locking level %s" % level
1568 return self.__keyring[level]._names()
1569
1570 def is_owned(self, level):
1571 """Check whether we are owning locks at the given level
1572
1573 """
1574 return self.__keyring[level].is_owned()
1575
1576 def list_owned(self, level):
1577 """Get the set of owned locks at the given level
1578
1579 """
1580 return self.__keyring[level].list_owned()
1581
1582 def check_owned(self, level, names, shared=-1):
1583 """Check if locks at a certain level are owned in a specific mode.
1584
1585 @see: L{LockSet.check_owned}
1586
1587 """
1588 return self.__keyring[level].check_owned(names, shared=shared)
1589
1590 def _upper_owned(self, level):
1591 """Check that we don't own any lock at a level greater than the given one.
1592
1593 """
1594 # This way of checking only works if LEVELS[i] = i, which we check for in
1595 # the test cases.
1596 return compat.any((self.is_owned(l) for l in LEVELS[level + 1:]))
1597
1598 def _BGL_owned(self): # pylint: disable=C0103
1599 """Check if the current thread owns the BGL.
1600
1601 Both an exclusive or a shared acquisition work.
1602
1603 """
1604 return BGL in self.__keyring[LEVEL_CLUSTER].list_owned()
1605
1606 @staticmethod
1607 def _contains_BGL(level, names): # pylint: disable=C0103
1608 """Check if the level contains the BGL.
1609
1610 Check if acting on the given level and set of names will change
1611 the status of the Big Ganeti Lock.
1612
1613 """
1614 return level == LEVEL_CLUSTER and (names is None or BGL in names)
1615
1616 def acquire(self, level, names, timeout=None, shared=0, priority=None):
1617 """Acquire a set of resource locks, at the same level.
1618
1619 @type level: member of locking.LEVELS
1620 @param level: the level at which the locks shall be acquired
1621 @type names: list of strings (or string)
1622 @param names: the names of the locks which shall be acquired
1623 (special lock names, or instance/node names)
1624 @type shared: integer (0/1) used as a boolean
1625 @param shared: whether to acquire in shared mode; by default
1626 an exclusive lock will be acquired
1627 @type timeout: float
1628 @param timeout: Maximum time to acquire all locks
1629 @type priority: integer
1630 @param priority: Priority for acquiring lock
1631
1632 """
1633 assert level in LEVELS, "Invalid locking level %s" % level
1634
1635 # Check that we are either acquiring the Big Ganeti Lock or we already own
1636 # it. Some "legacy" opcodes need to be sure they are run non-concurrently
1637 # so even if we've migrated we need to at least share the BGL to be
1638 # compatible with them. Of course if we own the BGL exclusively there's no
1639 # point in acquiring any other lock, unless perhaps we are half way through
1640 # the migration of the current opcode.
1641 assert (self._contains_BGL(level, names) or self._BGL_owned()), (
1642 "You must own the Big Ganeti Lock before acquiring any other")
1643
1644 # Check we don't own locks at the same or upper levels.
1645 assert not self._upper_owned(level), ("Cannot acquire locks at a level"
1646 " while owning some at a greater one")
1647
1648 # Acquire the locks in the set.
1649 return self.__keyring[level].acquire(names, shared=shared, timeout=timeout,
1650 priority=priority)
1651
1652 def downgrade(self, level, names=None):
1653 """Downgrade a set of resource locks from exclusive to shared mode.
1654
1655 You must have acquired the locks in exclusive mode.
1656
1657 @type level: member of locking.LEVELS
1658 @param level: the level at which the locks shall be downgraded
1659 @type names: list of strings, or None
1660 @param names: the names of the locks which shall be downgraded
1661 (defaults to all the locks acquired at the level)
1662
1663 """
1664 assert level in LEVELS, "Invalid locking level %s" % level
1665
1666 return self.__keyring[level].downgrade(names=names)
1667
1668 def release(self, level, names=None):
1669 """Release a set of resource locks, at the same level.
1670
1671 You must have acquired the locks, either in shared or in exclusive
1672 mode, before releasing them.
1673
1674 @type level: member of locking.LEVELS
1675 @param level: the level at which the locks shall be released
1676 @type names: list of strings, or None
1677 @param names: the names of the locks which shall be released
1678 (defaults to all the locks acquired at that level)
1679
1680 """
1681 assert level in LEVELS, "Invalid locking level %s" % level
1682 assert (not self._contains_BGL(level, names) or
1683 not self._upper_owned(LEVEL_CLUSTER)), (
1684 "Cannot release the Big Ganeti Lock while holding something"
1685 " at upper levels (%r)" %
1686 (utils.CommaJoin(["%s=%r" % (LEVEL_NAMES[i], self.list_owned(i))
1687 for i in self.__keyring.keys()]), ))
1688
1689 # Release will complain if we don't own the locks already
1690 return self.__keyring[level].release(names)
1691
1692 def add(self, level, names, acquired=0, shared=0):
1693 """Add locks at the specified level.
1694
1695 @type level: member of locking.LEVELS_MOD
1696 @param level: the level at which the locks shall be added
1697 @type names: list of strings
1698 @param names: names of the locks to acquire
1699 @type acquired: integer (0/1) used as a boolean
1700 @param acquired: whether to acquire the newly added locks
1701 @type shared: integer (0/1) used as a boolean
1702 @param shared: whether the acquisition will be shared
1703
1704 """
1705 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1706 assert self._BGL_owned(), ("You must own the BGL before performing other"
1707 " operations")
1708 assert not self._upper_owned(level), ("Cannot add locks at a level"
1709 " while owning some at a greater one")
1710 return self.__keyring[level].add(names, acquired=acquired, shared=shared)
1711
1712 def remove(self, level, names):
1713 """Remove locks from the specified level.
1714
1715 You must either already own the locks you are trying to remove
1716 exclusively or not own any lock at an upper level.
1717
1718 @type level: member of locking.LEVELS_MOD
1719 @param level: the level at which the locks shall be removed
1720 @type names: list of strings
1721 @param names: the names of the locks which shall be removed
1722 (special lock names, or instance/node names)
1723
1724 """
1725 assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1726 assert self._BGL_owned(), ("You must own the BGL before performing other"
1727 " operations")
1728 # Check we either own the level or don't own anything from here
1729 # up. LockSet.remove() will check the case in which we don't own
1730 # all the needed resources, or we have a shared ownership.
1731 assert self.is_owned(level) or not self._upper_owned(level), (
1732 "Cannot remove locks at a level while not owning it or"
1733 " owning some at a greater one")
1734 return self.__keyring[level].remove(names)
1735
1736
1737 def _MonitorSortKey((item, idx, num)):
1738 """Sorting key function.
1739
1740 Sort by name, registration order and then order of information. This provides
1741 a stable sort order over different providers, even if they return the same
1742 name.
1743
1744 """
1745 (name, _, _, _) = item
1746
1747 return (utils.NiceSortKey(name), num, idx)
1748
1749
1750 class LockMonitor(object):
1751 _LOCK_ATTR = "_lock"
1752
1753 def __init__(self):
1754 """Initializes this class.
1755
1756 """
1757 self._lock = SharedLock("LockMonitor")
1758
1759 # Counter for stable sorting
1760 self._counter = itertools.count(0)
1761
1762 # Tracked locks. Weak references are used to avoid issues with circular
1763 # references and deletion.
1764 self._locks = weakref.WeakKeyDictionary()
1765
1766 @ssynchronized(_LOCK_ATTR)
1767 def RegisterLock(self, provider):
1768 """Registers a new lock.
1769
1770 @param provider: Object with a callable method named C{GetLockInfo}, taking
1771 a single C{set} containing the requested information items
1772 @note: It would be nicer to only receive the function generating the
1773 requested information but, as it turns out, weak references to bound
1774 methods (e.g. C{self.GetLockInfo}) are tricky; there are several
1775 workarounds, but none of the ones I found works properly in combination
1776 with a standard C{WeakKeyDictionary}
1777
1778 """
1779 assert provider not in self._locks, "Duplicate registration"
1780
1781 # There used to be a check for duplicate names here. As it turned out, when
1782 # a lock is re-created with the same name in a very short timeframe, the
1783 # previous instance might not yet be removed from the weakref dictionary.
1784 # By keeping track of the order of incoming registrations, a stable sort
1785 # ordering can still be guaranteed.
1786
1787 self._locks[provider] = self._counter.next()
1788
1789 def _GetLockInfo(self, requested):
1790 """Get information from all locks.
1791
1792 """
1793 # Must hold lock while getting consistent list of tracked items
1794 self._lock.acquire(shared=1)
1795 try:
1796 items = self._locks.items()
1797 finally:
1798 self._lock.release()
1799
1800 return [(info, idx, num)
1801 for (provider, num) in items
1802 for (idx, info) in enumerate(provider.GetLockInfo(requested))]
1803
1804 def _Query(self, fields):
1805 """Queries information from all locks.
1806
1807 @type fields: list of strings
1808 @param fields: List of fields to return
1809
1810 """
1811 qobj = query.Query(query.LOCK_FIELDS, fields)
1812
1813 # Get all data with internal lock held and then sort by name and incoming
1814 # order
1815 lockinfo = sorted(self._GetLockInfo(qobj.RequestedData()),
1816 key=_MonitorSortKey)
1817
1818 # Extract lock information and build query data
1819 return (qobj, query.LockQueryData(map(compat.fst, lockinfo)))
1820
1821 def QueryLocks(self, fields):
1822 """Queries information from all locks.
1823
1824 @type fields: list of strings
1825 @param fields: List of fields to return
1826
1827 """
1828 (qobj, ctx) = self._Query(fields)
1829
1830 # Prepare query response
1831 return query.GetQueryResponse(qobj, ctx)