locking.py 37.8 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
#
#

# Copyright (C) 2006, 2007 Google Inc.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.

21
22
23
# Disable "Invalid name ..." message
# pylint: disable-msg=C0103

24
25
"""Module implementing the Ganeti locking code."""

26
27
import os
import select
28
import threading
29
30
import time
import errno
31

32
from ganeti import errors
33
from ganeti import utils
34
35


36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
def ssynchronized(lock, shared=0):
  """Shared Synchronization decorator.

  Calls the function holding the given lock, either in exclusive or shared
  mode. It requires the passed lock to be a SharedLock (or support its
  semantics).

  """
  def wrap(fn):
    def sync_function(*args, **kwargs):
      lock.acquire(shared=shared)
      try:
        return fn(*args, **kwargs)
      finally:
        lock.release()
    return sync_function
  return wrap


55
56
class _SingleNotifyPipeConditionWaiter(object):
  """Helper class for SingleNotifyPipeCondition
57
58
59
60
61
62
63

  """
  __slots__ = [
    "_fd",
    "_poller",
    ]

64
65
  def __init__(self, poller, fd):
    """Constructor for _SingleNotifyPipeConditionWaiter
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103

    @type poller: select.poll
    @param poller: Poller object
    @type fd: int
    @param fd: File descriptor to wait for

    """
    object.__init__(self)
    self._poller = poller
    self._fd = fd

  def __call__(self, timeout):
    """Wait for something to happen on the pipe.

    @type timeout: float or None
    @param timeout: Timeout for waiting (can be None)

    """
    start_time = time.time()
    remaining_time = timeout

    while timeout is None or remaining_time > 0:
      try:
        result = self._poller.poll(remaining_time)
      except EnvironmentError, err:
        if err.errno != errno.EINTR:
          raise
        result = None

      # Check whether we were notified
      if result and result[0][0] == self._fd:
        break

      # Re-calculate timeout if necessary
      if timeout is not None:
        remaining_time = start_time + timeout - time.time()


104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
class _BaseCondition(object):
  """Base class containing common code for conditions.

  Some of this code is taken from python's threading module.

  """
  __slots__ = [
    "_lock",
    "acquire",
    "release",
    ]

  def __init__(self, lock):
    """Constructor for _BaseCondition.

119
    @type lock: threading.Lock
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
    @param lock: condition base lock

    """
    object.__init__(self)

    # Recursive locks are not supported
    assert not hasattr(lock, "_acquire_restore")
    assert not hasattr(lock, "_release_save")

    self._lock = lock

    # Export the lock's acquire() and release() methods
    self.acquire = lock.acquire
    self.release = lock.release

  def _is_owned(self):
    """Check whether lock is owned by current thread.

    """
    if self._lock.acquire(0):
      self._lock.release()
      return False

    return True

  def _check_owned(self):
    """Raise an exception if the current thread doesn't own the lock.

    """
    if not self._is_owned():
      raise RuntimeError("cannot work with un-aquired lock")


153
154
class SingleNotifyPipeCondition(_BaseCondition):
  """Condition which can only be notified once.
155

156
157
158
159
160
  This condition class uses pipes and poll, internally, to be able to wait for
  notification with a timeout, without resorting to polling. It is almost
  compatible with Python's threading.Condition, with the following differences:
    - notifyAll can only be called once, and no wait can happen after that
    - notify is not supported, only notifyAll
161
162

  """
163
164

  __slots__ = _BaseCondition.__slots__ + [
165
166
167
168
    "_poller",
    "_read_fd",
    "_write_fd",
    "_nwaiters",
169
    "_notified",
170
171
    ]

172
  _waiter_class = _SingleNotifyPipeConditionWaiter
173

174
175
  def __init__(self, lock):
    """Constructor for SingleNotifyPipeCondition
176
177

    """
178
    _BaseCondition.__init__(self, lock)
179
    self._nwaiters = 0
180
181
182
183
    self._notified = False
    self._read_fd = None
    self._write_fd = None
    self._poller = None
184

185
  def _check_unnotified(self):
186
187
188
    """Throws an exception if already notified.

    """
189
190
    if self._notified:
      raise RuntimeError("cannot use already notified condition")
191

192
193
  def _Cleanup(self):
    """Cleanup open file descriptors, if any.
194
195

    """
196
197
198
    if self._read_fd is not None:
      os.close(self._read_fd)
      self._read_fd = None
199

200
201
202
203
    if self._write_fd is not None:
      os.close(self._write_fd)
      self._write_fd = None
    self._poller = None
204

205
206
  def wait(self, timeout=None):
    """Wait for a notification.
207

208
209
    @type timeout: float or None
    @param timeout: Waiting timeout (can be None)
210
211

    """
212
213
    self._check_owned()
    self._check_unnotified()
214

215
216
217
218
219
220
    self._nwaiters += 1
    try:
      if self._poller is None:
        (self._read_fd, self._write_fd) = os.pipe()
        self._poller = select.poll()
        self._poller.register(self._read_fd, select.POLLHUP)
221

222
223
224
225
226
227
228
229
230
231
232
233
      wait_fn = self._waiter_class(self._poller, self._read_fd)
      self.release()
      try:
        # Wait for notification
        wait_fn(timeout)
      finally:
        # Re-acquire lock
        self.acquire()
    finally:
      self._nwaiters -= 1
      if self._nwaiters == 0:
        self._Cleanup()
234
235
236
237
238

  def notifyAll(self):
    """Close the writing side of the pipe to notify all waiters.

    """
239
240
241
    self._check_owned()
    self._check_unnotified()
    self._notified = True
242
243
244
245
246
    if self._write_fd is not None:
      os.close(self._write_fd)
      self._write_fd = None


247
class PipeCondition(_BaseCondition):
Michael Hanselmann's avatar
Michael Hanselmann committed
248
249
250
251
252
253
254
255
256
  """Group-only non-polling condition with counters.

  This condition class uses pipes and poll, internally, to be able to wait for
  notification with a timeout, without resorting to polling. It is almost
  compatible with Python's threading.Condition, but only supports notifyAll and
  non-recursive locks. As an additional features it's able to report whether
  there are any waiting threads.

  """
257
  __slots__ = _BaseCondition.__slots__ + [
Michael Hanselmann's avatar
Michael Hanselmann committed
258
    "_nwaiters",
259
    "_single_condition",
Michael Hanselmann's avatar
Michael Hanselmann committed
260
261
    ]

262
  _single_condition_class = SingleNotifyPipeCondition
Michael Hanselmann's avatar
Michael Hanselmann committed
263
264
265
266
267

  def __init__(self, lock):
    """Initializes this class.

    """
268
    _BaseCondition.__init__(self, lock)
Michael Hanselmann's avatar
Michael Hanselmann committed
269
    self._nwaiters = 0
270
    self._single_condition = self._single_condition_class(self._lock)
Michael Hanselmann's avatar
Michael Hanselmann committed
271
272
273
274
275
276
277
278
279
280
281
282

  def wait(self, timeout=None):
    """Wait for a notification.

    @type timeout: float or None
    @param timeout: Waiting timeout (can be None)

    """
    self._check_owned()

    # Keep local reference to the pipe. It could be replaced by another thread
    # notifying while we're waiting.
283
    my_condition = self._single_condition
Michael Hanselmann's avatar
Michael Hanselmann committed
284
285
286
287

    assert self._nwaiters >= 0
    self._nwaiters += 1
    try:
288
      my_condition.wait(timeout)
Michael Hanselmann's avatar
Michael Hanselmann committed
289
290
291
292
293
294
295
296
297
    finally:
      assert self._nwaiters > 0
      self._nwaiters -= 1

  def notifyAll(self):
    """Notify all currently waiting threads.

    """
    self._check_owned()
298
299
    self._single_condition.notifyAll()
    self._single_condition = self._single_condition_class(self._lock)
Michael Hanselmann's avatar
Michael Hanselmann committed
300
301
302
303
304
305
306
307
308
309

  def has_waiting(self):
    """Returns whether there are active waiters.

    """
    self._check_owned()

    return bool(self._nwaiters)


310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
class _CountingCondition(object):
  """Wrapper for Python's built-in threading.Condition class.

  This wrapper keeps a count of active waiters. We can't access the internal
  "__waiters" attribute of threading.Condition because it's not thread-safe.

  """
  __slots__ = [
    "_cond",
    "_nwaiters",
    ]

  def __init__(self, lock):
    """Initializes this class.

    """
    object.__init__(self)
    self._cond = threading.Condition(lock=lock)
    self._nwaiters = 0

  def notifyAll(self):
    """Notifies the condition.

    """
    return self._cond.notifyAll()

  def wait(self, timeout=None):
    """Waits for the condition to be notified.

    @type timeout: float or None
340
    @param timeout: Waiting timeout (can be None)
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358

    """
    assert self._nwaiters >= 0

    self._nwaiters += 1
    try:
      return self._cond.wait(timeout=timeout)
    finally:
      self._nwaiters -= 1

  def has_waiting(self):
    """Returns whether there are active waiters.

    """
    return bool(self._nwaiters)


class SharedLock(object):
359
360
361
362
363
364
365
366
367
368
369
  """Implements a shared lock.

  Multiple threads can acquire the lock in a shared way, calling
  acquire_shared().  In order to acquire the lock in an exclusive way threads
  can call acquire_exclusive().

  The lock prevents starvation but does not guarantee that threads will acquire
  the shared lock in the order they queued for it, just that they will
  eventually do so.

  """
370
371
372
373
374
375
376
377
378
379
  __slots__ = [
    "__active_shr_c",
    "__inactive_shr_c",
    "__deleted",
    "__exc",
    "__lock",
    "__pending",
    "__shr",
    ]

380
  __condition_class = PipeCondition
381

382
  def __init__(self):
383
384
385
386
387
388
    """Construct a new SharedLock.

    """
    object.__init__(self)

    # Internal lock
389
390
    self.__lock = threading.Lock()

391
392
393
394
395
396
397
398
    # Queue containing waiting acquires
    self.__pending = []

    # Active and inactive conditions for shared locks
    self.__active_shr_c = self.__condition_class(self.__lock)
    self.__inactive_shr_c = self.__condition_class(self.__lock)

    # Current lock holders
399
400
401
    self.__shr = set()
    self.__exc = None

402
403
404
    # is this lock in the deleted state?
    self.__deleted = False

405
406
407
408
409
410
411
  def __check_deleted(self):
    """Raises an exception if the lock has been deleted.

    """
    if self.__deleted:
      raise errors.LockError("Deleted lock")

412
  def __is_sharer(self):
413
414
415
    """Is the current thread sharing the lock at this time?

    """
416
417
418
    return threading.currentThread() in self.__shr

  def __is_exclusive(self):
419
420
421
    """Is the current thread holding the lock exclusively at this time?

    """
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
    return threading.currentThread() == self.__exc

  def __is_owned(self, shared=-1):
    """Is the current thread somehow owning the lock at this time?

    This is a private version of the function, which presumes you're holding
    the internal lock.

    """
    if shared < 0:
      return self.__is_sharer() or self.__is_exclusive()
    elif shared:
      return self.__is_sharer()
    else:
      return self.__is_exclusive()

  def _is_owned(self, shared=-1):
    """Is the current thread somehow owning the lock at this time?

Iustin Pop's avatar
Iustin Pop committed
441
442
443
444
    @param shared:
        - < 0: check for any type of ownership (default)
        - 0: check for exclusive ownership
        - > 0: check for shared ownership
445
446
447
448

    """
    self.__lock.acquire()
    try:
449
      return self.__is_owned(shared=shared)
450
451
452
    finally:
      self.__lock.release()

453
454
  def _count_pending(self):
    """Returns the number of pending acquires.
455

456
    @rtype: int
457
458

    """
459
460
461
462
463
    self.__lock.acquire()
    try:
      return len(self.__pending)
    finally:
      self.__lock.release()
464

465
466
467
468
469
470
471
472
  def __do_acquire(self, shared):
    """Actually acquire the lock.

    """
    if shared:
      self.__shr.add(threading.currentThread())
    else:
      self.__exc = threading.currentThread()
473

474
475
  def __can_acquire(self, shared):
    """Determine whether lock can be acquired.
476
477

    """
478
479
480
481
    if shared:
      return self.__exc is None
    else:
      return len(self.__shr) == 0 and self.__exc is None
482

483
484
  def __is_on_top(self, cond):
    """Checks whether the passed condition is on top of the queue.
485

486
    The caller must make sure the queue isn't empty.
487

488
489
    """
    return self.__pending[0] == cond
Guido Trotter's avatar
Guido Trotter committed
490

491
  def __acquire_unlocked(self, shared, timeout):
492
    """Acquire a shared lock.
493

494
495
496
    @param shared: whether to acquire in shared mode; by default an
        exclusive lock will be acquired
    @param timeout: maximum waiting time before giving up
497
498

    """
499
    self.__check_deleted()
500

501
502
503
504
505
506
507
508
    # We cannot acquire the lock if we already have it
    assert not self.__is_owned(), "double acquire() on a non-recursive lock"

    # Check whether someone else holds the lock or there are pending acquires.
    if not self.__pending and self.__can_acquire(shared):
      # Apparently not, can acquire lock directly.
      self.__do_acquire(shared)
      return True
509

510
511
    if shared:
      wait_condition = self.__active_shr_c
512

513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
      # Check if we're not yet in the queue
      if wait_condition not in self.__pending:
        self.__pending.append(wait_condition)
    else:
      wait_condition = self.__condition_class(self.__lock)
      # Always add to queue
      self.__pending.append(wait_condition)

    try:
      # Wait until we become the topmost acquire in the queue or the timeout
      # expires.
      while not (self.__is_on_top(wait_condition) and
                 self.__can_acquire(shared)):
        # Wait for notification
        wait_condition.wait(timeout)
        self.__check_deleted()

        # A lot of code assumes blocking acquires always succeed. Loop
        # internally for that case.
        if timeout is not None:
          break

      if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
        self.__do_acquire(shared)
        return True
538
    finally:
539
540
541
      # Remove condition from queue if there are no more waiters
      if not wait_condition.has_waiting() and not self.__deleted:
        self.__pending.remove(wait_condition)
542

543
    return False
544

545
  def acquire(self, shared=0, timeout=None, test_notify=None):
546
547
    """Acquire a shared lock.

548
    @type shared: int
Iustin Pop's avatar
Iustin Pop committed
549
550
    @param shared: whether to acquire in shared mode; by default an
        exclusive lock will be acquired
551
552
    @type timeout: float
    @param timeout: maximum waiting time before giving up
553
554
    @type test_notify: callable or None
    @param test_notify: Special callback function for unittesting
555
556
557
558

    """
    self.__lock.acquire()
    try:
559
560
561
562
      # We already got the lock, notify now
      if __debug__ and callable(test_notify):
        test_notify()

563
      return self.__acquire_unlocked(shared, timeout)
564
565
566
567
568
569
570
571
572
573
574
575
    finally:
      self.__lock.release()

  def release(self):
    """Release a Shared Lock.

    You must have acquired the lock, either in shared or in exclusive mode,
    before calling this function.

    """
    self.__lock.acquire()
    try:
576
577
578
      assert self.__is_exclusive() or self.__is_sharer(), \
        "Cannot release non-owned lock"

579
580
581
      # Autodetect release type
      if self.__is_exclusive():
        self.__exc = None
582
      else:
583
584
        self.__shr.remove(threading.currentThread())

585
586
587
588
      # Notify topmost condition in queue
      if self.__pending:
        first_condition = self.__pending[0]
        first_condition.notifyAll()
Guido Trotter's avatar
Guido Trotter committed
589

590
591
592
        if first_condition == self.__active_shr_c:
          self.__active_shr_c = self.__inactive_shr_c
          self.__inactive_shr_c = first_condition
593
594
595
596

    finally:
      self.__lock.release()

597
  def delete(self, timeout=None):
598
599
600
601
602
603
    """Delete a Shared Lock.

    This operation will declare the lock for removal. First the lock will be
    acquired in exclusive mode if you don't already own it, then the lock
    will be put in a state where any future and pending acquire() fail.

604
605
    @type timeout: float
    @param timeout: maximum waiting time before giving up
606
607
608
609

    """
    self.__lock.acquire()
    try:
610
611
612
      assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"

      self.__check_deleted()
613

614
615
      # The caller is allowed to hold the lock exclusively already.
      acquired = self.__is_exclusive()
616

617
      if not acquired:
618
619
620
621
        acquired = self.__acquire_unlocked(0, timeout)

        assert self.__is_exclusive() and not self.__is_sharer(), \
          "Lock wasn't acquired in exclusive mode"
622
623
624
625

      if acquired:
        self.__deleted = True
        self.__exc = None
626

627
628
629
        # Notify all acquires. They'll throw an error.
        while self.__pending:
          self.__pending.pop().notifyAll()
630

631
      return acquired
632
633
634
    finally:
      self.__lock.release()

635

636
# Whenever we want to acquire a full LockSet we pass None as the value
Michael Hanselmann's avatar
Michael Hanselmann committed
637
# to acquire.  Hide this behind this nicely named constant.
638
639
640
ALL_SET = None


641
642
643
644
645
646
class _AcquireTimeout(Exception):
  """Internal exception to abort an acquire on a timeout.

  """


647
648
649
650
651
652
653
654
655
656
657
658
659
660
class LockSet:
  """Implements a set of locks.

  This abstraction implements a set of shared locks for the same resource type,
  distinguished by name. The user can lock a subset of the resources and the
  LockSet will take care of acquiring the locks always in the same order, thus
  preventing deadlock.

  All the locks needed in the same set must be acquired together, though.

  """
  def __init__(self, members=None):
    """Constructs a new LockSet.

Iustin Pop's avatar
Iustin Pop committed
661
    @param members: initial members of the set
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687

    """
    # Used internally to guarantee coherency.
    self.__lock = SharedLock()

    # The lockdict indexes the relationship name -> lock
    # The order-of-locking is implied by the alphabetical order of names
    self.__lockdict = {}

    if members is not None:
      for name in members:
        self.__lockdict[name] = SharedLock()

    # The owner dict contains the set of locks each thread owns. For
    # performance each thread can access its own key without a global lock on
    # this structure. It is paramount though that *no* other type of access is
    # done to this structure (eg. no looping over its keys). *_owner helper
    # function are defined to guarantee access is correct, but in general never
    # do anything different than __owners[threading.currentThread()], or there
    # will be trouble.
    self.__owners = {}

  def _is_owned(self):
    """Is the current thread a current level owner?"""
    return threading.currentThread() in self.__owners

Guido Trotter's avatar
Guido Trotter committed
688
  def _add_owned(self, name=None):
689
    """Note the current thread owns the given lock"""
Guido Trotter's avatar
Guido Trotter committed
690
691
692
    if name is None:
      if not self._is_owned():
        self.__owners[threading.currentThread()] = set()
693
    else:
Guido Trotter's avatar
Guido Trotter committed
694
695
696
697
698
699
      if self._is_owned():
        self.__owners[threading.currentThread()].add(name)
      else:
        self.__owners[threading.currentThread()] = set([name])

  def _del_owned(self, name=None):
700
701
    """Note the current thread owns the given lock"""

Guido Trotter's avatar
Guido Trotter committed
702
703
704
705
706
707
    if name is not None:
      self.__owners[threading.currentThread()].remove(name)

    # Only remove the key if we don't hold the set-lock as well
    if (not self.__lock._is_owned() and
        not self.__owners[threading.currentThread()]):
708
709
710
711
712
713
714
715
716
      del self.__owners[threading.currentThread()]

  def _list_owned(self):
    """Get the set of resource names owned by the current thread"""
    if self._is_owned():
      return self.__owners[threading.currentThread()].copy()
    else:
      return set()

717
718
719
720
721
722
  def _release_and_delete_owned(self):
    """Release and delete all resources owned by the current thread"""
    for lname in self._list_owned():
      self.__lockdict[lname].release()
      self._del_owned(name=lname)

723
724
725
726
727
728
729
  def __names(self):
    """Return the current set of names.

    Only call this function while holding __lock and don't iterate on the
    result after releasing the lock.

    """
730
    return self.__lockdict.keys()
731
732
733
734
735

  def _names(self):
    """Return a copy of the current set of elements.

    Used only for debugging purposes.
736

737
    """
738
739
740
741
742
743
    # If we don't already own the set-level lock acquired
    # we'll get it and note we need to release it later.
    release_lock = False
    if not self.__lock._is_owned():
      release_lock = True
      self.__lock.acquire(shared=1)
744
745
746
    try:
      result = self.__names()
    finally:
747
748
      if release_lock:
        self.__lock.release()
749
    return set(result)
750

751
  def acquire(self, names, timeout=None, shared=0, test_notify=None):
752
753
    """Acquire a set of resource locks.

Iustin Pop's avatar
Iustin Pop committed
754
755
756
757
    @param names: the names of the locks which shall be acquired
        (special lock names, or instance/node names)
    @param shared: whether to acquire in shared mode; by default an
        exclusive lock will be acquired
758
    @type timeout: float or None
759
    @param timeout: Maximum time to acquire all locks
760
761
    @type test_notify: callable or None
    @param test_notify: Special callback function for unittesting
762

763
    @return: Set of all locks successfully acquired or None in case of timeout
764

Iustin Pop's avatar
Iustin Pop committed
765
766
767
    @raise errors.LockError: when any lock we try to acquire has
        been deleted before we succeed. In this case none of the
        locks requested will be acquired.
768
769

    """
770
    assert timeout is None or timeout >= 0.0
771
772
773
774

    # Check we don't already own locks at this level
    assert not self._is_owned(), "Cannot acquire locks in the same set twice"

775
776
777
778
779
780
781
782
783
784
785
786
787
    # We need to keep track of how long we spent waiting for a lock. The
    # timeout passed to this function is over all lock acquires.
    remaining_timeout = timeout
    if timeout is None:
      start = None
      calc_remaining_timeout = lambda: None
    else:
      start = time.time()
      calc_remaining_timeout = lambda: (start + timeout) - time.time()

    want_all = names is None

    if want_all:
788
789
790
791
792
793
794
795
796
      # If no names are given acquire the whole set by not letting new names
      # being added before we release, and getting the current list of names.
      # Some of them may then be deleted later, but we'll cope with this.
      #
      # We'd like to acquire this lock in a shared way, as it's nice if
      # everybody else can use the instances at the same time. If are acquiring
      # them exclusively though they won't be able to do this anyway, though,
      # so we'll get the list lock exclusively as well in order to be able to
      # do add() on the set while owning it.
797
      self.__lock.acquire(shared=shared, timeout=remaining_timeout)
Guido Trotter's avatar
Guido Trotter committed
798
799
800
801
802
803
804
805
806
807
      try:
        # note we own the set-lock
        self._add_owned()
        names = self.__names()
      except:
        # We shouldn't have problems adding the lock to the owners list, but
        # if we did we'll try to release this lock and re-raise exception.
        # Of course something is going to be really wrong, after this.
        self.__lock.release()
        raise
808

809
810
811
      # Re-calculate timeout
      remaining_timeout = calc_remaining_timeout()

812
    try:
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
      try:
        # Support passing in a single resource to acquire rather than many
        if isinstance(names, basestring):
          names = [names]
        else:
          names = sorted(names)

        acquire_list = []
        # First we look the locks up on __lockdict. We have no way of being sure
        # they will still be there after, but this makes it a lot faster should
        # just one of them be the already wrong
        for lname in utils.UniqueSequence(names):
          try:
            lock = self.__lockdict[lname] # raises KeyError if lock is not there
            acquire_list.append((lname, lock))
          except KeyError:
            if want_all:
              # We are acquiring all the set, it doesn't matter if this
              # particular element is not there anymore.
              continue
            else:
              raise errors.LockError("Non-existing lock in set (%s)" % lname)

        # This will hold the locknames we effectively acquired.
        acquired = set()

        # Now acquire_list contains a sorted list of resources and locks we
        # want.  In order to get them we loop on this (private) list and
        # acquire() them.  We gave no real guarantee they will still exist till
        # this is done but .acquire() itself is safe and will alert us if the
        # lock gets deleted.
        for (lname, lock) in acquire_list:
          if __debug__ and callable(test_notify):
            test_notify_fn = lambda: test_notify(lname)
847
          else:
848
            test_notify_fn = None
849

850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
          try:
            if timeout is not None and remaining_timeout < 0:
              raise _AcquireTimeout()

            # raises LockError if the lock was deleted
            if not lock.acquire(shared=shared, timeout=remaining_timeout,
                                test_notify=test_notify_fn):
              # Couldn't get lock or timeout occurred
              if timeout is None:
                # This shouldn't happen as SharedLock.acquire(timeout=None) is
                # blocking.
                raise errors.LockError("Failed to get lock %s" % lname)

              raise _AcquireTimeout()

            # Re-calculate timeout
            remaining_timeout = calc_remaining_timeout()

            # now the lock cannot be deleted, we have it!
            self._add_owned(name=lname)
            acquired.add(lname)

          except _AcquireTimeout:
            # Release all acquired locks
            self._release_and_delete_owned()
            raise

          except errors.LockError:
            if want_all:
              # We are acquiring all the set, it doesn't matter if this
              # particular element is not there anymore.
              continue

            self._release_and_delete_owned()

            raise errors.LockError("Non-existing lock in set (%s)" % lname)

          except:
            # We shouldn't have problems adding the lock to the owners list, but
            # if we did we'll try to release this lock and re-raise exception.
            # Of course something is going to be really wrong, after this.
            if lock._is_owned():
              lock.release()
            raise

      except:
        # If something went wrong and we had the set-lock let's release it...
        if want_all:
          self.__lock.release()
        raise

    except _AcquireTimeout:
      if want_all:
        self._del_owned()

      return None
906

907
    return acquired
908
909
910
911
912
913
914

  def release(self, names=None):
    """Release a set of resource locks, at the same level.

    You must have acquired the locks, either in shared or in exclusive mode,
    before releasing them.

Iustin Pop's avatar
Iustin Pop committed
915
916
    @param names: the names of the locks which shall be released
        (defaults to all the locks acquired at that level).
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932

    """
    assert self._is_owned(), "release() on lock set while not owner"

    # Support passing in a single resource to release rather than many
    if isinstance(names, basestring):
      names = [names]

    if names is None:
      names = self._list_owned()
    else:
      names = set(names)
      assert self._list_owned().issuperset(names), (
               "release() on unheld resources %s" %
               names.difference(self._list_owned()))

933
934
935
936
    # First of all let's release the "all elements" lock, if set.
    # After this 'add' can work again
    if self.__lock._is_owned():
      self.__lock.release()
Guido Trotter's avatar
Guido Trotter committed
937
      self._del_owned()
938

939
940
941
942
    for lockname in names:
      # If we are sure the lock doesn't leave __lockdict without being
      # exclusively held we can do this...
      self.__lockdict[lockname].release()
Guido Trotter's avatar
Guido Trotter committed
943
      self._del_owned(name=lockname)
944
945
946
947

  def add(self, names, acquired=0, shared=0):
    """Add a new set of elements to the set

Iustin Pop's avatar
Iustin Pop committed
948
949
950
    @param names: names of the new elements to add
    @param acquired: pre-acquire the new resource?
    @param shared: is the pre-acquisition shared?
951
952

    """
953
954
955
    # Check we don't already own locks at this level
    assert not self._is_owned() or self.__lock._is_owned(shared=0), \
      "Cannot add locks if the set is only partially owned, or shared"
956

957
958
959
960
    # Support passing in a single resource to add rather than many
    if isinstance(names, basestring):
      names = [names]

961
    # If we don't already own the set-level lock acquired in an exclusive way
962
963
964
965
966
967
    # we'll get it and note we need to release it later.
    release_lock = False
    if not self.__lock._is_owned():
      release_lock = True
      self.__lock.acquire()

968
    try:
969
      invalid_names = set(self.__names()).intersection(names)
970
971
972
973
974
975
976
977
978
979
980
981
982
      if invalid_names:
        # This must be an explicit raise, not an assert, because assert is
        # turned off when using optimization, and this can happen because of
        # concurrency even if the user doesn't want it.
        raise errors.LockError("duplicate add() (%s)" % invalid_names)

      for lockname in names:
        lock = SharedLock()

        if acquired:
          lock.acquire(shared=shared)
          # now the lock cannot be deleted, we have it!
          try:
Guido Trotter's avatar
Guido Trotter committed
983
            self._add_owned(name=lockname)
984
985
986
987
988
989
990
991
992
993
994
995
996
          except:
            # We shouldn't have problems adding the lock to the owners list,
            # but if we did we'll try to release this lock and re-raise
            # exception.  Of course something is going to be really wrong,
            # after this.  On the other hand the lock hasn't been added to the
            # __lockdict yet so no other threads should be pending on it. This
            # release is just a safety measure.
            lock.release()
            raise

        self.__lockdict[lockname] = lock

    finally:
997
998
999
      # Only release __lock if we were not holding it previously.
      if release_lock:
        self.__lock.release()
1000
1001
1002

    return True

1003
  def remove(self, names):
1004
1005
1006
1007
1008
    """Remove elements from the lock set.

    You can either not hold anything in the lockset or already hold a superset
    of the elements you want to delete, exclusively.

Iustin Pop's avatar
Iustin Pop committed
1009
    @param names: names of the resource to remove.
1010

1011
    @return: a list of locks which we removed; the list is always
Iustin Pop's avatar
Iustin Pop committed
1012
1013
        equal to the names list if we were holding all the locks
        exclusively
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025

    """
    # Support passing in a single resource to remove rather than many
    if isinstance(names, basestring):
      names = [names]

    # If we own any subset of this lock it must be a superset of what we want
    # to delete. The ownership must also be exclusive, but that will be checked
    # by the lock itself.
    assert not self._is_owned() or self._list_owned().issuperset(names), (
      "remove() on acquired lockset while not owning all elements")

Guido Trotter's avatar
Guido Trotter committed
1026
    removed = []
1027
1028
1029
1030
1031
1032
1033
1034
1035

    for lname in names:
      # Calling delete() acquires the lock exclusively if we don't already own
      # it, and causes all pending and subsequent lock acquires to fail. It's
      # fine to call it out of order because delete() also implies release(),
      # and the assertion above guarantees that if we either already hold
      # everything we want to delete, or we hold none.
      try:
        self.__lockdict[lname].delete()
Guido Trotter's avatar
Guido Trotter committed
1036
        removed.append(lname)
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
      except (KeyError, errors.LockError):
        # This cannot happen if we were already holding it, verify:
        assert not self._is_owned(), "remove failed while holding lockset"
      else:
        # If no LockError was raised we are the ones who deleted the lock.
        # This means we can safely remove it from lockdict, as any further or
        # pending delete() or acquire() will fail (and nobody can have the lock
        # since before our call to delete()).
        #
        # This is done in an else clause because if the exception was thrown
        # it's the job of the one who actually deleted it.
        del self.__lockdict[lname]
        # And let's remove it from our private list if we owned it.
        if self._is_owned():
Guido Trotter's avatar
Guido Trotter committed
1051
          self._del_owned(name=lname)
1052

Guido Trotter's avatar
Guido Trotter committed
1053
    return removed
1054

1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065

# Locking levels, must be acquired in increasing order.
# Current rules are:
#   - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
#   acquired before performing any operation, either in shared or in exclusive
#   mode. acquiring the BGL in exclusive mode is discouraged and should be
#   avoided.
#   - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
#   If you need more than one node, or more than one instance, acquire them at
#   the same time.
LEVEL_CLUSTER = 0
1066
1067
LEVEL_INSTANCE = 1
LEVEL_NODE = 2
1068
1069

LEVELS = [LEVEL_CLUSTER,
1070
1071
          LEVEL_INSTANCE,
          LEVEL_NODE]
1072
1073
1074
1075

# Lock levels which are modifiable
LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE]

1076
1077
1078
1079
1080
1081
LEVEL_NAMES = {
  LEVEL_CLUSTER: "cluster",
  LEVEL_INSTANCE: "instance",
  LEVEL_NODE: "node",
  }

1082
# Constant for the big ganeti lock
1083
1084
1085
1086
1087
1088
BGL = 'BGL'


class GanetiLockManager:
  """The Ganeti Locking Library

Michael Hanselmann's avatar
Michael Hanselmann committed
1089
  The purpose of this small library is to manage locking for ganeti clusters
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
  in a central place, while at the same time doing dynamic checks against
  possible deadlocks. It will also make it easier to transition to a different
  lock type should we migrate away from python threads.

  """
  _instance = None

  def __init__(self, nodes=None, instances=None):
    """Constructs a new GanetiLockManager object.

1100
1101
    There should be only a GanetiLockManager object at any time, so this
    function raises an error if this is not the case.
1102

Iustin Pop's avatar
Iustin Pop committed
1103
1104
    @param nodes: list of node names
    @param instances: list of instance names
1105
1106

    """
Iustin Pop's avatar
Iustin Pop committed
1107
1108
1109
    assert self.__class__._instance is None, \
           "double GanetiLockManager instance"

1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
    self.__class__._instance = self

    # The keyring contains all the locks, at their level and in the correct
    # locking order.
    self.__keyring = {
      LEVEL_CLUSTER: LockSet([BGL]),
      LEVEL_NODE: LockSet(nodes),
      LEVEL_INSTANCE: LockSet(instances),
    }

  def _names(self, level):
    """List the lock names at the given level.

Iustin Pop's avatar
Iustin Pop committed
1123
1124
1125
    This can be used for debugging/testing purposes.

    @param level: the level whose list of locks to get
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136

    """
    assert level in LEVELS, "Invalid locking level %s" % level
    return self.__keyring[level]._names()

  def _is_owned(self, level):
    """Check whether we are owning locks at the given level

    """
    return self.__keyring[level]._is_owned()

1137
1138
  is_owned = _is_owned

1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
  def _list_owned(self, level):
    """Get the set of owned locks at the given level

    """
    return self.__keyring[level]._list_owned()

  def _upper_owned(self, level):
    """Check that we don't own any lock at a level greater than the given one.

    """
    # This way of checking only works if LEVELS[i] = i, which we check for in
    # the test cases.
    return utils.any((self._is_owned(l) for l in LEVELS[level + 1:]))

  def _BGL_owned(self):
    """Check if the current thread owns the BGL.

    Both an exclusive or a shared acquisition work.

    """
    return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned()

  def _contains_BGL(self, level, names):
Iustin Pop's avatar
Iustin Pop committed
1162
1163
1164
1165
    """Check if the level contains the BGL.

    Check if acting on the given level and set of names will change
    the status of the Big Ganeti Lock.
1166
1167
1168
1169

    """
    return level == LEVEL_CLUSTER and (names is None or BGL in names)

1170
  def acquire(self, level, names, timeout=None, shared=0):
1171
1172
    """Acquire a set of resource locks, at the same level.

Iustin Pop's avatar
Iustin Pop committed
1173
    @param level: the level at which the locks shall be acquired;
Michael Hanselmann's avatar
Michael Hanselmann committed
1174
        it must be a member of LEVELS.
Iustin Pop's avatar
Iustin Pop committed
1175
1176
1177
1178
    @param names: the names of the locks which shall be acquired
        (special lock names, or instance/node names)
    @param shared: whether to acquire in shared mode; by default
        an exclusive lock will be acquired
1179
1180
    @type timeout: float
    @param timeout: Maximum time to acquire all locks
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194

    """
    assert level in LEVELS, "Invalid locking level %s" % level

    # Check that we are either acquiring the Big Ganeti Lock or we already own
    # it. Some "legacy" opcodes need to be sure they are run non-concurrently
    # so even if we've migrated we need to at least share the BGL to be
    # compatible with them. Of course if we own the BGL exclusively there's no
    # point in acquiring any other lock, unless perhaps we are half way through
    # the migration of the current opcode.
    assert (self._contains_BGL(level, names) or self._BGL_owned()), (
            "You must own the Big Ganeti Lock before acquiring any other")

    # Check we don't own locks at the same or upper levels.
1195
    assert not self._upper_owned(level), ("Cannot acquire locks at a level"
1196
1197
1198
           " while owning some at a greater one")

    # Acquire the locks in the set.
1199
    return self.__keyring[level].acquire(names, shared=shared, timeout=timeout)
1200
1201
1202
1203

  def release(self, level, names=None):
    """Release a set of resource locks, at the same level.

Iustin Pop's avatar
Iustin Pop committed
1204
1205
    You must have acquired the locks, either in shared or in exclusive
    mode, before releasing them.
1206

Iustin Pop's avatar
Iustin Pop committed
1207
    @param level: the level at which the locks shall be released;
Michael Hanselmann's avatar
Michael Hanselmann committed
1208
        it must be a member of LEVELS
Iustin Pop's avatar
Iustin Pop committed
1209
1210
    @param names: the names of the locks which shall be released
        (defaults to all the locks acquired at that level)
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224

    """
    assert level in LEVELS, "Invalid locking level %s" % level
    assert (not self._contains_BGL(level, names) or
            not self._upper_owned(LEVEL_CLUSTER)), (
            "Cannot release the Big Ganeti Lock while holding something"
            " at upper levels")

    # Release will complain if we don't own the locks already
    return self.__keyring[level].release(names)

  def add(self, level, names, acquired=0, shared=0):
    """Add locks at the specified level.

Iustin Pop's avatar
Iustin Pop committed
1225
    @param level: the level at which the locks shall be added;
Michael Hanselmann's avatar
Michael Hanselmann committed
1226
        it must be a member of LEVELS_MOD.
Iustin Pop's avatar
Iustin Pop committed
1227
1228
1229
1230
    @param names: names of the locks to acquire
    @param acquired: whether to acquire the newly added locks
    @param shared: whether the acquisition will be shared

1231
1232
1233
1234
1235
1236
1237
1238
    """
    assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
    assert self._BGL_owned(), ("You must own the BGL before performing other"
           " operations")
    assert not self._upper_owned(level), ("Cannot add locks at a level"
           " while owning some at a greater one")
    return self.__keyring[level].add(names, acquired=acquired, shared=shared)

1239
  def remove(self, level, names):
1240
1241
    """Remove locks from the specified level.

Iustin Pop's avatar
Iustin Pop committed
1242
1243
    You must either already own the locks you are trying to remove
    exclusively or not own any lock at an upper level.
1244

Iustin Pop's avatar
Iustin Pop committed
1245
1246
1247
1248
    @param level: the level at which the locks shall be removed;
        it must be a member of LEVELS_MOD
    @param names: the names of the locks which shall be removed
        (special lock names, or instance/node names)
1249
1250
1251
1252
1253

    """
    assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
    assert self._BGL_owned(), ("You must own the BGL before performing other"
           " operations")
1254
1255
1256
    # Check we either own the level or don't own anything from here
    # up. LockSet.remove() will check the case in which we don't own
    # all the needed resources, or we have a shared ownership.
1257
1258
1259
    assert self._is_owned(level) or not self._upper_owned(level), (
           "Cannot remove locks at a level while not owning it or"
           " owning some at a greater one")
1260
    return self.__keyring[level].remove(names)