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#
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#
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# Copyright (C) 2006, 2007 Google Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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# General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301, USA.
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"""Module implementing the Ganeti locking code."""
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# pylint: disable-msg=W0613,W0201
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import threading
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# Wouldn't it be better to define LockingError in the locking module?
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# Well, for now that's how the rest of the code does it...
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from ganeti import errors
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from ganeti import utils
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31

    
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class SharedLock:
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  """Implements a shared lock.
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  Multiple threads can acquire the lock in a shared way, calling
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  acquire_shared().  In order to acquire the lock in an exclusive way threads
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  can call acquire_exclusive().
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  The lock prevents starvation but does not guarantee that threads will acquire
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  the shared lock in the order they queued for it, just that they will
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  eventually do so.
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  """
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  def __init__(self):
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    """Construct a new SharedLock"""
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    # we have two conditions, c_shr and c_exc, sharing the same lock.
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    self.__lock = threading.Lock()
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    self.__turn_shr = threading.Condition(self.__lock)
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    self.__turn_exc = threading.Condition(self.__lock)
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    # current lock holders
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    self.__shr = set()
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    self.__exc = None
54

    
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    # lock waiters
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    self.__nwait_exc = 0
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    self.__nwait_shr = 0
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    self.__npass_shr = 0
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    # is this lock in the deleted state?
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    self.__deleted = False
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  def __is_sharer(self):
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    """Is the current thread sharing the lock at this time?"""
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    return threading.currentThread() in self.__shr
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  def __is_exclusive(self):
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    """Is the current thread holding the lock exclusively at this time?"""
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    return threading.currentThread() == self.__exc
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  def __is_owned(self, shared=-1):
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    """Is the current thread somehow owning the lock at this time?
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74
    This is a private version of the function, which presumes you're holding
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    the internal lock.
76

77
    """
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    if shared < 0:
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      return self.__is_sharer() or self.__is_exclusive()
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    elif shared:
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      return self.__is_sharer()
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    else:
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      return self.__is_exclusive()
84

    
85
  def _is_owned(self, shared=-1):
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    """Is the current thread somehow owning the lock at this time?
87

88
    Args:
89
      shared:
90
        < 0: check for any type of ownership (default)
91
        0: check for exclusive ownership
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        > 0: check for shared ownership
93

94
    """
95
    self.__lock.acquire()
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    try:
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      result = self.__is_owned(shared=shared)
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    finally:
99
      self.__lock.release()
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101
    return result
102

    
103
  def __wait(self, c):
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    """Wait on the given condition, and raise an exception if the current lock
105
    is declared deleted in the meantime.
106

107
    Args:
108
      c: condition to wait on
109

110
    """
111
    c.wait()
112
    if self.__deleted:
113
      raise errors.LockError('deleted lock')
114

    
115
  def __exclusive_acquire(self):
116
    """Acquire the lock exclusively.
117

118
    This is a private function that presumes you are already holding the
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    internal lock. It's defined separately to avoid code duplication between
120
    acquire() and delete()
121

122
    """
123
    self.__nwait_exc += 1
124
    try:
125
      # This is to save ourselves from a nasty race condition that could
126
      # theoretically make the sharers starve.
127
      if self.__nwait_shr > 0 or self.__nwait_exc > 1:
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        self.__wait(self.__turn_exc)
129

    
130
      while len(self.__shr) > 0 or self.__exc is not None:
131
        self.__wait(self.__turn_exc)
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133
      self.__exc = threading.currentThread()
134
    finally:
135
      self.__nwait_exc -= 1
136

    
137
    assert self.__npass_shr == 0, "SharedLock: internal fairness violation"
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139
  def acquire(self, blocking=1, shared=0):
140
    """Acquire a shared lock.
141

142
    Args:
143
      shared: whether to acquire in shared mode. By default an exclusive lock
144
              will be acquired.
145
      blocking: whether to block while trying to acquire or to operate in try-lock mode.
146
                this locking mode is not supported yet.
147

148
    """
149
    if not blocking:
150
      # We don't have non-blocking mode for now
151
      raise NotImplementedError
152

    
153
    self.__lock.acquire()
154
    try:
155
      if self.__deleted:
156
        raise errors.LockError('deleted lock')
157

    
158
      # We cannot acquire the lock if we already have it
159
      assert not self.__is_owned(), "double acquire() on a non-recursive lock"
160
      assert self.__npass_shr >= 0, "Internal fairness condition weirdness"
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162
      if shared:
163
        self.__nwait_shr += 1
164
        try:
165
          wait = False
166
          # If there is an exclusive holder waiting we have to wait.  We'll
167
          # only do this once, though, when we start waiting for the lock. Then
168
          # we'll just wait while there are no exclusive holders.
169
          if self.__nwait_exc > 0:
170
            # TODO: if !blocking...
171
            wait = True
172
            self.__wait(self.__turn_shr)
173

    
174
          while self.__exc is not None:
175
            wait = True
176
            # TODO: if !blocking...
177
            self.__wait(self.__turn_shr)
178

    
179
          self.__shr.add(threading.currentThread())
180

    
181
          # If we were waiting note that we passed
182
          if wait:
183
            self.__npass_shr -= 1
184

    
185
        finally:
186
          self.__nwait_shr -= 1
187

    
188
        assert self.__npass_shr >= 0, "Internal fairness condition weirdness"
189
      else:
190
        # TODO: if !blocking...
191
        # (or modify __exclusive_acquire for non-blocking mode)
192
        self.__exclusive_acquire()
193

    
194
    finally:
195
      self.__lock.release()
196

    
197
    return True
198

    
199
  def release(self):
200
    """Release a Shared Lock.
201

202
    You must have acquired the lock, either in shared or in exclusive mode,
203
    before calling this function.
204

205
    """
206
    self.__lock.acquire()
207
    try:
208
      assert self.__npass_shr >= 0, "Internal fairness condition weirdness"
209
      # Autodetect release type
210
      if self.__is_exclusive():
211
        self.__exc = None
212

    
213
        # An exclusive holder has just had the lock, time to put it in shared
214
        # mode if there are shared holders waiting. Otherwise wake up the next
215
        # exclusive holder.
216
        if self.__nwait_shr > 0:
217
          # Make sure at least the ones which were blocked pass.
218
          self.__npass_shr = self.__nwait_shr
219
          self.__turn_shr.notifyAll()
220
        elif self.__nwait_exc > 0:
221
         self.__turn_exc.notify()
222

    
223
      elif self.__is_sharer():
224
        self.__shr.remove(threading.currentThread())
225

    
226
        # If there are shared holders waiting (and not just scheduled to pass)
227
        # there *must* be an exclusive holder waiting as well; otherwise what
228
        # were they waiting for?
229
        assert (self.__nwait_exc > 0 or self.__npass_shr > 0 or
230
                self.__nwait_shr == 0), \
231
               "Lock sharers waiting while no exclusive is queueing"
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233
        # If there are no more shared holders either in or scheduled to pass,
234
        # and some exclusive holders are waiting let's wake one up.
235
        if (len(self.__shr) == 0 and
236
            self.__nwait_exc > 0 and
237
            not self.__npass_shr > 0):
238
          self.__turn_exc.notify()
239

    
240
      else:
241
        assert False, "Cannot release non-owned lock"
242

    
243
    finally:
244
      self.__lock.release()
245

    
246
  def delete(self, blocking=1):
247
    """Delete a Shared Lock.
248

249
    This operation will declare the lock for removal. First the lock will be
250
    acquired in exclusive mode if you don't already own it, then the lock
251
    will be put in a state where any future and pending acquire() fail.
252

253
    Args:
254
      blocking: whether to block while trying to acquire or to operate in
255
                try-lock mode.  this locking mode is not supported yet unless
256
                you are already holding exclusively the lock.
257

258
    """
259
    self.__lock.acquire()
260
    try:
261
      assert not self.__is_sharer(), "cannot delete() a lock while sharing it"
262

    
263
      if self.__deleted:
264
        raise errors.LockError('deleted lock')
265

    
266
      if not self.__is_exclusive():
267
        if not blocking:
268
          # We don't have non-blocking mode for now
269
          raise NotImplementedError
270
        self.__exclusive_acquire()
271

    
272
      self.__deleted = True
273
      self.__exc = None
274
      # Wake up everybody, they will fail acquiring the lock and
275
      # raise an exception instead.
276
      self.__turn_exc.notifyAll()
277
      self.__turn_shr.notifyAll()
278

    
279
    finally:
280
      self.__lock.release()
281

    
282

    
283
class LockSet:
284
  """Implements a set of locks.
285

286
  This abstraction implements a set of shared locks for the same resource type,
287
  distinguished by name. The user can lock a subset of the resources and the
288
  LockSet will take care of acquiring the locks always in the same order, thus
289
  preventing deadlock.
290

291
  All the locks needed in the same set must be acquired together, though.
292

293
  """
294
  def __init__(self, members=None):
295
    """Constructs a new LockSet.
296

297
    Args:
298
      members: initial members of the set
299

300
    """
301
    # Used internally to guarantee coherency.
302
    self.__lock = SharedLock()
303

    
304
    # The lockdict indexes the relationship name -> lock
305
    # The order-of-locking is implied by the alphabetical order of names
306
    self.__lockdict = {}
307

    
308
    if members is not None:
309
      for name in members:
310
        self.__lockdict[name] = SharedLock()
311

    
312
    # The owner dict contains the set of locks each thread owns. For
313
    # performance each thread can access its own key without a global lock on
314
    # this structure. It is paramount though that *no* other type of access is
315
    # done to this structure (eg. no looping over its keys). *_owner helper
316
    # function are defined to guarantee access is correct, but in general never
317
    # do anything different than __owners[threading.currentThread()], or there
318
    # will be trouble.
319
    self.__owners = {}
320

    
321
  def _is_owned(self):
322
    """Is the current thread a current level owner?"""
323
    return threading.currentThread() in self.__owners
324

    
325
  def _add_owned(self, name=None):
326
    """Note the current thread owns the given lock"""
327
    if name is None:
328
      if not self._is_owned():
329
        self.__owners[threading.currentThread()] = set()
330
    else:
331
      if self._is_owned():
332
        self.__owners[threading.currentThread()].add(name)
333
      else:
334
        self.__owners[threading.currentThread()] = set([name])
335

    
336

    
337
  def _del_owned(self, name=None):
338
    """Note the current thread owns the given lock"""
339

    
340
    if name is not None:
341
      self.__owners[threading.currentThread()].remove(name)
342

    
343
    # Only remove the key if we don't hold the set-lock as well
344
    if (not self.__lock._is_owned() and
345
        not self.__owners[threading.currentThread()]):
346
      del self.__owners[threading.currentThread()]
347

    
348
  def _list_owned(self):
349
    """Get the set of resource names owned by the current thread"""
350
    if self._is_owned():
351
      return self.__owners[threading.currentThread()].copy()
352
    else:
353
      return set()
354

    
355
  def __names(self):
356
    """Return the current set of names.
357

358
    Only call this function while holding __lock and don't iterate on the
359
    result after releasing the lock.
360

361
    """
362
    return self.__lockdict.keys()
363

    
364
  def _names(self):
365
    """Return a copy of the current set of elements.
366

367
    Used only for debugging purposes.
368

369
    """
370
    self.__lock.acquire(shared=1)
371
    try:
372
      result = self.__names()
373
    finally:
374
      self.__lock.release()
375
    return set(result)
376

    
377
  def acquire(self, names, blocking=1, shared=0):
378
    """Acquire a set of resource locks.
379

380
    Args:
381
      names: the names of the locks which shall be acquired.
382
             (special lock names, or instance/node names)
383
      shared: whether to acquire in shared mode. By default an exclusive lock
384
              will be acquired.
385
      blocking: whether to block while trying to acquire or to operate in try-lock mode.
386
                this locking mode is not supported yet.
387

388
    Returns:
389
      True: when all the locks are successfully acquired
390

391
    Raises:
392
      errors.LockError: when any lock we try to acquire has been deleted
393
      before we succeed. In this case none of the locks requested will be
394
      acquired.
395

396
    """
397
    if not blocking:
398
      # We don't have non-blocking mode for now
399
      raise NotImplementedError
400

    
401
    # Check we don't already own locks at this level
402
    assert not self._is_owned(), "Cannot acquire locks in the same set twice"
403

    
404
    if names is None:
405
      # If no names are given acquire the whole set by not letting new names
406
      # being added before we release, and getting the current list of names.
407
      # Some of them may then be deleted later, but we'll cope with this.
408
      #
409
      # We'd like to acquire this lock in a shared way, as it's nice if
410
      # everybody else can use the instances at the same time. If are acquiring
411
      # them exclusively though they won't be able to do this anyway, though,
412
      # so we'll get the list lock exclusively as well in order to be able to
413
      # do add() on the set while owning it.
414
      self.__lock.acquire(shared=shared)
415
      try:
416
        # note we own the set-lock
417
        self._add_owned()
418
        names = self.__names()
419
      except:
420
        # We shouldn't have problems adding the lock to the owners list, but
421
        # if we did we'll try to release this lock and re-raise exception.
422
        # Of course something is going to be really wrong, after this.
423
        self.__lock.release()
424
        raise
425

    
426
    try:
427
      # Support passing in a single resource to acquire rather than many
428
      if isinstance(names, basestring):
429
        names = [names]
430
      else:
431
        names.sort()
432

    
433
      acquire_list = []
434
      # First we look the locks up on __lockdict. We have no way of being sure
435
      # they will still be there after, but this makes it a lot faster should
436
      # just one of them be the already wrong
437
      for lname in names:
438
        try:
439
          lock = self.__lockdict[lname] # raises KeyError if the lock is not there
440
          acquire_list.append((lname, lock))
441
        except (KeyError):
442
          if self.__lock._is_owned():
443
            # We are acquiring all the set, it doesn't matter if this particular
444
            # element is not there anymore.
445
            continue
446
          else:
447
            raise errors.LockError('non-existing lock in set (%s)' % lname)
448

    
449
      # This will hold the locknames we effectively acquired.
450
      acquired = set()
451
      # Now acquire_list contains a sorted list of resources and locks we want.
452
      # In order to get them we loop on this (private) list and acquire() them.
453
      # We gave no real guarantee they will still exist till this is done but
454
      # .acquire() itself is safe and will alert us if the lock gets deleted.
455
      for (lname, lock) in acquire_list:
456
        try:
457
          lock.acquire(shared=shared) # raises LockError if the lock is deleted
458
          # now the lock cannot be deleted, we have it!
459
          self._add_owned(name=lname)
460
          acquired.add(lname)
461
        except (errors.LockError):
462
          if self.__lock._is_owned():
463
            # We are acquiring all the set, it doesn't matter if this particular
464
            # element is not there anymore.
465
            continue
466
          else:
467
            name_fail = lname
468
            for lname in self._list_owned():
469
              self.__lockdict[lname].release()
470
              self._del_owned(name=lname)
471
            raise errors.LockError('non-existing lock in set (%s)' % name_fail)
472
        except:
473
          # We shouldn't have problems adding the lock to the owners list, but
474
          # if we did we'll try to release this lock and re-raise exception.
475
          # Of course something is going to be really wrong, after this.
476
          if lock._is_owned():
477
            lock.release()
478
            raise
479

    
480
    except:
481
      # If something went wrong and we had the set-lock let's release it...
482
      if self.__lock._is_owned():
483
        self.__lock.release()
484
      raise
485

    
486
    return acquired
487

    
488
  def release(self, names=None):
489
    """Release a set of resource locks, at the same level.
490

491
    You must have acquired the locks, either in shared or in exclusive mode,
492
    before releasing them.
493

494
    Args:
495
      names: the names of the locks which shall be released.
496
             (defaults to all the locks acquired at that level).
497

498
    """
499
    assert self._is_owned(), "release() on lock set while not owner"
500

    
501
    # Support passing in a single resource to release rather than many
502
    if isinstance(names, basestring):
503
      names = [names]
504

    
505
    if names is None:
506
      names = self._list_owned()
507
    else:
508
      names = set(names)
509
      assert self._list_owned().issuperset(names), (
510
               "release() on unheld resources %s" %
511
               names.difference(self._list_owned()))
512

    
513
    # First of all let's release the "all elements" lock, if set.
514
    # After this 'add' can work again
515
    if self.__lock._is_owned():
516
      self.__lock.release()
517
      self._del_owned()
518

    
519
    for lockname in names:
520
      # If we are sure the lock doesn't leave __lockdict without being
521
      # exclusively held we can do this...
522
      self.__lockdict[lockname].release()
523
      self._del_owned(name=lockname)
524

    
525
  def add(self, names, acquired=0, shared=0):
526
    """Add a new set of elements to the set
527

528
    Args:
529
      names: names of the new elements to add
530
      acquired: pre-acquire the new resource?
531
      shared: is the pre-acquisition shared?
532

533
    """
534

    
535
    assert not self.__lock._is_owned(shared=1), (
536
           "Cannot add new elements while sharing the set-lock")
537

    
538
    # Support passing in a single resource to add rather than many
539
    if isinstance(names, basestring):
540
      names = [names]
541

    
542
    # If we don't already own the set-level lock acquire it in an exclusive way
543
    # we'll get it and note we need to release it later.
544
    release_lock = False
545
    if not self.__lock._is_owned():
546
      release_lock = True
547
      self.__lock.acquire()
548

    
549
    try:
550
      invalid_names = set(self.__names()).intersection(names)
551
      if invalid_names:
552
        # This must be an explicit raise, not an assert, because assert is
553
        # turned off when using optimization, and this can happen because of
554
        # concurrency even if the user doesn't want it.
555
        raise errors.LockError("duplicate add() (%s)" % invalid_names)
556

    
557
      for lockname in names:
558
        lock = SharedLock()
559

    
560
        if acquired:
561
          lock.acquire(shared=shared)
562
          # now the lock cannot be deleted, we have it!
563
          try:
564
            self._add_owned(name=lockname)
565
          except:
566
            # We shouldn't have problems adding the lock to the owners list,
567
            # but if we did we'll try to release this lock and re-raise
568
            # exception.  Of course something is going to be really wrong,
569
            # after this.  On the other hand the lock hasn't been added to the
570
            # __lockdict yet so no other threads should be pending on it. This
571
            # release is just a safety measure.
572
            lock.release()
573
            raise
574

    
575
        self.__lockdict[lockname] = lock
576

    
577
    finally:
578
      # Only release __lock if we were not holding it previously.
579
      if release_lock:
580
        self.__lock.release()
581

    
582
    return True
583

    
584
  def remove(self, names, blocking=1):
585
    """Remove elements from the lock set.
586

587
    You can either not hold anything in the lockset or already hold a superset
588
    of the elements you want to delete, exclusively.
589

590
    Args:
591
      names: names of the resource to remove.
592
      blocking: whether to block while trying to acquire or to operate in
593
                try-lock mode.  this locking mode is not supported yet unless
594
                you are already holding exclusively the locks.
595

596
    Returns:
597
      A list of lock which we removed. The list is always equal to the names
598
      list if we were holding all the locks exclusively.
599

600
    """
601
    if not blocking and not self._is_owned():
602
      # We don't have non-blocking mode for now
603
      raise NotImplementedError
604

    
605
    # Support passing in a single resource to remove rather than many
606
    if isinstance(names, basestring):
607
      names = [names]
608

    
609
    # If we own any subset of this lock it must be a superset of what we want
610
    # to delete. The ownership must also be exclusive, but that will be checked
611
    # by the lock itself.
612
    assert not self._is_owned() or self._list_owned().issuperset(names), (
613
      "remove() on acquired lockset while not owning all elements")
614

    
615
    removed = []
616

    
617
    for lname in names:
618
      # Calling delete() acquires the lock exclusively if we don't already own
619
      # it, and causes all pending and subsequent lock acquires to fail. It's
620
      # fine to call it out of order because delete() also implies release(),
621
      # and the assertion above guarantees that if we either already hold
622
      # everything we want to delete, or we hold none.
623
      try:
624
        self.__lockdict[lname].delete()
625
        removed.append(lname)
626
      except (KeyError, errors.LockError):
627
        # This cannot happen if we were already holding it, verify:
628
        assert not self._is_owned(), "remove failed while holding lockset"
629
      else:
630
        # If no LockError was raised we are the ones who deleted the lock.
631
        # This means we can safely remove it from lockdict, as any further or
632
        # pending delete() or acquire() will fail (and nobody can have the lock
633
        # since before our call to delete()).
634
        #
635
        # This is done in an else clause because if the exception was thrown
636
        # it's the job of the one who actually deleted it.
637
        del self.__lockdict[lname]
638
        # And let's remove it from our private list if we owned it.
639
        if self._is_owned():
640
          self._del_owned(name=lname)
641

    
642
    return removed
643

    
644

    
645
# Locking levels, must be acquired in increasing order.
646
# Current rules are:
647
#   - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
648
#   acquired before performing any operation, either in shared or in exclusive
649
#   mode. acquiring the BGL in exclusive mode is discouraged and should be
650
#   avoided.
651
#   - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
652
#   If you need more than one node, or more than one instance, acquire them at
653
#   the same time.
654
#  - level LEVEL_CONFIG contains the configuration lock, which you must acquire
655
#  before reading or changing the config file.
656
LEVEL_CLUSTER = 0
657
LEVEL_NODE = 1
658
LEVEL_INSTANCE = 2
659
LEVEL_CONFIG = 3
660

    
661
LEVELS = [LEVEL_CLUSTER,
662
          LEVEL_NODE,
663
          LEVEL_INSTANCE,
664
          LEVEL_CONFIG]
665

    
666
# Lock levels which are modifiable
667
LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE]
668

    
669
# Constant for the big ganeti lock and config lock
670
BGL = 'BGL'
671
CONFIG = 'config'
672

    
673

    
674
class GanetiLockManager:
675
  """The Ganeti Locking Library
676

677
  The purpouse of this small library is to manage locking for ganeti clusters
678
  in a central place, while at the same time doing dynamic checks against
679
  possible deadlocks. It will also make it easier to transition to a different
680
  lock type should we migrate away from python threads.
681

682
  """
683
  _instance = None
684

    
685
  def __init__(self, nodes=None, instances=None):
686
    """Constructs a new GanetiLockManager object.
687

688
    There should be only a
689
    GanetiLockManager object at any time, so this function raises an error if this
690
    is not the case.
691

692
    Args:
693
      nodes: list of node names
694
      instances: list of instance names
695

696
    """
697
    assert self.__class__._instance is None, "double GanetiLockManager instance"
698
    self.__class__._instance = self
699

    
700
    # The keyring contains all the locks, at their level and in the correct
701
    # locking order.
702
    self.__keyring = {
703
      LEVEL_CLUSTER: LockSet([BGL]),
704
      LEVEL_NODE: LockSet(nodes),
705
      LEVEL_INSTANCE: LockSet(instances),
706
      LEVEL_CONFIG: LockSet([CONFIG]),
707
    }
708

    
709
  def _names(self, level):
710
    """List the lock names at the given level.
711
    Used for debugging/testing purposes.
712

713
    Args:
714
      level: the level whose list of locks to get
715

716
    """
717
    assert level in LEVELS, "Invalid locking level %s" % level
718
    return self.__keyring[level]._names()
719

    
720
  def _is_owned(self, level):
721
    """Check whether we are owning locks at the given level
722

723
    """
724
    return self.__keyring[level]._is_owned()
725

    
726
  def _list_owned(self, level):
727
    """Get the set of owned locks at the given level
728

729
    """
730
    return self.__keyring[level]._list_owned()
731

    
732
  def _upper_owned(self, level):
733
    """Check that we don't own any lock at a level greater than the given one.
734

735
    """
736
    # This way of checking only works if LEVELS[i] = i, which we check for in
737
    # the test cases.
738
    return utils.any((self._is_owned(l) for l in LEVELS[level + 1:]))
739

    
740
  def _BGL_owned(self):
741
    """Check if the current thread owns the BGL.
742

743
    Both an exclusive or a shared acquisition work.
744

745
    """
746
    return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned()
747

    
748
  def _contains_BGL(self, level, names):
749
    """Check if acting on the given level and set of names will change the
750
    status of the Big Ganeti Lock.
751

752
    """
753
    return level == LEVEL_CLUSTER and (names is None or BGL in names)
754

    
755
  def acquire(self, level, names, blocking=1, shared=0):
756
    """Acquire a set of resource locks, at the same level.
757

758
    Args:
759
      level: the level at which the locks shall be acquired.
760
             It must be a memmber of LEVELS.
761
      names: the names of the locks which shall be acquired.
762
             (special lock names, or instance/node names)
763
      shared: whether to acquire in shared mode. By default an exclusive lock
764
              will be acquired.
765
      blocking: whether to block while trying to acquire or to operate in try-lock mode.
766
                this locking mode is not supported yet.
767

768
    """
769
    assert level in LEVELS, "Invalid locking level %s" % level
770

    
771
    # Check that we are either acquiring the Big Ganeti Lock or we already own
772
    # it. Some "legacy" opcodes need to be sure they are run non-concurrently
773
    # so even if we've migrated we need to at least share the BGL to be
774
    # compatible with them. Of course if we own the BGL exclusively there's no
775
    # point in acquiring any other lock, unless perhaps we are half way through
776
    # the migration of the current opcode.
777
    assert (self._contains_BGL(level, names) or self._BGL_owned()), (
778
            "You must own the Big Ganeti Lock before acquiring any other")
779

    
780
    # Check we don't own locks at the same or upper levels.
781
    assert not self._upper_owned(level), ("Cannot acquire locks at a level"
782
           " while owning some at a greater one")
783

    
784
    # Acquire the locks in the set.
785
    return self.__keyring[level].acquire(names, shared=shared,
786
                                         blocking=blocking)
787

    
788
  def release(self, level, names=None):
789
    """Release a set of resource locks, at the same level.
790

791
    You must have acquired the locks, either in shared or in exclusive mode,
792
    before releasing them.
793

794
    Args:
795
      level: the level at which the locks shall be released.
796
             It must be a memmber of LEVELS.
797
      names: the names of the locks which shall be released.
798
             (defaults to all the locks acquired at that level).
799

800
    """
801
    assert level in LEVELS, "Invalid locking level %s" % level
802
    assert (not self._contains_BGL(level, names) or
803
            not self._upper_owned(LEVEL_CLUSTER)), (
804
            "Cannot release the Big Ganeti Lock while holding something"
805
            " at upper levels")
806

    
807
    # Release will complain if we don't own the locks already
808
    return self.__keyring[level].release(names)
809

    
810
  def add(self, level, names, acquired=0, shared=0):
811
    """Add locks at the specified level.
812

813
    Args:
814
      level: the level at which the locks shall be added.
815
             It must be a memmber of LEVELS_MOD.
816
      names: names of the locks to acquire
817
      acquired: whether to acquire the newly added locks
818
      shared: whether the acquisition will be shared
819
    """
820
    assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
821
    assert self._BGL_owned(), ("You must own the BGL before performing other"
822
           " operations")
823
    assert not self._upper_owned(level), ("Cannot add locks at a level"
824
           " while owning some at a greater one")
825
    return self.__keyring[level].add(names, acquired=acquired, shared=shared)
826

    
827
  def remove(self, level, names, blocking=1):
828
    """Remove locks from the specified level.
829

830
    You must either already own the locks you are trying to remove exclusively
831
    or not own any lock at an upper level.
832

833
    Args:
834
      level: the level at which the locks shall be removed.
835
             It must be a memmber of LEVELS_MOD.
836
      names: the names of the locks which shall be removed.
837
             (special lock names, or instance/node names)
838
      blocking: whether to block while trying to operate in try-lock mode.
839
                this locking mode is not supported yet.
840

841
    """
842
    assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
843
    assert self._BGL_owned(), ("You must own the BGL before performing other"
844
           " operations")
845
    # Check we either own the level or don't own anything from here up.
846
    # LockSet.remove() will check the case in which we don't own all the needed
847
    # resources, or we have a shared ownership.
848
    assert self._is_owned(level) or not self._upper_owned(level), (
849
           "Cannot remove locks at a level while not owning it or"
850
           " owning some at a greater one")
851
    return self.__keyring[level].remove(names, blocking=blocking)