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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=W0212
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# W0212 since e.g. LockSet methods use (a lot) the internals of
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# SharedLock
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import os
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import select
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import threading
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import time
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import errno
33

    
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from ganeti import errors
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from ganeti import utils
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def ssynchronized(lock, shared=0):
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  """Shared Synchronization decorator.
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  Calls the function holding the given lock, either in exclusive or shared
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  mode. It requires the passed lock to be a SharedLock (or support its
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  semantics).
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  """
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  def wrap(fn):
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    def sync_function(*args, **kwargs):
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      lock.acquire(shared=shared)
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      try:
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        return fn(*args, **kwargs)
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      finally:
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        lock.release()
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    return sync_function
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  return wrap
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class RunningTimeout(object):
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  """Class to calculate remaining timeout when doing several operations.
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  """
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  __slots__ = [
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    "_allow_negative",
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    "_start_time",
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    "_time_fn",
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    "_timeout",
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    ]
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  def __init__(self, timeout, allow_negative, _time_fn=time.time):
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    """Initializes this class.
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    @type timeout: float
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    @param timeout: Timeout duration
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    @type allow_negative: bool
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    @param allow_negative: Whether to return values below zero
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    @param _time_fn: Time function for unittests
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77
    """
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    object.__init__(self)
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    if timeout is not None and timeout < 0.0:
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      raise ValueError("Timeout must not be negative")
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    self._timeout = timeout
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    self._allow_negative = allow_negative
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    self._time_fn = _time_fn
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    self._start_time = None
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  def Remaining(self):
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    """Returns the remaining timeout.
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    """
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    if self._timeout is None:
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      return None
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    # Get start time on first calculation
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    if self._start_time is None:
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      self._start_time = self._time_fn()
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    # Calculate remaining time
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    remaining_timeout = self._start_time + self._timeout - self._time_fn()
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103
    if not self._allow_negative:
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      # Ensure timeout is always >= 0
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      return max(0.0, remaining_timeout)
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    return remaining_timeout
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class _SingleNotifyPipeConditionWaiter(object):
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  """Helper class for SingleNotifyPipeCondition
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113
  """
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  __slots__ = [
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    "_fd",
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    "_poller",
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    ]
118

    
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  def __init__(self, poller, fd):
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    """Constructor for _SingleNotifyPipeConditionWaiter
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122
    @type poller: select.poll
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    @param poller: Poller object
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    @type fd: int
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    @param fd: File descriptor to wait for
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127
    """
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    object.__init__(self)
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    self._poller = poller
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    self._fd = fd
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  def __call__(self, timeout):
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    """Wait for something to happen on the pipe.
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    @type timeout: float or None
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    @param timeout: Timeout for waiting (can be None)
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138
    """
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    running_timeout = RunningTimeout(timeout, True)
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    while True:
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      remaining_time = running_timeout.Remaining()
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144
      if remaining_time is not None and remaining_time < 0.0:
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        break
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147
      try:
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        result = self._poller.poll(remaining_time)
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      except EnvironmentError, err:
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        if err.errno != errno.EINTR:
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          raise
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        result = None
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      # Check whether we were notified
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      if result and result[0][0] == self._fd:
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        break
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class _BaseCondition(object):
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  """Base class containing common code for conditions.
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  Some of this code is taken from python's threading module.
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  """
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  __slots__ = [
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    "_lock",
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    "acquire",
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    "release",
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    ]
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171
  def __init__(self, lock):
172
    """Constructor for _BaseCondition.
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174
    @type lock: threading.Lock
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    @param lock: condition base lock
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177
    """
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    object.__init__(self)
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    # Recursive locks are not supported
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    assert not hasattr(lock, "_acquire_restore")
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    assert not hasattr(lock, "_release_save")
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    self._lock = lock
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    # Export the lock's acquire() and release() methods
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    self.acquire = lock.acquire
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    self.release = lock.release
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190
  def _is_owned(self):
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    """Check whether lock is owned by current thread.
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193
    """
194
    if self._lock.acquire(0):
195
      self._lock.release()
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      return False
197

    
198
    return True
199

    
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  def _check_owned(self):
201
    """Raise an exception if the current thread doesn't own the lock.
202

203
    """
204
    if not self._is_owned():
205
      raise RuntimeError("cannot work with un-aquired lock")
206

    
207

    
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class SingleNotifyPipeCondition(_BaseCondition):
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  """Condition which can only be notified once.
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211
  This condition class uses pipes and poll, internally, to be able to wait for
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  notification with a timeout, without resorting to polling. It is almost
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  compatible with Python's threading.Condition, with the following differences:
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    - notifyAll can only be called once, and no wait can happen after that
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    - notify is not supported, only notifyAll
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  """
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219
  __slots__ = _BaseCondition.__slots__ + [
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    "_poller",
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    "_read_fd",
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    "_write_fd",
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    "_nwaiters",
224
    "_notified",
225
    ]
226

    
227
  _waiter_class = _SingleNotifyPipeConditionWaiter
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229
  def __init__(self, lock):
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    """Constructor for SingleNotifyPipeCondition
231

232
    """
233
    _BaseCondition.__init__(self, lock)
234
    self._nwaiters = 0
235
    self._notified = False
236
    self._read_fd = None
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    self._write_fd = None
238
    self._poller = None
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240
  def _check_unnotified(self):
241
    """Throws an exception if already notified.
242

243
    """
244
    if self._notified:
245
      raise RuntimeError("cannot use already notified condition")
246

    
247
  def _Cleanup(self):
248
    """Cleanup open file descriptors, if any.
249

250
    """
251
    if self._read_fd is not None:
252
      os.close(self._read_fd)
253
      self._read_fd = None
254

    
255
    if self._write_fd is not None:
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      os.close(self._write_fd)
257
      self._write_fd = None
258
    self._poller = None
259

    
260
  def wait(self, timeout=None):
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    """Wait for a notification.
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263
    @type timeout: float or None
264
    @param timeout: Waiting timeout (can be None)
265

266
    """
267
    self._check_owned()
268
    self._check_unnotified()
269

    
270
    self._nwaiters += 1
271
    try:
272
      if self._poller is None:
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        (self._read_fd, self._write_fd) = os.pipe()
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        self._poller = select.poll()
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        self._poller.register(self._read_fd, select.POLLHUP)
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      wait_fn = self._waiter_class(self._poller, self._read_fd)
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      self.release()
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      try:
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        # Wait for notification
281
        wait_fn(timeout)
282
      finally:
283
        # Re-acquire lock
284
        self.acquire()
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    finally:
286
      self._nwaiters -= 1
287
      if self._nwaiters == 0:
288
        self._Cleanup()
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290
  def notifyAll(self): # pylint: disable-msg=C0103
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    """Close the writing side of the pipe to notify all waiters.
292

293
    """
294
    self._check_owned()
295
    self._check_unnotified()
296
    self._notified = True
297
    if self._write_fd is not None:
298
      os.close(self._write_fd)
299
      self._write_fd = None
300

    
301

    
302
class PipeCondition(_BaseCondition):
303
  """Group-only non-polling condition with counters.
304

305
  This condition class uses pipes and poll, internally, to be able to wait for
306
  notification with a timeout, without resorting to polling. It is almost
307
  compatible with Python's threading.Condition, but only supports notifyAll and
308
  non-recursive locks. As an additional features it's able to report whether
309
  there are any waiting threads.
310

311
  """
312
  __slots__ = _BaseCondition.__slots__ + [
313
    "_nwaiters",
314
    "_single_condition",
315
    ]
316

    
317
  _single_condition_class = SingleNotifyPipeCondition
318

    
319
  def __init__(self, lock):
320
    """Initializes this class.
321

322
    """
323
    _BaseCondition.__init__(self, lock)
324
    self._nwaiters = 0
325
    self._single_condition = self._single_condition_class(self._lock)
326

    
327
  def wait(self, timeout=None):
328
    """Wait for a notification.
329

330
    @type timeout: float or None
331
    @param timeout: Waiting timeout (can be None)
332

333
    """
334
    self._check_owned()
335

    
336
    # Keep local reference to the pipe. It could be replaced by another thread
337
    # notifying while we're waiting.
338
    my_condition = self._single_condition
339

    
340
    assert self._nwaiters >= 0
341
    self._nwaiters += 1
342
    try:
343
      my_condition.wait(timeout)
344
    finally:
345
      assert self._nwaiters > 0
346
      self._nwaiters -= 1
347

    
348
  def notifyAll(self): # pylint: disable-msg=C0103
349
    """Notify all currently waiting threads.
350

351
    """
352
    self._check_owned()
353
    self._single_condition.notifyAll()
354
    self._single_condition = self._single_condition_class(self._lock)
355

    
356
  def has_waiting(self):
357
    """Returns whether there are active waiters.
358

359
    """
360
    self._check_owned()
361

    
362
    return bool(self._nwaiters)
363

    
364

    
365
class _CountingCondition(object):
366
  """Wrapper for Python's built-in threading.Condition class.
367

368
  This wrapper keeps a count of active waiters. We can't access the internal
369
  "__waiters" attribute of threading.Condition because it's not thread-safe.
370

371
  """
372
  __slots__ = [
373
    "_cond",
374
    "_nwaiters",
375
    ]
376

    
377
  def __init__(self, lock):
378
    """Initializes this class.
379

380
    """
381
    object.__init__(self)
382
    self._cond = threading.Condition(lock=lock)
383
    self._nwaiters = 0
384

    
385
  def notifyAll(self): # pylint: disable-msg=C0103
386
    """Notifies the condition.
387

388
    """
389
    return self._cond.notifyAll()
390

    
391
  def wait(self, timeout=None):
392
    """Waits for the condition to be notified.
393

394
    @type timeout: float or None
395
    @param timeout: Waiting timeout (can be None)
396

397
    """
398
    assert self._nwaiters >= 0
399

    
400
    self._nwaiters += 1
401
    try:
402
      return self._cond.wait(timeout=timeout)
403
    finally:
404
      self._nwaiters -= 1
405

    
406
  def has_waiting(self):
407
    """Returns whether there are active waiters.
408

409
    """
410
    return bool(self._nwaiters)
411

    
412

    
413
class SharedLock(object):
414
  """Implements a shared lock.
415

416
  Multiple threads can acquire the lock in a shared way, calling
417
  acquire_shared().  In order to acquire the lock in an exclusive way threads
418
  can call acquire_exclusive().
419

420
  The lock prevents starvation but does not guarantee that threads will acquire
421
  the shared lock in the order they queued for it, just that they will
422
  eventually do so.
423

424
  """
425
  __slots__ = [
426
    "__active_shr_c",
427
    "__inactive_shr_c",
428
    "__deleted",
429
    "__exc",
430
    "__lock",
431
    "__pending",
432
    "__shr",
433
    ]
434

    
435
  __condition_class = PipeCondition
436

    
437
  def __init__(self):
438
    """Construct a new SharedLock.
439

440
    """
441
    object.__init__(self)
442

    
443
    # Internal lock
444
    self.__lock = threading.Lock()
445

    
446
    # Queue containing waiting acquires
447
    self.__pending = []
448

    
449
    # Active and inactive conditions for shared locks
450
    self.__active_shr_c = self.__condition_class(self.__lock)
451
    self.__inactive_shr_c = self.__condition_class(self.__lock)
452

    
453
    # Current lock holders
454
    self.__shr = set()
455
    self.__exc = None
456

    
457
    # is this lock in the deleted state?
458
    self.__deleted = False
459

    
460
  def __check_deleted(self):
461
    """Raises an exception if the lock has been deleted.
462

463
    """
464
    if self.__deleted:
465
      raise errors.LockError("Deleted lock")
466

    
467
  def __is_sharer(self):
468
    """Is the current thread sharing the lock at this time?
469

470
    """
471
    return threading.currentThread() in self.__shr
472

    
473
  def __is_exclusive(self):
474
    """Is the current thread holding the lock exclusively at this time?
475

476
    """
477
    return threading.currentThread() == self.__exc
478

    
479
  def __is_owned(self, shared=-1):
480
    """Is the current thread somehow owning the lock at this time?
481

482
    This is a private version of the function, which presumes you're holding
483
    the internal lock.
484

485
    """
486
    if shared < 0:
487
      return self.__is_sharer() or self.__is_exclusive()
488
    elif shared:
489
      return self.__is_sharer()
490
    else:
491
      return self.__is_exclusive()
492

    
493
  def _is_owned(self, shared=-1):
494
    """Is the current thread somehow owning the lock at this time?
495

496
    @param shared:
497
        - < 0: check for any type of ownership (default)
498
        - 0: check for exclusive ownership
499
        - > 0: check for shared ownership
500

501
    """
502
    self.__lock.acquire()
503
    try:
504
      return self.__is_owned(shared=shared)
505
    finally:
506
      self.__lock.release()
507

    
508
  def _count_pending(self):
509
    """Returns the number of pending acquires.
510

511
    @rtype: int
512

513
    """
514
    self.__lock.acquire()
515
    try:
516
      return len(self.__pending)
517
    finally:
518
      self.__lock.release()
519

    
520
  def __do_acquire(self, shared):
521
    """Actually acquire the lock.
522

523
    """
524
    if shared:
525
      self.__shr.add(threading.currentThread())
526
    else:
527
      self.__exc = threading.currentThread()
528

    
529
  def __can_acquire(self, shared):
530
    """Determine whether lock can be acquired.
531

532
    """
533
    if shared:
534
      return self.__exc is None
535
    else:
536
      return len(self.__shr) == 0 and self.__exc is None
537

    
538
  def __is_on_top(self, cond):
539
    """Checks whether the passed condition is on top of the queue.
540

541
    The caller must make sure the queue isn't empty.
542

543
    """
544
    return self.__pending[0] == cond
545

    
546
  def __acquire_unlocked(self, shared, timeout):
547
    """Acquire a shared lock.
548

549
    @param shared: whether to acquire in shared mode; by default an
550
        exclusive lock will be acquired
551
    @param timeout: maximum waiting time before giving up
552

553
    """
554
    self.__check_deleted()
555

    
556
    # We cannot acquire the lock if we already have it
557
    assert not self.__is_owned(), "double acquire() on a non-recursive lock"
558

    
559
    # Check whether someone else holds the lock or there are pending acquires.
560
    if not self.__pending and self.__can_acquire(shared):
561
      # Apparently not, can acquire lock directly.
562
      self.__do_acquire(shared)
563
      return True
564

    
565
    if shared:
566
      wait_condition = self.__active_shr_c
567

    
568
      # Check if we're not yet in the queue
569
      if wait_condition not in self.__pending:
570
        self.__pending.append(wait_condition)
571
    else:
572
      wait_condition = self.__condition_class(self.__lock)
573
      # Always add to queue
574
      self.__pending.append(wait_condition)
575

    
576
    try:
577
      # Wait until we become the topmost acquire in the queue or the timeout
578
      # expires.
579
      while not (self.__is_on_top(wait_condition) and
580
                 self.__can_acquire(shared)):
581
        # Wait for notification
582
        wait_condition.wait(timeout)
583
        self.__check_deleted()
584

    
585
        # A lot of code assumes blocking acquires always succeed. Loop
586
        # internally for that case.
587
        if timeout is not None:
588
          break
589

    
590
      if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
591
        self.__do_acquire(shared)
592
        return True
593
    finally:
594
      # Remove condition from queue if there are no more waiters
595
      if not wait_condition.has_waiting() and not self.__deleted:
596
        self.__pending.remove(wait_condition)
597

    
598
    return False
599

    
600
  def acquire(self, shared=0, timeout=None, test_notify=None):
601
    """Acquire a shared lock.
602

603
    @type shared: int
604
    @param shared: whether to acquire in shared mode; by default an
605
        exclusive lock will be acquired
606
    @type timeout: float
607
    @param timeout: maximum waiting time before giving up
608
    @type test_notify: callable or None
609
    @param test_notify: Special callback function for unittesting
610

611
    """
612
    self.__lock.acquire()
613
    try:
614
      # We already got the lock, notify now
615
      if __debug__ and callable(test_notify):
616
        test_notify()
617

    
618
      return self.__acquire_unlocked(shared, timeout)
619
    finally:
620
      self.__lock.release()
621

    
622
  def release(self):
623
    """Release a Shared Lock.
624

625
    You must have acquired the lock, either in shared or in exclusive mode,
626
    before calling this function.
627

628
    """
629
    self.__lock.acquire()
630
    try:
631
      assert self.__is_exclusive() or self.__is_sharer(), \
632
        "Cannot release non-owned lock"
633

    
634
      # Autodetect release type
635
      if self.__is_exclusive():
636
        self.__exc = None
637
      else:
638
        self.__shr.remove(threading.currentThread())
639

    
640
      # Notify topmost condition in queue
641
      if self.__pending:
642
        first_condition = self.__pending[0]
643
        first_condition.notifyAll()
644

    
645
        if first_condition == self.__active_shr_c:
646
          self.__active_shr_c = self.__inactive_shr_c
647
          self.__inactive_shr_c = first_condition
648

    
649
    finally:
650
      self.__lock.release()
651

    
652
  def delete(self, timeout=None):
653
    """Delete a Shared Lock.
654

655
    This operation will declare the lock for removal. First the lock will be
656
    acquired in exclusive mode if you don't already own it, then the lock
657
    will be put in a state where any future and pending acquire() fail.
658

659
    @type timeout: float
660
    @param timeout: maximum waiting time before giving up
661

662
    """
663
    self.__lock.acquire()
664
    try:
665
      assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"
666

    
667
      self.__check_deleted()
668

    
669
      # The caller is allowed to hold the lock exclusively already.
670
      acquired = self.__is_exclusive()
671

    
672
      if not acquired:
673
        acquired = self.__acquire_unlocked(0, timeout)
674

    
675
        assert self.__is_exclusive() and not self.__is_sharer(), \
676
          "Lock wasn't acquired in exclusive mode"
677

    
678
      if acquired:
679
        self.__deleted = True
680
        self.__exc = None
681

    
682
        # Notify all acquires. They'll throw an error.
683
        while self.__pending:
684
          self.__pending.pop().notifyAll()
685

    
686
      return acquired
687
    finally:
688
      self.__lock.release()
689

    
690

    
691
# Whenever we want to acquire a full LockSet we pass None as the value
692
# to acquire.  Hide this behind this nicely named constant.
693
ALL_SET = None
694

    
695

    
696
class _AcquireTimeout(Exception):
697
  """Internal exception to abort an acquire on a timeout.
698

699
  """
700

    
701

    
702
class LockSet:
703
  """Implements a set of locks.
704

705
  This abstraction implements a set of shared locks for the same resource type,
706
  distinguished by name. The user can lock a subset of the resources and the
707
  LockSet will take care of acquiring the locks always in the same order, thus
708
  preventing deadlock.
709

710
  All the locks needed in the same set must be acquired together, though.
711

712
  """
713
  def __init__(self, members=None):
714
    """Constructs a new LockSet.
715

716
    @param members: initial members of the set
717

718
    """
719
    # Used internally to guarantee coherency.
720
    self.__lock = SharedLock()
721

    
722
    # The lockdict indexes the relationship name -> lock
723
    # The order-of-locking is implied by the alphabetical order of names
724
    self.__lockdict = {}
725

    
726
    if members is not None:
727
      for name in members:
728
        self.__lockdict[name] = SharedLock()
729

    
730
    # The owner dict contains the set of locks each thread owns. For
731
    # performance each thread can access its own key without a global lock on
732
    # this structure. It is paramount though that *no* other type of access is
733
    # done to this structure (eg. no looping over its keys). *_owner helper
734
    # function are defined to guarantee access is correct, but in general never
735
    # do anything different than __owners[threading.currentThread()], or there
736
    # will be trouble.
737
    self.__owners = {}
738

    
739
  def _is_owned(self):
740
    """Is the current thread a current level owner?"""
741
    return threading.currentThread() in self.__owners
742

    
743
  def _add_owned(self, name=None):
744
    """Note the current thread owns the given lock"""
745
    if name is None:
746
      if not self._is_owned():
747
        self.__owners[threading.currentThread()] = set()
748
    else:
749
      if self._is_owned():
750
        self.__owners[threading.currentThread()].add(name)
751
      else:
752
        self.__owners[threading.currentThread()] = set([name])
753

    
754
  def _del_owned(self, name=None):
755
    """Note the current thread owns the given lock"""
756

    
757
    assert not (name is None and self.__lock._is_owned()), \
758
           "Cannot hold internal lock when deleting owner status"
759

    
760
    if name is not None:
761
      self.__owners[threading.currentThread()].remove(name)
762

    
763
    # Only remove the key if we don't hold the set-lock as well
764
    if (not self.__lock._is_owned() and
765
        not self.__owners[threading.currentThread()]):
766
      del self.__owners[threading.currentThread()]
767

    
768
  def _list_owned(self):
769
    """Get the set of resource names owned by the current thread"""
770
    if self._is_owned():
771
      return self.__owners[threading.currentThread()].copy()
772
    else:
773
      return set()
774

    
775
  def _release_and_delete_owned(self):
776
    """Release and delete all resources owned by the current thread"""
777
    for lname in self._list_owned():
778
      lock = self.__lockdict[lname]
779
      if lock._is_owned():
780
        lock.release()
781
      self._del_owned(name=lname)
782

    
783
  def __names(self):
784
    """Return the current set of names.
785

786
    Only call this function while holding __lock and don't iterate on the
787
    result after releasing the lock.
788

789
    """
790
    return self.__lockdict.keys()
791

    
792
  def _names(self):
793
    """Return a copy of the current set of elements.
794

795
    Used only for debugging purposes.
796

797
    """
798
    # If we don't already own the set-level lock acquired
799
    # we'll get it and note we need to release it later.
800
    release_lock = False
801
    if not self.__lock._is_owned():
802
      release_lock = True
803
      self.__lock.acquire(shared=1)
804
    try:
805
      result = self.__names()
806
    finally:
807
      if release_lock:
808
        self.__lock.release()
809
    return set(result)
810

    
811
  def acquire(self, names, timeout=None, shared=0, test_notify=None):
812
    """Acquire a set of resource locks.
813

814
    @param names: the names of the locks which shall be acquired
815
        (special lock names, or instance/node names)
816
    @param shared: whether to acquire in shared mode; by default an
817
        exclusive lock will be acquired
818
    @type timeout: float or None
819
    @param timeout: Maximum time to acquire all locks
820
    @type test_notify: callable or None
821
    @param test_notify: Special callback function for unittesting
822

823
    @return: Set of all locks successfully acquired or None in case of timeout
824

825
    @raise errors.LockError: when any lock we try to acquire has
826
        been deleted before we succeed. In this case none of the
827
        locks requested will be acquired.
828

829
    """
830
    assert timeout is None or timeout >= 0.0
831

    
832
    # Check we don't already own locks at this level
833
    assert not self._is_owned(), "Cannot acquire locks in the same set twice"
834

    
835
    # We need to keep track of how long we spent waiting for a lock. The
836
    # timeout passed to this function is over all lock acquires.
837
    running_timeout = RunningTimeout(timeout, False)
838

    
839
    try:
840
      if names is not None:
841
        # Support passing in a single resource to acquire rather than many
842
        if isinstance(names, basestring):
843
          names = [names]
844
        else:
845
          names = sorted(names)
846

    
847
        return self.__acquire_inner(names, False, shared,
848
                                    running_timeout.Remaining, test_notify)
849

    
850
      else:
851
        # If no names are given acquire the whole set by not letting new names
852
        # being added before we release, and getting the current list of names.
853
        # Some of them may then be deleted later, but we'll cope with this.
854
        #
855
        # We'd like to acquire this lock in a shared way, as it's nice if
856
        # everybody else can use the instances at the same time. If are
857
        # acquiring them exclusively though they won't be able to do this
858
        # anyway, though, so we'll get the list lock exclusively as well in
859
        # order to be able to do add() on the set while owning it.
860
        if not self.__lock.acquire(shared=shared,
861
                                   timeout=running_timeout.Remaining()):
862
          raise _AcquireTimeout()
863
        try:
864
          # note we own the set-lock
865
          self._add_owned()
866

    
867
          return self.__acquire_inner(self.__names(), True, shared,
868
                                      running_timeout.Remaining, test_notify)
869
        except:
870
          # We shouldn't have problems adding the lock to the owners list, but
871
          # if we did we'll try to release this lock and re-raise exception.
872
          # Of course something is going to be really wrong, after this.
873
          self.__lock.release()
874
          self._del_owned()
875
          raise
876

    
877
    except _AcquireTimeout:
878
      return None
879

    
880
  def __acquire_inner(self, names, want_all, shared, timeout_fn, test_notify):
881
    """Inner logic for acquiring a number of locks.
882

883
    @param names: Names of the locks to be acquired
884
    @param want_all: Whether all locks in the set should be acquired
885
    @param shared: Whether to acquire in shared mode
886
    @param timeout_fn: Function returning remaining timeout
887
    @param test_notify: Special callback function for unittesting
888

889
    """
890
    acquire_list = []
891

    
892
    # First we look the locks up on __lockdict. We have no way of being sure
893
    # they will still be there after, but this makes it a lot faster should
894
    # just one of them be the already wrong
895
    for lname in utils.UniqueSequence(names):
896
      try:
897
        lock = self.__lockdict[lname] # raises KeyError if lock is not there
898
        acquire_list.append((lname, lock))
899
      except KeyError:
900
        if want_all:
901
          # We are acquiring all the set, it doesn't matter if this particular
902
          # element is not there anymore.
903
          continue
904

    
905
        raise errors.LockError("Non-existing lock in set (%s)" % lname)
906

    
907
    # This will hold the locknames we effectively acquired.
908
    acquired = set()
909

    
910
    try:
911
      # Now acquire_list contains a sorted list of resources and locks we
912
      # want.  In order to get them we loop on this (private) list and
913
      # acquire() them.  We gave no real guarantee they will still exist till
914
      # this is done but .acquire() itself is safe and will alert us if the
915
      # lock gets deleted.
916
      for (lname, lock) in acquire_list:
917
        if __debug__ and callable(test_notify):
918
          test_notify_fn = lambda: test_notify(lname)
919
        else:
920
          test_notify_fn = None
921

    
922
        timeout = timeout_fn()
923

    
924
        try:
925
          # raises LockError if the lock was deleted
926
          acq_success = lock.acquire(shared=shared, timeout=timeout,
927
                                     test_notify=test_notify_fn)
928
        except errors.LockError:
929
          if want_all:
930
            # We are acquiring all the set, it doesn't matter if this
931
            # particular element is not there anymore.
932
            continue
933

    
934
          raise errors.LockError("Non-existing lock in set (%s)" % lname)
935

    
936
        if not acq_success:
937
          # Couldn't get lock or timeout occurred
938
          if timeout is None:
939
            # This shouldn't happen as SharedLock.acquire(timeout=None) is
940
            # blocking.
941
            raise errors.LockError("Failed to get lock %s" % lname)
942

    
943
          raise _AcquireTimeout()
944

    
945
        try:
946
          # now the lock cannot be deleted, we have it!
947
          self._add_owned(name=lname)
948
          acquired.add(lname)
949

    
950
        except:
951
          # We shouldn't have problems adding the lock to the owners list, but
952
          # if we did we'll try to release this lock and re-raise exception.
953
          # Of course something is going to be really wrong after this.
954
          if lock._is_owned():
955
            lock.release()
956
          raise
957

    
958
    except:
959
      # Release all owned locks
960
      self._release_and_delete_owned()
961
      raise
962

    
963
    return acquired
964

    
965
  def release(self, names=None):
966
    """Release a set of resource locks, at the same level.
967

968
    You must have acquired the locks, either in shared or in exclusive mode,
969
    before releasing them.
970

971
    @param names: the names of the locks which shall be released
972
        (defaults to all the locks acquired at that level).
973

974
    """
975
    assert self._is_owned(), "release() on lock set while not owner"
976

    
977
    # Support passing in a single resource to release rather than many
978
    if isinstance(names, basestring):
979
      names = [names]
980

    
981
    if names is None:
982
      names = self._list_owned()
983
    else:
984
      names = set(names)
985
      assert self._list_owned().issuperset(names), (
986
               "release() on unheld resources %s" %
987
               names.difference(self._list_owned()))
988

    
989
    # First of all let's release the "all elements" lock, if set.
990
    # After this 'add' can work again
991
    if self.__lock._is_owned():
992
      self.__lock.release()
993
      self._del_owned()
994

    
995
    for lockname in names:
996
      # If we are sure the lock doesn't leave __lockdict without being
997
      # exclusively held we can do this...
998
      self.__lockdict[lockname].release()
999
      self._del_owned(name=lockname)
1000

    
1001
  def add(self, names, acquired=0, shared=0):
1002
    """Add a new set of elements to the set
1003

1004
    @param names: names of the new elements to add
1005
    @param acquired: pre-acquire the new resource?
1006
    @param shared: is the pre-acquisition shared?
1007

1008
    """
1009
    # Check we don't already own locks at this level
1010
    assert not self._is_owned() or self.__lock._is_owned(shared=0), \
1011
      "Cannot add locks if the set is only partially owned, or shared"
1012

    
1013
    # Support passing in a single resource to add rather than many
1014
    if isinstance(names, basestring):
1015
      names = [names]
1016

    
1017
    # If we don't already own the set-level lock acquired in an exclusive way
1018
    # we'll get it and note we need to release it later.
1019
    release_lock = False
1020
    if not self.__lock._is_owned():
1021
      release_lock = True
1022
      self.__lock.acquire()
1023

    
1024
    try:
1025
      invalid_names = set(self.__names()).intersection(names)
1026
      if invalid_names:
1027
        # This must be an explicit raise, not an assert, because assert is
1028
        # turned off when using optimization, and this can happen because of
1029
        # concurrency even if the user doesn't want it.
1030
        raise errors.LockError("duplicate add() (%s)" % invalid_names)
1031

    
1032
      for lockname in names:
1033
        lock = SharedLock()
1034

    
1035
        if acquired:
1036
          lock.acquire(shared=shared)
1037
          # now the lock cannot be deleted, we have it!
1038
          try:
1039
            self._add_owned(name=lockname)
1040
          except:
1041
            # We shouldn't have problems adding the lock to the owners list,
1042
            # but if we did we'll try to release this lock and re-raise
1043
            # exception.  Of course something is going to be really wrong,
1044
            # after this.  On the other hand the lock hasn't been added to the
1045
            # __lockdict yet so no other threads should be pending on it. This
1046
            # release is just a safety measure.
1047
            lock.release()
1048
            raise
1049

    
1050
        self.__lockdict[lockname] = lock
1051

    
1052
    finally:
1053
      # Only release __lock if we were not holding it previously.
1054
      if release_lock:
1055
        self.__lock.release()
1056

    
1057
    return True
1058

    
1059
  def remove(self, names):
1060
    """Remove elements from the lock set.
1061

1062
    You can either not hold anything in the lockset or already hold a superset
1063
    of the elements you want to delete, exclusively.
1064

1065
    @param names: names of the resource to remove.
1066

1067
    @return: a list of locks which we removed; the list is always
1068
        equal to the names list if we were holding all the locks
1069
        exclusively
1070

1071
    """
1072
    # Support passing in a single resource to remove rather than many
1073
    if isinstance(names, basestring):
1074
      names = [names]
1075

    
1076
    # If we own any subset of this lock it must be a superset of what we want
1077
    # to delete. The ownership must also be exclusive, but that will be checked
1078
    # by the lock itself.
1079
    assert not self._is_owned() or self._list_owned().issuperset(names), (
1080
      "remove() on acquired lockset while not owning all elements")
1081

    
1082
    removed = []
1083

    
1084
    for lname in names:
1085
      # Calling delete() acquires the lock exclusively if we don't already own
1086
      # it, and causes all pending and subsequent lock acquires to fail. It's
1087
      # fine to call it out of order because delete() also implies release(),
1088
      # and the assertion above guarantees that if we either already hold
1089
      # everything we want to delete, or we hold none.
1090
      try:
1091
        self.__lockdict[lname].delete()
1092
        removed.append(lname)
1093
      except (KeyError, errors.LockError):
1094
        # This cannot happen if we were already holding it, verify:
1095
        assert not self._is_owned(), "remove failed while holding lockset"
1096
      else:
1097
        # If no LockError was raised we are the ones who deleted the lock.
1098
        # This means we can safely remove it from lockdict, as any further or
1099
        # pending delete() or acquire() will fail (and nobody can have the lock
1100
        # since before our call to delete()).
1101
        #
1102
        # This is done in an else clause because if the exception was thrown
1103
        # it's the job of the one who actually deleted it.
1104
        del self.__lockdict[lname]
1105
        # And let's remove it from our private list if we owned it.
1106
        if self._is_owned():
1107
          self._del_owned(name=lname)
1108

    
1109
    return removed
1110

    
1111

    
1112
# Locking levels, must be acquired in increasing order.
1113
# Current rules are:
1114
#   - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
1115
#   acquired before performing any operation, either in shared or in exclusive
1116
#   mode. acquiring the BGL in exclusive mode is discouraged and should be
1117
#   avoided.
1118
#   - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
1119
#   If you need more than one node, or more than one instance, acquire them at
1120
#   the same time.
1121
LEVEL_CLUSTER = 0
1122
LEVEL_INSTANCE = 1
1123
LEVEL_NODE = 2
1124

    
1125
LEVELS = [LEVEL_CLUSTER,
1126
          LEVEL_INSTANCE,
1127
          LEVEL_NODE]
1128

    
1129
# Lock levels which are modifiable
1130
LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE]
1131

    
1132
LEVEL_NAMES = {
1133
  LEVEL_CLUSTER: "cluster",
1134
  LEVEL_INSTANCE: "instance",
1135
  LEVEL_NODE: "node",
1136
  }
1137

    
1138
# Constant for the big ganeti lock
1139
BGL = 'BGL'
1140

    
1141

    
1142
class GanetiLockManager:
1143
  """The Ganeti Locking Library
1144

1145
  The purpose of this small library is to manage locking for ganeti clusters
1146
  in a central place, while at the same time doing dynamic checks against
1147
  possible deadlocks. It will also make it easier to transition to a different
1148
  lock type should we migrate away from python threads.
1149

1150
  """
1151
  _instance = None
1152

    
1153
  def __init__(self, nodes=None, instances=None):
1154
    """Constructs a new GanetiLockManager object.
1155

1156
    There should be only a GanetiLockManager object at any time, so this
1157
    function raises an error if this is not the case.
1158

1159
    @param nodes: list of node names
1160
    @param instances: list of instance names
1161

1162
    """
1163
    assert self.__class__._instance is None, \
1164
           "double GanetiLockManager instance"
1165

    
1166
    self.__class__._instance = self
1167

    
1168
    # The keyring contains all the locks, at their level and in the correct
1169
    # locking order.
1170
    self.__keyring = {
1171
      LEVEL_CLUSTER: LockSet([BGL]),
1172
      LEVEL_NODE: LockSet(nodes),
1173
      LEVEL_INSTANCE: LockSet(instances),
1174
    }
1175

    
1176
  def _names(self, level):
1177
    """List the lock names at the given level.
1178

1179
    This can be used for debugging/testing purposes.
1180

1181
    @param level: the level whose list of locks to get
1182

1183
    """
1184
    assert level in LEVELS, "Invalid locking level %s" % level
1185
    return self.__keyring[level]._names()
1186

    
1187
  def _is_owned(self, level):
1188
    """Check whether we are owning locks at the given level
1189

1190
    """
1191
    return self.__keyring[level]._is_owned()
1192

    
1193
  is_owned = _is_owned
1194

    
1195
  def _list_owned(self, level):
1196
    """Get the set of owned locks at the given level
1197

1198
    """
1199
    return self.__keyring[level]._list_owned()
1200

    
1201
  def _upper_owned(self, level):
1202
    """Check that we don't own any lock at a level greater than the given one.
1203

1204
    """
1205
    # This way of checking only works if LEVELS[i] = i, which we check for in
1206
    # the test cases.
1207
    return utils.any((self._is_owned(l) for l in LEVELS[level + 1:]))
1208

    
1209
  def _BGL_owned(self): # pylint: disable-msg=C0103
1210
    """Check if the current thread owns the BGL.
1211

1212
    Both an exclusive or a shared acquisition work.
1213

1214
    """
1215
    return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned()
1216

    
1217
  @staticmethod
1218
  def _contains_BGL(level, names): # pylint: disable-msg=C0103
1219
    """Check if the level contains the BGL.
1220

1221
    Check if acting on the given level and set of names will change
1222
    the status of the Big Ganeti Lock.
1223

1224
    """
1225
    return level == LEVEL_CLUSTER and (names is None or BGL in names)
1226

    
1227
  def acquire(self, level, names, timeout=None, shared=0):
1228
    """Acquire a set of resource locks, at the same level.
1229

1230
    @param level: the level at which the locks shall be acquired;
1231
        it must be a member of LEVELS.
1232
    @param names: the names of the locks which shall be acquired
1233
        (special lock names, or instance/node names)
1234
    @param shared: whether to acquire in shared mode; by default
1235
        an exclusive lock will be acquired
1236
    @type timeout: float
1237
    @param timeout: Maximum time to acquire all locks
1238

1239
    """
1240
    assert level in LEVELS, "Invalid locking level %s" % level
1241

    
1242
    # Check that we are either acquiring the Big Ganeti Lock or we already own
1243
    # it. Some "legacy" opcodes need to be sure they are run non-concurrently
1244
    # so even if we've migrated we need to at least share the BGL to be
1245
    # compatible with them. Of course if we own the BGL exclusively there's no
1246
    # point in acquiring any other lock, unless perhaps we are half way through
1247
    # the migration of the current opcode.
1248
    assert (self._contains_BGL(level, names) or self._BGL_owned()), (
1249
            "You must own the Big Ganeti Lock before acquiring any other")
1250

    
1251
    # Check we don't own locks at the same or upper levels.
1252
    assert not self._upper_owned(level), ("Cannot acquire locks at a level"
1253
           " while owning some at a greater one")
1254

    
1255
    # Acquire the locks in the set.
1256
    return self.__keyring[level].acquire(names, shared=shared, timeout=timeout)
1257

    
1258
  def release(self, level, names=None):
1259
    """Release a set of resource locks, at the same level.
1260

1261
    You must have acquired the locks, either in shared or in exclusive
1262
    mode, before releasing them.
1263

1264
    @param level: the level at which the locks shall be released;
1265
        it must be a member of LEVELS
1266
    @param names: the names of the locks which shall be released
1267
        (defaults to all the locks acquired at that level)
1268

1269
    """
1270
    assert level in LEVELS, "Invalid locking level %s" % level
1271
    assert (not self._contains_BGL(level, names) or
1272
            not self._upper_owned(LEVEL_CLUSTER)), (
1273
            "Cannot release the Big Ganeti Lock while holding something"
1274
            " at upper levels (%r)" %
1275
            (utils.CommaJoin(["%s=%r" % (LEVEL_NAMES[i], self._list_owned(i))
1276
                              for i in self.__keyring.keys()]), ))
1277

    
1278
    # Release will complain if we don't own the locks already
1279
    return self.__keyring[level].release(names)
1280

    
1281
  def add(self, level, names, acquired=0, shared=0):
1282
    """Add locks at the specified level.
1283

1284
    @param level: the level at which the locks shall be added;
1285
        it must be a member of LEVELS_MOD.
1286
    @param names: names of the locks to acquire
1287
    @param acquired: whether to acquire the newly added locks
1288
    @param shared: whether the acquisition will be shared
1289

1290
    """
1291
    assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1292
    assert self._BGL_owned(), ("You must own the BGL before performing other"
1293
           " operations")
1294
    assert not self._upper_owned(level), ("Cannot add locks at a level"
1295
           " while owning some at a greater one")
1296
    return self.__keyring[level].add(names, acquired=acquired, shared=shared)
1297

    
1298
  def remove(self, level, names):
1299
    """Remove locks from the specified level.
1300

1301
    You must either already own the locks you are trying to remove
1302
    exclusively or not own any lock at an upper level.
1303

1304
    @param level: the level at which the locks shall be removed;
1305
        it must be a member of LEVELS_MOD
1306
    @param names: the names of the locks which shall be removed
1307
        (special lock names, or instance/node names)
1308

1309
    """
1310
    assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1311
    assert self._BGL_owned(), ("You must own the BGL before performing other"
1312
           " operations")
1313
    # Check we either own the level or don't own anything from here
1314
    # up. LockSet.remove() will check the case in which we don't own
1315
    # all the needed resources, or we have a shared ownership.
1316
    assert self._is_owned(level) or not self._upper_owned(level), (
1317
           "Cannot remove locks at a level while not owning it or"
1318
           " owning some at a greater one")
1319
    return self.__keyring[level].remove(names)