lib/locking.py

   1 #
   2 #
   3
   4 # Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Google Inc.
   5 #
   6 # This program is free software; you can redistribute it and/or modify
   7 # it under the terms of the GNU General Public License as published by
   8 # the Free Software Foundation; either version 2 of the License, or
   9 # (at your option) any later version.
  10 #
  11 # This program is distributed in the hope that it will be useful, but
  12 # WITHOUT ANY WARRANTY; without even the implied warranty of
  13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 # General Public License for more details.
  15 #
  16 # You should have received a copy of the GNU General Public License
  17 # along with this program; if not, write to the Free Software
  18 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 # 02110-1301, USA.
  20
  21 """Module implementing the Ganeti locking code."""
  22
  23 # pylint: disable=W0212
  24
  25 # W0212 since e.g. LockSet methods use (a lot) the internals of
  26 # SharedLock
  27
  28 import os
  29 import select
  30 import threading
  31 import errno
  32 import weakref
  33 import logging
  34 import heapq
  35 import itertools
  36 import time
  37
  38 from ganeti import errors
  39 from ganeti import utils
  40 from ganeti import compat
  41 from ganeti import query
  42
  43
  44 _EXCLUSIVE_TEXT = "exclusive"
  45 _SHARED_TEXT = "shared"
  46 _DELETED_TEXT = "deleted"
  47
  48 _DEFAULT_PRIORITY = 0
  49
  50
  51 def ssynchronized(mylock, shared=0):
  52   """Shared Synchronization decorator.
  53
  54   Calls the function holding the given lock, either in exclusive or shared
  55   mode. It requires the passed lock to be a SharedLock (or support its
  56   semantics).
  57
  58   @type mylock: lockable object or string
  59   @param mylock: lock to acquire or class member name of the lock to acquire
  60
  61   """
  62   def wrap(fn):
  63     def sync_function(*args, **kwargs):
  64       if isinstance(mylock, basestring):
  65         assert args, "cannot ssynchronize on non-class method: self not found"
  66         # args[0] is "self"
  67         lock = getattr(args[0], mylock)
  68       else:
  69         lock = mylock
  70       lock.acquire(shared=shared)
  71       try:
  72         return fn(*args, **kwargs)
  73       finally:
  74         lock.release()
  75     return sync_function
  76   return wrap
  77
  78
  79 class _SingleNotifyPipeConditionWaiter(object):
  80   """Helper class for SingleNotifyPipeCondition
  81
  82   """
  83   __slots__ = [
  84     "_fd",
  85     "_poller",
  86     ]
  87
  88   def __init__(self, poller, fd):
  89     """Constructor for _SingleNotifyPipeConditionWaiter
  90
  91     @type poller: select.poll
  92     @param poller: Poller object
  93     @type fd: int
  94     @param fd: File descriptor to wait for
  95
  96     """
  97     object.__init__(self)
  98     self._poller = poller
  99     self._fd = fd
 100
 101   def __call__(self, timeout):
 102     """Wait for something to happen on the pipe.
 103
 104     @type timeout: float or None
 105     @param timeout: Timeout for waiting (can be None)
 106
 107     """
 108     running_timeout = utils.RunningTimeout(timeout, True)
 109
 110     while True:
 111       remaining_time = running_timeout.Remaining()
 112
 113       if remaining_time is not None:
 114         if remaining_time < 0.0:
 115           break
 116
 117         # Our calculation uses seconds, poll() wants milliseconds
 118         remaining_time *= 1000
 119
 120       try:
 121         result = self._poller.poll(remaining_time)
 122       except EnvironmentError, err:
 123         if err.errno != errno.EINTR:
 124           raise
 125         result = None
 126
 127       # Check whether we were notified
 128       if result and result[0][0] == self._fd:
 129         break
 130
 131
 132 class _BaseCondition(object):
 133   """Base class containing common code for conditions.
 134
 135   Some of this code is taken from python's threading module.
 136
 137   """
 138   __slots__ = [
 139     "_lock",
 140     "acquire",
 141     "release",
 142     "_is_owned",
 143     "_acquire_restore",
 144     "_release_save",
 145     ]
 146
 147   def __init__(self, lock):
 148     """Constructor for _BaseCondition.
 149
 150     @type lock: threading.Lock
 151     @param lock: condition base lock
 152
 153     """
 154     object.__init__(self)
 155
 156     try:
 157       self._release_save = lock._release_save
 158     except AttributeError:
 159       self._release_save = self._base_release_save
 160     try:
 161       self._acquire_restore = lock._acquire_restore
 162     except AttributeError:
 163       self._acquire_restore = self._base_acquire_restore
 164     try:
 165       self._is_owned = lock.is_owned
 166     except AttributeError:
 167       self._is_owned = self._base_is_owned
 168
 169     self._lock = lock
 170
 171     # Export the lock's acquire() and release() methods
 172     self.acquire = lock.acquire
 173     self.release = lock.release
 174
 175   def _base_is_owned(self):
 176     """Check whether lock is owned by current thread.
 177
 178     """
 179     if self._lock.acquire(0):
 180       self._lock.release()
 181       return False
 182     return True
 183
 184   def _base_release_save(self):
 185     self._lock.release()
 186
 187   def _base_acquire_restore(self, _):
 188     self._lock.acquire()
 189
 190   def _check_owned(self):
 191     """Raise an exception if the current thread doesn't own the lock.
 192
 193     """
 194     if not self._is_owned():
 195       raise RuntimeError("cannot work with un-aquired lock")
 196
 197
 198 class SingleNotifyPipeCondition(_BaseCondition):
 199   """Condition which can only be notified once.
 200
 201   This condition class uses pipes and poll, internally, to be able to wait for
 202   notification with a timeout, without resorting to polling. It is almost
 203   compatible with Python's threading.Condition, with the following differences:
 204     - notifyAll can only be called once, and no wait can happen after that
 205     - notify is not supported, only notifyAll
 206
 207   """
 208
 209   __slots__ = [
 210     "_poller",
 211     "_read_fd",
 212     "_write_fd",
 213     "_nwaiters",
 214     "_notified",
 215     ]
 216
 217   _waiter_class = _SingleNotifyPipeConditionWaiter
 218
 219   def __init__(self, lock):
 220     """Constructor for SingleNotifyPipeCondition
 221
 222     """
 223     _BaseCondition.__init__(self, lock)
 224     self._nwaiters = 0
 225     self._notified = False
 226     self._read_fd = None
 227     self._write_fd = None
 228     self._poller = None
 229
 230   def _check_unnotified(self):
 231     """Throws an exception if already notified.
 232
 233     """
 234     if self._notified:
 235       raise RuntimeError("cannot use already notified condition")
 236
 237   def _Cleanup(self):
 238     """Cleanup open file descriptors, if any.
 239
 240     """
 241     if self._read_fd is not None:
 242       os.close(self._read_fd)
 243       self._read_fd = None
 244
 245     if self._write_fd is not None:
 246       os.close(self._write_fd)
 247       self._write_fd = None
 248     self._poller = None
 249
 250   def wait(self, timeout):
 251     """Wait for a notification.
 252
 253     @type timeout: float or None
 254     @param timeout: Waiting timeout (can be None)
 255
 256     """
 257     self._check_owned()
 258     self._check_unnotified()
 259
 260     self._nwaiters += 1
 261     try:
 262       if self._poller is None:
 263         (self._read_fd, self._write_fd) = os.pipe()
 264         self._poller = select.poll()
 265         self._poller.register(self._read_fd, select.POLLHUP)
 266
 267       wait_fn = self._waiter_class(self._poller, self._read_fd)
 268       state = self._release_save()
 269       try:
 270         # Wait for notification
 271         wait_fn(timeout)
 272       finally:
 273         # Re-acquire lock
 274         self._acquire_restore(state)
 275     finally:
 276       self._nwaiters -= 1
 277       if self._nwaiters == 0:
 278         self._Cleanup()
 279
 280   def notifyAll(self): # pylint: disable=C0103
 281     """Close the writing side of the pipe to notify all waiters.
 282
 283     """
 284     self._check_owned()
 285     self._check_unnotified()
 286     self._notified = True
 287     if self._write_fd is not None:
 288       os.close(self._write_fd)
 289       self._write_fd = None
 290
 291
 292 class PipeCondition(_BaseCondition):
 293   """Group-only non-polling condition with counters.
 294
 295   This condition class uses pipes and poll, internally, to be able to wait for
 296   notification with a timeout, without resorting to polling. It is almost
 297   compatible with Python's threading.Condition, but only supports notifyAll and
 298   non-recursive locks. As an additional features it's able to report whether
 299   there are any waiting threads.
 300
 301   """
 302   __slots__ = [
 303     "_waiters",
 304     "_single_condition",
 305     ]
 306
 307   _single_condition_class = SingleNotifyPipeCondition
 308
 309   def __init__(self, lock):
 310     """Initializes this class.
 311
 312     """
 313     _BaseCondition.__init__(self, lock)
 314     self._waiters = set()
 315     self._single_condition = self._single_condition_class(self._lock)
 316
 317   def wait(self, timeout):
 318     """Wait for a notification.
 319
 320     @type timeout: float or None
 321     @param timeout: Waiting timeout (can be None)
 322
 323     """
 324     self._check_owned()
 325
 326     # Keep local reference to the pipe. It could be replaced by another thread
 327     # notifying while we're waiting.
 328     cond = self._single_condition
 329
 330     self._waiters.add(threading.currentThread())
 331     try:
 332       cond.wait(timeout)
 333     finally:
 334       self._check_owned()
 335       self._waiters.remove(threading.currentThread())
 336
 337   def notifyAll(self): # pylint: disable=C0103
 338     """Notify all currently waiting threads.
 339
 340     """
 341     self._check_owned()
 342     self._single_condition.notifyAll()
 343     self._single_condition = self._single_condition_class(self._lock)
 344
 345   def get_waiting(self):
 346     """Returns a list of all waiting threads.
 347
 348     """
 349     self._check_owned()
 350
 351     return self._waiters
 352
 353   def has_waiting(self):
 354     """Returns whether there are active waiters.
 355
 356     """
 357     self._check_owned()
 358
 359     return bool(self._waiters)
 360
 361   def __repr__(self):
 362     return ("<%s.%s waiters=%s at %#x>" %
 363             (self.__class__.__module__, self.__class__.__name__,
 364              self._waiters, id(self)))
 365
 366
 367 class _PipeConditionWithMode(PipeCondition):
 368   __slots__ = [
 369     "shared",
 370     ]
 371
 372   def __init__(self, lock, shared):
 373     """Initializes this class.
 374
 375     """
 376     self.shared = shared
 377     PipeCondition.__init__(self, lock)
 378
 379
 380 class SharedLock(object):
 381   """Implements a shared lock.
 382
 383   Multiple threads can acquire the lock in a shared way by calling
 384   C{acquire(shared=1)}. In order to acquire the lock in an exclusive way
 385   threads can call C{acquire(shared=0)}.
 386
 387   Notes on data structures: C{__pending} contains a priority queue (heapq) of
 388   all pending acquires: C{[(priority1: prioqueue1), (priority2: prioqueue2),
 389   ...]}. Each per-priority queue contains a normal in-order list of conditions
 390   to be notified when the lock can be acquired. Shared locks are grouped
 391   together by priority and the condition for them is stored in
 392   C{__pending_shared} if it already exists. C{__pending_by_prio} keeps
 393   references for the per-priority queues indexed by priority for faster access.
 394
 395   @type name: string
 396   @ivar name: the name of the lock
 397
 398   """
 399   __slots__ = [
 400     "__weakref__",
 401     "__deleted",
 402     "__exc",
 403     "__lock",
 404     "__pending",
 405     "__pending_by_prio",
 406     "__pending_shared",
 407     "__shr",
 408     "__time_fn",
 409     "name",
 410     ]
 411
 412   __condition_class = _PipeConditionWithMode
 413
 414   def __init__(self, name, monitor=None, _time_fn=time.time):
 415     """Construct a new SharedLock.
 416
 417     @param name: the name of the lock
 418     @type monitor: L{LockMonitor}
 419     @param monitor: Lock monitor with which to register
 420
 421     """
 422     object.__init__(self)
 423
 424     self.name = name
 425
 426     # Used for unittesting
 427     self.__time_fn = _time_fn
 428
 429     # Internal lock
 430     self.__lock = threading.Lock()
 431
 432     # Queue containing waiting acquires
 433     self.__pending = []
 434     self.__pending_by_prio = {}
 435     self.__pending_shared = {}
 436
 437     # Current lock holders
 438     self.__shr = set()
 439     self.__exc = None
 440
 441     # is this lock in the deleted state?
 442     self.__deleted = False
 443
 444     # Register with lock monitor
 445     if monitor:
 446       logging.debug("Adding lock %s to monitor", name)
 447       monitor.RegisterLock(self)
 448
 449   def __repr__(self):
 450     return ("<%s.%s name=%s at %#x>" %
 451             (self.__class__.__module__, self.__class__.__name__,
 452              self.name, id(self)))
 453
 454   def GetLockInfo(self, requested):
 455     """Retrieves information for querying locks.
 456
 457     @type requested: set
 458     @param requested: Requested information, see C{query.LQ_*}
 459
 460     """
 461     self.__lock.acquire()
 462     try:
 463       # Note: to avoid unintentional race conditions, no references to
 464       # modifiable objects should be returned unless they were created in this
 465       # function.
 466       mode = None
 467       owner_names = None
 468
 469       if query.LQ_MODE in requested:
 470         if self.__deleted:
 471           mode = _DELETED_TEXT
 472           assert not (self.__exc or self.__shr)
 473         elif self.__exc:
 474           mode = _EXCLUSIVE_TEXT
 475         elif self.__shr:
 476           mode = _SHARED_TEXT
 477
 478       # Current owner(s) are wanted
 479       if query.LQ_OWNER in requested:
 480         if self.__exc:
 481           owner = [self.__exc]
 482         else:
 483           owner = self.__shr
 484
 485         if owner:
 486           assert not self.__deleted
 487           owner_names = [i.getName() for i in owner]
 488
 489       # Pending acquires are wanted
 490       if query.LQ_PENDING in requested:
 491         pending = []
 492
 493         # Sorting instead of copying and using heaq functions for simplicity
 494         for (_, prioqueue) in sorted(self.__pending):
 495           for cond in prioqueue:
 496             if cond.shared:
 497               pendmode = _SHARED_TEXT
 498             else:
 499               pendmode = _EXCLUSIVE_TEXT
 500
 501             # List of names will be sorted in L{query._GetLockPending}
 502             pending.append((pendmode, [i.getName()
 503                                        for i in cond.get_waiting()]))
 504       else:
 505         pending = None
 506
 507       return [(self.name, mode, owner_names, pending)]
 508     finally:
 509       self.__lock.release()
 510
 511   def __check_deleted(self):
 512     """Raises an exception if the lock has been deleted.
 513
 514     """
 515     if self.__deleted:
 516       raise errors.LockError("Deleted lock %s" % self.name)
 517
 518   def __is_sharer(self):
 519     """Is the current thread sharing the lock at this time?
 520
 521     """
 522     return threading.currentThread() in self.__shr
 523
 524   def __is_exclusive(self):
 525     """Is the current thread holding the lock exclusively at this time?
 526
 527     """
 528     return threading.currentThread() == self.__exc
 529
 530   def __is_owned(self, shared=-1):
 531     """Is the current thread somehow owning the lock at this time?
 532
 533     This is a private version of the function, which presumes you're holding
 534     the internal lock.
 535
 536     """
 537     if shared < 0:
 538       return self.__is_sharer() or self.__is_exclusive()
 539     elif shared:
 540       return self.__is_sharer()
 541     else:
 542       return self.__is_exclusive()
 543
 544   def is_owned(self, shared=-1):
 545     """Is the current thread somehow owning the lock at this time?
 546
 547     @param shared:
 548         - < 0: check for any type of ownership (default)
 549         - 0: check for exclusive ownership
 550         - > 0: check for shared ownership
 551
 552     """
 553     self.__lock.acquire()
 554     try:
 555       return self.__is_owned(shared=shared)
 556     finally:
 557       self.__lock.release()
 558
 559   #: Necessary to remain compatible with threading.Condition, which tries to
 560   #: retrieve a locks' "_is_owned" attribute
 561   _is_owned = is_owned
 562
 563   def _count_pending(self):
 564     """Returns the number of pending acquires.
 565
 566     @rtype: int
 567
 568     """
 569     self.__lock.acquire()
 570     try:
 571       return sum(len(prioqueue) for (_, prioqueue) in self.__pending)
 572     finally:
 573       self.__lock.release()
 574
 575   def _check_empty(self):
 576     """Checks whether there are any pending acquires.
 577
 578     @rtype: bool
 579
 580     """
 581     self.__lock.acquire()
 582     try:
 583       # Order is important: __find_first_pending_queue modifies __pending
 584       (_, prioqueue) = self.__find_first_pending_queue()
 585
 586       return not (prioqueue or
 587                   self.__pending or
 588                   self.__pending_by_prio or
 589                   self.__pending_shared)
 590     finally:
 591       self.__lock.release()
 592
 593   def __do_acquire(self, shared):
 594     """Actually acquire the lock.
 595
 596     """
 597     if shared:
 598       self.__shr.add(threading.currentThread())
 599     else:
 600       self.__exc = threading.currentThread()
 601
 602   def __can_acquire(self, shared):
 603     """Determine whether lock can be acquired.
 604
 605     """
 606     if shared:
 607       return self.__exc is None
 608     else:
 609       return len(self.__shr) == 0 and self.__exc is None
 610
 611   def __find_first_pending_queue(self):
 612     """Tries to find the topmost queued entry with pending acquires.
 613
 614     Removes empty entries while going through the list.
 615
 616     """
 617     while self.__pending:
 618       (priority, prioqueue) = self.__pending[0]
 619
 620       if prioqueue:
 621         return (priority, prioqueue)
 622
 623       # Remove empty queue
 624       heapq.heappop(self.__pending)
 625       del self.__pending_by_prio[priority]
 626       assert priority not in self.__pending_shared
 627
 628     return (None, None)
 629
 630   def __is_on_top(self, cond):
 631     """Checks whether the passed condition is on top of the queue.
 632
 633     The caller must make sure the queue isn't empty.
 634
 635     """
 636     (_, prioqueue) = self.__find_first_pending_queue()
 637
 638     return cond == prioqueue[0]
 639
 640   def __acquire_unlocked(self, shared, timeout, priority):
 641     """Acquire a shared lock.
 642
 643     @param shared: whether to acquire in shared mode; by default an
 644         exclusive lock will be acquired
 645     @param timeout: maximum waiting time before giving up
 646     @type priority: integer
 647     @param priority: Priority for acquiring lock
 648
 649     """
 650     self.__check_deleted()
 651
 652     # We cannot acquire the lock if we already have it
 653     assert not self.__is_owned(), ("double acquire() on a non-recursive lock"
 654                                    " %s" % self.name)
 655
 656     # Remove empty entries from queue
 657     self.__find_first_pending_queue()
 658
 659     # Check whether someone else holds the lock or there are pending acquires.
 660     if not self.__pending and self.__can_acquire(shared):
 661       # Apparently not, can acquire lock directly.
 662       self.__do_acquire(shared)
 663       return True
 664
 665     prioqueue = self.__pending_by_prio.get(priority, None)
 666
 667     if shared:
 668       # Try to re-use condition for shared acquire
 669       wait_condition = self.__pending_shared.get(priority, None)
 670       assert (wait_condition is None or
 671               (wait_condition.shared and wait_condition in prioqueue))
 672     else:
 673       wait_condition = None
 674
 675     if wait_condition is None:
 676       if prioqueue is None:
 677         assert priority not in self.__pending_by_prio
 678
 679         prioqueue = []
 680         heapq.heappush(self.__pending, (priority, prioqueue))
 681         self.__pending_by_prio[priority] = prioqueue
 682
 683       wait_condition = self.__condition_class(self.__lock, shared)
 684       prioqueue.append(wait_condition)
 685
 686       if shared:
 687         # Keep reference for further shared acquires on same priority. This is
 688         # better than trying to find it in the list of pending acquires.
 689         assert priority not in self.__pending_shared
 690         self.__pending_shared[priority] = wait_condition
 691
 692     wait_start = self.__time_fn()
 693     acquired = False
 694
 695     try:
 696       # Wait until we become the topmost acquire in the queue or the timeout
 697       # expires.
 698       while True:
 699         if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
 700           self.__do_acquire(shared)
 701           acquired = True
 702           break
 703
 704         # A lot of code assumes blocking acquires always succeed, therefore we
 705         # can never return False for a blocking acquire
 706         if (timeout is not None and
 707             utils.TimeoutExpired(wait_start, timeout, _time_fn=self.__time_fn)):
 708           break
 709
 710         # Wait for notification
 711         wait_condition.wait(timeout)
 712         self.__check_deleted()
 713     finally:
 714       # Remove condition from queue if there are no more waiters
 715       if not wait_condition.has_waiting():
 716         prioqueue.remove(wait_condition)
 717         if wait_condition.shared:
 718           # Remove from list of shared acquires if it wasn't while releasing
 719           # (e.g. on lock deletion)
 720           self.__pending_shared.pop(priority, None)
 721
 722     return acquired
 723
 724   def acquire(self, shared=0, timeout=None, priority=None,
 725               test_notify=None):
 726     """Acquire a shared lock.
 727
 728     @type shared: integer (0/1) used as a boolean
 729     @param shared: whether to acquire in shared mode; by default an
 730         exclusive lock will be acquired
 731     @type timeout: float
 732     @param timeout: maximum waiting time before giving up
 733     @type priority: integer
 734     @param priority: Priority for acquiring lock
 735     @type test_notify: callable or None
 736     @param test_notify: Special callback function for unittesting
 737
 738     """
 739     if priority is None:
 740       priority = _DEFAULT_PRIORITY
 741
 742     self.__lock.acquire()
 743     try:
 744       # We already got the lock, notify now
 745       if __debug__ and callable(test_notify):
 746         test_notify()
 747
 748       return self.__acquire_unlocked(shared, timeout, priority)
 749     finally:
 750       self.__lock.release()
 751
 752   def downgrade(self):
 753     """Changes the lock mode from exclusive to shared.
 754
 755     Pending acquires in shared mode on the same priority will go ahead.
 756
 757     """
 758     self.__lock.acquire()
 759     try:
 760       assert self.__is_owned(), "Lock must be owned"
 761
 762       if self.__is_exclusive():
 763         # Do nothing if the lock is already acquired in shared mode
 764         self.__exc = None
 765         self.__do_acquire(1)
 766
 767         # Important: pending shared acquires should only jump ahead if there
 768         # was a transition from exclusive to shared, otherwise an owner of a
 769         # shared lock can keep calling this function to push incoming shared
 770         # acquires
 771         (priority, prioqueue) = self.__find_first_pending_queue()
 772         if prioqueue:
 773           # Is there a pending shared acquire on this priority?
 774           cond = self.__pending_shared.pop(priority, None)
 775           if cond:
 776             assert cond.shared
 777             assert cond in prioqueue
 778
 779             # Ensure shared acquire is on top of queue
 780             if len(prioqueue) > 1:
 781               prioqueue.remove(cond)
 782               prioqueue.insert(0, cond)
 783
 784             # Notify
 785             cond.notifyAll()
 786
 787       assert not self.__is_exclusive()
 788       assert self.__is_sharer()
 789
 790       return True
 791     finally:
 792       self.__lock.release()
 793
 794   def release(self):
 795     """Release a Shared Lock.
 796
 797     You must have acquired the lock, either in shared or in exclusive mode,
 798     before calling this function.
 799
 800     """
 801     self.__lock.acquire()
 802     try:
 803       assert self.__is_exclusive() or self.__is_sharer(), \
 804         "Cannot release non-owned lock"
 805
 806       # Autodetect release type
 807       if self.__is_exclusive():
 808         self.__exc = None
 809         notify = True
 810       else:
 811         self.__shr.remove(threading.currentThread())
 812         notify = not self.__shr
 813
 814       # Notify topmost condition in queue if there are no owners left (for
 815       # shared locks)
 816       if notify:
 817         self.__notify_topmost()
 818     finally:
 819       self.__lock.release()
 820
 821   def __notify_topmost(self):
 822     """Notifies topmost condition in queue of pending acquires.
 823
 824     """
 825     (priority, prioqueue) = self.__find_first_pending_queue()
 826     if prioqueue:
 827       cond = prioqueue[0]
 828       cond.notifyAll()
 829       if cond.shared:
 830         # Prevent further shared acquires from sneaking in while waiters are
 831         # notified
 832         self.__pending_shared.pop(priority, None)
 833
 834   def _notify_topmost(self):
 835     """Exported version of L{__notify_topmost}.
 836
 837     """
 838     self.__lock.acquire()
 839     try:
 840       return self.__notify_topmost()
 841     finally:
 842       self.__lock.release()
 843
 844   def delete(self, timeout=None, priority=None):
 845     """Delete a Shared Lock.
 846
 847     This operation will declare the lock for removal. First the lock will be
 848     acquired in exclusive mode if you don't already own it, then the lock
 849     will be put in a state where any future and pending acquire() fail.
 850
 851     @type timeout: float
 852     @param timeout: maximum waiting time before giving up
 853     @type priority: integer
 854     @param priority: Priority for acquiring lock
 855
 856     """
 857     if priority is None:
 858       priority = _DEFAULT_PRIORITY
 859
 860     self.__lock.acquire()
 861     try:
 862       assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"
 863
 864       self.__check_deleted()
 865
 866       # The caller is allowed to hold the lock exclusively already.
 867       acquired = self.__is_exclusive()
 868
 869       if not acquired:
 870         acquired = self.__acquire_unlocked(0, timeout, priority)
 871
 872       if acquired:
 873         assert self.__is_exclusive() and not self.__is_sharer(), \
 874           "Lock wasn't acquired in exclusive mode"
 875
 876         self.__deleted = True
 877         self.__exc = None
 878
 879         assert not (self.__exc or self.__shr), "Found owner during deletion"
 880
 881         # Notify all acquires. They'll throw an error.
 882         for (_, prioqueue) in self.__pending:
 883           for cond in prioqueue:
 884             cond.notifyAll()
 885
 886         assert self.__deleted
 887
 888       return acquired
 889     finally:
 890       self.__lock.release()
 891
 892   def _release_save(self):
 893     shared = self.__is_sharer()
 894     self.release()
 895     return shared
 896
 897   def _acquire_restore(self, shared):
 898     self.acquire(shared=shared)
 899
 900
 901 # Whenever we want to acquire a full LockSet we pass None as the value
 902 # to acquire.  Hide this behind this nicely named constant.
 903 ALL_SET = None
 904
 905
 906 class _AcquireTimeout(Exception):
 907   """Internal exception to abort an acquire on a timeout.
 908
 909   """
 910
 911
 912 class LockSet:
 913   """Implements a set of locks.
 914
 915   This abstraction implements a set of shared locks for the same resource type,
 916   distinguished by name. The user can lock a subset of the resources and the
 917   LockSet will take care of acquiring the locks always in the same order, thus
 918   preventing deadlock.
 919
 920   All the locks needed in the same set must be acquired together, though.
 921
 922   @type name: string
 923   @ivar name: the name of the lockset
 924
 925   """
 926   def __init__(self, members, name, monitor=None):
 927     """Constructs a new LockSet.
 928
 929     @type members: list of strings
 930     @param members: initial members of the set
 931     @type monitor: L{LockMonitor}
 932     @param monitor: Lock monitor with which to register member locks
 933
 934     """
 935     assert members is not None, "members parameter is not a list"
 936     self.name = name
 937
 938     # Lock monitor
 939     self.__monitor = monitor
 940
 941     # Used internally to guarantee coherency
 942     self.__lock = SharedLock(self._GetLockName("[lockset]"), monitor=monitor)
 943
 944     # The lockdict indexes the relationship name -> lock
 945     # The order-of-locking is implied by the alphabetical order of names
 946     self.__lockdict = {}
 947
 948     for mname in members:
 949       self.__lockdict[mname] = SharedLock(self._GetLockName(mname),
 950                                           monitor=monitor)
 951
 952     # The owner dict contains the set of locks each thread owns. For
 953     # performance each thread can access its own key without a global lock on
 954     # this structure. It is paramount though that *no* other type of access is
 955     # done to this structure (eg. no looping over its keys). *_owner helper
 956     # function are defined to guarantee access is correct, but in general never
 957     # do anything different than __owners[threading.currentThread()], or there
 958     # will be trouble.
 959     self.__owners = {}
 960
 961   def _GetLockName(self, mname):
 962     """Returns the name for a member lock.
 963
 964     """
 965     return "%s/%s" % (self.name, mname)
 966
 967   def _get_lock(self):
 968     """Returns the lockset-internal lock.
 969
 970     """
 971     return self.__lock
 972
 973   def _get_lockdict(self):
 974     """Returns the lockset-internal lock dictionary.
 975
 976     Accessing this structure is only safe in single-thread usage or when the
 977     lockset-internal lock is held.
 978
 979     """
 980     return self.__lockdict
 981
 982   def is_owned(self):
 983     """Is the current thread a current level owner?
 984
 985     @note: Use L{check_owned} to check if a specific lock is held
 986
 987     """
 988     return threading.currentThread() in self.__owners
 989
 990   def check_owned(self, names, shared=-1):
 991     """Check if locks are owned in a specific mode.
 992
 993     @type names: sequence or string
 994     @param names: Lock names (or a single lock name)
 995     @param shared: See L{SharedLock.is_owned}
 996     @rtype: bool
 997     @note: Use L{is_owned} to check if the current thread holds I{any} lock and
 998       L{list_owned} to get the names of all owned locks
 999
1000     """
1001     if isinstance(names, basestring):
1002       names = [names]
1003
1004     # Avoid check if no locks are owned anyway
1005     if names and self.is_owned():
1006       candidates = []
1007
1008       # Gather references to all locks (in case they're deleted in the meantime)
1009       for lname in names:
1010         try:
1011           lock = self.__lockdict[lname]
1012         except KeyError:
1013           raise errors.LockError("Non-existing lock '%s' in set '%s' (it may"
1014                                  " have been removed)" % (lname, self.name))
1015         else:
1016           candidates.append(lock)
1017
1018       return compat.all(lock.is_owned(shared=shared) for lock in candidates)
1019     else:
1020       return False
1021
1022   def _add_owned(self, name=None):
1023     """Note the current thread owns the given lock"""
1024     if name is None:
1025       if not self.is_owned():
1026         self.__owners[threading.currentThread()] = set()
1027     else:
1028       if self.is_owned():
1029         self.__owners[threading.currentThread()].add(name)
1030       else:
1031         self.__owners[threading.currentThread()] = set([name])
1032
1033   def _del_owned(self, name=None):
1034     """Note the current thread owns the given lock"""
1035
1036     assert not (name is None and self.__lock.is_owned()), \
1037            "Cannot hold internal lock when deleting owner status"
1038
1039     if name is not None:
1040       self.__owners[threading.currentThread()].remove(name)
1041
1042     # Only remove the key if we don't hold the set-lock as well
1043     if (not self.__lock.is_owned() and
1044         not self.__owners[threading.currentThread()]):
1045       del self.__owners[threading.currentThread()]
1046
1047   def list_owned(self):
1048     """Get the set of resource names owned by the current thread"""
1049     if self.is_owned():
1050       return self.__owners[threading.currentThread()].copy()
1051     else:
1052       return set()
1053
1054   def _release_and_delete_owned(self):
1055     """Release and delete all resources owned by the current thread"""
1056     for lname in self.list_owned():
1057       lock = self.__lockdict[lname]
1058       if lock.is_owned():
1059         lock.release()
1060       self._del_owned(name=lname)
1061
1062   def __names(self):
1063     """Return the current set of names.
1064
1065     Only call this function while holding __lock and don't iterate on the
1066     result after releasing the lock.
1067
1068     """
1069     return self.__lockdict.keys()
1070
1071   def _names(self):
1072     """Return a copy of the current set of elements.
1073
1074     Used only for debugging purposes.
1075
1076     """
1077     # If we don't already own the set-level lock acquired
1078     # we'll get it and note we need to release it later.
1079     release_lock = False
1080     if not self.__lock.is_owned():
1081       release_lock = True
1082       self.__lock.acquire(shared=1)
1083     try:
1084       result = self.__names()
1085     finally:
1086       if release_lock:
1087         self.__lock.release()
1088     return set(result)
1089
1090   def acquire(self, names, timeout=None, shared=0, priority=None,
1091               test_notify=None):
1092     """Acquire a set of resource locks.
1093
1094     @type names: list of strings (or string)
1095     @param names: the names of the locks which shall be acquired
1096         (special lock names, or instance/node names)
1097     @type shared: integer (0/1) used as a boolean
1098     @param shared: whether to acquire in shared mode; by default an
1099         exclusive lock will be acquired
1100     @type timeout: float or None
1101     @param timeout: Maximum time to acquire all locks
1102     @type priority: integer
1103     @param priority: Priority for acquiring locks
1104     @type test_notify: callable or None
1105     @param test_notify: Special callback function for unittesting
1106
1107     @return: Set of all locks successfully acquired or None in case of timeout
1108
1109     @raise errors.LockError: when any lock we try to acquire has
1110         been deleted before we succeed. In this case none of the
1111         locks requested will be acquired.
1112
1113     """
1114     assert timeout is None or timeout >= 0.0
1115
1116     # Check we don't already own locks at this level
1117     assert not self.is_owned(), ("Cannot acquire locks in the same set twice"
1118                                  " (lockset %s)" % self.name)
1119
1120     if priority is None:
1121       priority = _DEFAULT_PRIORITY
1122
1123     # We need to keep track of how long we spent waiting for a lock. The
1124     # timeout passed to this function is over all lock acquires.
1125     running_timeout = utils.RunningTimeout(timeout, False)
1126
1127     try:
1128       if names is not None:
1129         # Support passing in a single resource to acquire rather than many
1130         if isinstance(names, basestring):
1131           names = [names]
1132
1133         return self.__acquire_inner(names, False, shared, priority,
1134                                     running_timeout.Remaining, test_notify)
1135
1136       else:
1137         # If no names are given acquire the whole set by not letting new names
1138         # being added before we release, and getting the current list of names.
1139         # Some of them may then be deleted later, but we'll cope with this.
1140         #
1141         # We'd like to acquire this lock in a shared way, as it's nice if
1142         # everybody else can use the instances at the same time. If we are
1143         # acquiring them exclusively though they won't be able to do this
1144         # anyway, though, so we'll get the list lock exclusively as well in
1145         # order to be able to do add() on the set while owning it.
1146         if not self.__lock.acquire(shared=shared, priority=priority,
1147                                    timeout=running_timeout.Remaining()):
1148           raise _AcquireTimeout()
1149         try:
1150           # note we own the set-lock
1151           self._add_owned()
1152
1153           return self.__acquire_inner(self.__names(), True, shared, priority,
1154                                       running_timeout.Remaining, test_notify)
1155         except:
1156           # We shouldn't have problems adding the lock to the owners list, but
1157           # if we did we'll try to release this lock and re-raise exception.
1158           # Of course something is going to be really wrong, after this.
1159           self.__lock.release()
1160           self._del_owned()
1161           raise
1162
1163     except _AcquireTimeout:
1164       return None
1165
1166   def __acquire_inner(self, names, want_all, shared, priority,
1167                       timeout_fn, test_notify):
1168     """Inner logic for acquiring a number of locks.
1169
1170     @param names: Names of the locks to be acquired
1171     @param want_all: Whether all locks in the set should be acquired
1172     @param shared: Whether to acquire in shared mode
1173     @param timeout_fn: Function returning remaining timeout
1174     @param priority: Priority for acquiring locks
1175     @param test_notify: Special callback function for unittesting
1176
1177     """
1178     acquire_list = []
1179
1180     # First we look the locks up on __lockdict. We have no way of being sure
1181     # they will still be there after, but this makes it a lot faster should
1182     # just one of them be the already wrong. Using a sorted sequence to prevent
1183     # deadlocks.
1184     for lname in sorted(utils.UniqueSequence(names)):
1185       try:
1186         lock = self.__lockdict[lname] # raises KeyError if lock is not there
1187       except KeyError:
1188         if want_all:
1189           # We are acquiring all the set, it doesn't matter if this particular
1190           # element is not there anymore.
1191           continue
1192
1193         raise errors.LockError("Non-existing lock %s in set %s (it may have"
1194                                " been removed)" % (lname, self.name))
1195
1196       acquire_list.append((lname, lock))
1197
1198     # This will hold the locknames we effectively acquired.
1199     acquired = set()
1200
1201     try:
1202       # Now acquire_list contains a sorted list of resources and locks we
1203       # want.  In order to get them we loop on this (private) list and
1204       # acquire() them.  We gave no real guarantee they will still exist till
1205       # this is done but .acquire() itself is safe and will alert us if the
1206       # lock gets deleted.
1207       for (lname, lock) in acquire_list:
1208         if __debug__ and callable(test_notify):
1209           test_notify_fn = lambda: test_notify(lname)
1210         else:
1211           test_notify_fn = None
1212
1213         timeout = timeout_fn()
1214
1215         try:
1216           # raises LockError if the lock was deleted
1217           acq_success = lock.acquire(shared=shared, timeout=timeout,
1218                                      priority=priority,
1219                                      test_notify=test_notify_fn)
1220         except errors.LockError:
1221           if want_all:
1222             # We are acquiring all the set, it doesn't matter if this
1223             # particular element is not there anymore.
1224             continue
1225
1226           raise errors.LockError("Non-existing lock %s in set %s (it may"
1227                                  " have been removed)" % (lname, self.name))
1228
1229         if not acq_success:
1230           # Couldn't get lock or timeout occurred
1231           if timeout is None:
1232             # This shouldn't happen as SharedLock.acquire(timeout=None) is
1233             # blocking.
1234             raise errors.LockError("Failed to get lock %s (set %s)" %
1235                                    (lname, self.name))
1236
1237           raise _AcquireTimeout()
1238
1239         try:
1240           # now the lock cannot be deleted, we have it!
1241           self._add_owned(name=lname)
1242           acquired.add(lname)
1243
1244         except:
1245           # We shouldn't have problems adding the lock to the owners list, but
1246           # if we did we'll try to release this lock and re-raise exception.
1247           # Of course something is going to be really wrong after this.
1248           if lock.is_owned():
1249             lock.release()
1250           raise
1251
1252     except:
1253       # Release all owned locks
1254       self._release_and_delete_owned()
1255       raise
1256
1257     return acquired
1258
1259   def downgrade(self, names=None):
1260     """Downgrade a set of resource locks from exclusive to shared mode.
1261
1262     The locks must have been acquired in exclusive mode.
1263
1264     """
1265     assert self.is_owned(), ("downgrade on lockset %s while not owning any"
1266                              " lock" % self.name)
1267
1268     # Support passing in a single resource to downgrade rather than many
1269     if isinstance(names, basestring):
1270       names = [names]
1271
1272     owned = self.list_owned()
1273
1274     if names is None:
1275       names = owned
1276     else:
1277       names = set(names)
1278       assert owned.issuperset(names), \
1279         ("downgrade() on unheld resources %s (set %s)" %
1280          (names.difference(owned), self.name))
1281
1282     for lockname in names:
1283       self.__lockdict[lockname].downgrade()
1284
1285     # Do we own the lockset in exclusive mode?
1286     if self.__lock.is_owned(shared=0):
1287       # Have all locks been downgraded?
1288       if not compat.any(lock.is_owned(shared=0)
1289                         for lock in self.__lockdict.values()):
1290         self.__lock.downgrade()
1291         assert self.__lock.is_owned(shared=1)
1292
1293     return True
1294
1295   def release(self, names=None):
1296     """Release a set of resource locks, at the same level.
1297
1298     You must have acquired the locks, either in shared or in exclusive mode,
1299     before releasing them.
1300
1301     @type names: list of strings, or None
1302     @param names: the names of the locks which shall be released
1303         (defaults to all the locks acquired at that level).
1304
1305     """
1306     assert self.is_owned(), ("release() on lock set %s while not owner" %
1307                              self.name)
1308
1309     # Support passing in a single resource to release rather than many
1310     if isinstance(names, basestring):
1311       names = [names]
1312
1313     if names is None:
1314       names = self.list_owned()
1315     else:
1316       names = set(names)
1317       assert self.list_owned().issuperset(names), (
1318                "release() on unheld resources %s (set %s)" %
1319                (names.difference(self.list_owned()), self.name))
1320
1321     # First of all let's release the "all elements" lock, if set.
1322     # After this 'add' can work again
1323     if self.__lock.is_owned():
1324       self.__lock.release()
1325       self._del_owned()
1326
1327     for lockname in names:
1328       # If we are sure the lock doesn't leave __lockdict without being
1329       # exclusively held we can do this...
1330       self.__lockdict[lockname].release()
1331       self._del_owned(name=lockname)
1332
1333   def add(self, names, acquired=0, shared=0):
1334     """Add a new set of elements to the set
1335
1336     @type names: list of strings
1337     @param names: names of the new elements to add
1338     @type acquired: integer (0/1) used as a boolean
1339     @param acquired: pre-acquire the new resource?
1340     @type shared: integer (0/1) used as a boolean
1341     @param shared: is the pre-acquisition shared?
1342
1343     """
1344     # Check we don't already own locks at this level
1345     assert not self.is_owned() or self.__lock.is_owned(shared=0), \
1346       ("Cannot add locks if the set %s is only partially owned, or shared" %
1347        self.name)
1348
1349     # Support passing in a single resource to add rather than many
1350     if isinstance(names, basestring):
1351       names = [names]
1352
1353     # If we don't already own the set-level lock acquired in an exclusive way
1354     # we'll get it and note we need to release it later.
1355     release_lock = False
1356     if not self.__lock.is_owned():
1357       release_lock = True
1358       self.__lock.acquire()
1359
1360     try:
1361       invalid_names = set(self.__names()).intersection(names)
1362       if invalid_names:
1363         # This must be an explicit raise, not an assert, because assert is
1364         # turned off when using optimization, and this can happen because of
1365         # concurrency even if the user doesn't want it.
1366         raise errors.LockError("duplicate add(%s) on lockset %s" %
1367                                (invalid_names, self.name))
1368
1369       for lockname in names:
1370         lock = SharedLock(self._GetLockName(lockname), monitor=self.__monitor)
1371
1372         if acquired:
1373           # No need for priority or timeout here as this lock has just been
1374           # created
1375           lock.acquire(shared=shared)
1376           # now the lock cannot be deleted, we have it!
1377           try:
1378             self._add_owned(name=lockname)
1379           except:
1380             # We shouldn't have problems adding the lock to the owners list,
1381             # but if we did we'll try to release this lock and re-raise
1382             # exception.  Of course something is going to be really wrong,
1383             # after this.  On the other hand the lock hasn't been added to the
1384             # __lockdict yet so no other threads should be pending on it. This
1385             # release is just a safety measure.
1386             lock.release()
1387             raise
1388
1389         self.__lockdict[lockname] = lock
1390
1391     finally:
1392       # Only release __lock if we were not holding it previously.
1393       if release_lock:
1394         self.__lock.release()
1395
1396     return True
1397
1398   def remove(self, names):
1399     """Remove elements from the lock set.
1400
1401     You can either not hold anything in the lockset or already hold a superset
1402     of the elements you want to delete, exclusively.
1403
1404     @type names: list of strings
1405     @param names: names of the resource to remove.
1406
1407     @return: a list of locks which we removed; the list is always
1408         equal to the names list if we were holding all the locks
1409         exclusively
1410
1411     """
1412     # Support passing in a single resource to remove rather than many
1413     if isinstance(names, basestring):
1414       names = [names]
1415
1416     # If we own any subset of this lock it must be a superset of what we want
1417     # to delete. The ownership must also be exclusive, but that will be checked
1418     # by the lock itself.
1419     assert not self.is_owned() or self.list_owned().issuperset(names), (
1420       "remove() on acquired lockset %s while not owning all elements" %
1421       self.name)
1422
1423     removed = []
1424
1425     for lname in names:
1426       # Calling delete() acquires the lock exclusively if we don't already own
1427       # it, and causes all pending and subsequent lock acquires to fail. It's
1428       # fine to call it out of order because delete() also implies release(),
1429       # and the assertion above guarantees that if we either already hold
1430       # everything we want to delete, or we hold none.
1431       try:
1432         self.__lockdict[lname].delete()
1433         removed.append(lname)
1434       except (KeyError, errors.LockError):
1435         # This cannot happen if we were already holding it, verify:
1436         assert not self.is_owned(), ("remove failed while holding lockset %s" %
1437                                      self.name)
1438       else:
1439         # If no LockError was raised we are the ones who deleted the lock.
1440         # This means we can safely remove it from lockdict, as any further or
1441         # pending delete() or acquire() will fail (and nobody can have the lock
1442         # since before our call to delete()).
1443         #
1444         # This is done in an else clause because if the exception was thrown
1445         # it's the job of the one who actually deleted it.
1446         del self.__lockdict[lname]
1447         # And let's remove it from our private list if we owned it.
1448         if self.is_owned():
1449           self._del_owned(name=lname)
1450
1451     return removed
1452
1453
1454 # Locking levels, must be acquired in increasing order.
1455 # Current rules are:
1456 #   - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
1457 #   acquired before performing any operation, either in shared or in exclusive
1458 #   mode. acquiring the BGL in exclusive mode is discouraged and should be
1459 #   avoided.
1460 #   - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
1461 #   If you need more than one node, or more than one instance, acquire them at
1462 #   the same time.
1463 LEVEL_CLUSTER = 0
1464 LEVEL_INSTANCE = 1
1465 LEVEL_NODEGROUP = 2
1466 LEVEL_NODE = 3
1467 #: Level for node resources, used for operations with possibly high impact on
1468 #: the node's disks.
1469 LEVEL_NODE_RES = 4
1470
1471 LEVELS = [
1472   LEVEL_CLUSTER,
1473   LEVEL_INSTANCE,
1474   LEVEL_NODEGROUP,
1475   LEVEL_NODE,
1476   LEVEL_NODE_RES,
1477   ]
1478
1479 # Lock levels which are modifiable
1480 LEVELS_MOD = frozenset([
1481   LEVEL_NODE_RES,
1482   LEVEL_NODE,
1483   LEVEL_NODEGROUP,
1484   LEVEL_INSTANCE,
1485   ])
1486
1487 #: Lock level names (make sure to use singular form)
1488 LEVEL_NAMES = {
1489   LEVEL_CLUSTER: "cluster",
1490   LEVEL_INSTANCE: "instance",
1491   LEVEL_NODEGROUP: "nodegroup",
1492   LEVEL_NODE: "node",
1493   LEVEL_NODE_RES: "node-res",
1494   }
1495
1496 # Constant for the big ganeti lock
1497 BGL = "BGL"
1498
1499
1500 class GanetiLockManager:
1501   """The Ganeti Locking Library
1502
1503   The purpose of this small library is to manage locking for ganeti clusters
1504   in a central place, while at the same time doing dynamic checks against
1505   possible deadlocks. It will also make it easier to transition to a different
1506   lock type should we migrate away from python threads.
1507
1508   """
1509   _instance = None
1510
1511   def __init__(self, nodes, nodegroups, instances):
1512     """Constructs a new GanetiLockManager object.
1513
1514     There should be only a GanetiLockManager object at any time, so this
1515     function raises an error if this is not the case.
1516
1517     @param nodes: list of node names
1518     @param nodegroups: list of nodegroup uuids
1519     @param instances: list of instance names
1520
1521     """
1522     assert self.__class__._instance is None, \
1523            "double GanetiLockManager instance"
1524
1525     self.__class__._instance = self
1526
1527     self._monitor = LockMonitor()
1528
1529     # The keyring contains all the locks, at their level and in the correct
1530     # locking order.
1531     self.__keyring = {
1532       LEVEL_CLUSTER: LockSet([BGL], "cluster", monitor=self._monitor),
1533       LEVEL_NODE: LockSet(nodes, "node", monitor=self._monitor),
1534       LEVEL_NODE_RES: LockSet(nodes, "node-res", monitor=self._monitor),
1535       LEVEL_NODEGROUP: LockSet(nodegroups, "nodegroup", monitor=self._monitor),
1536       LEVEL_INSTANCE: LockSet(instances, "instance",
1537                               monitor=self._monitor),
1538       }
1539
1540     assert compat.all(ls.name == LEVEL_NAMES[level]
1541                       for (level, ls) in self.__keyring.items())
1542
1543   def AddToLockMonitor(self, provider):
1544     """Registers a new lock with the monitor.
1545
1546     See L{LockMonitor.RegisterLock}.
1547
1548     """
1549     return self._monitor.RegisterLock(provider)
1550
1551   def QueryLocks(self, fields):
1552     """Queries information from all locks.
1553
1554     See L{LockMonitor.QueryLocks}.
1555
1556     """
1557     return self._monitor.QueryLocks(fields)
1558
1559   def _names(self, level):
1560     """List the lock names at the given level.
1561
1562     This can be used for debugging/testing purposes.
1563
1564     @param level: the level whose list of locks to get
1565
1566     """
1567     assert level in LEVELS, "Invalid locking level %s" % level
1568     return self.__keyring[level]._names()
1569
1570   def is_owned(self, level):
1571     """Check whether we are owning locks at the given level
1572
1573     """
1574     return self.__keyring[level].is_owned()
1575
1576   def list_owned(self, level):
1577     """Get the set of owned locks at the given level
1578
1579     """
1580     return self.__keyring[level].list_owned()
1581
1582   def check_owned(self, level, names, shared=-1):
1583     """Check if locks at a certain level are owned in a specific mode.
1584
1585     @see: L{LockSet.check_owned}
1586
1587     """
1588     return self.__keyring[level].check_owned(names, shared=shared)
1589
1590   def _upper_owned(self, level):
1591     """Check that we don't own any lock at a level greater than the given one.
1592
1593     """
1594     # This way of checking only works if LEVELS[i] = i, which we check for in
1595     # the test cases.
1596     return compat.any((self.is_owned(l) for l in LEVELS[level + 1:]))
1597
1598   def _BGL_owned(self): # pylint: disable=C0103
1599     """Check if the current thread owns the BGL.
1600
1601     Both an exclusive or a shared acquisition work.
1602
1603     """
1604     return BGL in self.__keyring[LEVEL_CLUSTER].list_owned()
1605
1606   @staticmethod
1607   def _contains_BGL(level, names): # pylint: disable=C0103
1608     """Check if the level contains the BGL.
1609
1610     Check if acting on the given level and set of names will change
1611     the status of the Big Ganeti Lock.
1612
1613     """
1614     return level == LEVEL_CLUSTER and (names is None or BGL in names)
1615
1616   def acquire(self, level, names, timeout=None, shared=0, priority=None):
1617     """Acquire a set of resource locks, at the same level.
1618
1619     @type level: member of locking.LEVELS
1620     @param level: the level at which the locks shall be acquired
1621     @type names: list of strings (or string)
1622     @param names: the names of the locks which shall be acquired
1623         (special lock names, or instance/node names)
1624     @type shared: integer (0/1) used as a boolean
1625     @param shared: whether to acquire in shared mode; by default
1626         an exclusive lock will be acquired
1627     @type timeout: float
1628     @param timeout: Maximum time to acquire all locks
1629     @type priority: integer
1630     @param priority: Priority for acquiring lock
1631
1632     """
1633     assert level in LEVELS, "Invalid locking level %s" % level
1634
1635     # Check that we are either acquiring the Big Ganeti Lock or we already own
1636     # it. Some "legacy" opcodes need to be sure they are run non-concurrently
1637     # so even if we've migrated we need to at least share the BGL to be
1638     # compatible with them. Of course if we own the BGL exclusively there's no
1639     # point in acquiring any other lock, unless perhaps we are half way through
1640     # the migration of the current opcode.
1641     assert (self._contains_BGL(level, names) or self._BGL_owned()), (
1642       "You must own the Big Ganeti Lock before acquiring any other")
1643
1644     # Check we don't own locks at the same or upper levels.
1645     assert not self._upper_owned(level), ("Cannot acquire locks at a level"
1646                                           " while owning some at a greater one")
1647
1648     # Acquire the locks in the set.
1649     return self.__keyring[level].acquire(names, shared=shared, timeout=timeout,
1650                                          priority=priority)
1651
1652   def downgrade(self, level, names=None):
1653     """Downgrade a set of resource locks from exclusive to shared mode.
1654
1655     You must have acquired the locks in exclusive mode.
1656
1657     @type level: member of locking.LEVELS
1658     @param level: the level at which the locks shall be downgraded
1659     @type names: list of strings, or None
1660     @param names: the names of the locks which shall be downgraded
1661         (defaults to all the locks acquired at the level)
1662
1663     """
1664     assert level in LEVELS, "Invalid locking level %s" % level
1665
1666     return self.__keyring[level].downgrade(names=names)
1667
1668   def release(self, level, names=None):
1669     """Release a set of resource locks, at the same level.
1670
1671     You must have acquired the locks, either in shared or in exclusive
1672     mode, before releasing them.
1673
1674     @type level: member of locking.LEVELS
1675     @param level: the level at which the locks shall be released
1676     @type names: list of strings, or None
1677     @param names: the names of the locks which shall be released
1678         (defaults to all the locks acquired at that level)
1679
1680     """
1681     assert level in LEVELS, "Invalid locking level %s" % level
1682     assert (not self._contains_BGL(level, names) or
1683             not self._upper_owned(LEVEL_CLUSTER)), (
1684               "Cannot release the Big Ganeti Lock while holding something"
1685               " at upper levels (%r)" %
1686               (utils.CommaJoin(["%s=%r" % (LEVEL_NAMES[i], self.list_owned(i))
1687                                 for i in self.__keyring.keys()]), ))
1688
1689     # Release will complain if we don't own the locks already
1690     return self.__keyring[level].release(names)
1691
1692   def add(self, level, names, acquired=0, shared=0):
1693     """Add locks at the specified level.
1694
1695     @type level: member of locking.LEVELS_MOD
1696     @param level: the level at which the locks shall be added
1697     @type names: list of strings
1698     @param names: names of the locks to acquire
1699     @type acquired: integer (0/1) used as a boolean
1700     @param acquired: whether to acquire the newly added locks
1701     @type shared: integer (0/1) used as a boolean
1702     @param shared: whether the acquisition will be shared
1703
1704     """
1705     assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1706     assert self._BGL_owned(), ("You must own the BGL before performing other"
1707                                " operations")
1708     assert not self._upper_owned(level), ("Cannot add locks at a level"
1709                                           " while owning some at a greater one")
1710     return self.__keyring[level].add(names, acquired=acquired, shared=shared)
1711
1712   def remove(self, level, names):
1713     """Remove locks from the specified level.
1714
1715     You must either already own the locks you are trying to remove
1716     exclusively or not own any lock at an upper level.
1717
1718     @type level: member of locking.LEVELS_MOD
1719     @param level: the level at which the locks shall be removed
1720     @type names: list of strings
1721     @param names: the names of the locks which shall be removed
1722         (special lock names, or instance/node names)
1723
1724     """
1725     assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
1726     assert self._BGL_owned(), ("You must own the BGL before performing other"
1727                                " operations")
1728     # Check we either own the level or don't own anything from here
1729     # up. LockSet.remove() will check the case in which we don't own
1730     # all the needed resources, or we have a shared ownership.
1731     assert self.is_owned(level) or not self._upper_owned(level), (
1732            "Cannot remove locks at a level while not owning it or"
1733            " owning some at a greater one")
1734     return self.__keyring[level].remove(names)
1735
1736
1737 def _MonitorSortKey((item, idx, num)):
1738   """Sorting key function.
1739
1740   Sort by name, registration order and then order of information. This provides
1741   a stable sort order over different providers, even if they return the same
1742   name.
1743
1744   """
1745   (name, _, _, _) = item
1746
1747   return (utils.NiceSortKey(name), num, idx)
1748
1749
1750 class LockMonitor(object):
1751   _LOCK_ATTR = "_lock"
1752
1753   def __init__(self):
1754     """Initializes this class.
1755
1756     """
1757     self._lock = SharedLock("LockMonitor")
1758
1759     # Counter for stable sorting
1760     self._counter = itertools.count(0)
1761
1762     # Tracked locks. Weak references are used to avoid issues with circular
1763     # references and deletion.
1764     self._locks = weakref.WeakKeyDictionary()
1765
1766   @ssynchronized(_LOCK_ATTR)
1767   def RegisterLock(self, provider):
1768     """Registers a new lock.
1769
1770     @param provider: Object with a callable method named C{GetLockInfo}, taking
1771       a single C{set} containing the requested information items
1772     @note: It would be nicer to only receive the function generating the
1773       requested information but, as it turns out, weak references to bound
1774       methods (e.g. C{self.GetLockInfo}) are tricky; there are several
1775       workarounds, but none of the ones I found works properly in combination
1776       with a standard C{WeakKeyDictionary}
1777
1778     """
1779     assert provider not in self._locks, "Duplicate registration"
1780
1781     # There used to be a check for duplicate names here. As it turned out, when
1782     # a lock is re-created with the same name in a very short timeframe, the
1783     # previous instance might not yet be removed from the weakref dictionary.
1784     # By keeping track of the order of incoming registrations, a stable sort
1785     # ordering can still be guaranteed.
1786
1787     self._locks[provider] = self._counter.next()
1788
1789   def _GetLockInfo(self, requested):
1790     """Get information from all locks.
1791
1792     """
1793     # Must hold lock while getting consistent list of tracked items
1794     self._lock.acquire(shared=1)
1795     try:
1796       items = self._locks.items()
1797     finally:
1798       self._lock.release()
1799
1800     return [(info, idx, num)
1801             for (provider, num) in items
1802             for (idx, info) in enumerate(provider.GetLockInfo(requested))]
1803
1804   def _Query(self, fields):
1805     """Queries information from all locks.
1806
1807     @type fields: list of strings
1808     @param fields: List of fields to return
1809
1810     """
1811     qobj = query.Query(query.LOCK_FIELDS, fields)
1812
1813     # Get all data with internal lock held and then sort by name and incoming
1814     # order
1815     lockinfo = sorted(self._GetLockInfo(qobj.RequestedData()),
1816                       key=_MonitorSortKey)
1817
1818     # Extract lock information and build query data
1819     return (qobj, query.LockQueryData(map(compat.fst, lockinfo)))
1820
1821   def QueryLocks(self, fields):
1822     """Queries information from all locks.
1823
1824     @type fields: list of strings
1825     @param fields: List of fields to return
1826
1827     """
1828     (qobj, ctx) = self._Query(fields)
1829
1830     # Prepare query response
1831     return query.GetQueryResponse(qobj, ctx)