Instance policy command line support

[ganeti-local] / lib / locking.py

diff --git a/lib/locking.py b/lib/locking.py
index 901fdac..e5861c5 100644 (file)
--- a/lib/locking.py
+++ b/lib/locking.py
@@ -1,7 +1,7 @@
 #
 #
 
 #
 #
 

-# Copyright (C) 2006, 2007 Google Inc.
+# Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Google Inc.

 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by

@@ -20,26 +20,52 @@
 
 """Module implementing the Ganeti locking code."""
 
 
 """Module implementing the Ganeti locking code."""
 

+# pylint: disable=W0212
+
+# W0212 since e.g. LockSet methods use (a lot) the internals of
+# SharedLock
+

 import os
 import select
 import threading
 import os
 import select
 import threading

-import time

 import errno
 import errno

+import weakref
+import logging
+import heapq
+import itertools

 
 from ganeti import errors
 from ganeti import utils
 
 from ganeti import errors
 from ganeti import utils

+from ganeti import compat
+from ganeti import query
+
+
+_EXCLUSIVE_TEXT = "exclusive"
+_SHARED_TEXT = "shared"
+_DELETED_TEXT = "deleted"

 
 

+_DEFAULT_PRIORITY = 0

 
 

-def ssynchronized(lock, shared=0):
+
+def ssynchronized(mylock, shared=0):

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

+  @type mylock: lockable object or string
+  @param mylock: lock to acquire or class member name of the lock to acquire
+

   """
   def wrap(fn):
     def sync_function(*args, **kwargs):
   """
   def wrap(fn):
     def sync_function(*args, **kwargs):

+      if isinstance(mylock, basestring):
+        assert args, "cannot ssynchronize on non-class method: self not found"
+        # args[0] is "self"
+        lock = getattr(args[0], mylock)
+      else:
+        lock = mylock

       lock.acquire(shared=shared)
       try:
         return fn(*args, **kwargs)
       lock.acquire(shared=shared)
       try:
         return fn(*args, **kwargs)

@@ -49,21 +75,18 @@ def ssynchronized(lock, shared=0):
   return wrap
 
 
   return wrap
 
 

-class _SingleActionPipeConditionWaiter(object):
-  """Callable helper class for _SingleActionPipeCondition.
+class _SingleNotifyPipeConditionWaiter(object):
+  """Helper class for SingleNotifyPipeCondition

 
   """
   __slots__ = [
 
   """
   __slots__ = [

-    "_cond",

     "_fd",
     "_poller",
     ]
 
     "_fd",
     "_poller",
     ]
 

-  def __init__(self, cond, poller, fd):
-    """Initializes this class.
+  def __init__(self, poller, fd):
+    """Constructor for _SingleNotifyPipeConditionWaiter

 
 

-    @type cond: L{_SingleActionPipeCondition}
-    @param cond: Parent condition

     @type poller: select.poll
     @param poller: Poller object
     @type fd: int
     @type poller: select.poll
     @param poller: Poller object
     @type fd: int

@@ -71,8 +94,6 @@ class _SingleActionPipeConditionWaiter(object):
 
     """
     object.__init__(self)
 
     """
     object.__init__(self)

-
-    self._cond = cond

     self._poller = poller
     self._fd = fd
 
     self._poller = poller
     self._fd = fd
 

@@ -83,10 +104,18 @@ class _SingleActionPipeConditionWaiter(object):
     @param timeout: Timeout for waiting (can be None)
 
     """
     @param timeout: Timeout for waiting (can be None)
 
     """

-    start_time = time.time()
-    remaining_time = timeout
+    running_timeout = utils.RunningTimeout(timeout, True)
+
+    while True:
+      remaining_time = running_timeout.Remaining()
+
+      if remaining_time is not None:
+        if remaining_time < 0.0:
+          break
+
+        # Our calculation uses seconds, poll() wants milliseconds
+        remaining_time *= 1000

 
 

-    while timeout is None or remaining_time > 0:

       try:
         result = self._poller.poll(remaining_time)
       except EnvironmentError, err:
       try:
         result = self._poller.poll(remaining_time)
       except EnvironmentError, err:

@@ -98,110 +127,114 @@ class _SingleActionPipeConditionWaiter(object):
       if result and result[0][0] == self._fd:
         break
 
       if result and result[0][0] == self._fd:
         break
 

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

 
 

+class _BaseCondition(object):
+  """Base class containing common code for conditions.

 
 

-class _SingleActionPipeCondition(object):
-  """Wrapper around a pipe for usage inside conditions.
-
-  This class contains a POSIX pipe(2) and a poller to poll it. The pipe is
-  always allocated when constructing the class. Extra care is taken to always
-  close the file descriptors.
-
-  An additional class, L{_SingleActionPipeConditionWaiter}, is used to wait for
-  notifications.
-
-  Warning: This class is designed to be used as the underlying component of a
-  locking condition, but is not by itself thread safe, and needs to be
-  protected by an external lock.
+  Some of this code is taken from python's threading module.

 
   """
   __slots__ = [
 
   """
   __slots__ = [

-    "_poller",
-    "_read_fd",
-    "_write_fd",
-    "_nwaiters",
+    "_lock",
+    "acquire",
+    "release",
+    "_is_owned",
+    "_acquire_restore",
+    "_release_save",

     ]
 
     ]
 

-  _waiter_class = _SingleActionPipeConditionWaiter
+  def __init__(self, lock):
+    """Constructor for _BaseCondition.

 
 

-  def __init__(self):
-    """Initializes this class.
+    @type lock: threading.Lock
+    @param lock: condition base lock

 
     """
     object.__init__(self)
 
 
     """
     object.__init__(self)
 

-    self._nwaiters = 0
-
-    # Just assume the unpacking is successful, otherwise error handling gets
-    # very complicated.
-    (self._read_fd, self._write_fd) = os.pipe()

     try:
     try:

-      # The poller looks for closure of the write side
-      poller = select.poll()
-      poller.register(self._read_fd, select.POLLHUP)
-
-      self._poller = poller
-    except:
-      if self._read_fd is not None:
-        os.close(self._read_fd)
-      if self._write_fd is not None:
-        os.close(self._write_fd)
-      raise
+      self._release_save = lock._release_save
+    except AttributeError:
+      self._release_save = self._base_release_save
+    try:
+      self._acquire_restore = lock._acquire_restore
+    except AttributeError:
+      self._acquire_restore = self._base_acquire_restore
+    try:
+      self._is_owned = lock.is_owned
+    except AttributeError:
+      self._is_owned = self._base_is_owned

 
 

-    # There should be no code here anymore, otherwise the pipe file descriptors
-    # may be not be cleaned up properly in case of errors.
+    self._lock = lock

 
 

-  def StartWaiting(self):
-    """Return function to wait for notification.
+    # Export the lock's acquire() and release() methods
+    self.acquire = lock.acquire
+    self.release = lock.release

 
 

-    @rtype: L{_SingleActionPipeConditionWaiter}
-    @return: Function to wait for notification
+  def _base_is_owned(self):
+    """Check whether lock is owned by current thread.

 
     """
 
     """

-    assert self._nwaiters >= 0
+    if self._lock.acquire(0):
+      self._lock.release()
+      return False
+    return True

 
 

-    if self._poller is None:
-      raise RuntimeError("Already cleaned up")
+  def _base_release_save(self):
+    self._lock.release()

 
 

-    # Create waiter function and increase number of waiters
-    wait_fn = self._waiter_class(self, self._poller, self._read_fd)
-    self._nwaiters += 1
-    return wait_fn
+  def _base_acquire_restore(self, _):
+    self._lock.acquire()

 
 

-  def DoneWaiting(self):
-    """Decrement number of waiters and automatic cleanup.
+  def _check_owned(self):
+    """Raise an exception if the current thread doesn't own the lock.

 
 

-    Must be called after waiting for a notification.
+    """
+    if not self._is_owned():
+      raise RuntimeError("cannot work with un-aquired lock")

 
 

-    @rtype: bool
-    @return: Whether this was the last waiter

 
 

-    """
-    assert self._nwaiters > 0
+class SingleNotifyPipeCondition(_BaseCondition):
+  """Condition which can only be notified once.

 
 

-    self._nwaiters -= 1
+  This condition class uses pipes and poll, internally, to be able to wait for
+  notification with a timeout, without resorting to polling. It is almost
+  compatible with Python's threading.Condition, with the following differences:
+    - notifyAll can only be called once, and no wait can happen after that
+    - notify is not supported, only notifyAll

 
 

-    if self._nwaiters == 0:
-      self._Cleanup()
-      return True
+  """

 
 

-    return False
+  __slots__ = [
+    "_poller",
+    "_read_fd",
+    "_write_fd",
+    "_nwaiters",
+    "_notified",
+    ]

 
 

-  def notifyAll(self):
-    """Close the writing side of the pipe to notify all waiters.
+  _waiter_class = _SingleNotifyPipeConditionWaiter

 
 

-    """
-    if self._write_fd is None:
-      raise RuntimeError("Can only notify once")
+  def __init__(self, lock):
+    """Constructor for SingleNotifyPipeCondition

 
 

-    os.close(self._write_fd)
+    """
+    _BaseCondition.__init__(self, lock)
+    self._nwaiters = 0
+    self._notified = False
+    self._read_fd = None

     self._write_fd = None
     self._write_fd = None

+    self._poller = None
+
+  def _check_unnotified(self):
+    """Throws an exception if already notified.
+
+    """
+    if self._notified:
+      raise RuntimeError("cannot use already notified condition")

 
   def _Cleanup(self):
 
   def _Cleanup(self):

-    """Close all file descriptors.
+    """Cleanup open file descriptors, if any.

 
     """
     if self._read_fd is not None:
 
     """
     if self._read_fd is not None:

@@ -211,19 +244,51 @@ class _SingleActionPipeCondition(object):
     if self._write_fd is not None:
       os.close(self._write_fd)
       self._write_fd = None
     if self._write_fd is not None:
       os.close(self._write_fd)
       self._write_fd = None

-

     self._poller = None
 
     self._poller = None
 

-  def __del__(self):
-    """Called on object deletion.
+  def wait(self, timeout):
+    """Wait for a notification.
+
+    @type timeout: float or None
+    @param timeout: Waiting timeout (can be None)
+
+    """
+    self._check_owned()
+    self._check_unnotified()
+
+    self._nwaiters += 1
+    try:
+      if self._poller is None:
+        (self._read_fd, self._write_fd) = os.pipe()
+        self._poller = select.poll()
+        self._poller.register(self._read_fd, select.POLLHUP)
+
+      wait_fn = self._waiter_class(self._poller, self._read_fd)
+      state = self._release_save()
+      try:
+        # Wait for notification
+        wait_fn(timeout)
+      finally:
+        # Re-acquire lock
+        self._acquire_restore(state)
+    finally:
+      self._nwaiters -= 1
+      if self._nwaiters == 0:
+        self._Cleanup()

 
 

-    Ensure no file descriptors are left open.
+  def notifyAll(self): # pylint: disable=C0103
+    """Close the writing side of the pipe to notify all waiters.

 
     """
 
     """

-    self._Cleanup()
+    self._check_owned()
+    self._check_unnotified()
+    self._notified = True
+    if self._write_fd is not None:
+      os.close(self._write_fd)
+      self._write_fd = None

 
 
 
 

-class _PipeCondition(object):
+class PipeCondition(_BaseCondition):

   """Group-only non-polling condition with counters.
 
   This condition class uses pipes and poll, internally, to be able to wait for
   """Group-only non-polling condition with counters.
 
   This condition class uses pipes and poll, internally, to be able to wait for

@@ -234,52 +299,21 @@ class _PipeCondition(object):
 
   """
   __slots__ = [
 
   """
   __slots__ = [

-    "_lock",
-    "_nwaiters",
-    "_pipe",
-    "acquire",
-    "release",
+    "_waiters",
+    "_single_condition",

     ]
 
     ]
 

-  _pipe_class = _SingleActionPipeCondition
+  _single_condition_class = SingleNotifyPipeCondition

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

-    object.__init__(self)
-
-    # Recursive locks are not supported
-    assert not hasattr(lock, "_acquire_restore")
-    assert not hasattr(lock, "_release_save")
-
-    self._lock = lock
-
-    # Export the lock's acquire() and release() methods
-    self.acquire = lock.acquire
-    self.release = lock.release
-
-    self._nwaiters = 0
-    self._pipe = None
-
-  def _is_owned(self):
-    """Check whether lock is owned by current thread.
-
-    """
-    if self._lock.acquire(0):
-      self._lock.release()
-      return False
-
-    return True
-
-  def _check_owned(self):
-    """Raise an exception if the current thread doesn't own the lock.
-
-    """
-    if not self._is_owned():
-      raise RuntimeError("cannot work with un-aquired lock")
+    _BaseCondition.__init__(self, lock)
+    self._waiters = set()
+    self._single_condition = self._single_condition_class(self._lock)

 
 

-  def wait(self, timeout=None):
+  def wait(self, timeout):

     """Wait for a notification.
 
     @type timeout: float or None
     """Wait for a notification.
 
     @type timeout: float or None

@@ -288,47 +322,32 @@ class _PipeCondition(object):
     """
     self._check_owned()
 
     """
     self._check_owned()
 

-    if not self._pipe:
-      self._pipe = self._pipe_class()
-

     # Keep local reference to the pipe. It could be replaced by another thread
     # notifying while we're waiting.
     # Keep local reference to the pipe. It could be replaced by another thread
     # notifying while we're waiting.

-    pipe = self._pipe
+    cond = self._single_condition

 
 

-    assert self._nwaiters >= 0
-    self._nwaiters += 1
+    self._waiters.add(threading.currentThread())

     try:
     try:

-      # Get function to wait on the pipe
-      wait_fn = pipe.StartWaiting()
-      try:
-        # Release lock while waiting
-        self.release()
-        try:
-          # Wait for notification
-          wait_fn(timeout)
-        finally:
-          # Re-acquire lock
-          self.acquire()
-      finally:
-        # Destroy pipe if this was the last waiter and the current pipe is
-        # still the same. The same pipe cannot be reused after cleanup.
-        if pipe.DoneWaiting() and pipe == self._pipe:
-          self._pipe = None
+      cond.wait(timeout)

     finally:
     finally:

-      assert self._nwaiters > 0
-      self._nwaiters -= 1
+      self._check_owned()
+      self._waiters.remove(threading.currentThread())

 
 

-  def notifyAll(self):
+  def notifyAll(self): # pylint: disable=C0103

     """Notify all currently waiting threads.
 
     """
     self._check_owned()
     """Notify all currently waiting threads.
 
     """
     self._check_owned()

+    self._single_condition.notifyAll()
+    self._single_condition = self._single_condition_class(self._lock)

 
 

-    # Notify and forget pipe. A new one will be created on the next call to
-    # wait.
-    if self._pipe is not None:
-      self._pipe.notifyAll()
-      self._pipe = None
+  def get_waiting(self):
+    """Returns a list of all waiting threads.
+
+    """
+    self._check_owned()
+
+    return self._waiters

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

@@ -336,96 +355,74 @@ class _PipeCondition(object):
     """
     self._check_owned()
 
     """
     self._check_owned()
 

-    return bool(self._nwaiters)
-
-
-class _CountingCondition(object):
-  """Wrapper for Python's built-in threading.Condition class.
+    return bool(self._waiters)

 
 

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

 
 

-  """
+class _PipeConditionWithMode(PipeCondition):

   __slots__ = [
   __slots__ = [

-    "_cond",
-    "_nwaiters",
+    "shared",

     ]
 
     ]
 

-  def __init__(self, lock):
+  def __init__(self, lock, shared):

     """Initializes this class.
 
     """
     """Initializes this class.
 
     """

-    object.__init__(self)
-    self._cond = threading.Condition(lock=lock)
-    self._nwaiters = 0
-
-  def notifyAll(self):
-    """Notifies the condition.
-
-    """
-    return self._cond.notifyAll()
-
-  def wait(self, timeout=None):
-    """Waits for the condition to be notified.
-
-    @type timeout: float or None
-    @param timeout: Timeout in seconds
-
-    """
-    assert self._nwaiters >= 0
-
-    self._nwaiters += 1
-    try:
-      return self._cond.wait(timeout=timeout)
-    finally:
-      self._nwaiters -= 1
-
-  def has_waiting(self):
-    """Returns whether there are active waiters.
-
-    """
-    return bool(self._nwaiters)
+    self.shared = shared
+    PipeCondition.__init__(self, lock)

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

-  Multiple threads can acquire the lock in a shared way, calling
-  acquire_shared().  In order to acquire the lock in an exclusive way threads
-  can call acquire_exclusive().
+  Multiple threads can acquire the lock in a shared way by calling
+  C{acquire(shared=1)}. In order to acquire the lock in an exclusive way
+  threads can call C{acquire(shared=0)}.
+
+  Notes on data structures: C{__pending} contains a priority queue (heapq) of
+  all pending acquires: C{[(priority1: prioqueue1), (priority2: prioqueue2),
+  ...]}. Each per-priority queue contains a normal in-order list of conditions
+  to be notified when the lock can be acquired. Shared locks are grouped
+  together by priority and the condition for them is stored in
+  C{__pending_shared} if it already exists. C{__pending_by_prio} keeps
+  references for the per-priority queues indexed by priority for faster access.

 
 

-  The lock prevents starvation but does not guarantee that threads will acquire
-  the shared lock in the order they queued for it, just that they will
-  eventually do so.
+  @type name: string
+  @ivar name: the name of the lock

 
   """
   __slots__ = [
 
   """
   __slots__ = [

-    "__active_shr_c",
-    "__inactive_shr_c",
+    "__weakref__",

     "__deleted",
     "__exc",
     "__lock",
     "__pending",
     "__deleted",
     "__exc",
     "__lock",
     "__pending",

+    "__pending_by_prio",
+    "__pending_shared",

     "__shr",
     "__shr",

+    "name",

     ]
 
     ]
 

-  __condition_class = _CountingCondition
+  __condition_class = _PipeConditionWithMode

 
 

-  def __init__(self):
+  def __init__(self, name, monitor=None):

     """Construct a new SharedLock.
 
     """Construct a new SharedLock.
 

+    @param name: the name of the lock
+    @type monitor: L{LockMonitor}
+    @param monitor: Lock monitor with which to register
+

     """
     object.__init__(self)
 
     """
     object.__init__(self)
 

+    self.name = name
+

     # Internal lock
     self.__lock = threading.Lock()
 
     # Queue containing waiting acquires
     self.__pending = []
     # Internal lock
     self.__lock = threading.Lock()
 
     # Queue containing waiting acquires
     self.__pending = []

-
-    # Active and inactive conditions for shared locks
-    self.__active_shr_c = self.__condition_class(self.__lock)
-    self.__inactive_shr_c = self.__condition_class(self.__lock)
+    self.__pending_by_prio = {}
+    self.__pending_shared = {}

 
     # Current lock holders
     self.__shr = set()
 
     # Current lock holders
     self.__shr = set()

@@ -434,12 +431,74 @@ class SharedLock(object):
     # is this lock in the deleted state?
     self.__deleted = False
 
     # is this lock in the deleted state?
     self.__deleted = False
 

+    # Register with lock monitor
+    if monitor:
+      logging.debug("Adding lock %s to monitor", name)
+      monitor.RegisterLock(self)
+
+  def GetLockInfo(self, requested):
+    """Retrieves information for querying locks.
+
+    @type requested: set
+    @param requested: Requested information, see C{query.LQ_*}
+
+    """
+    self.__lock.acquire()
+    try:
+      # Note: to avoid unintentional race conditions, no references to
+      # modifiable objects should be returned unless they were created in this
+      # function.
+      mode = None
+      owner_names = None
+
+      if query.LQ_MODE in requested:
+        if self.__deleted:
+          mode = _DELETED_TEXT
+          assert not (self.__exc or self.__shr)
+        elif self.__exc:
+          mode = _EXCLUSIVE_TEXT
+        elif self.__shr:
+          mode = _SHARED_TEXT
+
+      # Current owner(s) are wanted
+      if query.LQ_OWNER in requested:
+        if self.__exc:
+          owner = [self.__exc]
+        else:
+          owner = self.__shr
+
+        if owner:
+          assert not self.__deleted
+          owner_names = [i.getName() for i in owner]
+
+      # Pending acquires are wanted
+      if query.LQ_PENDING in requested:
+        pending = []
+
+        # Sorting instead of copying and using heaq functions for simplicity
+        for (_, prioqueue) in sorted(self.__pending):
+          for cond in prioqueue:
+            if cond.shared:
+              pendmode = _SHARED_TEXT
+            else:
+              pendmode = _EXCLUSIVE_TEXT
+
+            # List of names will be sorted in L{query._GetLockPending}
+            pending.append((pendmode, [i.getName()
+                                       for i in cond.get_waiting()]))
+      else:
+        pending = None
+
+      return [(self.name, mode, owner_names, pending)]
+    finally:
+      self.__lock.release()
+

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

-      raise errors.LockError("Deleted lock")
+      raise errors.LockError("Deleted lock %s" % self.name)

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

@@ -467,7 +526,7 @@ class SharedLock(object):
     else:
       return self.__is_exclusive()
 
     else:
       return self.__is_exclusive()
 

-  def _is_owned(self, shared=-1):
+  def is_owned(self, shared=-1):

     """Is the current thread somehow owning the lock at this time?
 
     @param shared:
     """Is the current thread somehow owning the lock at this time?
 
     @param shared:

@@ -482,6 +541,10 @@ class SharedLock(object):
     finally:
       self.__lock.release()
 
     finally:
       self.__lock.release()
 

+  #: Necessary to remain compatible with threading.Condition, which tries to
+  #: retrieve a locks' "_is_owned" attribute
+  _is_owned = is_owned
+

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

@@ -490,7 +553,25 @@ class SharedLock(object):
     """
     self.__lock.acquire()
     try:
     """
     self.__lock.acquire()
     try:

-      return len(self.__pending)
+      return sum(len(prioqueue) for (_, prioqueue) in self.__pending)
+    finally:
+      self.__lock.release()
+
+  def _check_empty(self):
+    """Checks whether there are any pending acquires.
+
+    @rtype: bool
+
+    """
+    self.__lock.acquire()
+    try:
+      # Order is important: __find_first_pending_queue modifies __pending
+      (_, prioqueue) = self.__find_first_pending_queue()
+
+      return not (prioqueue or
+                  self.__pending or
+                  self.__pending_by_prio or
+                  self.__pending_shared)

     finally:
       self.__lock.release()
 
     finally:
       self.__lock.release()
 

@@ -512,26 +593,53 @@ class SharedLock(object):
     else:
       return len(self.__shr) == 0 and self.__exc is None
 
     else:
       return len(self.__shr) == 0 and self.__exc is None
 

+  def __find_first_pending_queue(self):
+    """Tries to find the topmost queued entry with pending acquires.
+
+    Removes empty entries while going through the list.
+
+    """
+    while self.__pending:
+      (priority, prioqueue) = self.__pending[0]
+
+      if prioqueue:
+        return (priority, prioqueue)
+
+      # Remove empty queue
+      heapq.heappop(self.__pending)
+      del self.__pending_by_prio[priority]
+      assert priority not in self.__pending_shared
+
+    return (None, None)
+

   def __is_on_top(self, cond):
     """Checks whether the passed condition is on top of the queue.
 
     The caller must make sure the queue isn't empty.
 
     """
   def __is_on_top(self, cond):
     """Checks whether the passed condition is on top of the queue.
 
     The caller must make sure the queue isn't empty.
 
     """

-    return self.__pending[0] == cond
+    (_, prioqueue) = self.__find_first_pending_queue()

 
 

-  def __acquire_unlocked(self, shared=0, timeout=None):
+    return cond == prioqueue[0]
+
+  def __acquire_unlocked(self, shared, timeout, priority):

     """Acquire a shared lock.
 
     @param shared: whether to acquire in shared mode; by default an
         exclusive lock will be acquired
     @param timeout: maximum waiting time before giving up
     """Acquire a shared lock.
 
     @param shared: whether to acquire in shared mode; by default an
         exclusive lock will be acquired
     @param timeout: maximum waiting time before giving up

+    @type priority: integer
+    @param priority: Priority for acquiring lock

 
     """
     self.__check_deleted()
 
     # We cannot acquire the lock if we already have it
 
     """
     self.__check_deleted()
 
     # We cannot acquire the lock if we already have it

-    assert not self.__is_owned(), "double acquire() on a non-recursive lock"
+    assert not self.__is_owned(), ("double acquire() on a non-recursive lock"
+                                   " %s" % self.name)
+
+    # Remove empty entries from queue
+    self.__find_first_pending_queue()

 
     # Check whether someone else holds the lock or there are pending acquires.
     if not self.__pending and self.__can_acquire(shared):
 
     # Check whether someone else holds the lock or there are pending acquires.
     if not self.__pending and self.__can_acquire(shared):

@@ -539,20 +647,37 @@ class SharedLock(object):
       self.__do_acquire(shared)
       return True
 
       self.__do_acquire(shared)
       return True
 

-    if shared:
-      wait_condition = self.__active_shr_c
+    prioqueue = self.__pending_by_prio.get(priority, None)

 
 

-      # Check if we're not yet in the queue
-      if wait_condition not in self.__pending:
-        self.__pending.append(wait_condition)
+    if shared:
+      # Try to re-use condition for shared acquire
+      wait_condition = self.__pending_shared.get(priority, None)
+      assert (wait_condition is None or
+              (wait_condition.shared and wait_condition in prioqueue))

     else:
     else:

-      wait_condition = self.__condition_class(self.__lock)
-      # Always add to queue
-      self.__pending.append(wait_condition)
+      wait_condition = None
+
+    if wait_condition is None:
+      if prioqueue is None:
+        assert priority not in self.__pending_by_prio
+
+        prioqueue = []
+        heapq.heappush(self.__pending, (priority, prioqueue))
+        self.__pending_by_prio[priority] = prioqueue
+
+      wait_condition = self.__condition_class(self.__lock, shared)
+      prioqueue.append(wait_condition)
+
+      if shared:
+        # Keep reference for further shared acquires on same priority. This is
+        # better than trying to find it in the list of pending acquires.
+        assert priority not in self.__pending_shared
+        self.__pending_shared[priority] = wait_condition

 
     try:
       # Wait until we become the topmost acquire in the queue or the timeout
       # expires.
 
     try:
       # Wait until we become the topmost acquire in the queue or the timeout
       # expires.

+      # TODO: Decrease timeout with spurious notifications

       while not (self.__is_on_top(wait_condition) and
                  self.__can_acquire(shared)):
         # Wait for notification
       while not (self.__is_on_top(wait_condition) and
                  self.__can_acquire(shared)):
         # Wait for notification

@@ -569,24 +694,82 @@ class SharedLock(object):
         return True
     finally:
       # Remove condition from queue if there are no more waiters
         return True
     finally:
       # Remove condition from queue if there are no more waiters

-      if not wait_condition.has_waiting() and not self.__deleted:
-        self.__pending.remove(wait_condition)
+      if not wait_condition.has_waiting():
+        prioqueue.remove(wait_condition)
+        if wait_condition.shared:
+          # Remove from list of shared acquires if it wasn't while releasing
+          # (e.g. on lock deletion)
+          self.__pending_shared.pop(priority, None)

 
     return False
 
 
     return False
 

-  def acquire(self, shared=0, timeout=None):
+  def acquire(self, shared=0, timeout=None, priority=None,
+              test_notify=None):

     """Acquire a shared lock.
 
     """Acquire a shared lock.
 

-    @type shared: int
+    @type shared: integer (0/1) used as a boolean

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

+    @type priority: integer
+    @param priority: Priority for acquiring lock
+    @type test_notify: callable or None
+    @param test_notify: Special callback function for unittesting

 
     """
 
     """

+    if priority is None:
+      priority = _DEFAULT_PRIORITY
+

     self.__lock.acquire()
     try:
     self.__lock.acquire()
     try:

-      return self.__acquire_unlocked(shared, timeout)
+      # We already got the lock, notify now
+      if __debug__ and callable(test_notify):
+        test_notify()
+
+      return self.__acquire_unlocked(shared, timeout, priority)
+    finally:
+      self.__lock.release()
+
+  def downgrade(self):
+    """Changes the lock mode from exclusive to shared.
+
+    Pending acquires in shared mode on the same priority will go ahead.
+
+    """
+    self.__lock.acquire()
+    try:
+      assert self.__is_owned(), "Lock must be owned"
+
+      if self.__is_exclusive():
+        # Do nothing if the lock is already acquired in shared mode
+        self.__exc = None
+        self.__do_acquire(1)
+
+        # Important: pending shared acquires should only jump ahead if there
+        # was a transition from exclusive to shared, otherwise an owner of a
+        # shared lock can keep calling this function to push incoming shared
+        # acquires
+        (priority, prioqueue) = self.__find_first_pending_queue()
+        if prioqueue:
+          # Is there a pending shared acquire on this priority?
+          cond = self.__pending_shared.pop(priority, None)
+          if cond:
+            assert cond.shared
+            assert cond in prioqueue
+
+            # Ensure shared acquire is on top of queue
+            if len(prioqueue) > 1:
+              prioqueue.remove(cond)
+              prioqueue.insert(0, cond)
+
+            # Notify
+            cond.notifyAll()
+
+      assert not self.__is_exclusive()
+      assert self.__is_sharer()
+
+      return True

     finally:
       self.__lock.release()
 
     finally:
       self.__lock.release()
 

@@ -609,18 +792,19 @@ class SharedLock(object):
         self.__shr.remove(threading.currentThread())
 
       # Notify topmost condition in queue
         self.__shr.remove(threading.currentThread())
 
       # Notify topmost condition in queue

-      if self.__pending:
-        first_condition = self.__pending[0]
-        first_condition.notifyAll()
-
-        if first_condition == self.__active_shr_c:
-          self.__active_shr_c = self.__inactive_shr_c
-          self.__inactive_shr_c = first_condition
+      (priority, prioqueue) = self.__find_first_pending_queue()
+      if prioqueue:
+        cond = prioqueue[0]
+        cond.notifyAll()
+        if cond.shared:
+          # Prevent further shared acquires from sneaking in while waiters are
+          # notified
+          self.__pending_shared.pop(priority, None)

 
     finally:
       self.__lock.release()
 
 
     finally:
       self.__lock.release()
 

-  def delete(self, timeout=None):
+  def delete(self, timeout=None, priority=None):

     """Delete a Shared Lock.
 
     This operation will declare the lock for removal. First the lock will be
     """Delete a Shared Lock.
 
     This operation will declare the lock for removal. First the lock will be

@@ -629,8 +813,13 @@ class SharedLock(object):
 
     @type timeout: float
     @param timeout: maximum waiting time before giving up
 
     @type timeout: float
     @param timeout: maximum waiting time before giving up

+    @type priority: integer
+    @param priority: Priority for acquiring lock

 
     """
 
     """

+    if priority is None:
+      priority = _DEFAULT_PRIORITY
+

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

@@ -641,26 +830,48 @@ class SharedLock(object):
       acquired = self.__is_exclusive()
 
       if not acquired:
       acquired = self.__is_exclusive()
 
       if not acquired:

-        acquired = self.__acquire_unlocked(timeout)
+        acquired = self.__acquire_unlocked(0, timeout, priority)
+
+        assert self.__is_exclusive() and not self.__is_sharer(), \
+          "Lock wasn't acquired in exclusive mode"

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

+        assert not (self.__exc or self.__shr), "Found owner during deletion"
+

         # Notify all acquires. They'll throw an error.
         # Notify all acquires. They'll throw an error.

-        while self.__pending:
-          self.__pending.pop().notifyAll()
+        for (_, prioqueue) in self.__pending:
+          for cond in prioqueue:
+            cond.notifyAll()
+
+        assert self.__deleted

 
       return acquired
     finally:
       self.__lock.release()
 
 
       return acquired
     finally:
       self.__lock.release()
 

+  def _release_save(self):
+    shared = self.__is_sharer()
+    self.release()
+    return shared
+
+  def _acquire_restore(self, shared):
+    self.acquire(shared=shared)
+

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

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

 class LockSet:
   """Implements a set of locks.
 
 class LockSet:
   """Implements a set of locks.
 

@@ -671,23 +882,35 @@ class LockSet:
 
   All the locks needed in the same set must be acquired together, though.
 
 
   All the locks needed in the same set must be acquired together, though.
 

+  @type name: string
+  @ivar name: the name of the lockset
+

   """
   """

-  def __init__(self, members=None):
+  def __init__(self, members, name, monitor=None):

     """Constructs a new LockSet.
 
     """Constructs a new LockSet.
 

+    @type members: list of strings

     @param members: initial members of the set
     @param members: initial members of the set

+    @type monitor: L{LockMonitor}
+    @param monitor: Lock monitor with which to register member locks

 
     """
 
     """

-    # Used internally to guarantee coherency.
-    self.__lock = SharedLock()
+    assert members is not None, "members parameter is not a list"
+    self.name = name
+
+    # Lock monitor
+    self.__monitor = monitor
+
+    # Used internally to guarantee coherency
+    self.__lock = SharedLock(self._GetLockName("[lockset]"), monitor=monitor)

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

-    if members is not None:
-      for name in members:
-        self.__lockdict[name] = SharedLock()
+    for mname in members:
+      self.__lockdict[mname] = SharedLock(self._GetLockName(mname),
+                                          monitor=monitor)

 
     # The owner dict contains the set of locks each thread owns. For
     # performance each thread can access its own key without a global lock on
 
     # The owner dict contains the set of locks each thread owns. For
     # performance each thread can access its own key without a global lock on

@@ -698,17 +921,74 @@ class LockSet:
     # will be trouble.
     self.__owners = {}
 
     # will be trouble.
     self.__owners = {}
 

-  def _is_owned(self):
-    """Is the current thread a current level owner?"""
+  def _GetLockName(self, mname):
+    """Returns the name for a member lock.
+
+    """
+    return "%s/%s" % (self.name, mname)
+
+  def _get_lock(self):
+    """Returns the lockset-internal lock.
+
+    """
+    return self.__lock
+
+  def _get_lockdict(self):
+    """Returns the lockset-internal lock dictionary.
+
+    Accessing this structure is only safe in single-thread usage or when the
+    lockset-internal lock is held.
+
+    """
+    return self.__lockdict
+
+  def is_owned(self):
+    """Is the current thread a current level owner?
+
+    @note: Use L{check_owned} to check if a specific lock is held
+
+    """

     return threading.currentThread() in self.__owners
 
     return threading.currentThread() in self.__owners
 

+  def check_owned(self, names, shared=-1):
+    """Check if locks are owned in a specific mode.
+
+    @type names: sequence or string
+    @param names: Lock names (or a single lock name)
+    @param shared: See L{SharedLock.is_owned}
+    @rtype: bool
+    @note: Use L{is_owned} to check if the current thread holds I{any} lock and
+      L{list_owned} to get the names of all owned locks
+
+    """
+    if isinstance(names, basestring):
+      names = [names]
+
+    # Avoid check if no locks are owned anyway
+    if names and self.is_owned():
+      candidates = []
+
+      # Gather references to all locks (in case they're deleted in the meantime)
+      for lname in names:
+        try:
+          lock = self.__lockdict[lname]
+        except KeyError:
+          raise errors.LockError("Non-existing lock '%s' in set '%s' (it may"
+                                 " have been removed)" % (lname, self.name))
+        else:
+          candidates.append(lock)
+
+      return compat.all(lock.is_owned(shared=shared) for lock in candidates)
+    else:
+      return False
+

   def _add_owned(self, name=None):
     """Note the current thread owns the given lock"""
     if name is None:
   def _add_owned(self, name=None):
     """Note the current thread owns the given lock"""
     if name is None:

-      if not self._is_owned():
+      if not self.is_owned():

         self.__owners[threading.currentThread()] = set()
     else:
         self.__owners[threading.currentThread()] = set()
     else:

-      if self._is_owned():
+      if self.is_owned():

         self.__owners[threading.currentThread()].add(name)
       else:
         self.__owners[threading.currentThread()] = set([name])
         self.__owners[threading.currentThread()].add(name)
       else:
         self.__owners[threading.currentThread()] = set([name])

@@ -716,21 +996,32 @@ class LockSet:
   def _del_owned(self, name=None):
     """Note the current thread owns the given lock"""
 
   def _del_owned(self, name=None):
     """Note the current thread owns the given lock"""
 

+    assert not (name is None and self.__lock.is_owned()), \
+           "Cannot hold internal lock when deleting owner status"
+

     if name is not None:
       self.__owners[threading.currentThread()].remove(name)
 
     # Only remove the key if we don't hold the set-lock as well
     if name is not None:
       self.__owners[threading.currentThread()].remove(name)
 
     # Only remove the key if we don't hold the set-lock as well

-    if (not self.__lock._is_owned() and
+    if (not self.__lock.is_owned() and

         not self.__owners[threading.currentThread()]):
       del self.__owners[threading.currentThread()]
 
         not self.__owners[threading.currentThread()]):
       del self.__owners[threading.currentThread()]
 

-  def _list_owned(self):
+  def list_owned(self):

     """Get the set of resource names owned by the current thread"""
     """Get the set of resource names owned by the current thread"""

-    if self._is_owned():
+    if self.is_owned():

       return self.__owners[threading.currentThread()].copy()
     else:
       return set()
 
       return self.__owners[threading.currentThread()].copy()
     else:
       return set()
 

+  def _release_and_delete_owned(self):
+    """Release and delete all resources owned by the current thread"""
+    for lname in self.list_owned():
+      lock = self.__lockdict[lname]
+      if lock.is_owned():
+        lock.release()
+      self._del_owned(name=lname)
+

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

@@ -749,7 +1040,7 @@ class LockSet:
     # If we don't already own the set-level lock acquired
     # we'll get it and note we need to release it later.
     release_lock = False
     # If we don't already own the set-level lock acquired
     # we'll get it and note we need to release it later.
     release_lock = False

-    if not self.__lock._is_owned():
+    if not self.__lock.is_owned():

       release_lock = True
       self.__lock.acquire(shared=1)
     try:
       release_lock = True
       self.__lock.acquire(shared=1)
     try:

@@ -759,141 +1050,240 @@ class LockSet:
         self.__lock.release()
     return set(result)
 
         self.__lock.release()
     return set(result)
 

-  def acquire(self, names, blocking=1, shared=0):
+  def acquire(self, names, timeout=None, shared=0, priority=None,
+              test_notify=None):

     """Acquire a set of resource locks.
 
     """Acquire a set of resource locks.
 

+    @type names: list of strings (or string)

     @param names: the names of the locks which shall be acquired
         (special lock names, or instance/node names)
     @param names: the names of the locks which shall be acquired
         (special lock names, or instance/node names)

+    @type shared: integer (0/1) used as a boolean

     @param shared: whether to acquire in shared mode; by default an
         exclusive lock will be acquired
     @param shared: whether to acquire in shared mode; by default an
         exclusive lock will be acquired

-    @param blocking: whether to block while trying to acquire or to
-        operate in try-lock mode (this locking mode is not supported yet)
+    @type timeout: float or None
+    @param timeout: Maximum time to acquire all locks
+    @type priority: integer
+    @param priority: Priority for acquiring locks
+    @type test_notify: callable or None
+    @param test_notify: Special callback function for unittesting

 
 

-    @return: True when all the locks are successfully acquired
+    @return: Set of all locks successfully acquired or None in case of timeout

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

-    if not blocking:
-      # We don't have non-blocking mode for now
-      raise NotImplementedError
+    assert timeout is None or timeout >= 0.0

 
     # Check we don't already own locks at this level
 
     # Check we don't already own locks at this level

-    assert not self._is_owned(), "Cannot acquire locks in the same set twice"
+    assert not self.is_owned(), ("Cannot acquire locks in the same set twice"
+                                 " (lockset %s)" % self.name)

 
 

-    if names is None:
-      # If no names are given acquire the whole set by not letting new names
-      # being added before we release, and getting the current list of names.
-      # Some of them may then be deleted later, but we'll cope with this.
-      #
-      # We'd like to acquire this lock in a shared way, as it's nice if
-      # everybody else can use the instances at the same time. If are acquiring
-      # them exclusively though they won't be able to do this anyway, though,
-      # so we'll get the list lock exclusively as well in order to be able to
-      # do add() on the set while owning it.
-      self.__lock.acquire(shared=shared)
-      try:
-        # note we own the set-lock
-        self._add_owned()
-        names = self.__names()
-      except:
-        # We shouldn't have problems adding the lock to the owners list, but
-        # if we did we'll try to release this lock and re-raise exception.
-        # Of course something is going to be really wrong, after this.
-        self.__lock.release()
-        raise
+    if priority is None:
+      priority = _DEFAULT_PRIORITY
+
+    # We need to keep track of how long we spent waiting for a lock. The
+    # timeout passed to this function is over all lock acquires.
+    running_timeout = utils.RunningTimeout(timeout, False)

 
     try:
 
     try:

-      # Support passing in a single resource to acquire rather than many
-      if isinstance(names, basestring):
-        names = [names]
+      if names is not None:
+        # Support passing in a single resource to acquire rather than many
+        if isinstance(names, basestring):
+          names = [names]
+
+        return self.__acquire_inner(names, False, shared, priority,
+                                    running_timeout.Remaining, test_notify)
+

       else:
       else:

-        names = sorted(names)
+        # If no names are given acquire the whole set by not letting new names
+        # being added before we release, and getting the current list of names.
+        # Some of them may then be deleted later, but we'll cope with this.
+        #
+        # We'd like to acquire this lock in a shared way, as it's nice if
+        # everybody else can use the instances at the same time. If we are
+        # acquiring them exclusively though they won't be able to do this
+        # anyway, though, so we'll get the list lock exclusively as well in
+        # order to be able to do add() on the set while owning it.
+        if not self.__lock.acquire(shared=shared, priority=priority,
+                                   timeout=running_timeout.Remaining()):
+          raise _AcquireTimeout()
+        try:
+          # note we own the set-lock
+          self._add_owned()
+
+          return self.__acquire_inner(self.__names(), True, shared, priority,
+                                      running_timeout.Remaining, test_notify)
+        except:
+          # We shouldn't have problems adding the lock to the owners list, but
+          # if we did we'll try to release this lock and re-raise exception.
+          # Of course something is going to be really wrong, after this.
+          self.__lock.release()
+          self._del_owned()
+          raise
+
+    except _AcquireTimeout:
+      return None
+
+  def __acquire_inner(self, names, want_all, shared, priority,
+                      timeout_fn, test_notify):
+    """Inner logic for acquiring a number of locks.
+
+    @param names: Names of the locks to be acquired
+    @param want_all: Whether all locks in the set should be acquired
+    @param shared: Whether to acquire in shared mode
+    @param timeout_fn: Function returning remaining timeout
+    @param priority: Priority for acquiring locks
+    @param test_notify: Special callback function for unittesting
+
+    """
+    acquire_list = []
+
+    # First we look the locks up on __lockdict. We have no way of being sure
+    # they will still be there after, but this makes it a lot faster should
+    # just one of them be the already wrong. Using a sorted sequence to prevent
+    # deadlocks.
+    for lname in sorted(utils.UniqueSequence(names)):
+      try:
+        lock = self.__lockdict[lname] # raises KeyError if lock is not there
+      except KeyError:
+        if want_all:
+          # We are acquiring all the set, it doesn't matter if this particular
+          # element is not there anymore.
+          continue
+
+        raise errors.LockError("Non-existing lock %s in set %s (it may have"
+                               " been removed)" % (lname, self.name))
+
+      acquire_list.append((lname, lock))
+
+    # This will hold the locknames we effectively acquired.
+    acquired = set()
+
+    try:
+      # Now acquire_list contains a sorted list of resources and locks we
+      # want.  In order to get them we loop on this (private) list and
+      # acquire() them.  We gave no real guarantee they will still exist till
+      # this is done but .acquire() itself is safe and will alert us if the
+      # lock gets deleted.
+      for (lname, lock) in acquire_list:
+        if __debug__ and callable(test_notify):
+          test_notify_fn = lambda: test_notify(lname)
+        else:
+          test_notify_fn = None
+
+        timeout = timeout_fn()

 
 

-      acquire_list = []
-      # First we look the locks up on __lockdict. We have no way of being sure
-      # they will still be there after, but this makes it a lot faster should
-      # just one of them be the already wrong
-      for lname in utils.UniqueSequence(names):

         try:
         try:

-          lock = self.__lockdict[lname] # raises KeyError if lock is not there
-          acquire_list.append((lname, lock))
-        except (KeyError):
-          if self.__lock._is_owned():
+          # raises LockError if the lock was deleted
+          acq_success = lock.acquire(shared=shared, timeout=timeout,
+                                     priority=priority,
+                                     test_notify=test_notify_fn)
+        except errors.LockError:
+          if want_all:

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

-          else:
-            raise errors.LockError('non-existing lock in set (%s)' % lname)
-
-      # This will hold the locknames we effectively acquired.
-      acquired = set()
-      # Now acquire_list contains a sorted list of resources and locks we want.
-      # In order to get them we loop on this (private) list and acquire() them.
-      # We gave no real guarantee they will still exist till this is done but
-      # .acquire() itself is safe and will alert us if the lock gets deleted.
-      for (lname, lock) in acquire_list:
+
+          raise errors.LockError("Non-existing lock %s in set %s (it may"
+                                 " have been removed)" % (lname, self.name))
+
+        if not acq_success:
+          # Couldn't get lock or timeout occurred
+          if timeout is None:
+            # This shouldn't happen as SharedLock.acquire(timeout=None) is
+            # blocking.
+            raise errors.LockError("Failed to get lock %s (set %s)" %
+                                   (lname, self.name))
+
+          raise _AcquireTimeout()
+

         try:
         try:

-          lock.acquire(shared=shared) # raises LockError if the lock is deleted

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

-        except (errors.LockError):
-          if self.__lock._is_owned():
-            # We are acquiring all the set, it doesn't matter if this
-            # particular element is not there anymore.
-            continue
-          else:
-            name_fail = lname
-            for lname in self._list_owned():
-              self.__lockdict[lname].release()
-              self._del_owned(name=lname)
-            raise errors.LockError('non-existing lock in set (%s)' % name_fail)
+

         except:
           # We shouldn't have problems adding the lock to the owners list, but
           # if we did we'll try to release this lock and re-raise exception.
         except:
           # We shouldn't have problems adding the lock to the owners list, but
           # if we did we'll try to release this lock and re-raise exception.

-          # Of course something is going to be really wrong, after this.
-          if lock._is_owned():
+          # Of course something is going to be really wrong after this.
+          if lock.is_owned():

             lock.release()
           raise
 
     except:
             lock.release()
           raise
 
     except:

-      # If something went wrong and we had the set-lock let's release it...
-      if self.__lock._is_owned():
-        self.__lock.release()
+      # Release all owned locks
+      self._release_and_delete_owned()

       raise
 
     return acquired
 
       raise
 
     return acquired
 

+  def downgrade(self, names=None):
+    """Downgrade a set of resource locks from exclusive to shared mode.
+
+    The locks must have been acquired in exclusive mode.
+
+    """
+    assert self.is_owned(), ("downgrade on lockset %s while not owning any"
+                             " lock" % self.name)
+
+    # Support passing in a single resource to downgrade rather than many
+    if isinstance(names, basestring):
+      names = [names]
+
+    owned = self.list_owned()
+
+    if names is None:
+      names = owned
+    else:
+      names = set(names)
+      assert owned.issuperset(names), \
+        ("downgrade() on unheld resources %s (set %s)" %
+         (names.difference(owned), self.name))
+
+    for lockname in names:
+      self.__lockdict[lockname].downgrade()
+
+    # Do we own the lockset in exclusive mode?
+    if self.__lock.is_owned(shared=0):
+      # Have all locks been downgraded?
+      if not compat.any(lock.is_owned(shared=0)
+                        for lock in self.__lockdict.values()):
+        self.__lock.downgrade()
+        assert self.__lock.is_owned(shared=1)
+
+    return True
+

   def release(self, names=None):
     """Release a set of resource locks, at the same level.
 
     You must have acquired the locks, either in shared or in exclusive mode,
     before releasing them.
 
   def release(self, names=None):
     """Release a set of resource locks, at the same level.
 
     You must have acquired the locks, either in shared or in exclusive mode,
     before releasing them.
 

+    @type names: list of strings, or None

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

-    assert self._is_owned(), "release() on lock set while not owner"
+    assert self.is_owned(), ("release() on lock set %s while not owner" %
+                             self.name)

 
     # Support passing in a single resource to release rather than many
     if isinstance(names, basestring):
       names = [names]
 
     if names is None:
 
     # Support passing in a single resource to release rather than many
     if isinstance(names, basestring):
       names = [names]
 
     if names is None:

-      names = self._list_owned()
+      names = self.list_owned()

     else:
       names = set(names)
     else:
       names = set(names)

-      assert self._list_owned().issuperset(names), (
-               "release() on unheld resources %s" %
-               names.difference(self._list_owned()))
+      assert self.list_owned().issuperset(names), (
+               "release() on unheld resources %s (set %s)" %
+               (names.difference(self.list_owned()), self.name))

 
     # First of all let's release the "all elements" lock, if set.
     # After this 'add' can work again
 
     # First of all let's release the "all elements" lock, if set.
     # After this 'add' can work again

-    if self.__lock._is_owned():
+    if self.__lock.is_owned():

       self.__lock.release()
       self._del_owned()
 
       self.__lock.release()
       self._del_owned()
 

@@ -906,14 +1296,18 @@ class LockSet:
   def add(self, names, acquired=0, shared=0):
     """Add a new set of elements to the set
 
   def add(self, names, acquired=0, shared=0):
     """Add a new set of elements to the set
 

+    @type names: list of strings

     @param names: names of the new elements to add
     @param names: names of the new elements to add

+    @type acquired: integer (0/1) used as a boolean

     @param acquired: pre-acquire the new resource?
     @param acquired: pre-acquire the new resource?

+    @type shared: integer (0/1) used as a boolean

     @param shared: is the pre-acquisition shared?
 
     """
     # Check we don't already own locks at this level
     @param shared: is the pre-acquisition shared?
 
     """
     # Check we don't already own locks at this level

-    assert not self._is_owned() or self.__lock._is_owned(shared=0), \
-      "Cannot add locks if the set is only partially owned, or shared"
+    assert not self.is_owned() or self.__lock.is_owned(shared=0), \
+      ("Cannot add locks if the set %s is only partially owned, or shared" %
+       self.name)

 
     # Support passing in a single resource to add rather than many
     if isinstance(names, basestring):
 
     # Support passing in a single resource to add rather than many
     if isinstance(names, basestring):

@@ -922,7 +1316,7 @@ class LockSet:
     # If we don't already own the set-level lock acquired in an exclusive way
     # we'll get it and note we need to release it later.
     release_lock = False
     # If we don't already own the set-level lock acquired in an exclusive way
     # we'll get it and note we need to release it later.
     release_lock = False

-    if not self.__lock._is_owned():
+    if not self.__lock.is_owned():

       release_lock = True
       self.__lock.acquire()
 
       release_lock = True
       self.__lock.acquire()
 

@@ -932,12 +1326,15 @@ class LockSet:
         # This must be an explicit raise, not an assert, because assert is
         # turned off when using optimization, and this can happen because of
         # concurrency even if the user doesn't want it.
         # This must be an explicit raise, not an assert, because assert is
         # turned off when using optimization, and this can happen because of
         # concurrency even if the user doesn't want it.

-        raise errors.LockError("duplicate add() (%s)" % invalid_names)
+        raise errors.LockError("duplicate add(%s) on lockset %s" %
+                               (invalid_names, self.name))

 
       for lockname in names:
 
       for lockname in names:

-        lock = SharedLock()
+        lock = SharedLock(self._GetLockName(lockname), monitor=self.__monitor)

 
         if acquired:
 
         if acquired:

+          # No need for priority or timeout here as this lock has just been
+          # created

           lock.acquire(shared=shared)
           # now the lock cannot be deleted, we have it!
           try:
           lock.acquire(shared=shared)
           # now the lock cannot be deleted, we have it!
           try:

@@ -961,26 +1358,20 @@ class LockSet:
 
     return True
 
 
     return True
 

-  def remove(self, names, blocking=1):
+  def remove(self, names):

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

+    @type names: list of strings

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

-    @param blocking: whether to block while trying to acquire or to
-        operate in try-lock mode (this locking mode is not supported
-        yet unless you are already holding exclusively the locks)

 
 

-    @return:: a list of locks which we removed; the list is always
+    @return: a list of locks which we removed; the list is always

         equal to the names list if we were holding all the locks
         exclusively
 
     """
         equal to the names list if we were holding all the locks
         exclusively
 
     """

-    if not blocking and not self._is_owned():
-      # We don't have non-blocking mode for now
-      raise NotImplementedError
-

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

@@ -988,8 +1379,9 @@ class LockSet:
     # If we own any subset of this lock it must be a superset of what we want
     # to delete. The ownership must also be exclusive, but that will be checked
     # by the lock itself.
     # If we own any subset of this lock it must be a superset of what we want
     # to delete. The ownership must also be exclusive, but that will be checked
     # by the lock itself.

-    assert not self._is_owned() or self._list_owned().issuperset(names), (
-      "remove() on acquired lockset while not owning all elements")
+    assert not self.is_owned() or self.list_owned().issuperset(names), (
+      "remove() on acquired lockset %s while not owning all elements" %
+      self.name)

 
     removed = []
 
 
     removed = []
 

@@ -1004,7 +1396,8 @@ class LockSet:
         removed.append(lname)
       except (KeyError, errors.LockError):
         # This cannot happen if we were already holding it, verify:
         removed.append(lname)
       except (KeyError, errors.LockError):
         # This cannot happen if we were already holding it, verify:

-        assert not self._is_owned(), "remove failed while holding lockset"
+        assert not self.is_owned(), ("remove failed while holding lockset %s" %
+                                     self.name)

       else:
         # If no LockError was raised we are the ones who deleted the lock.
         # This means we can safely remove it from lockdict, as any further or
       else:
         # If no LockError was raised we are the ones who deleted the lock.
         # This means we can safely remove it from lockdict, as any further or

@@ -1015,7 +1408,7 @@ class LockSet:
         # it's the job of the one who actually deleted it.
         del self.__lockdict[lname]
         # And let's remove it from our private list if we owned it.
         # it's the job of the one who actually deleted it.
         del self.__lockdict[lname]
         # And let's remove it from our private list if we owned it.

-        if self._is_owned():
+        if self.is_owned():

           self._del_owned(name=lname)
 
     return removed
           self._del_owned(name=lname)
 
     return removed

@@ -1032,19 +1425,33 @@ class LockSet:
 #   the same time.
 LEVEL_CLUSTER = 0
 LEVEL_INSTANCE = 1
 #   the same time.
 LEVEL_CLUSTER = 0
 LEVEL_INSTANCE = 1

-LEVEL_NODE = 2
-
-LEVELS = [LEVEL_CLUSTER,
-          LEVEL_INSTANCE,
-          LEVEL_NODE]
+LEVEL_NODEGROUP = 2
+LEVEL_NODE = 3
+LEVEL_NODE_RES = 4
+
+LEVELS = [
+  LEVEL_CLUSTER,
+  LEVEL_INSTANCE,
+  LEVEL_NODEGROUP,
+  LEVEL_NODE,
+  LEVEL_NODE_RES,
+  ]

 
 # Lock levels which are modifiable
 
 # Lock levels which are modifiable

-LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE]
-
+LEVELS_MOD = frozenset([
+  LEVEL_NODE_RES,
+  LEVEL_NODE,
+  LEVEL_NODEGROUP,
+  LEVEL_INSTANCE,
+  ])
+
+#: Lock level names (make sure to use singular form)

 LEVEL_NAMES = {
   LEVEL_CLUSTER: "cluster",
   LEVEL_INSTANCE: "instance",
 LEVEL_NAMES = {
   LEVEL_CLUSTER: "cluster",
   LEVEL_INSTANCE: "instance",

+  LEVEL_NODEGROUP: "nodegroup",

   LEVEL_NODE: "node",
   LEVEL_NODE: "node",

+  LEVEL_NODE_RES: "node-res",

   }
 
 # Constant for the big ganeti lock
   }
 
 # Constant for the big ganeti lock

@@ -1062,13 +1469,14 @@ class GanetiLockManager:
   """
   _instance = None
 
   """
   _instance = None
 

-  def __init__(self, nodes=None, instances=None):
+  def __init__(self, nodes, nodegroups, instances):

     """Constructs a new GanetiLockManager object.
 
     There should be only a GanetiLockManager object at any time, so this
     function raises an error if this is not the case.
 
     @param nodes: list of node names
     """Constructs a new GanetiLockManager object.
 
     There should be only a GanetiLockManager object at any time, so this
     function raises an error if this is not the case.
 
     @param nodes: list of node names

+    @param nodegroups: list of nodegroup uuids

     @param instances: list of instance names
 
     """
     @param instances: list of instance names
 
     """

@@ -1077,13 +1485,45 @@ class GanetiLockManager:
 
     self.__class__._instance = self
 
 
     self.__class__._instance = self
 

+    self._monitor = LockMonitor()
+

     # The keyring contains all the locks, at their level and in the correct
     # locking order.
     self.__keyring = {
     # The keyring contains all the locks, at their level and in the correct
     # locking order.
     self.__keyring = {

-      LEVEL_CLUSTER: LockSet([BGL]),
-      LEVEL_NODE: LockSet(nodes),
-      LEVEL_INSTANCE: LockSet(instances),
-    }
+      LEVEL_CLUSTER: LockSet([BGL], "cluster", monitor=self._monitor),
+      LEVEL_NODE: LockSet(nodes, "node", monitor=self._monitor),
+      LEVEL_NODE_RES: LockSet(nodes, "node-res", monitor=self._monitor),
+      LEVEL_NODEGROUP: LockSet(nodegroups, "nodegroup", monitor=self._monitor),
+      LEVEL_INSTANCE: LockSet(instances, "instance",
+                              monitor=self._monitor),
+      }
+
+    assert compat.all(ls.name == LEVEL_NAMES[level]
+                      for (level, ls) in self.__keyring.items())
+
+  def AddToLockMonitor(self, provider):
+    """Registers a new lock with the monitor.
+
+    See L{LockMonitor.RegisterLock}.
+
+    """
+    return self._monitor.RegisterLock(provider)
+
+  def QueryLocks(self, fields):
+    """Queries information from all locks.
+
+    See L{LockMonitor.QueryLocks}.
+
+    """
+    return self._monitor.QueryLocks(fields)
+
+  def OldStyleQueryLocks(self, fields):
+    """Queries information from all locks, returning old-style data.
+
+    See L{LockMonitor.OldStyleQueryLocks}.
+
+    """
+    return self._monitor.OldStyleQueryLocks(fields)

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

@@ -1096,19 +1536,25 @@ class GanetiLockManager:
     assert level in LEVELS, "Invalid locking level %s" % level
     return self.__keyring[level]._names()
 
     assert level in LEVELS, "Invalid locking level %s" % level
     return self.__keyring[level]._names()
 

-  def _is_owned(self, level):
+  def is_owned(self, level):

     """Check whether we are owning locks at the given level
 
     """
     """Check whether we are owning locks at the given level
 
     """

-    return self.__keyring[level]._is_owned()
+    return self.__keyring[level].is_owned()

 
 

-  is_owned = _is_owned
-
-  def _list_owned(self, level):
+  def list_owned(self, level):

     """Get the set of owned locks at the given level
 
     """
     """Get the set of owned locks at the given level
 
     """

-    return self.__keyring[level]._list_owned()
+    return self.__keyring[level].list_owned()
+
+  def check_owned(self, level, names, shared=-1):
+    """Check if locks at a certain level are owned in a specific mode.
+
+    @see: L{LockSet.check_owned}
+
+    """
+    return self.__keyring[level].check_owned(names, shared=shared)

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

@@ -1116,17 +1562,18 @@ class GanetiLockManager:
     """
     # This way of checking only works if LEVELS[i] = i, which we check for in
     # the test cases.
     """
     # This way of checking only works if LEVELS[i] = i, which we check for in
     # the test cases.

-    return utils.any((self._is_owned(l) for l in LEVELS[level + 1:]))
+    return compat.any((self.is_owned(l) for l in LEVELS[level + 1:]))

 
 

-  def _BGL_owned(self):
+  def _BGL_owned(self): # pylint: disable=C0103

     """Check if the current thread owns the BGL.
 
     Both an exclusive or a shared acquisition work.
 
     """
     """Check if the current thread owns the BGL.
 
     Both an exclusive or a shared acquisition work.
 
     """

-    return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned()
+    return BGL in self.__keyring[LEVEL_CLUSTER].list_owned()

 
 

-  def _contains_BGL(self, level, names):
+  @staticmethod
+  def _contains_BGL(level, names): # pylint: disable=C0103

     """Check if the level contains the BGL.
 
     Check if acting on the given level and set of names will change
     """Check if the level contains the BGL.
 
     Check if acting on the given level and set of names will change

@@ -1135,17 +1582,21 @@ class GanetiLockManager:
     """
     return level == LEVEL_CLUSTER and (names is None or BGL in names)
 
     """
     return level == LEVEL_CLUSTER and (names is None or BGL in names)
 

-  def acquire(self, level, names, blocking=1, shared=0):
+  def acquire(self, level, names, timeout=None, shared=0, priority=None):

     """Acquire a set of resource locks, at the same level.
 
     """Acquire a set of resource locks, at the same level.
 

-    @param level: the level at which the locks shall be acquired;
-        it must be a member of LEVELS.
+    @type level: member of locking.LEVELS
+    @param level: the level at which the locks shall be acquired
+    @type names: list of strings (or string)

     @param names: the names of the locks which shall be acquired
         (special lock names, or instance/node names)
     @param names: the names of the locks which shall be acquired
         (special lock names, or instance/node names)

+    @type shared: integer (0/1) used as a boolean

     @param shared: whether to acquire in shared mode; by default
         an exclusive lock will be acquired
     @param shared: whether to acquire in shared mode; by default
         an exclusive lock will be acquired

-    @param blocking: whether to block while trying to acquire or to
-        operate in try-lock mode (this locking mode is not supported yet)
+    @type timeout: float
+    @param timeout: Maximum time to acquire all locks
+    @type priority: integer
+    @param priority: Priority for acquiring lock

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

@@ -1164,8 +1615,24 @@ class GanetiLockManager:
            " while owning some at a greater one")
 
     # Acquire the locks in the set.
            " while owning some at a greater one")
 
     # Acquire the locks in the set.

-    return self.__keyring[level].acquire(names, shared=shared,
-                                         blocking=blocking)
+    return self.__keyring[level].acquire(names, shared=shared, timeout=timeout,
+                                         priority=priority)
+
+  def downgrade(self, level, names=None):
+    """Downgrade a set of resource locks from exclusive to shared mode.
+
+    You must have acquired the locks in exclusive mode.
+
+    @type level: member of locking.LEVELS
+    @param level: the level at which the locks shall be downgraded
+    @type names: list of strings, or None
+    @param names: the names of the locks which shall be downgraded
+        (defaults to all the locks acquired at the level)
+
+    """
+    assert level in LEVELS, "Invalid locking level %s" % level
+
+    return self.__keyring[level].downgrade(names=names)

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

@@ -1173,8 +1640,9 @@ class GanetiLockManager:
     You must have acquired the locks, either in shared or in exclusive
     mode, before releasing them.
 
     You must have acquired the locks, either in shared or in exclusive
     mode, before releasing them.
 

-    @param level: the level at which the locks shall be released;
-        it must be a member of LEVELS
+    @type level: member of locking.LEVELS
+    @param level: the level at which the locks shall be released
+    @type names: list of strings, or None

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

@@ -1183,7 +1651,9 @@ class GanetiLockManager:
     assert (not self._contains_BGL(level, names) or
             not self._upper_owned(LEVEL_CLUSTER)), (
             "Cannot release the Big Ganeti Lock while holding something"
     assert (not self._contains_BGL(level, names) or
             not self._upper_owned(LEVEL_CLUSTER)), (
             "Cannot release the Big Ganeti Lock while holding something"

-            " at upper levels")
+            " at upper levels (%r)" %
+            (utils.CommaJoin(["%s=%r" % (LEVEL_NAMES[i], self.list_owned(i))
+                              for i in self.__keyring.keys()]), ))

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

@@ -1191,10 +1661,13 @@ class GanetiLockManager:
   def add(self, level, names, acquired=0, shared=0):
     """Add locks at the specified level.
 
   def add(self, level, names, acquired=0, shared=0):
     """Add locks at the specified level.
 

-    @param level: the level at which the locks shall be added;
-        it must be a member of LEVELS_MOD.
+    @type level: member of locking.LEVELS_MOD
+    @param level: the level at which the locks shall be added
+    @type names: list of strings

     @param names: names of the locks to acquire
     @param names: names of the locks to acquire

+    @type acquired: integer (0/1) used as a boolean

     @param acquired: whether to acquire the newly added locks
     @param acquired: whether to acquire the newly added locks

+    @type shared: integer (0/1) used as a boolean

     @param shared: whether the acquisition will be shared
 
     """
     @param shared: whether the acquisition will be shared
 
     """

@@ -1205,18 +1678,17 @@ class GanetiLockManager:
            " while owning some at a greater one")
     return self.__keyring[level].add(names, acquired=acquired, shared=shared)
 
            " while owning some at a greater one")
     return self.__keyring[level].add(names, acquired=acquired, shared=shared)
 

-  def remove(self, level, names, blocking=1):
+  def remove(self, level, names):

     """Remove locks from the specified level.
 
     You must either already own the locks you are trying to remove
     exclusively or not own any lock at an upper level.
 
     """Remove locks from the specified level.
 
     You must either already own the locks you are trying to remove
     exclusively or not own any lock at an upper level.
 

-    @param level: the level at which the locks shall be removed;
-        it must be a member of LEVELS_MOD
+    @type level: member of locking.LEVELS_MOD
+    @param level: the level at which the locks shall be removed
+    @type names: list of strings

     @param names: the names of the locks which shall be removed
         (special lock names, or instance/node names)
     @param names: the names of the locks which shall be removed
         (special lock names, or instance/node names)

-    @param blocking: whether to block while trying to operate in
-        try-lock mode (this locking mode is not supported yet)

 
     """
     assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
 
     """
     assert level in LEVELS_MOD, "Invalid or immutable level %s" % level

@@ -1225,7 +1697,115 @@ class GanetiLockManager:
     # Check we either own the level or don't own anything from here
     # up. LockSet.remove() will check the case in which we don't own
     # all the needed resources, or we have a shared ownership.
     # Check we either own the level or don't own anything from here
     # up. LockSet.remove() will check the case in which we don't own
     # all the needed resources, or we have a shared ownership.

-    assert self._is_owned(level) or not self._upper_owned(level), (
+    assert self.is_owned(level) or not self._upper_owned(level), (

            "Cannot remove locks at a level while not owning it or"
            " owning some at a greater one")
            "Cannot remove locks at a level while not owning it or"
            " owning some at a greater one")

-    return self.__keyring[level].remove(names, blocking=blocking)
+    return self.__keyring[level].remove(names)
+
+
+def _MonitorSortKey((item, idx, num)):
+  """Sorting key function.
+
+  Sort by name, registration order and then order of information. This provides
+  a stable sort order over different providers, even if they return the same
+  name.
+
+  """
+  (name, _, _, _) = item
+
+  return (utils.NiceSortKey(name), num, idx)
+
+
+class LockMonitor(object):
+  _LOCK_ATTR = "_lock"
+
+  def __init__(self):
+    """Initializes this class.
+
+    """
+    self._lock = SharedLock("LockMonitor")
+
+    # Counter for stable sorting
+    self._counter = itertools.count(0)
+
+    # Tracked locks. Weak references are used to avoid issues with circular
+    # references and deletion.
+    self._locks = weakref.WeakKeyDictionary()
+
+  @ssynchronized(_LOCK_ATTR)
+  def RegisterLock(self, provider):
+    """Registers a new lock.
+
+    @param provider: Object with a callable method named C{GetLockInfo}, taking
+      a single C{set} containing the requested information items
+    @note: It would be nicer to only receive the function generating the
+      requested information but, as it turns out, weak references to bound
+      methods (e.g. C{self.GetLockInfo}) are tricky; there are several
+      workarounds, but none of the ones I found works properly in combination
+      with a standard C{WeakKeyDictionary}
+
+    """
+    assert provider not in self._locks, "Duplicate registration"
+
+    # There used to be a check for duplicate names here. As it turned out, when
+    # a lock is re-created with the same name in a very short timeframe, the
+    # previous instance might not yet be removed from the weakref dictionary.
+    # By keeping track of the order of incoming registrations, a stable sort
+    # ordering can still be guaranteed.
+
+    self._locks[provider] = self._counter.next()
+
+  def _GetLockInfo(self, requested):
+    """Get information from all locks.
+
+    """
+    # Must hold lock while getting consistent list of tracked items
+    self._lock.acquire(shared=1)
+    try:
+      items = self._locks.items()
+    finally:
+      self._lock.release()
+
+    return [(info, idx, num)
+            for (provider, num) in items
+            for (idx, info) in enumerate(provider.GetLockInfo(requested))]
+
+  def _Query(self, fields):
+    """Queries information from all locks.
+
+    @type fields: list of strings
+    @param fields: List of fields to return
+
+    """
+    qobj = query.Query(query.LOCK_FIELDS, fields)
+
+    # Get all data with internal lock held and then sort by name and incoming
+    # order
+    lockinfo = sorted(self._GetLockInfo(qobj.RequestedData()),
+                      key=_MonitorSortKey)
+
+    # Extract lock information and build query data
+    return (qobj, query.LockQueryData(map(compat.fst, lockinfo)))
+
+  def QueryLocks(self, fields):
+    """Queries information from all locks.
+
+    @type fields: list of strings
+    @param fields: List of fields to return
+
+    """
+    (qobj, ctx) = self._Query(fields)
+
+    # Prepare query response
+    return query.GetQueryResponse(qobj, ctx)
+
+  def OldStyleQueryLocks(self, fields):
+    """Queries information from all locks, returning old-style data.
+
+    @type fields: list of strings
+    @param fields: List of fields to return
+
+    """
+    (qobj, ctx) = self._Query(fields)
+
+    return qobj.OldStyleQuery(ctx)