utils.log: Split formatter building into separate function

[ganeti-local] / lib / locking.py

diff --git a/lib/locking.py b/lib/locking.py
index f30e8b7..3575085 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 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

@@ -28,23 +28,44 @@
 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 operator

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

+from ganeti import compat
+from ganeti import query

 
 
 
 

-def ssynchronized(lock, shared=0):
+_EXCLUSIVE_TEXT = "exclusive"
+_SHARED_TEXT = "shared"
+_DELETED_TEXT = "deleted"
+
+_DEFAULT_PRIORITY = 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)

@@ -54,59 +75,6 @@ def ssynchronized(lock, shared=0):
   return wrap
 
 
   return wrap
 
 

-class RunningTimeout(object):
-  """Class to calculate remaining timeout when doing several operations.
-
-  """
-  __slots__ = [
-    "_allow_negative",
-    "_start_time",
-    "_time_fn",
-    "_timeout",
-    ]
-
-  def __init__(self, timeout, allow_negative, _time_fn=time.time):
-    """Initializes this class.
-
-    @type timeout: float
-    @param timeout: Timeout duration
-    @type allow_negative: bool
-    @param allow_negative: Whether to return values below zero
-    @param _time_fn: Time function for unittests
-
-    """
-    object.__init__(self)
-
-    if timeout is not None and timeout < 0.0:
-      raise ValueError("Timeout must not be negative")
-
-    self._timeout = timeout
-    self._allow_negative = allow_negative
-    self._time_fn = _time_fn
-
-    self._start_time = None
-
-  def Remaining(self):
-    """Returns the remaining timeout.
-
-    """
-    if self._timeout is None:
-      return None
-
-    # Get start time on first calculation
-    if self._start_time is None:
-      self._start_time = self._time_fn()
-
-    # Calculate remaining time
-    remaining_timeout = self._start_time + self._timeout - self._time_fn()
-
-    if not self._allow_negative:
-      # Ensure timeout is always >= 0
-      return max(0.0, remaining_timeout)
-
-    return remaining_timeout
-
-

 class _SingleNotifyPipeConditionWaiter(object):
   """Helper class for SingleNotifyPipeCondition
 
 class _SingleNotifyPipeConditionWaiter(object):
   """Helper class for SingleNotifyPipeCondition
 

@@ -136,13 +104,17 @@ class _SingleNotifyPipeConditionWaiter(object):
     @param timeout: Timeout for waiting (can be None)
 
     """
     @param timeout: Timeout for waiting (can be None)
 
     """

-    running_timeout = RunningTimeout(timeout, True)
+    running_timeout = utils.RunningTimeout(timeout, True)

 
     while True:
       remaining_time = running_timeout.Remaining()
 
 
     while True:
       remaining_time = running_timeout.Remaining()
 

-      if remaining_time is not None and remaining_time < 0.0:
-        break
+      if remaining_time is not None:
+        if remaining_time < 0.0:
+          break
+
+        # Our calculation uses seconds, poll() wants milliseconds
+        remaining_time *= 1000

 
       try:
         result = self._poller.poll(remaining_time)
 
       try:
         result = self._poller.poll(remaining_time)

@@ -166,6 +138,9 @@ class _BaseCondition(object):
     "_lock",
     "acquire",
     "release",
     "_lock",
     "acquire",
     "release",

+    "_is_owned",
+    "_acquire_restore",
+    "_release_save",

     ]
 
   def __init__(self, lock):
     ]
 
   def __init__(self, lock):

@@ -177,9 +152,18 @@ class _BaseCondition(object):
     """
     object.__init__(self)
 
     """
     object.__init__(self)
 

-    # Recursive locks are not supported
-    assert not hasattr(lock, "_acquire_restore")
-    assert not hasattr(lock, "_release_save")
+    try:
+      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

 
     self._lock = lock
 
 
     self._lock = lock
 

@@ -187,16 +171,21 @@ class _BaseCondition(object):
     self.acquire = lock.acquire
     self.release = lock.release
 
     self.acquire = lock.acquire
     self.release = lock.release
 

-  def _is_owned(self):
+  def _base_is_owned(self):

     """Check whether lock is owned by current thread.
 
     """
     if self._lock.acquire(0):
       self._lock.release()
       return False
     """Check whether lock is owned by current thread.
 
     """
     if self._lock.acquire(0):
       self._lock.release()
       return False

-

     return True
 
     return True
 

+  def _base_release_save(self):
+    self._lock.release()
+
+  def _base_acquire_restore(self, _):
+    self._lock.acquire()
+

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

@@ -216,7 +205,7 @@ class SingleNotifyPipeCondition(_BaseCondition):
 
   """
 
 
   """
 

-  __slots__ = _BaseCondition.__slots__ + [
+  __slots__ = [

     "_poller",
     "_read_fd",
     "_write_fd",
     "_poller",
     "_read_fd",
     "_write_fd",

@@ -275,13 +264,13 @@ class SingleNotifyPipeCondition(_BaseCondition):
         self._poller.register(self._read_fd, select.POLLHUP)
 
       wait_fn = self._waiter_class(self._poller, self._read_fd)
         self._poller.register(self._read_fd, select.POLLHUP)
 
       wait_fn = self._waiter_class(self._poller, self._read_fd)

-      self.release()
+      state = self._release_save()

       try:
         # Wait for notification
         wait_fn(timeout)
       finally:
         # Re-acquire lock
       try:
         # Wait for notification
         wait_fn(timeout)
       finally:
         # Re-acquire lock

-        self.acquire()
+        self._acquire_restore(state)

     finally:
       self._nwaiters -= 1
       if self._nwaiters == 0:
     finally:
       self._nwaiters -= 1
       if self._nwaiters == 0:

@@ -309,8 +298,8 @@ class PipeCondition(_BaseCondition):
   there are any waiting threads.
 
   """
   there are any waiting threads.
 
   """

-  __slots__ = _BaseCondition.__slots__ + [
-    "_nwaiters",
+  __slots__ = [
+    "_waiters",

     "_single_condition",
     ]
 
     "_single_condition",
     ]
 

@@ -321,7 +310,7 @@ class PipeCondition(_BaseCondition):
 
     """
     _BaseCondition.__init__(self, lock)
 
     """
     _BaseCondition.__init__(self, lock)

-    self._nwaiters = 0
+    self._waiters = set()

     self._single_condition = self._single_condition_class(self._lock)
 
   def wait(self, timeout=None):
     self._single_condition = self._single_condition_class(self._lock)
 
   def wait(self, timeout=None):

@@ -335,15 +324,14 @@ class PipeCondition(_BaseCondition):
 
     # 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.

-    my_condition = self._single_condition
+    cond = self._single_condition

 
 

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

     try:
     try:

-      my_condition.wait(timeout)
+      cond.wait(timeout)

     finally:
     finally:

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

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

@@ -353,102 +341,88 @@ class PipeCondition(_BaseCondition):
     self._single_condition.notifyAll()
     self._single_condition = self._single_condition_class(self._lock)
 
     self._single_condition.notifyAll()
     self._single_condition = self._single_condition_class(self._lock)
 

-  def has_waiting(self):
-    """Returns whether there are active waiters.
+  def get_waiting(self):
+    """Returns a list of all waiting threads.

 
     """
     self._check_owned()
 
 
     """
     self._check_owned()
 

-    return bool(self._nwaiters)
+    return self._waiters

 
 

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

 
 

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

 
 

-  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.
+    return bool(self._waiters)

 
 

-  """
+
+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): # pylint: disable-msg=C0103
-    """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: Waiting timeout (can be None)
-
-    """
-    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)}.

 
 

-  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.
+  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.
+
+  @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 = PipeCondition
+  __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()

@@ -457,12 +431,73 @@ 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:
+      monitor.RegisterLock(self)
+
+  def GetInfo(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?

@@ -513,7 +548,23 @@ 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
+      return not (self.__find_first_pending_queue() or
+                  self.__pending or
+                  self.__pending_by_prio or
+                  self.__pending_shared)

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

@@ -535,26 +586,52 @@ 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 not prioqueue:
+        heapq.heappop(self.__pending)
+        del self.__pending_by_prio[priority]
+        assert priority not in self.__pending_shared
+        continue
+
+      if prioqueue:
+        return prioqueue
+
+    return 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
+    return cond == self.__find_first_pending_queue()[0]

 
 

-  def __acquire_unlocked(self, shared, timeout):
+  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):

@@ -562,20 +639,37 @@ 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

@@ -592,30 +686,38 @@ 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:
+          del self.__pending_shared[priority]

 
     return False
 
 
     return False
 

-  def acquire(self, shared=0, timeout=None, test_notify=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
 
     """
     @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:
       # We already got the lock, notify now
       if __debug__ and callable(test_notify):
         test_notify()
 
     self.__lock.acquire()
     try:
       # We already got the lock, notify now
       if __debug__ and callable(test_notify):
         test_notify()
 

-      return self.__acquire_unlocked(shared, timeout)
+      return self.__acquire_unlocked(shared, timeout, priority)

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

@@ -638,18 +740,14 @@ 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
+      prioqueue = self.__find_first_pending_queue()
+      if prioqueue:
+        prioqueue[0].notifyAll()

 
     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

@@ -658,8 +756,13 @@ 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"

@@ -670,7 +773,7 @@ class SharedLock(object):
       acquired = self.__is_exclusive()
 
       if not acquired:
       acquired = self.__is_exclusive()
 
       if not acquired:

-        acquired = self.__acquire_unlocked(0, timeout)
+        acquired = self.__acquire_unlocked(0, timeout, priority)

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

@@ -679,14 +782,27 @@ class SharedLock(object):
         self.__deleted = True
         self.__exc = None
 
         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.
 
 # Whenever we want to acquire a full LockSet we pass None as the value
 # to acquire.  Hide this behind this nicely named constant.

@@ -709,23 +825,35 @@ 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

 
     """
 
     """

+    assert members is not None, "members parameter is not a list"
+    self.name = name
+
+    # Lock monitor
+    self.__monitor = monitor
+

     # Used internally to guarantee coherency.
     # Used internally to guarantee coherency.

-    self.__lock = SharedLock()
+    self.__lock = SharedLock(name)

 
     # 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

@@ -736,6 +864,12 @@ class LockSet:
     # will be trouble.
     self.__owners = {}
 
     # will be trouble.
     self.__owners = {}
 

+  def _GetLockName(self, mname):
+    """Returns the name for a member lock.
+
+    """
+    return "%s/%s" % (self.name, mname)
+

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

@@ -808,15 +942,20 @@ class LockSet:
         self.__lock.release()
     return set(result)
 
         self.__lock.release()
     return set(result)
 

-  def acquire(self, names, timeout=None, shared=0, test_notify=None):
+  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
     @type timeout: float or None
     @param timeout: Maximum time to acquire all locks
     @param shared: whether to acquire in shared mode; by default an
         exclusive lock will be acquired
     @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
 
     @type test_notify: callable or None
     @param test_notify: Special callback function for unittesting
 

@@ -830,11 +969,15 @@ class LockSet:
     assert timeout is None or timeout >= 0.0
 
     # Check we don't already own locks at this level
     assert timeout is None or timeout >= 0.0
 
     # 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 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.
 
     # 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 = RunningTimeout(timeout, False)
+    running_timeout = utils.RunningTimeout(timeout, False)

 
     try:
       if names is not None:
 
     try:
       if names is not None:

@@ -842,7 +985,7 @@ class LockSet:
         if isinstance(names, basestring):
           names = [names]
 
         if isinstance(names, basestring):
           names = [names]
 

-        return self.__acquire_inner(names, False, shared,
+        return self.__acquire_inner(names, False, shared, priority,

                                     running_timeout.Remaining, test_notify)
 
       else:
                                     running_timeout.Remaining, test_notify)
 
       else:

@@ -851,18 +994,18 @@ class LockSet:
         # 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
         # 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
+        # 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.
         # 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,
+        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()
 
                                    timeout=running_timeout.Remaining()):
           raise _AcquireTimeout()
         try:
           # note we own the set-lock
           self._add_owned()
 

-          return self.__acquire_inner(self.__names(), True, shared,
+          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
                                       running_timeout.Remaining, test_notify)
         except:
           # We shouldn't have problems adding the lock to the owners list, but

@@ -875,13 +1018,15 @@ class LockSet:
     except _AcquireTimeout:
       return None
 
     except _AcquireTimeout:
       return None
 

-  def __acquire_inner(self, names, want_all, shared, timeout_fn, test_notify):
+  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
     """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
 
     """
     @param test_notify: Special callback function for unittesting
 
     """

@@ -900,7 +1045,8 @@ class LockSet:
           # element is not there anymore.
           continue
 
           # element is not there anymore.
           continue
 

-        raise errors.LockError("Non-existing lock in set (%s)" % lname)
+        raise errors.LockError("Non-existing lock %s in set %s (it may have"
+                               " been removed)" % (lname, self.name))

 
       acquire_list.append((lname, lock))
 
 
       acquire_list.append((lname, lock))
 

@@ -924,6 +1070,7 @@ class LockSet:
         try:
           # raises LockError if the lock was deleted
           acq_success = lock.acquire(shared=shared, timeout=timeout,
         try:
           # 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:
                                      test_notify=test_notify_fn)
         except errors.LockError:
           if want_all:

@@ -931,14 +1078,16 @@ class LockSet:
             # particular element is not there anymore.
             continue
 
             # particular element is not there anymore.
             continue
 

-          raise errors.LockError("Non-existing lock in set (%s)" % lname)
+          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.
 
         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" % lname)
+            raise errors.LockError("Failed to get lock %s (set %s)" %
+                                   (lname, self.name))

 
           raise _AcquireTimeout()
 
 
           raise _AcquireTimeout()
 

@@ -968,11 +1117,13 @@ class LockSet:
     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.
 

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

@@ -983,8 +1134,8 @@ class LockSet:
     else:
       names = set(names)
       assert self._list_owned().issuperset(names), (
     else:
       names = set(names)
       assert self._list_owned().issuperset(names), (

-               "release() on unheld resources %s" %
-               names.difference(self._list_owned()))
+               "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

@@ -1001,14 +1152,18 @@ 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
     assert not self._is_owned() or self.__lock._is_owned(shared=0), \
     @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"
+      ("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):

@@ -1027,12 +1182,15 @@ 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:

@@ -1062,6 +1220,7 @@ class LockSet:
     You can either not hold anything in the lockset or already hold a superset
     of the elements you want to delete, exclusively.
 
     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.
 
     @return: a list of locks which we removed; the list is always
     @param names: names of the resource to remove.
 
     @return: a list of locks which we removed; the list is always

@@ -1077,7 +1236,8 @@ class LockSet:
     # 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), (
     # 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")
+      "remove() on acquired lockset %s while not owning all elements" %
+      self.name)

 
     removed = []
 
 
     removed = []
 

@@ -1092,7 +1252,8 @@ 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

@@ -1120,18 +1281,21 @@ class LockSet:
 #   the same time.
 LEVEL_CLUSTER = 0
 LEVEL_INSTANCE = 1
 #   the same time.
 LEVEL_CLUSTER = 0
 LEVEL_INSTANCE = 1

-LEVEL_NODE = 2
+LEVEL_NODEGROUP = 2
+LEVEL_NODE = 3

 
 LEVELS = [LEVEL_CLUSTER,
           LEVEL_INSTANCE,
 
 LEVELS = [LEVEL_CLUSTER,
           LEVEL_INSTANCE,

+          LEVEL_NODEGROUP,

           LEVEL_NODE]
 
 # Lock levels which are modifiable
           LEVEL_NODE]
 
 # Lock levels which are modifiable

-LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE]
+LEVELS_MOD = [LEVEL_NODE, LEVEL_NODEGROUP, LEVEL_INSTANCE]

 
 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",
   }
 

@@ -1150,13 +1314,14 @@ 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
 
     """

@@ -1165,13 +1330,33 @@ 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], "BGL", monitor=self._monitor),
+      LEVEL_NODE: LockSet(nodes, "nodes", monitor=self._monitor),
+      LEVEL_NODEGROUP: LockSet(nodegroups, "nodegroups", monitor=self._monitor),
+      LEVEL_INSTANCE: LockSet(instances, "instances",
+                              monitor=self._monitor),
+      }
+
+  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.

@@ -1204,7 +1389,7 @@ 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): # pylint: disable-msg=C0103
     """Check if the current thread owns the BGL.
 
   def _BGL_owned(self): # pylint: disable-msg=C0103
     """Check if the current thread owns the BGL.

@@ -1224,17 +1409,21 @@ 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, timeout=None, 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
     @type timeout: float
     @param timeout: Maximum time to acquire all locks
     @param shared: whether to acquire in shared mode; by default
         an exclusive lock will be acquired
     @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

@@ -1253,7 +1442,8 @@ 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, timeout=timeout)
+    return self.__keyring[level].acquire(names, shared=shared, timeout=timeout,
+                                         priority=priority)

 
   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.

@@ -1261,8 +1451,9 @@ 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)
 

@@ -1281,10 +1472,13 @@ 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
 
     """

@@ -1301,8 +1495,9 @@ class GanetiLockManager:
     You must either already own the locks you are trying to remove
     exclusively or not own any lock at an upper 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)
 

@@ -1317,3 +1512,73 @@ class GanetiLockManager:
            "Cannot remove locks at a level while not owning it or"
            " owning some at a greater one")
     return self.__keyring[level].remove(names)
            "Cannot remove locks at a level while not owning it or"
            " owning some at a greater one")
     return self.__keyring[level].remove(names)

+
+
+class LockMonitor(object):
+  _LOCK_ATTR = "_lock"
+
+  def __init__(self):
+    """Initializes this class.
+
+    """
+    self._lock = SharedLock("LockMonitor")
+
+    # Tracked locks. Weak references are used to avoid issues with circular
+    # references and deletion.
+    self._locks = weakref.WeakKeyDictionary()
+
+  @ssynchronized(_LOCK_ATTR)
+  def RegisterLock(self, lock):
+    """Registers a new lock.
+
+    """
+    logging.debug("Registering lock %s", lock.name)
+    assert lock not in self._locks, "Duplicate lock registration"
+    assert not compat.any(lock.name == i.name for i in self._locks.keys()), \
+           "Found duplicate lock name"
+    self._locks[lock] = None
+
+  @ssynchronized(_LOCK_ATTR)
+  def _GetLockInfo(self, requested):
+    """Get information from all locks while the monitor lock is held.
+
+    """
+    return [lock.GetInfo(requested) for lock in self._locks.keys()]
+
+  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 and sort by name
+    lockinfo = utils.NiceSort(self._GetLockInfo(qobj.RequestedData()),
+                              key=operator.itemgetter(0))
+
+    return (qobj, query.LockQueryData(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)