Remove deprecated “QueryLocks” LUXI request
[ganeti-local] / lib / jqueue.py
index d8249df..34ac6a7 100644 (file)
@@ -1,7 +1,7 @@
 #
 #
 
-# Copyright (C) 2006, 2007, 2008 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
@@ -29,28 +29,43 @@ used by all other classes in this module.
 
 """
 
-import os
 import logging
-import threading
 import errno
-import re
 import time
 import weakref
+import threading
+import itertools
 
+try:
+  # pylint: disable=E0611
+  from pyinotify import pyinotify
+except ImportError:
+  import pyinotify
+
+from ganeti import asyncnotifier
 from ganeti import constants
 from ganeti import serializer
 from ganeti import workerpool
+from ganeti import locking
 from ganeti import opcodes
 from ganeti import errors
 from ganeti import mcpu
 from ganeti import utils
 from ganeti import jstore
 from ganeti import rpc
+from ganeti import runtime
+from ganeti import netutils
+from ganeti import compat
+from ganeti import ht
 
 
 JOBQUEUE_THREADS = 25
 JOBS_PER_ARCHIVE_DIRECTORY = 10000
 
+# member lock names to be passed to @ssynchronized decorator
+_LOCK = "_lock"
+_QUEUE = "_queue"
+
 
 class CancelJob(Exception):
   """Special exception to cancel a job.
@@ -81,7 +96,7 @@ class _QueuedOpCode(object):
   @ivar stop_timestamp: timestamp for the end of the execution
 
   """
-  __slots__ = ["input", "status", "result", "log",
+  __slots__ = ["input", "status", "result", "log", "priority",
                "start_timestamp", "exec_timestamp", "end_timestamp",
                "__weakref__"]
 
@@ -100,6 +115,9 @@ class _QueuedOpCode(object):
     self.exec_timestamp = None
     self.end_timestamp = None
 
+    # Get initial priority (it might change during the lifetime of this opcode)
+    self.priority = getattr(op, "priority", constants.OP_PRIO_DEFAULT)
+
   @classmethod
   def Restore(cls, state):
     """Restore the _QueuedOpCode from the serialized form.
@@ -118,6 +136,7 @@ class _QueuedOpCode(object):
     obj.start_timestamp = state.get("start_timestamp", None)
     obj.exec_timestamp = state.get("exec_timestamp", None)
     obj.end_timestamp = state.get("end_timestamp", None)
+    obj.priority = state.get("priority", constants.OP_PRIO_DEFAULT)
     return obj
 
   def Serialize(self):
@@ -135,6 +154,7 @@ class _QueuedOpCode(object):
       "start_timestamp": self.start_timestamp,
       "exec_timestamp": self.exec_timestamp,
       "end_timestamp": self.end_timestamp,
+      "priority": self.priority,
       }
 
 
@@ -154,17 +174,15 @@ class _QueuedJob(object):
   @ivar received_timestamp: the timestamp for when the job was received
   @ivar start_timestmap: the timestamp for start of execution
   @ivar end_timestamp: the timestamp for end of execution
-  @ivar lock_status: In-memory locking information for debugging
-  @ivar change: a Condition variable we use for waiting for job changes
+  @ivar writable: Whether the job is allowed to be modified
 
   """
-  # pylint: disable-msg=W0212
-  __slots__ = ["queue", "id", "ops", "log_serial",
+  # pylint: disable=W0212
+  __slots__ = ["queue", "id", "ops", "log_serial", "ops_iter", "cur_opctx",
                "received_timestamp", "start_timestamp", "end_timestamp",
-               "lock_status", "change",
-               "__weakref__"]
+               "__weakref__", "processor_lock", "writable"]
 
-  def __init__(self, queue, job_id, ops):
+  def __init__(self, queue, job_id, ops, writable):
     """Constructor for the _QueuedJob.
 
     @type queue: L{JobQueue}
@@ -174,6 +192,8 @@ class _QueuedJob(object):
     @type ops: list
     @param ops: the list of opcodes we hold, which will be encapsulated
         in _QueuedOpCodes
+    @type writable: bool
+    @param writable: Whether job can be modified
 
     """
     if not ops:
@@ -187,11 +207,22 @@ class _QueuedJob(object):
     self.start_timestamp = None
     self.end_timestamp = None
 
-    # In-memory attributes
-    self.lock_status = None
+    self._InitInMemory(self, writable)
 
-    # Condition to wait for changes
-    self.change = threading.Condition(self.queue._lock)
+  @staticmethod
+  def _InitInMemory(obj, writable):
+    """Initializes in-memory variables.
+
+    """
+    obj.writable = writable
+    obj.ops_iter = None
+    obj.cur_opctx = None
+
+    # Read-only jobs are not processed and therefore don't need a lock
+    if writable:
+      obj.processor_lock = threading.Lock()
+    else:
+      obj.processor_lock = None
 
   def __repr__(self):
     status = ["%s.%s" % (self.__class__.__module__, self.__class__.__name__),
@@ -201,13 +232,15 @@ class _QueuedJob(object):
     return "<%s at %#x>" % (" ".join(status), id(self))
 
   @classmethod
-  def Restore(cls, queue, state):
+  def Restore(cls, queue, state, writable):
     """Restore a _QueuedJob from serialized state:
 
     @type queue: L{JobQueue}
     @param queue: to which queue the restored job belongs
     @type state: dict
     @param state: the serialized state
+    @type writable: bool
+    @param writable: Whether job can be modified
     @rtype: _JobQueue
     @return: the restored _JobQueue instance
 
@@ -219,9 +252,6 @@ class _QueuedJob(object):
     obj.start_timestamp = state.get("start_timestamp", None)
     obj.end_timestamp = state.get("end_timestamp", None)
 
-    # In-memory attributes
-    obj.lock_status = None
-
     obj.ops = []
     obj.log_serial = 0
     for op_state in state["ops"]:
@@ -230,8 +260,7 @@ class _QueuedJob(object):
         obj.log_serial = max(obj.log_serial, log_entry[0])
       obj.ops.append(op)
 
-    # Condition to wait for changes
-    obj.change = threading.Condition(obj.queue._lock)
+    cls._InitInMemory(obj, writable)
 
     return obj
 
@@ -283,8 +312,8 @@ class _QueuedJob(object):
 
       if op.status == constants.OP_STATUS_QUEUED:
         pass
-      elif op.status == constants.OP_STATUS_WAITLOCK:
-        status = constants.JOB_STATUS_WAITLOCK
+      elif op.status == constants.OP_STATUS_WAITING:
+        status = constants.JOB_STATUS_WAITING
       elif op.status == constants.OP_STATUS_RUNNING:
         status = constants.JOB_STATUS_RUNNING
       elif op.status == constants.OP_STATUS_CANCELING:
@@ -303,6 +332,24 @@ class _QueuedJob(object):
 
     return status
 
+  def CalcPriority(self):
+    """Gets the current priority for this job.
+
+    Only unfinished opcodes are considered. When all are done, the default
+    priority is used.
+
+    @rtype: int
+
+    """
+    priorities = [op.priority for op in self.ops
+                  if op.status not in constants.OPS_FINALIZED]
+
+    if not priorities:
+      # All opcodes are done, assume default priority
+      return constants.OP_PRIO_DEFAULT
+
+    return min(priorities)
+
   def GetLogEntries(self, newer_than):
     """Selectively returns the log entries.
 
@@ -342,6 +389,8 @@ class _QueuedJob(object):
         row.append(self.id)
       elif fname == "status":
         row.append(self.CalcStatus())
+      elif fname == "priority":
+        row.append(self.CalcPriority())
       elif fname == "ops":
         row.append([op.input.__getstate__() for op in self.ops])
       elif fname == "opresult":
@@ -356,14 +405,14 @@ class _QueuedJob(object):
         row.append([op.exec_timestamp for op in self.ops])
       elif fname == "opend":
         row.append([op.end_timestamp for op in self.ops])
+      elif fname == "oppriority":
+        row.append([op.priority for op in self.ops])
       elif fname == "received_ts":
         row.append(self.received_timestamp)
       elif fname == "start_ts":
         row.append(self.start_timestamp)
       elif fname == "end_ts":
         row.append(self.end_timestamp)
-      elif fname == "lock_status":
-        row.append(self.lock_status)
       elif fname == "summary":
         row.append([op.input.Summary() for op in self.ops])
       else:
@@ -390,6 +439,37 @@ class _QueuedJob(object):
       op.result = result
       not_marked = False
 
+  def Finalize(self):
+    """Marks the job as finalized.
+
+    """
+    self.end_timestamp = TimeStampNow()
+
+  def Cancel(self):
+    """Marks job as canceled/-ing if possible.
+
+    @rtype: tuple; (bool, string)
+    @return: Boolean describing whether job was successfully canceled or marked
+      as canceling and a text message
+
+    """
+    status = self.CalcStatus()
+
+    if status == constants.JOB_STATUS_QUEUED:
+      self.MarkUnfinishedOps(constants.OP_STATUS_CANCELED,
+                             "Job canceled by request")
+      self.Finalize()
+      return (True, "Job %s canceled" % self.id)
+
+    elif status == constants.JOB_STATUS_WAITING:
+      # The worker will notice the new status and cancel the job
+      self.MarkUnfinishedOps(constants.OP_STATUS_CANCELING, None)
+      return (True, "Job %s will be canceled" % self.id)
+
+    else:
+      logging.debug("Job %s is no longer waiting in the queue", self.id)
+      return (False, "Job %s is no longer waiting in the queue" % self.id)
+
 
 class _OpExecCallbacks(mcpu.OpExecCbBase):
   def __init__(self, queue, job, op):
@@ -403,197 +483,1002 @@ class _OpExecCallbacks(mcpu.OpExecCbBase):
     @param op: OpCode
 
     """
-    assert queue, "Queue is missing"
-    assert job, "Job is missing"
-    assert op, "Opcode is missing"
+    assert queue, "Queue is missing"
+    assert job, "Job is missing"
+    assert op, "Opcode is missing"
+
+    self._queue = queue
+    self._job = job
+    self._op = op
+
+  def _CheckCancel(self):
+    """Raises an exception to cancel the job if asked to.
+
+    """
+    # Cancel here if we were asked to
+    if self._op.status == constants.OP_STATUS_CANCELING:
+      logging.debug("Canceling opcode")
+      raise CancelJob()
+
+  @locking.ssynchronized(_QUEUE, shared=1)
+  def NotifyStart(self):
+    """Mark the opcode as running, not lock-waiting.
+
+    This is called from the mcpu code as a notifier function, when the LU is
+    finally about to start the Exec() method. Of course, to have end-user
+    visible results, the opcode must be initially (before calling into
+    Processor.ExecOpCode) set to OP_STATUS_WAITING.
+
+    """
+    assert self._op in self._job.ops
+    assert self._op.status in (constants.OP_STATUS_WAITING,
+                               constants.OP_STATUS_CANCELING)
+
+    # Cancel here if we were asked to
+    self._CheckCancel()
+
+    logging.debug("Opcode is now running")
+
+    self._op.status = constants.OP_STATUS_RUNNING
+    self._op.exec_timestamp = TimeStampNow()
+
+    # And finally replicate the job status
+    self._queue.UpdateJobUnlocked(self._job)
+
+  @locking.ssynchronized(_QUEUE, shared=1)
+  def _AppendFeedback(self, timestamp, log_type, log_msg):
+    """Internal feedback append function, with locks
+
+    """
+    self._job.log_serial += 1
+    self._op.log.append((self._job.log_serial, timestamp, log_type, log_msg))
+    self._queue.UpdateJobUnlocked(self._job, replicate=False)
+
+  def Feedback(self, *args):
+    """Append a log entry.
+
+    """
+    assert len(args) < 3
+
+    if len(args) == 1:
+      log_type = constants.ELOG_MESSAGE
+      log_msg = args[0]
+    else:
+      (log_type, log_msg) = args
+
+    # The time is split to make serialization easier and not lose
+    # precision.
+    timestamp = utils.SplitTime(time.time())
+    self._AppendFeedback(timestamp, log_type, log_msg)
+
+  def CheckCancel(self):
+    """Check whether job has been cancelled.
+
+    """
+    assert self._op.status in (constants.OP_STATUS_WAITING,
+                               constants.OP_STATUS_CANCELING)
+
+    # Cancel here if we were asked to
+    self._CheckCancel()
+
+  def SubmitManyJobs(self, jobs):
+    """Submits jobs for processing.
+
+    See L{JobQueue.SubmitManyJobs}.
+
+    """
+    # Locking is done in job queue
+    return self._queue.SubmitManyJobs(jobs)
+
+
+class _JobChangesChecker(object):
+  def __init__(self, fields, prev_job_info, prev_log_serial):
+    """Initializes this class.
+
+    @type fields: list of strings
+    @param fields: Fields requested by LUXI client
+    @type prev_job_info: string
+    @param prev_job_info: previous job info, as passed by the LUXI client
+    @type prev_log_serial: string
+    @param prev_log_serial: previous job serial, as passed by the LUXI client
+
+    """
+    self._fields = fields
+    self._prev_job_info = prev_job_info
+    self._prev_log_serial = prev_log_serial
+
+  def __call__(self, job):
+    """Checks whether job has changed.
+
+    @type job: L{_QueuedJob}
+    @param job: Job object
+
+    """
+    assert not job.writable, "Expected read-only job"
+
+    status = job.CalcStatus()
+    job_info = job.GetInfo(self._fields)
+    log_entries = job.GetLogEntries(self._prev_log_serial)
+
+    # Serializing and deserializing data can cause type changes (e.g. from
+    # tuple to list) or precision loss. We're doing it here so that we get
+    # the same modifications as the data received from the client. Without
+    # this, the comparison afterwards might fail without the data being
+    # significantly different.
+    # TODO: we just deserialized from disk, investigate how to make sure that
+    # the job info and log entries are compatible to avoid this further step.
+    # TODO: Doing something like in testutils.py:UnifyValueType might be more
+    # efficient, though floats will be tricky
+    job_info = serializer.LoadJson(serializer.DumpJson(job_info))
+    log_entries = serializer.LoadJson(serializer.DumpJson(log_entries))
+
+    # Don't even try to wait if the job is no longer running, there will be
+    # no changes.
+    if (status not in (constants.JOB_STATUS_QUEUED,
+                       constants.JOB_STATUS_RUNNING,
+                       constants.JOB_STATUS_WAITING) or
+        job_info != self._prev_job_info or
+        (log_entries and self._prev_log_serial != log_entries[0][0])):
+      logging.debug("Job %s changed", job.id)
+      return (job_info, log_entries)
+
+    return None
+
+
+class _JobFileChangesWaiter(object):
+  def __init__(self, filename):
+    """Initializes this class.
+
+    @type filename: string
+    @param filename: Path to job file
+    @raises errors.InotifyError: if the notifier cannot be setup
+
+    """
+    self._wm = pyinotify.WatchManager()
+    self._inotify_handler = \
+      asyncnotifier.SingleFileEventHandler(self._wm, self._OnInotify, filename)
+    self._notifier = \
+      pyinotify.Notifier(self._wm, default_proc_fun=self._inotify_handler)
+    try:
+      self._inotify_handler.enable()
+    except Exception:
+      # pyinotify doesn't close file descriptors automatically
+      self._notifier.stop()
+      raise
+
+  def _OnInotify(self, notifier_enabled):
+    """Callback for inotify.
+
+    """
+    if not notifier_enabled:
+      self._inotify_handler.enable()
+
+  def Wait(self, timeout):
+    """Waits for the job file to change.
+
+    @type timeout: float
+    @param timeout: Timeout in seconds
+    @return: Whether there have been events
+
+    """
+    assert timeout >= 0
+    have_events = self._notifier.check_events(timeout * 1000)
+    if have_events:
+      self._notifier.read_events()
+    self._notifier.process_events()
+    return have_events
+
+  def Close(self):
+    """Closes underlying notifier and its file descriptor.
+
+    """
+    self._notifier.stop()
+
+
+class _JobChangesWaiter(object):
+  def __init__(self, filename):
+    """Initializes this class.
+
+    @type filename: string
+    @param filename: Path to job file
+
+    """
+    self._filewaiter = None
+    self._filename = filename
+
+  def Wait(self, timeout):
+    """Waits for a job to change.
+
+    @type timeout: float
+    @param timeout: Timeout in seconds
+    @return: Whether there have been events
+
+    """
+    if self._filewaiter:
+      return self._filewaiter.Wait(timeout)
+
+    # Lazy setup: Avoid inotify setup cost when job file has already changed.
+    # If this point is reached, return immediately and let caller check the job
+    # file again in case there were changes since the last check. This avoids a
+    # race condition.
+    self._filewaiter = _JobFileChangesWaiter(self._filename)
+
+    return True
+
+  def Close(self):
+    """Closes underlying waiter.
+
+    """
+    if self._filewaiter:
+      self._filewaiter.Close()
+
+
+class _WaitForJobChangesHelper(object):
+  """Helper class using inotify to wait for changes in a job file.
+
+  This class takes a previous job status and serial, and alerts the client when
+  the current job status has changed.
+
+  """
+  @staticmethod
+  def _CheckForChanges(counter, job_load_fn, check_fn):
+    if counter.next() > 0:
+      # If this isn't the first check the job is given some more time to change
+      # again. This gives better performance for jobs generating many
+      # changes/messages.
+      time.sleep(0.1)
+
+    job = job_load_fn()
+    if not job:
+      raise errors.JobLost()
+
+    result = check_fn(job)
+    if result is None:
+      raise utils.RetryAgain()
+
+    return result
+
+  def __call__(self, filename, job_load_fn,
+               fields, prev_job_info, prev_log_serial, timeout):
+    """Waits for changes on a job.
+
+    @type filename: string
+    @param filename: File on which to wait for changes
+    @type job_load_fn: callable
+    @param job_load_fn: Function to load job
+    @type fields: list of strings
+    @param fields: Which fields to check for changes
+    @type prev_job_info: list or None
+    @param prev_job_info: Last job information returned
+    @type prev_log_serial: int
+    @param prev_log_serial: Last job message serial number
+    @type timeout: float
+    @param timeout: maximum time to wait in seconds
+
+    """
+    counter = itertools.count()
+    try:
+      check_fn = _JobChangesChecker(fields, prev_job_info, prev_log_serial)
+      waiter = _JobChangesWaiter(filename)
+      try:
+        return utils.Retry(compat.partial(self._CheckForChanges,
+                                          counter, job_load_fn, check_fn),
+                           utils.RETRY_REMAINING_TIME, timeout,
+                           wait_fn=waiter.Wait)
+      finally:
+        waiter.Close()
+    except (errors.InotifyError, errors.JobLost):
+      return None
+    except utils.RetryTimeout:
+      return constants.JOB_NOTCHANGED
+
+
+def _EncodeOpError(err):
+  """Encodes an error which occurred while processing an opcode.
+
+  """
+  if isinstance(err, errors.GenericError):
+    to_encode = err
+  else:
+    to_encode = errors.OpExecError(str(err))
+
+  return errors.EncodeException(to_encode)
+
+
+class _TimeoutStrategyWrapper:
+  def __init__(self, fn):
+    """Initializes this class.
+
+    """
+    self._fn = fn
+    self._next = None
+
+  def _Advance(self):
+    """Gets the next timeout if necessary.
+
+    """
+    if self._next is None:
+      self._next = self._fn()
+
+  def Peek(self):
+    """Returns the next timeout.
+
+    """
+    self._Advance()
+    return self._next
+
+  def Next(self):
+    """Returns the current timeout and advances the internal state.
+
+    """
+    self._Advance()
+    result = self._next
+    self._next = None
+    return result
+
+
+class _OpExecContext:
+  def __init__(self, op, index, log_prefix, timeout_strategy_factory):
+    """Initializes this class.
+
+    """
+    self.op = op
+    self.index = index
+    self.log_prefix = log_prefix
+    self.summary = op.input.Summary()
+
+    # Create local copy to modify
+    if getattr(op.input, opcodes.DEPEND_ATTR, None):
+      self.jobdeps = op.input.depends[:]
+    else:
+      self.jobdeps = None
+
+    self._timeout_strategy_factory = timeout_strategy_factory
+    self._ResetTimeoutStrategy()
+
+  def _ResetTimeoutStrategy(self):
+    """Creates a new timeout strategy.
+
+    """
+    self._timeout_strategy = \
+      _TimeoutStrategyWrapper(self._timeout_strategy_factory().NextAttempt)
+
+  def CheckPriorityIncrease(self):
+    """Checks whether priority can and should be increased.
+
+    Called when locks couldn't be acquired.
+
+    """
+    op = self.op
+
+    # Exhausted all retries and next round should not use blocking acquire
+    # for locks?
+    if (self._timeout_strategy.Peek() is None and
+        op.priority > constants.OP_PRIO_HIGHEST):
+      logging.debug("Increasing priority")
+      op.priority -= 1
+      self._ResetTimeoutStrategy()
+      return True
+
+    return False
+
+  def GetNextLockTimeout(self):
+    """Returns the next lock acquire timeout.
+
+    """
+    return self._timeout_strategy.Next()
+
+
+class _JobProcessor(object):
+  (DEFER,
+   WAITDEP,
+   FINISHED) = range(1, 4)
+
+  def __init__(self, queue, opexec_fn, job,
+               _timeout_strategy_factory=mcpu.LockAttemptTimeoutStrategy):
+    """Initializes this class.
+
+    """
+    self.queue = queue
+    self.opexec_fn = opexec_fn
+    self.job = job
+    self._timeout_strategy_factory = _timeout_strategy_factory
+
+  @staticmethod
+  def _FindNextOpcode(job, timeout_strategy_factory):
+    """Locates the next opcode to run.
+
+    @type job: L{_QueuedJob}
+    @param job: Job object
+    @param timeout_strategy_factory: Callable to create new timeout strategy
+
+    """
+    # Create some sort of a cache to speed up locating next opcode for future
+    # lookups
+    # TODO: Consider splitting _QueuedJob.ops into two separate lists, one for
+    # pending and one for processed ops.
+    if job.ops_iter is None:
+      job.ops_iter = enumerate(job.ops)
+
+    # Find next opcode to run
+    while True:
+      try:
+        (idx, op) = job.ops_iter.next()
+      except StopIteration:
+        raise errors.ProgrammerError("Called for a finished job")
+
+      if op.status == constants.OP_STATUS_RUNNING:
+        # Found an opcode already marked as running
+        raise errors.ProgrammerError("Called for job marked as running")
+
+      opctx = _OpExecContext(op, idx, "Op %s/%s" % (idx + 1, len(job.ops)),
+                             timeout_strategy_factory)
+
+      if op.status not in constants.OPS_FINALIZED:
+        return opctx
+
+      # This is a job that was partially completed before master daemon
+      # shutdown, so it can be expected that some opcodes are already
+      # completed successfully (if any did error out, then the whole job
+      # should have been aborted and not resubmitted for processing).
+      logging.info("%s: opcode %s already processed, skipping",
+                   opctx.log_prefix, opctx.summary)
+
+  @staticmethod
+  def _MarkWaitlock(job, op):
+    """Marks an opcode as waiting for locks.
+
+    The job's start timestamp is also set if necessary.
+
+    @type job: L{_QueuedJob}
+    @param job: Job object
+    @type op: L{_QueuedOpCode}
+    @param op: Opcode object
+
+    """
+    assert op in job.ops
+    assert op.status in (constants.OP_STATUS_QUEUED,
+                         constants.OP_STATUS_WAITING)
+
+    update = False
+
+    op.result = None
+
+    if op.status == constants.OP_STATUS_QUEUED:
+      op.status = constants.OP_STATUS_WAITING
+      update = True
+
+    if op.start_timestamp is None:
+      op.start_timestamp = TimeStampNow()
+      update = True
+
+    if job.start_timestamp is None:
+      job.start_timestamp = op.start_timestamp
+      update = True
+
+    assert op.status == constants.OP_STATUS_WAITING
+
+    return update
+
+  @staticmethod
+  def _CheckDependencies(queue, job, opctx):
+    """Checks if an opcode has dependencies and if so, processes them.
+
+    @type queue: L{JobQueue}
+    @param queue: Queue object
+    @type job: L{_QueuedJob}
+    @param job: Job object
+    @type opctx: L{_OpExecContext}
+    @param opctx: Opcode execution context
+    @rtype: bool
+    @return: Whether opcode will be re-scheduled by dependency tracker
+
+    """
+    op = opctx.op
+
+    result = False
+
+    while opctx.jobdeps:
+      (dep_job_id, dep_status) = opctx.jobdeps[0]
+
+      (depresult, depmsg) = queue.depmgr.CheckAndRegister(job, dep_job_id,
+                                                          dep_status)
+      assert ht.TNonEmptyString(depmsg), "No dependency message"
+
+      logging.info("%s: %s", opctx.log_prefix, depmsg)
+
+      if depresult == _JobDependencyManager.CONTINUE:
+        # Remove dependency and continue
+        opctx.jobdeps.pop(0)
+
+      elif depresult == _JobDependencyManager.WAIT:
+        # Need to wait for notification, dependency tracker will re-add job
+        # to workerpool
+        result = True
+        break
+
+      elif depresult == _JobDependencyManager.CANCEL:
+        # Job was cancelled, cancel this job as well
+        job.Cancel()
+        assert op.status == constants.OP_STATUS_CANCELING
+        break
+
+      elif depresult in (_JobDependencyManager.WRONGSTATUS,
+                         _JobDependencyManager.ERROR):
+        # Job failed or there was an error, this job must fail
+        op.status = constants.OP_STATUS_ERROR
+        op.result = _EncodeOpError(errors.OpExecError(depmsg))
+        break
+
+      else:
+        raise errors.ProgrammerError("Unknown dependency result '%s'" %
+                                     depresult)
+
+    return result
+
+  def _ExecOpCodeUnlocked(self, opctx):
+    """Processes one opcode and returns the result.
+
+    """
+    op = opctx.op
+
+    assert op.status == constants.OP_STATUS_WAITING
+
+    timeout = opctx.GetNextLockTimeout()
+
+    try:
+      # Make sure not to hold queue lock while calling ExecOpCode
+      result = self.opexec_fn(op.input,
+                              _OpExecCallbacks(self.queue, self.job, op),
+                              timeout=timeout, priority=op.priority)
+    except mcpu.LockAcquireTimeout:
+      assert timeout is not None, "Received timeout for blocking acquire"
+      logging.debug("Couldn't acquire locks in %0.6fs", timeout)
+
+      assert op.status in (constants.OP_STATUS_WAITING,
+                           constants.OP_STATUS_CANCELING)
+
+      # Was job cancelled while we were waiting for the lock?
+      if op.status == constants.OP_STATUS_CANCELING:
+        return (constants.OP_STATUS_CANCELING, None)
+
+      # Stay in waitlock while trying to re-acquire lock
+      return (constants.OP_STATUS_WAITING, None)
+    except CancelJob:
+      logging.exception("%s: Canceling job", opctx.log_prefix)
+      assert op.status == constants.OP_STATUS_CANCELING
+      return (constants.OP_STATUS_CANCELING, None)
+    except Exception, err: # pylint: disable=W0703
+      logging.exception("%s: Caught exception in %s",
+                        opctx.log_prefix, opctx.summary)
+      return (constants.OP_STATUS_ERROR, _EncodeOpError(err))
+    else:
+      logging.debug("%s: %s successful",
+                    opctx.log_prefix, opctx.summary)
+      return (constants.OP_STATUS_SUCCESS, result)
+
+  def __call__(self, _nextop_fn=None):
+    """Continues execution of a job.
+
+    @param _nextop_fn: Callback function for tests
+    @return: C{FINISHED} if job is fully processed, C{DEFER} if the job should
+      be deferred and C{WAITDEP} if the dependency manager
+      (L{_JobDependencyManager}) will re-schedule the job when appropriate
+
+    """
+    queue = self.queue
+    job = self.job
+
+    logging.debug("Processing job %s", job.id)
+
+    queue.acquire(shared=1)
+    try:
+      opcount = len(job.ops)
+
+      assert job.writable, "Expected writable job"
+
+      # Don't do anything for finalized jobs
+      if job.CalcStatus() in constants.JOBS_FINALIZED:
+        return self.FINISHED
+
+      # Is a previous opcode still pending?
+      if job.cur_opctx:
+        opctx = job.cur_opctx
+        job.cur_opctx = None
+      else:
+        if __debug__ and _nextop_fn:
+          _nextop_fn()
+        opctx = self._FindNextOpcode(job, self._timeout_strategy_factory)
+
+      op = opctx.op
+
+      # Consistency check
+      assert compat.all(i.status in (constants.OP_STATUS_QUEUED,
+                                     constants.OP_STATUS_CANCELING)
+                        for i in job.ops[opctx.index + 1:])
+
+      assert op.status in (constants.OP_STATUS_QUEUED,
+                           constants.OP_STATUS_WAITING,
+                           constants.OP_STATUS_CANCELING)
+
+      assert (op.priority <= constants.OP_PRIO_LOWEST and
+              op.priority >= constants.OP_PRIO_HIGHEST)
+
+      waitjob = None
+
+      if op.status != constants.OP_STATUS_CANCELING:
+        assert op.status in (constants.OP_STATUS_QUEUED,
+                             constants.OP_STATUS_WAITING)
+
+        # Prepare to start opcode
+        if self._MarkWaitlock(job, op):
+          # Write to disk
+          queue.UpdateJobUnlocked(job)
+
+        assert op.status == constants.OP_STATUS_WAITING
+        assert job.CalcStatus() == constants.JOB_STATUS_WAITING
+        assert job.start_timestamp and op.start_timestamp
+        assert waitjob is None
+
+        # Check if waiting for a job is necessary
+        waitjob = self._CheckDependencies(queue, job, opctx)
+
+        assert op.status in (constants.OP_STATUS_WAITING,
+                             constants.OP_STATUS_CANCELING,
+                             constants.OP_STATUS_ERROR)
+
+        if not (waitjob or op.status in (constants.OP_STATUS_CANCELING,
+                                         constants.OP_STATUS_ERROR)):
+          logging.info("%s: opcode %s waiting for locks",
+                       opctx.log_prefix, opctx.summary)
+
+          assert not opctx.jobdeps, "Not all dependencies were removed"
+
+          queue.release()
+          try:
+            (op_status, op_result) = self._ExecOpCodeUnlocked(opctx)
+          finally:
+            queue.acquire(shared=1)
+
+          op.status = op_status
+          op.result = op_result
+
+          assert not waitjob
+
+        if op.status == constants.OP_STATUS_WAITING:
+          # Couldn't get locks in time
+          assert not op.end_timestamp
+        else:
+          # Finalize opcode
+          op.end_timestamp = TimeStampNow()
+
+          if op.status == constants.OP_STATUS_CANCELING:
+            assert not compat.any(i.status != constants.OP_STATUS_CANCELING
+                                  for i in job.ops[opctx.index:])
+          else:
+            assert op.status in constants.OPS_FINALIZED
+
+      if op.status == constants.OP_STATUS_WAITING or waitjob:
+        finalize = False
+
+        if not waitjob and opctx.CheckPriorityIncrease():
+          # Priority was changed, need to update on-disk file
+          queue.UpdateJobUnlocked(job)
+
+        # Keep around for another round
+        job.cur_opctx = opctx
+
+        assert (op.priority <= constants.OP_PRIO_LOWEST and
+                op.priority >= constants.OP_PRIO_HIGHEST)
+
+        # In no case must the status be finalized here
+        assert job.CalcStatus() == constants.JOB_STATUS_WAITING
+
+      else:
+        # Ensure all opcodes so far have been successful
+        assert (opctx.index == 0 or
+                compat.all(i.status == constants.OP_STATUS_SUCCESS
+                           for i in job.ops[:opctx.index]))
+
+        # Reset context
+        job.cur_opctx = None
+
+        if op.status == constants.OP_STATUS_SUCCESS:
+          finalize = False
+
+        elif op.status == constants.OP_STATUS_ERROR:
+          # Ensure failed opcode has an exception as its result
+          assert errors.GetEncodedError(job.ops[opctx.index].result)
+
+          to_encode = errors.OpExecError("Preceding opcode failed")
+          job.MarkUnfinishedOps(constants.OP_STATUS_ERROR,
+                                _EncodeOpError(to_encode))
+          finalize = True
+
+          # Consistency check
+          assert compat.all(i.status == constants.OP_STATUS_ERROR and
+                            errors.GetEncodedError(i.result)
+                            for i in job.ops[opctx.index:])
+
+        elif op.status == constants.OP_STATUS_CANCELING:
+          job.MarkUnfinishedOps(constants.OP_STATUS_CANCELED,
+                                "Job canceled by request")
+          finalize = True
+
+        else:
+          raise errors.ProgrammerError("Unknown status '%s'" % op.status)
+
+        if opctx.index == (opcount - 1):
+          # Finalize on last opcode
+          finalize = True
+
+        if finalize:
+          # All opcodes have been run, finalize job
+          job.Finalize()
+
+        # Write to disk. If the job status is final, this is the final write
+        # allowed. Once the file has been written, it can be archived anytime.
+        queue.UpdateJobUnlocked(job)
+
+        assert not waitjob
+
+        if finalize:
+          logging.info("Finished job %s, status = %s", job.id, job.CalcStatus())
+          return self.FINISHED
+
+      assert not waitjob or queue.depmgr.JobWaiting(job)
+
+      if waitjob:
+        return self.WAITDEP
+      else:
+        return self.DEFER
+    finally:
+      assert job.writable, "Job became read-only while being processed"
+      queue.release()
+
+
+def _EvaluateJobProcessorResult(depmgr, job, result):
+  """Looks at a result from L{_JobProcessor} for a job.
+
+  To be used in a L{_JobQueueWorker}.
+
+  """
+  if result == _JobProcessor.FINISHED:
+    # Notify waiting jobs
+    depmgr.NotifyWaiters(job.id)
+
+  elif result == _JobProcessor.DEFER:
+    # Schedule again
+    raise workerpool.DeferTask(priority=job.CalcPriority())
+
+  elif result == _JobProcessor.WAITDEP:
+    # No-op, dependency manager will re-schedule
+    pass
+
+  else:
+    raise errors.ProgrammerError("Job processor returned unknown status %s" %
+                                 (result, ))
+
+
+class _JobQueueWorker(workerpool.BaseWorker):
+  """The actual job workers.
+
+  """
+  def RunTask(self, job): # pylint: disable=W0221
+    """Job executor.
+
+    @type job: L{_QueuedJob}
+    @param job: the job to be processed
+
+    """
+    assert job.writable, "Expected writable job"
+
+    # Ensure only one worker is active on a single job. If a job registers for
+    # a dependency job, and the other job notifies before the first worker is
+    # done, the job can end up in the tasklist more than once.
+    job.processor_lock.acquire()
+    try:
+      return self._RunTaskInner(job)
+    finally:
+      job.processor_lock.release()
+
+  def _RunTaskInner(self, job):
+    """Executes a job.
+
+    Must be called with per-job lock acquired.
+
+    """
+    queue = job.queue
+    assert queue == self.pool.queue
+
+    setname_fn = lambda op: self.SetTaskName(self._GetWorkerName(job, op))
+    setname_fn(None)
+
+    proc = mcpu.Processor(queue.context, job.id)
+
+    # Create wrapper for setting thread name
+    wrap_execop_fn = compat.partial(self._WrapExecOpCode, setname_fn,
+                                    proc.ExecOpCode)
+
+    _EvaluateJobProcessorResult(queue.depmgr, job,
+                                _JobProcessor(queue, wrap_execop_fn, job)())
+
+  @staticmethod
+  def _WrapExecOpCode(setname_fn, execop_fn, op, *args, **kwargs):
+    """Updates the worker thread name to include a short summary of the opcode.
+
+    @param setname_fn: Callable setting worker thread name
+    @param execop_fn: Callable for executing opcode (usually
+                      L{mcpu.Processor.ExecOpCode})
+
+    """
+    setname_fn(op)
+    try:
+      return execop_fn(op, *args, **kwargs)
+    finally:
+      setname_fn(None)
+
+  @staticmethod
+  def _GetWorkerName(job, op):
+    """Sets the worker thread name.
+
+    @type job: L{_QueuedJob}
+    @type op: L{opcodes.OpCode}
+
+    """
+    parts = ["Job%s" % job.id]
+
+    if op:
+      parts.append(op.TinySummary())
+
+    return "/".join(parts)
+
+
+class _JobQueueWorkerPool(workerpool.WorkerPool):
+  """Simple class implementing a job-processing workerpool.
+
+  """
+  def __init__(self, queue):
+    super(_JobQueueWorkerPool, self).__init__("Jq",
+                                              JOBQUEUE_THREADS,
+                                              _JobQueueWorker)
+    self.queue = queue
+
+
+class _JobDependencyManager:
+  """Keeps track of job dependencies.
+
+  """
+  (WAIT,
+   ERROR,
+   CANCEL,
+   CONTINUE,
+   WRONGSTATUS) = range(1, 6)
+
+  def __init__(self, getstatus_fn, enqueue_fn):
+    """Initializes this class.
+
+    """
+    self._getstatus_fn = getstatus_fn
+    self._enqueue_fn = enqueue_fn
 
-    self._queue = queue
-    self._job = job
-    self._op = op
+    self._waiters = {}
+    self._lock = locking.SharedLock("JobDepMgr")
 
-  def NotifyStart(self):
-    """Mark the opcode as running, not lock-waiting.
+  @locking.ssynchronized(_LOCK, shared=1)
+  def GetLockInfo(self, requested): # pylint: disable=W0613
+    """Retrieves information about waiting jobs.
 
-    This is called from the mcpu code as a notifier function, when the LU is
-    finally about to start the Exec() method. Of course, to have end-user
-    visible results, the opcode must be initially (before calling into
-    Processor.ExecOpCode) set to OP_STATUS_WAITLOCK.
+    @type requested: set
+    @param requested: Requested information, see C{query.LQ_*}
 
     """
-    self._queue.acquire()
-    try:
-      assert self._op.status in (constants.OP_STATUS_WAITLOCK,
-                                 constants.OP_STATUS_CANCELING)
+    # No need to sort here, that's being done by the lock manager and query
+    # library. There are no priorities for notifying jobs, hence all show up as
+    # one item under "pending".
+    return [("job/%s" % job_id, None, None,
+             [("job", [job.id for job in waiters])])
+            for job_id, waiters in self._waiters.items()
+            if waiters]
+
+  @locking.ssynchronized(_LOCK, shared=1)
+  def JobWaiting(self, job):
+    """Checks if a job is waiting.
 
-      # All locks are acquired by now
-      self._job.lock_status = None
+    """
+    return compat.any(job in jobs
+                      for jobs in self._waiters.values())
 
-      # Cancel here if we were asked to
-      if self._op.status == constants.OP_STATUS_CANCELING:
-        raise CancelJob()
+  @locking.ssynchronized(_LOCK)
+  def CheckAndRegister(self, job, dep_job_id, dep_status):
+    """Checks if a dependency job has the requested status.
 
-      self._op.status = constants.OP_STATUS_RUNNING
-      self._op.exec_timestamp = TimeStampNow()
-    finally:
-      self._queue.release()
+    If the other job is not yet in a finalized status, the calling job will be
+    notified (re-added to the workerpool) at a later point.
 
-  def Feedback(self, *args):
-    """Append a log entry.
+    @type job: L{_QueuedJob}
+    @param job: Job object
+    @type dep_job_id: string
+    @param dep_job_id: ID of dependency job
+    @type dep_status: list
+    @param dep_status: Required status
 
     """
-    assert len(args) < 3
-
-    if len(args) == 1:
-      log_type = constants.ELOG_MESSAGE
-      log_msg = args[0]
-    else:
-      (log_type, log_msg) = args
+    assert ht.TString(job.id)
+    assert ht.TString(dep_job_id)
+    assert ht.TListOf(ht.TElemOf(constants.JOBS_FINALIZED))(dep_status)
 
-    # The time is split to make serialization easier and not lose
-    # precision.
-    timestamp = utils.SplitTime(time.time())
+    if job.id == dep_job_id:
+      return (self.ERROR, "Job can't depend on itself")
 
-    self._queue.acquire()
+    # Get status of dependency job
     try:
-      self._job.log_serial += 1
-      self._op.log.append((self._job.log_serial, timestamp, log_type, log_msg))
-
-      self._job.change.notifyAll()
-    finally:
-      self._queue.release()
+      status = self._getstatus_fn(dep_job_id)
+    except errors.JobLost, err:
+      return (self.ERROR, "Dependency error: %s" % err)
 
-  def ReportLocks(self, msg):
-    """Write locking information to the job.
+    assert status in constants.JOB_STATUS_ALL
 
-    Called whenever the LU processor is waiting for a lock or has acquired one.
+    job_id_waiters = self._waiters.setdefault(dep_job_id, set())
 
-    """
-    # Not getting the queue lock because this is a single assignment
-    self._job.lock_status = msg
+    if status not in constants.JOBS_FINALIZED:
+      # Register for notification and wait for job to finish
+      job_id_waiters.add(job)
+      return (self.WAIT,
+              "Need to wait for job %s, wanted status '%s'" %
+              (dep_job_id, dep_status))
 
+    # Remove from waiters list
+    if job in job_id_waiters:
+      job_id_waiters.remove(job)
 
-class _JobQueueWorker(workerpool.BaseWorker):
-  """The actual job workers.
+    if (status == constants.JOB_STATUS_CANCELED and
+        constants.JOB_STATUS_CANCELED not in dep_status):
+      return (self.CANCEL, "Dependency job %s was cancelled" % dep_job_id)
 
-  """
-  def RunTask(self, job): # pylint: disable-msg=W0221
-    """Job executor.
+    elif not dep_status or status in dep_status:
+      return (self.CONTINUE,
+              "Dependency job %s finished with status '%s'" %
+              (dep_job_id, status))
 
-    This functions processes a job. It is closely tied to the _QueuedJob and
-    _QueuedOpCode classes.
+    else:
+      return (self.WRONGSTATUS,
+              "Dependency job %s finished with status '%s',"
+              " not one of '%s' as required" %
+              (dep_job_id, status, utils.CommaJoin(dep_status)))
 
-    @type job: L{_QueuedJob}
-    @param job: the job to be processed
+  def _RemoveEmptyWaitersUnlocked(self):
+    """Remove all jobs without actual waiters.
 
     """
-    logging.info("Processing job %s", job.id)
-    proc = mcpu.Processor(self.pool.queue.context, job.id)
-    queue = job.queue
-    try:
-      try:
-        count = len(job.ops)
-        for idx, op in enumerate(job.ops):
-          op_summary = op.input.Summary()
-          if op.status == constants.OP_STATUS_SUCCESS:
-            # this is a job that was partially completed before master
-            # daemon shutdown, so it can be expected that some opcodes
-            # are already completed successfully (if any did error
-            # out, then the whole job should have been aborted and not
-            # resubmitted for processing)
-            logging.info("Op %s/%s: opcode %s already processed, skipping",
-                         idx + 1, count, op_summary)
-            continue
-          try:
-            logging.info("Op %s/%s: Starting opcode %s", idx + 1, count,
-                         op_summary)
-
-            queue.acquire()
-            try:
-              if op.status == constants.OP_STATUS_CANCELED:
-                raise CancelJob()
-              assert op.status == constants.OP_STATUS_QUEUED
-              op.status = constants.OP_STATUS_WAITLOCK
-              op.result = None
-              op.start_timestamp = TimeStampNow()
-              if idx == 0: # first opcode
-                job.start_timestamp = op.start_timestamp
-              queue.UpdateJobUnlocked(job)
-
-              input_opcode = op.input
-            finally:
-              queue.release()
-
-            # Make sure not to hold queue lock while calling ExecOpCode
-            result = proc.ExecOpCode(input_opcode,
-                                     _OpExecCallbacks(queue, job, op))
-
-            queue.acquire()
-            try:
-              op.status = constants.OP_STATUS_SUCCESS
-              op.result = result
-              op.end_timestamp = TimeStampNow()
-              queue.UpdateJobUnlocked(job)
-            finally:
-              queue.release()
-
-            logging.info("Op %s/%s: Successfully finished opcode %s",
-                         idx + 1, count, op_summary)
-          except CancelJob:
-            # Will be handled further up
-            raise
-          except Exception, err:
-            queue.acquire()
-            try:
-              try:
-                op.status = constants.OP_STATUS_ERROR
-                if isinstance(err, errors.GenericError):
-                  op.result = errors.EncodeException(err)
-                else:
-                  op.result = str(err)
-                op.end_timestamp = TimeStampNow()
-                logging.info("Op %s/%s: Error in opcode %s: %s",
-                             idx + 1, count, op_summary, err)
-              finally:
-                queue.UpdateJobUnlocked(job)
-            finally:
-              queue.release()
-            raise
-
-      except CancelJob:
-        queue.acquire()
-        try:
-          queue.CancelJobUnlocked(job)
-        finally:
-          queue.release()
-      except errors.GenericError, err:
-        logging.exception("Ganeti exception")
-      except:
-        logging.exception("Unhandled exception")
-    finally:
-      queue.acquire()
-      try:
-        try:
-          job.lock_status = None
-          job.end_timestamp = TimeStampNow()
-          queue.UpdateJobUnlocked(job)
-        finally:
-          job_id = job.id
-          status = job.CalcStatus()
-      finally:
-        queue.release()
+    for job_id in [job_id for (job_id, waiters) in self._waiters.items()
+                   if not waiters]:
+      del self._waiters[job_id]
 
-      logging.info("Finished job %s, status = %s", job_id, status)
+  def NotifyWaiters(self, job_id):
+    """Notifies all jobs waiting for a certain job ID.
 
+    @attention: Do not call until L{CheckAndRegister} returned a status other
+      than C{WAITDEP} for C{job_id}, or behaviour is undefined
+    @type job_id: string
+    @param job_id: Job ID
 
-class _JobQueueWorkerPool(workerpool.WorkerPool):
-  """Simple class implementing a job-processing workerpool.
+    """
+    assert ht.TString(job_id)
 
-  """
-  def __init__(self, queue):
-    super(_JobQueueWorkerPool, self).__init__("JobQueue",
-                                              JOBQUEUE_THREADS,
-                                              _JobQueueWorker)
-    self.queue = queue
+    self._lock.acquire()
+    try:
+      self._RemoveEmptyWaitersUnlocked()
+
+      jobs = self._waiters.pop(job_id, None)
+    finally:
+      self._lock.release()
+
+    if jobs:
+      # Re-add jobs to workerpool
+      logging.debug("Re-adding %s jobs which were waiting for job %s",
+                    len(jobs), job_id)
+      self._enqueue_fn(jobs)
 
 
 def _RequireOpenQueue(fn):
@@ -605,30 +1490,51 @@ def _RequireOpenQueue(fn):
   that the decorated function is called with a first argument that has
   a '_queue_filelock' argument.
 
-  @warning: Use this decorator only after utils.LockedMethod!
+  @warning: Use this decorator only after locking.ssynchronized
 
   Example::
-    @utils.LockedMethod
+    @locking.ssynchronized(_LOCK)
     @_RequireOpenQueue
     def Example(self):
       pass
 
   """
   def wrapper(self, *args, **kwargs):
-    # pylint: disable-msg=W0212
+    # pylint: disable=W0212
     assert self._queue_filelock is not None, "Queue should be open"
     return fn(self, *args, **kwargs)
   return wrapper
 
 
-class JobQueue(object):
-  """Queue used to manage the jobs.
+def _RequireNonDrainedQueue(fn):
+  """Decorator checking for a non-drained queue.
 
-  @cvar _RE_JOB_FILE: regex matching the valid job file names
+  To be used with functions submitting new jobs.
 
   """
-  _RE_JOB_FILE = re.compile(r"^job-(%s)$" % constants.JOB_ID_TEMPLATE)
+  def wrapper(self, *args, **kwargs):
+    """Wrapper function.
+
+    @raise errors.JobQueueDrainError: if the job queue is marked for draining
+
+    """
+    # Ok when sharing the big job queue lock, as the drain file is created when
+    # the lock is exclusive.
+    # Needs access to protected member, pylint: disable=W0212
+    if self._drained:
+      raise errors.JobQueueDrainError("Job queue is drained, refusing job")
+
+    if not self._accepting_jobs:
+      raise errors.JobQueueError("Job queue is shutting down, refusing job")
+
+    return fn(self, *args, **kwargs)
+  return wrapper
+
+
+class JobQueue(object):
+  """Queue used to manage the jobs.
 
+  """
   def __init__(self, context):
     """Constructor for JobQueue.
 
@@ -644,13 +1550,21 @@ class JobQueue(object):
     """
     self.context = context
     self._memcache = weakref.WeakValueDictionary()
-    self._my_hostname = utils.HostInfo().name
+    self._my_hostname = netutils.Hostname.GetSysName()
+
+    # The Big JobQueue lock. If a code block or method acquires it in shared
+    # mode safe it must guarantee concurrency with all the code acquiring it in
+    # shared mode, including itself. In order not to acquire it at all
+    # concurrency must be guaranteed with all code acquiring it in shared mode
+    # and all code acquiring it exclusively.
+    self._lock = locking.SharedLock("JobQueue")
 
-    # Locking
-    self._lock = threading.Lock()
     self.acquire = self._lock.acquire
     self.release = self._lock.release
 
+    # Accept jobs by default
+    self._accepting_jobs = True
+
     # Initialize the queue, and acquire the filelock.
     # This ensures no other process is working on the job queue.
     self._queue_filelock = jstore.InitAndVerifyQueue(must_lock=True)
@@ -670,59 +1584,88 @@ class JobQueue(object):
 
     # TODO: Check consistency across nodes
 
-    self._queue_size = 0
+    self._queue_size = None
     self._UpdateQueueSizeUnlocked()
-    self._drained = self._IsQueueMarkedDrain()
+    assert ht.TInt(self._queue_size)
+    self._drained = jstore.CheckDrainFlag()
+
+    # Job dependencies
+    self.depmgr = _JobDependencyManager(self._GetJobStatusForDependencies,
+                                        self._EnqueueJobs)
+    self.context.glm.AddToLockMonitor(self.depmgr)
 
     # Setup worker pool
     self._wpool = _JobQueueWorkerPool(self)
     try:
-      # We need to lock here because WorkerPool.AddTask() may start a job while
-      # we're still doing our work.
-      self.acquire()
-      try:
-        logging.info("Inspecting job queue")
-
-        all_job_ids = self._GetJobIDsUnlocked()
-        jobs_count = len(all_job_ids)
-        lastinfo = time.time()
-        for idx, job_id in enumerate(all_job_ids):
-          # Give an update every 1000 jobs or 10 seconds
-          if (idx % 1000 == 0 or time.time() >= (lastinfo + 10.0) or
-              idx == (jobs_count - 1)):
-            logging.info("Job queue inspection: %d/%d (%0.1f %%)",
-                         idx, jobs_count - 1, 100.0 * (idx + 1) / jobs_count)
-            lastinfo = time.time()
-
-          job = self._LoadJobUnlocked(job_id)
-
-          # a failure in loading the job can cause 'None' to be returned
-          if job is None:
-            continue
-
-          status = job.CalcStatus()
-
-          if status in (constants.JOB_STATUS_QUEUED, ):
-            self._wpool.AddTask(job)
-
-          elif status in (constants.JOB_STATUS_RUNNING,
-                          constants.JOB_STATUS_WAITLOCK,
-                          constants.JOB_STATUS_CANCELING):
-            logging.warning("Unfinished job %s found: %s", job.id, job)
-            try:
-              job.MarkUnfinishedOps(constants.OP_STATUS_ERROR,
-                                    "Unclean master daemon shutdown")
-            finally:
-              self.UpdateJobUnlocked(job)
-
-        logging.info("Job queue inspection finished")
-      finally:
-        self.release()
+      self._InspectQueue()
     except:
       self._wpool.TerminateWorkers()
       raise
 
-  @utils.LockedMethod
+  @locking.ssynchronized(_LOCK)
+  @_RequireOpenQueue
+  def _InspectQueue(self):
+    """Loads the whole job queue and resumes unfinished jobs.
+
+    This function needs the lock here because WorkerPool.AddTask() may start a
+    job while we're still doing our work.
+
+    """
+    logging.info("Inspecting job queue")
+
+    restartjobs = []
+
+    all_job_ids = self._GetJobIDsUnlocked()
+    jobs_count = len(all_job_ids)
+    lastinfo = time.time()
+    for idx, job_id in enumerate(all_job_ids):
+      # Give an update every 1000 jobs or 10 seconds
+      if (idx % 1000 == 0 or time.time() >= (lastinfo + 10.0) or
+          idx == (jobs_count - 1)):
+        logging.info("Job queue inspection: %d/%d (%0.1f %%)",
+                     idx, jobs_count - 1, 100.0 * (idx + 1) / jobs_count)
+        lastinfo = time.time()
+
+      job = self._LoadJobUnlocked(job_id)
+
+      # a failure in loading the job can cause 'None' to be returned
+      if job is None:
+        continue
+
+      status = job.CalcStatus()
+
+      if status == constants.JOB_STATUS_QUEUED:
+        restartjobs.append(job)
+
+      elif status in (constants.JOB_STATUS_RUNNING,
+                      constants.JOB_STATUS_WAITING,
+                      constants.JOB_STATUS_CANCELING):
+        logging.warning("Unfinished job %s found: %s", job.id, job)
+
+        if status == constants.JOB_STATUS_WAITING:
+          # Restart job
+          job.MarkUnfinishedOps(constants.OP_STATUS_QUEUED, None)
+          restartjobs.append(job)
+        else:
+          job.MarkUnfinishedOps(constants.OP_STATUS_ERROR,
+                                "Unclean master daemon shutdown")
+          job.Finalize()
+
+        self.UpdateJobUnlocked(job)
+
+    if restartjobs:
+      logging.info("Restarting %s jobs", len(restartjobs))
+      self._EnqueueJobsUnlocked(restartjobs)
+
+    logging.info("Job queue inspection finished")
+
+  def _GetRpc(self, address_list):
+    """Gets RPC runner with context.
+
+    """
+    return rpc.JobQueueRunner(self.context, address_list)
+
+  @locking.ssynchronized(_LOCK)
   @_RequireOpenQueue
   def AddNode(self, node):
     """Register a new node with the queue.
@@ -735,7 +1678,7 @@ class JobQueue(object):
     assert node_name != self._my_hostname
 
     # Clean queue directory on added node
-    result = rpc.RpcRunner.call_jobqueue_purge(node_name)
+    result = self._GetRpc(None).call_jobqueue_purge(node_name)
     msg = result.fail_msg
     if msg:
       logging.warning("Cannot cleanup queue directory on node %s: %s",
@@ -753,13 +1696,15 @@ class JobQueue(object):
     # Upload current serial file
     files.append(constants.JOB_QUEUE_SERIAL_FILE)
 
+    # Static address list
+    addrs = [node.primary_ip]
+
     for file_name in files:
       # Read file content
       content = utils.ReadFile(file_name)
 
-      result = rpc.RpcRunner.call_jobqueue_update([node_name],
-                                                  [node.primary_ip],
-                                                  file_name, content)
+      result = self._GetRpc(addrs).call_jobqueue_update([node_name], file_name,
+                                                        content)
       msg = result[node_name].fail_msg
       if msg:
         logging.error("Failed to upload file %s to node %s: %s",
@@ -767,7 +1712,7 @@ class JobQueue(object):
 
     self._nodes[node_name] = node.primary_ip
 
-  @utils.LockedMethod
+  @locking.ssynchronized(_LOCK)
   @_RequireOpenQueue
   def RemoveNode(self, node_name):
     """Callback called when removing nodes from the cluster.
@@ -818,6 +1763,7 @@ class JobQueue(object):
         names and the second one with the node addresses
 
     """
+    # TODO: Change to "tuple(map(list, zip(*self._nodes.items())))"?
     name_list = self._nodes.keys()
     addr_list = [self._nodes[name] for name in name_list]
     return name_list, addr_list
@@ -836,11 +1782,13 @@ class JobQueue(object):
     @param replicate: whether to spread the changes to the remote nodes
 
     """
-    utils.WriteFile(file_name, data=data)
+    getents = runtime.GetEnts()
+    utils.WriteFile(file_name, data=data, uid=getents.masterd_uid,
+                    gid=getents.masterd_gid)
 
     if replicate:
       names, addrs = self._GetNodeIp()
-      result = rpc.RpcRunner.call_jobqueue_update(names, addrs, file_name, data)
+      result = self._GetRpc(addrs).call_jobqueue_update(names, file_name, data)
       self._CheckRpcResult(result, self._nodes, "Updating %s" % file_name)
 
   def _RenameFilesUnlocked(self, rename):
@@ -859,7 +1807,7 @@ class JobQueue(object):
 
     # ... and on all nodes
     names, addrs = self._GetNodeIp()
-    result = rpc.RpcRunner.call_jobqueue_rename(names, addrs, rename)
+    result = self._GetRpc(addrs).call_jobqueue_rename(names, rename)
     self._CheckRpcResult(result, self._nodes, "Renaming files (%r)" % rename)
 
   @staticmethod
@@ -906,7 +1854,8 @@ class JobQueue(object):
     @return: a string representing the job identifier.
 
     """
-    assert count > 0
+    assert ht.TPositiveInt(count)
+
     # New number
     serial = self._last_serial + count
 
@@ -915,10 +1864,13 @@ class JobQueue(object):
                              "%s\n" % serial, True)
 
     result = [self._FormatJobID(v)
-              for v in range(self._last_serial, serial + 1)]
+              for v in range(self._last_serial + 1, serial + 1)]
+
     # Keep it only if we were able to write the file
     self._last_serial = serial
 
+    assert len(result) == count
+
     return result
 
   @staticmethod
@@ -946,7 +1898,8 @@ class JobQueue(object):
     return utils.PathJoin(constants.JOB_QUEUE_ARCHIVE_DIR,
                           cls._GetArchiveDirectory(job_id), "job-%s" % job_id)
 
-  def _GetJobIDsUnlocked(self, sort=True):
+  @staticmethod
+  def _GetJobIDsUnlocked(sort=True):
     """Return all known job IDs.
 
     The method only looks at disk because it's a requirement that all
@@ -961,7 +1914,7 @@ class JobQueue(object):
     """
     jlist = []
     for filename in utils.ListVisibleFiles(constants.QUEUE_DIR):
-      m = self._RE_JOB_FILE.match(filename)
+      m = constants.JOB_FILE_RE.match(filename)
       if m:
         jlist.append(m.group(1))
     if sort:
@@ -983,10 +1936,13 @@ class JobQueue(object):
     job = self._memcache.get(job_id, None)
     if job:
       logging.debug("Found job %s in memcache", job_id)
+      assert job.writable, "Found read-only job in memcache"
       return job
 
     try:
-      job = self._LoadJobFromDisk(job_id)
+      job = self._LoadJobFromDisk(job_id, False)
+      if job is None:
+        return job
     except errors.JobFileCorrupted:
       old_path = self._GetJobPath(job_id)
       new_path = self._GetArchivedJobPath(job_id)
@@ -999,54 +1955,59 @@ class JobQueue(object):
         self._RenameFilesUnlocked([(old_path, new_path)])
       return None
 
+    assert job.writable, "Job just loaded is not writable"
+
     self._memcache[job_id] = job
     logging.debug("Added job %s to the cache", job_id)
     return job
 
-  def _LoadJobFromDisk(self, job_id):
+  def _LoadJobFromDisk(self, job_id, try_archived, writable=None):
     """Load the given job file from disk.
 
     Given a job file, read, load and restore it in a _QueuedJob format.
 
     @type job_id: string
     @param job_id: job identifier
+    @type try_archived: bool
+    @param try_archived: Whether to try loading an archived job
     @rtype: L{_QueuedJob} or None
     @return: either None or the job object
 
     """
-    filepath = self._GetJobPath(job_id)
-    logging.debug("Loading job from %s", filepath)
-    try:
-      raw_data = utils.ReadFile(filepath)
-    except EnvironmentError, err:
-      if err.errno in (errno.ENOENT, ):
-        return None
-      raise
+    path_functions = [(self._GetJobPath, True)]
 
-    try:
-      data = serializer.LoadJson(raw_data)
-      job = _QueuedJob.Restore(self, data)
-    except Exception, err: # pylint: disable-msg=W0703
-      raise errors.JobFileCorrupted(err)
+    if try_archived:
+      path_functions.append((self._GetArchivedJobPath, False))
 
-    return job
+    raw_data = None
+    writable_default = None
 
-  def _GetJobsUnlocked(self, job_ids):
-    """Return a list of jobs based on their IDs.
+    for (fn, writable_default) in path_functions:
+      filepath = fn(job_id)
+      logging.debug("Loading job from %s", filepath)
+      try:
+        raw_data = utils.ReadFile(filepath)
+      except EnvironmentError, err:
+        if err.errno != errno.ENOENT:
+          raise
+      else:
+        break
 
-    @type job_ids: list
-    @param job_ids: either an empty list (meaning all jobs),
-        or a list of job IDs
-    @rtype: list
-    @return: the list of job objects
+    if not raw_data:
+      return None
 
-    """
-    if not job_ids:
-      job_ids = self._GetJobIDsUnlocked()
+    if writable is None:
+      writable = writable_default
+
+    try:
+      data = serializer.LoadJson(raw_data)
+      job = _QueuedJob.Restore(self, data, writable)
+    except Exception, err: # pylint: disable=W0703
+      raise errors.JobFileCorrupted(err)
 
-    return [self._LoadJobUnlocked(job_id) for job_id in job_ids]
+    return job
 
-  def SafeLoadJobFromDisk(self, job_id):
+  def SafeLoadJobFromDisk(self, job_id, try_archived, writable=None):
     """Load the given job file from disk.
 
     Given a job file, read, load and restore it in a _QueuedJob format.
@@ -1055,36 +2016,25 @@ class JobQueue(object):
 
     @type job_id: string
     @param job_id: job identifier
+    @type try_archived: bool
+    @param try_archived: Whether to try loading an archived job
     @rtype: L{_QueuedJob} or None
     @return: either None or the job object
 
     """
     try:
-      return self._LoadJobFromDisk(job_id)
+      return self._LoadJobFromDisk(job_id, try_archived, writable=writable)
     except (errors.JobFileCorrupted, EnvironmentError):
       logging.exception("Can't load/parse job %s", job_id)
       return None
 
-  @staticmethod
-  def _IsQueueMarkedDrain():
-    """Check if the queue is marked from drain.
-
-    This currently uses the queue drain file, which makes it a
-    per-node flag. In the future this can be moved to the config file.
-
-    @rtype: boolean
-    @return: True of the job queue is marked for draining
-
-    """
-    return os.path.exists(constants.JOB_QUEUE_DRAIN_FILE)
-
   def _UpdateQueueSizeUnlocked(self):
     """Update the queue size.
 
     """
     self._queue_size = len(self._GetJobIDsUnlocked(sort=False))
 
-  @utils.LockedMethod
+  @locking.ssynchronized(_LOCK)
   @_RequireOpenQueue
   def SetDrainFlag(self, drain_flag):
     """Sets the drain flag for the queue.
@@ -1093,10 +2043,7 @@ class JobQueue(object):
     @param drain_flag: Whether to set or unset the drain flag
 
     """
-    if drain_flag:
-      utils.WriteFile(constants.JOB_QUEUE_DRAIN_FILE, data="", close=True)
-    else:
-      utils.RemoveFile(constants.JOB_QUEUE_DRAIN_FILE)
+    jstore.SetDrainFlag(drain_flag)
 
     self._drained = drain_flag
 
@@ -1115,19 +2062,28 @@ class JobQueue(object):
     @param ops: The list of OpCodes that will become the new job.
     @rtype: L{_QueuedJob}
     @return: the job object to be queued
-    @raise errors.JobQueueDrainError: if the job queue is marked for draining
     @raise errors.JobQueueFull: if the job queue has too many jobs in it
+    @raise errors.GenericError: If an opcode is not valid
 
     """
-    # Ok when sharing the big job queue lock, as the drain file is created when
-    # the lock is exclusive.
-    if self._drained:
-      raise errors.JobQueueDrainError("Job queue is drained, refusing job")
-
     if self._queue_size >= constants.JOB_QUEUE_SIZE_HARD_LIMIT:
       raise errors.JobQueueFull()
 
-    job = _QueuedJob(self, job_id, ops)
+    job = _QueuedJob(self, job_id, ops, True)
+
+    # Check priority
+    for idx, op in enumerate(job.ops):
+      if op.priority not in constants.OP_PRIO_SUBMIT_VALID:
+        allowed = utils.CommaJoin(constants.OP_PRIO_SUBMIT_VALID)
+        raise errors.GenericError("Opcode %s has invalid priority %s, allowed"
+                                  " are %s" % (idx, op.priority, allowed))
+
+      dependencies = getattr(op.input, opcodes.DEPEND_ATTR, None)
+      if not opcodes.TNoRelativeJobDependencies(dependencies):
+        raise errors.GenericError("Opcode %s has invalid dependencies, must"
+                                  " match %s: %s" %
+                                  (idx, opcodes.TNoRelativeJobDependencies,
+                                   dependencies))
 
     # Write to disk
     self.UpdateJobUnlocked(job)
@@ -1139,42 +2095,158 @@ class JobQueue(object):
 
     return job
 
-  @utils.LockedMethod
+  @locking.ssynchronized(_LOCK)
   @_RequireOpenQueue
+  @_RequireNonDrainedQueue
   def SubmitJob(self, ops):
     """Create and store a new job.
 
     @see: L{_SubmitJobUnlocked}
 
     """
-    job_id = self._NewSerialsUnlocked(1)[0]
-    self._wpool.AddTask(self._SubmitJobUnlocked(job_id, ops))
+    (job_id, ) = self._NewSerialsUnlocked(1)
+    self._EnqueueJobsUnlocked([self._SubmitJobUnlocked(job_id, ops)])
     return job_id
 
-  @utils.LockedMethod
+  @locking.ssynchronized(_LOCK)
   @_RequireOpenQueue
+  @_RequireNonDrainedQueue
   def SubmitManyJobs(self, jobs):
     """Create and store multiple jobs.
 
     @see: L{_SubmitJobUnlocked}
 
     """
-    results = []
-    tasks = []
     all_job_ids = self._NewSerialsUnlocked(len(jobs))
-    for job_id, ops in zip(all_job_ids, jobs):
-      try:
-        tasks.append((self._SubmitJobUnlocked(job_id, ops), ))
-        status = True
-        data = job_id
-      except errors.GenericError, err:
-        data = str(err)
-        status = False
-      results.append((status, data))
-    self._wpool.AddManyTasks(tasks)
+
+    (results, added_jobs) = \
+      self._SubmitManyJobsUnlocked(jobs, all_job_ids, [])
+
+    self._EnqueueJobsUnlocked(added_jobs)
 
     return results
 
+  @staticmethod
+  def _FormatSubmitError(msg, ops):
+    """Formats errors which occurred while submitting a job.
+
+    """
+    return ("%s; opcodes %s" %
+            (msg, utils.CommaJoin(op.Summary() for op in ops)))
+
+  @staticmethod
+  def _ResolveJobDependencies(resolve_fn, deps):
+    """Resolves relative job IDs in dependencies.
+
+    @type resolve_fn: callable
+    @param resolve_fn: Function to resolve a relative job ID
+    @type deps: list
+    @param deps: Dependencies
+    @rtype: list
+    @return: Resolved dependencies
+
+    """
+    result = []
+
+    for (dep_job_id, dep_status) in deps:
+      if ht.TRelativeJobId(dep_job_id):
+        assert ht.TInt(dep_job_id) and dep_job_id < 0
+        try:
+          job_id = resolve_fn(dep_job_id)
+        except IndexError:
+          # Abort
+          return (False, "Unable to resolve relative job ID %s" % dep_job_id)
+      else:
+        job_id = dep_job_id
+
+      result.append((job_id, dep_status))
+
+    return (True, result)
+
+  def _SubmitManyJobsUnlocked(self, jobs, job_ids, previous_job_ids):
+    """Create and store multiple jobs.
+
+    @see: L{_SubmitJobUnlocked}
+
+    """
+    results = []
+    added_jobs = []
+
+    def resolve_fn(job_idx, reljobid):
+      assert reljobid < 0
+      return (previous_job_ids + job_ids[:job_idx])[reljobid]
+
+    for (idx, (job_id, ops)) in enumerate(zip(job_ids, jobs)):
+      for op in ops:
+        if getattr(op, opcodes.DEPEND_ATTR, None):
+          (status, data) = \
+            self._ResolveJobDependencies(compat.partial(resolve_fn, idx),
+                                         op.depends)
+          if not status:
+            # Abort resolving dependencies
+            assert ht.TNonEmptyString(data), "No error message"
+            break
+          # Use resolved dependencies
+          op.depends = data
+      else:
+        try:
+          job = self._SubmitJobUnlocked(job_id, ops)
+        except errors.GenericError, err:
+          status = False
+          data = self._FormatSubmitError(str(err), ops)
+        else:
+          status = True
+          data = job_id
+          added_jobs.append(job)
+
+      results.append((status, data))
+
+    return (results, added_jobs)
+
+  @locking.ssynchronized(_LOCK)
+  def _EnqueueJobs(self, jobs):
+    """Helper function to add jobs to worker pool's queue.
+
+    @type jobs: list
+    @param jobs: List of all jobs
+
+    """
+    return self._EnqueueJobsUnlocked(jobs)
+
+  def _EnqueueJobsUnlocked(self, jobs):
+    """Helper function to add jobs to worker pool's queue.
+
+    @type jobs: list
+    @param jobs: List of all jobs
+
+    """
+    assert self._lock.is_owned(shared=0), "Must own lock in exclusive mode"
+    self._wpool.AddManyTasks([(job, ) for job in jobs],
+                             priority=[job.CalcPriority() for job in jobs])
+
+  def _GetJobStatusForDependencies(self, job_id):
+    """Gets the status of a job for dependencies.
+
+    @type job_id: string
+    @param job_id: Job ID
+    @raise errors.JobLost: If job can't be found
+
+    """
+    if not isinstance(job_id, basestring):
+      job_id = self._FormatJobID(job_id)
+
+    # Not using in-memory cache as doing so would require an exclusive lock
+
+    # Try to load from disk
+    job = self.SafeLoadJobFromDisk(job_id, True, writable=False)
+
+    assert not job.writable, "Got writable job" # pylint: disable=E1101
+
+    if job:
+      return job.CalcStatus()
+
+    raise errors.JobLost("Job %s not found" % job_id)
+
   @_RequireOpenQueue
   def UpdateJobUnlocked(self, job, replicate=True):
     """Update a job's on disk storage.
@@ -1189,16 +2261,16 @@ class JobQueue(object):
     @param replicate: whether to replicate the change to remote nodes
 
     """
+    if __debug__:
+      finalized = job.CalcStatus() in constants.JOBS_FINALIZED
+      assert (finalized ^ (job.end_timestamp is None))
+      assert job.writable, "Can't update read-only job"
+
     filename = self._GetJobPath(job.id)
-    data = serializer.DumpJson(job.Serialize(), indent=False)
+    data = serializer.DumpJson(job.Serialize())
     logging.debug("Writing job %s to %s", job.id, filename)
     self._UpdateJobQueueFile(filename, data, replicate)
 
-    # Notify waiters about potential changes
-    job.change.notifyAll()
-
-  @utils.LockedMethod
-  @_RequireOpenQueue
   def WaitForJobChanges(self, job_id, fields, prev_job_info, prev_log_serial,
                         timeout):
     """Waits for changes in a job.
@@ -1212,7 +2284,7 @@ class JobQueue(object):
     @type prev_log_serial: int
     @param prev_log_serial: Last job message serial number
     @type timeout: float
-    @param timeout: maximum time to wait
+    @param timeout: maximum time to wait in seconds
     @rtype: tuple (job info, log entries)
     @return: a tuple of the job information as required via
         the fields parameter, and the log entries as a list
@@ -1223,46 +2295,15 @@ class JobQueue(object):
         as such by the clients
 
     """
-    job = self._LoadJobUnlocked(job_id)
-    if not job:
-      logging.debug("Job %s not found", job_id)
-      return None
-
-    def _CheckForChanges():
-      logging.debug("Waiting for changes in job %s", job_id)
+    load_fn = compat.partial(self.SafeLoadJobFromDisk, job_id, False,
+                             writable=False)
 
-      status = job.CalcStatus()
-      job_info = job.GetInfo(fields)
-      log_entries = job.GetLogEntries(prev_log_serial)
-
-      # Serializing and deserializing data can cause type changes (e.g. from
-      # tuple to list) or precision loss. We're doing it here so that we get
-      # the same modifications as the data received from the client. Without
-      # this, the comparison afterwards might fail without the data being
-      # significantly different.
-      job_info = serializer.LoadJson(serializer.DumpJson(job_info))
-      log_entries = serializer.LoadJson(serializer.DumpJson(log_entries))
-
-      # Don't even try to wait if the job is no longer running, there will be
-      # no changes.
-      if (status not in (constants.JOB_STATUS_QUEUED,
-                         constants.JOB_STATUS_RUNNING,
-                         constants.JOB_STATUS_WAITLOCK) or
-          prev_job_info != job_info or
-          (log_entries and prev_log_serial != log_entries[0][0])):
-        logging.debug("Job %s changed", job_id)
-        return (job_info, log_entries)
-
-      raise utils.RetryAgain()
+    helper = _WaitForJobChangesHelper()
 
-    try:
-      # Setting wait function to release the queue lock while waiting
-      return utils.Retry(_CheckForChanges, utils.RETRY_REMAINING_TIME, timeout,
-                         wait_fn=job.change.wait)
-    except utils.RetryTimeout:
-      return constants.JOB_NOTCHANGED
+    return helper(self._GetJobPath(job_id), load_fn,
+                  fields, prev_job_info, prev_log_serial, timeout)
 
-  @utils.LockedMethod
+  @locking.ssynchronized(_LOCK)
   @_RequireOpenQueue
   def CancelJob(self, job_id):
     """Cancels a job.
@@ -1280,36 +2321,17 @@ class JobQueue(object):
       logging.debug("Job %s not found", job_id)
       return (False, "Job %s not found" % job_id)
 
-    job_status = job.CalcStatus()
-
-    if job_status not in (constants.JOB_STATUS_QUEUED,
-                          constants.JOB_STATUS_WAITLOCK):
-      logging.debug("Job %s is no longer waiting in the queue", job.id)
-      return (False, "Job %s is no longer waiting in the queue" % job.id)
-
-    if job_status == constants.JOB_STATUS_QUEUED:
-      self.CancelJobUnlocked(job)
-      return (True, "Job %s canceled" % job.id)
-
-    elif job_status == constants.JOB_STATUS_WAITLOCK:
-      # The worker will notice the new status and cancel the job
-      try:
-        job.MarkUnfinishedOps(constants.OP_STATUS_CANCELING, None)
-      finally:
-        self.UpdateJobUnlocked(job)
-      return (True, "Job %s will be canceled" % job.id)
+    assert job.writable, "Can't cancel read-only job"
 
-  @_RequireOpenQueue
-  def CancelJobUnlocked(self, job):
-    """Marks a job as canceled.
+    (success, msg) = job.Cancel()
 
-    """
-    try:
-      job.MarkUnfinishedOps(constants.OP_STATUS_CANCELED,
-                            "Job canceled by request")
-    finally:
+    if success:
+      # If the job was finalized (e.g. cancelled), this is the final write
+      # allowed. The job can be archived anytime.
       self.UpdateJobUnlocked(job)
 
+    return (success, msg)
+
   @_RequireOpenQueue
   def _ArchiveJobsUnlocked(self, jobs):
     """Archives jobs.
@@ -1323,9 +2345,9 @@ class JobQueue(object):
     archive_jobs = []
     rename_files = []
     for job in jobs:
-      if job.CalcStatus() not in (constants.JOB_STATUS_CANCELED,
-                                  constants.JOB_STATUS_SUCCESS,
-                                  constants.JOB_STATUS_ERROR):
+      assert job.writable, "Can't archive read-only job"
+
+      if job.CalcStatus() not in constants.JOBS_FINALIZED:
         logging.debug("Job %s is not yet done", job.id)
         continue
 
@@ -1348,7 +2370,7 @@ class JobQueue(object):
     self._UpdateQueueSizeUnlocked()
     return len(archive_jobs)
 
-  @utils.LockedMethod
+  @locking.ssynchronized(_LOCK)
   @_RequireOpenQueue
   def ArchiveJob(self, job_id):
     """Archives a job.
@@ -1370,7 +2392,7 @@ class JobQueue(object):
 
     return self._ArchiveJobsUnlocked([job]) == 1
 
-  @utils.LockedMethod
+  @locking.ssynchronized(_LOCK)
   @_RequireOpenQueue
   def AutoArchiveJobs(self, age, timeout):
     """Archives all jobs based on age.
@@ -1426,14 +2448,9 @@ class JobQueue(object):
 
     return (archived_count, len(all_job_ids) - last_touched)
 
-  @utils.LockedMethod
-  @_RequireOpenQueue
   def QueryJobs(self, job_ids, fields):
     """Returns a list of jobs in queue.
 
-    This is a wrapper of L{_GetJobsUnlocked}, which actually does the
-    processing for each job.
-
     @type job_ids: list
     @param job_ids: sequence of job identifiers or None for all
     @type fields: list
@@ -1444,16 +2461,48 @@ class JobQueue(object):
 
     """
     jobs = []
+    list_all = False
+    if not job_ids:
+      # Since files are added to/removed from the queue atomically, there's no
+      # risk of getting the job ids in an inconsistent state.
+      job_ids = self._GetJobIDsUnlocked()
+      list_all = True
 
-    for job in self._GetJobsUnlocked(job_ids):
-      if job is None:
-        jobs.append(None)
-      else:
+    for job_id in job_ids:
+      job = self.SafeLoadJobFromDisk(job_id, True)
+      if job is not None:
         jobs.append(job.GetInfo(fields))
+      elif not list_all:
+        jobs.append(None)
 
     return jobs
 
-  @utils.LockedMethod
+  @locking.ssynchronized(_LOCK)
+  def PrepareShutdown(self):
+    """Prepare to stop the job queue.
+
+    Disables execution of jobs in the workerpool and returns whether there are
+    any jobs currently running. If the latter is the case, the job queue is not
+    yet ready for shutdown. Once this function returns C{True} L{Shutdown} can
+    be called without interfering with any job. Queued and unfinished jobs will
+    be resumed next time.
+
+    Once this function has been called no new job submissions will be accepted
+    (see L{_RequireNonDrainedQueue}).
+
+    @rtype: bool
+    @return: Whether there are any running jobs
+
+    """
+    if self._accepting_jobs:
+      self._accepting_jobs = False
+
+      # Tell worker pool to stop processing pending tasks
+      self._wpool.SetActive(False)
+
+    return self._wpool.HasRunningTasks()
+
+  @locking.ssynchronized(_LOCK)
   @_RequireOpenQueue
   def Shutdown(self):
     """Stops the job queue.