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#
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#
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# Copyright (C) 2006, 2007 Google Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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# General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301, USA.
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"""Module implementing the job queue handling."""
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import errno
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from ganeti import constants
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from ganeti import errors
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from ganeti import utils
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def _ReadNumericFile(file_name):
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  """Reads a file containing a number.
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  @rtype: None or int
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  @return: None if file is not found, otherwise number
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  """
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  try:
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    return int(utils.ReadFile(file_name))
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  except EnvironmentError, err:
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    if err.errno in (errno.ENOENT, ):
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      return None
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    raise
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def ReadSerial():
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  """Read the serial file.
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  The queue should be locked while this function is called.
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  """
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  return _ReadNumericFile(constants.JOB_QUEUE_SERIAL_FILE)
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def ReadVersion():
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  """Read the queue version.
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  The queue should be locked while this function is called.
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  """
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  return _ReadNumericFile(constants.JOB_QUEUE_VERSION_FILE)
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def InitAndVerifyQueue(must_lock):
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  """Open and lock job queue.
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  If necessary, the queue is automatically initialized.
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  @type must_lock: bool
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  @param must_lock: Whether an exclusive lock must be held.
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  @rtype: utils.FileLock
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  @return: Lock object for the queue. This can be used to change the
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           locking mode.
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  """
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  dirs = [(d, constants.JOB_QUEUE_DIRS_MODE) for d in constants.JOB_QUEUE_DIRS]
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  utils.EnsureDirs(dirs)
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  # Lock queue
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  queue_lock = utils.FileLock.Open(constants.JOB_QUEUE_LOCK_FILE)
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  try:
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    # The queue needs to be locked in exclusive mode to write to the serial and
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    # version files.
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    if must_lock:
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      queue_lock.Exclusive(blocking=True)
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      holding_lock = True
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    else:
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      try:
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        queue_lock.Exclusive(blocking=False)
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        holding_lock = True
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      except errors.LockError:
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        # Ignore errors and assume the process keeping the lock checked
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        # everything.
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        holding_lock = False
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    if holding_lock:
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      # Verify version
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      version = ReadVersion()
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      if version is None:
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        # Write new version file
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        utils.WriteFile(constants.JOB_QUEUE_VERSION_FILE,
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                        data="%s\n" % constants.JOB_QUEUE_VERSION)
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        # Read again
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        version = ReadVersion()
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      if version != constants.JOB_QUEUE_VERSION:
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        raise errors.JobQueueError("Found job queue version %s, expected %s",
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                                   version, constants.JOB_QUEUE_VERSION)
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      serial = ReadSerial()
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      if serial is None:
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        # Write new serial file
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        utils.WriteFile(constants.JOB_QUEUE_SERIAL_FILE,
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                        data="%s\n" % 0)
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        # Read again
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        serial = ReadSerial()
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      if serial is None:
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        # There must be a serious problem
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        raise errors.JobQueueError("Can't read/parse the job queue"
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                                   " serial file")
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      if not must_lock:
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        # There's no need for more error handling. Closing the lock
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        # file below in case of an error will unlock it anyway.
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        queue_lock.Unlock()
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  except:
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    queue_lock.Close()
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    raise
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  return queue_lock