Source Code for Module ganeti.jstore

  1  # 
  2  # 
  3   
  4  # Copyright (C) 2006, 2007 Google Inc. 
  5  # 
  6  # This program is free software; you can redistribute it and/or modify 
  7  # it under the terms of the GNU General Public License as published by 
  8  # the Free Software Foundation; either version 2 of the License, or 
  9  # (at your option) any later version. 
 10  # 
 11  # This program is distributed in the hope that it will be useful, but 
 12  # WITHOUT ANY WARRANTY; without even the implied warranty of 
 13  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU 
 14  # General Public License for more details. 
 15  # 
 16  # You should have received a copy of the GNU General Public License 
 17  # along with this program; if not, write to the Free Software 
 18  # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 
 19  # 02110-1301, USA. 
 20   
 21   
 22  """Module implementing the job queue handling.""" 
 23   
 24  import errno 
 25   
 26  from ganeti import constants 
 27  from ganeti import errors 
 28  from ganeti import utils 
 29   
 30   
 31 -def _ReadNumericFile(file_name): 
 32    """Reads a file containing a number. 
 33   
 34    @rtype: None or int 
 35    @return: None if file is not found, otherwise number 
 36   
 37    """ 
 38    try: 
 39      return int(utils.ReadFile(file_name)) 
 40    except EnvironmentError, err: 
 41      if err.errno in (errno.ENOENT, ): 
 42        return None 
 43      raise 
 44   
 45   
 46 -def ReadSerial(): 
 47    """Read the serial file. 
 48   
 49    The queue should be locked while this function is called. 
 50   
 51    """ 
 52    return _ReadNumericFile(constants.JOB_QUEUE_SERIAL_FILE) 
 53   
 54   
 55 -def ReadVersion(): 
 56    """Read the queue version. 
 57   
 58    The queue should be locked while this function is called. 
 59   
 60    """ 
 61    return _ReadNumericFile(constants.JOB_QUEUE_VERSION_FILE) 
 62   
 63   
 64 -def InitAndVerifyQueue(must_lock): 
 65    """Open and lock job queue. 
 66   
 67    If necessary, the queue is automatically initialized. 
 68   
 69    @type must_lock: bool 
 70    @param must_lock: Whether an exclusive lock must be held. 
 71    @rtype: utils.FileLock 
 72    @return: Lock object for the queue. This can be used to change the 
 73             locking mode. 
 74   
 75    """ 
 76    dirs = [(d, constants.JOB_QUEUE_DIRS_MODE) for d in constants.JOB_QUEUE_DIRS] 
 77    utils.EnsureDirs(dirs) 
 78   
 79    # Lock queue 
 80    queue_lock = utils.FileLock.Open(constants.JOB_QUEUE_LOCK_FILE) 
 81    try: 
 82      # The queue needs to be locked in exclusive mode to write to the serial and 
 83      # version files. 
 84      if must_lock: 
 85        queue_lock.Exclusive(blocking=True) 
 86        holding_lock = True 
 87      else: 
 88        try: 
 89          queue_lock.Exclusive(blocking=False) 
 90          holding_lock = True 
 91        except errors.LockError: 
 92          # Ignore errors and assume the process keeping the lock checked 
 93          # everything. 
 94          holding_lock = False 
 95   
 96      if holding_lock: 
 97        # Verify version 
 98        version = ReadVersion() 
 99        if version is None: 
100          # Write new version file 
101          utils.WriteFile(constants.JOB_QUEUE_VERSION_FILE, 
102                          data="%s\n" % constants.JOB_QUEUE_VERSION) 
103   
104          # Read again 
105          version = ReadVersion() 
106   
107        if version != constants.JOB_QUEUE_VERSION: 
108          raise errors.JobQueueError("Found job queue version %s, expected %s", 
109                                     version, constants.JOB_QUEUE_VERSION) 
110   
111        serial = ReadSerial() 
112        if serial is None: 
113          # Write new serial file 
114          utils.WriteFile(constants.JOB_QUEUE_SERIAL_FILE, 
115                          data="%s\n" % 0) 
116   
117          # Read again 
118          serial = ReadSerial() 
119   
120        if serial is None: 
121          # There must be a serious problem 
122          raise errors.JobQueueError("Can't read/parse the job queue" 
123                                     " serial file") 
124   
125        if not must_lock: 
126          # There's no need for more error handling. Closing the lock 
127          # file below in case of an error will unlock it anyway. 
128          queue_lock.Unlock() 
129   
130    except: 
131      queue_lock.Close() 
132      raise 
133   
134    return queue_lock 
135