root / lib / jstore.py @ 6df291d4
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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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fd = open(file_name, "r") |
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except IOError, 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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try:
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return int(fd.read(128)) |
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finally:
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fd.close() |
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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
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