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#
# Locking.py - functions for locking/unlocking files
#
# Copyright (c) 2006-2007 The DITrack Project, www.ditrack.org.
#
# $Id: Locking.py 1696 2007-07-10 22:45:31Z vss $
# $HeadURL: https://svn.xiolabs.com/ditrack/src/tags/0.8/DITrack/Util/Locking.py $
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# * Redistributions of source code must retain the above copyright notice,
# this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above copyright notice,
# this list of conditions and the following disclaimer in the documentation
# and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
#
import datetime
import errno
import os
import time
class FileIsLockedError(Exception):
message = "File is locked"
if os.name == "posix":
import fcntl
class LockObject:
def __init__(self, mode, fileobj):
self.fileobj = fileobj
self.mode = mode
self.datetime = datetime.datetime.now()
self.pid = os.getpid
if os.name == "posix":
if mode == "w":
operation = fcntl.LOCK_EX | fcntl.LOCK_NB
else:
operation = fcntl.LOCK_SH | fcntl.LOCK_NB
try:
fcntl.flock(self.fileobj.fileno(), operation)
except IOError, (errid, strerror):
if ((errid == errno.EACCES) or (errid == errno.EAGAIN)):
raise FileIsLockedError
else:
raise
def __del__(self):
self.unlock()
def unlock(self):
if os.name == "posix":
fcntl.flock(self.fileobj.fileno(), fcntl.LOCK_UN)
def lock(fileobj, mode, timeout=0):
"""
Lock the file object.
The mode parameter should be "r" (shared/read lock) or
"w" (exclusive/write lock).
FileIsLockedError would be raised if:
- there's already a read lock on fileobj and
this is an attempt to create write lock
- there's already a write lock on fileobj and
this is an attempt to create read/write lock
One fileobj is permitted to have several shared locks
at once, but it is not so for exclusive lock.
"""
if os.name == "posix":
for i in range(timeout+1):
try:
lockobj = LockObject(mode, fileobj)
return lockobj
except FileIsLockedError:
pass
if timeout:
time.sleep(1)
else:
raise FileIsLockedError
else:
return None
def unlock(lockobj):
if os.name == "posix":
if lockobj:
lockobj.unlock()
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