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#!/usr/bin/python
# -*- coding: utf-8 -*-
# File: flocker.py
#
# Handles all file locking.
#
# Copyright:
# (c) 2015 Devan Franchini
# Distributed under the terms of the GNU General Public License v2
#
# Author(s):
# Michał Górny <mgorny@gentoo.org>
# Devan Franchini <twitch153@gentoo.org>
#
#===============================================================================
#
# Dependencies
#
#-------------------------------------------------------------------------------
import fcntl
from layman.compatibility import fileopen
class LockingException(Exception):
'''
Exception class for relay errors properly
'''
def __init__(self, msg):
self.msg = msg
def __str__(self):
return repr(self.msg)
class FileLocker(object):
def __init__(self):
self.files = {}
self.locked = set()
def lock_file(self, path, exclusive=False):
'''Lock the file located at path.'''
file_mode = 'r'
lock_mode = fcntl.LOCK_SH
if exclusive:
file_mode = 'w+'
lock_mode = fcntl.LOCK_EX
if path in self.locked:
raise LockingException('"%(path)s" is already locked.'
% {'path': path})
self.locked.add(path)
fcntl.flock(self.get_file(path, file_mode).fileno(), lock_mode)
def unlock_file(self, path):
'''Unlock the file located at path.'''
if path not in self.locked:
raise LockingException('"%(path)s" is not locked, unlocking failed'
% {'path': path})
fcntl.flock(self.get_file(path).fileno(), fcntl.LOCK_UN)
self.locked.discard(path)
def get_file(self, path, mode='r'):
'''Obtains file object for given path'''
if mode not in ('r', 'w+'):
raise LockingException('Invalid mode %(mode)s' % {'mode': mode})
if (path not in self.files or self.files[path].closed or
self.files[path].mode != mode):
self.files[path] = fileopen(path, mode)
f = self.files[path]
f.seek(0)
return f
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