Source code for lago.dirlock
# Copyright 2014 Red Hat, Inc.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
#
# Refer to the README and COPYING files for full details of the license
#
import json
import os
import time
import lockfile
import utils
[docs]def _lock_path(path):
return os.path.join(path, '.rwlock')
[docs]def trylock(path, excl, key_path):
"""
Tries once to get a lock to the given dir
Args:
path(str): path to the directory to lock
excl(bool): If the lock should be exclusive
key_path(str): path to the file that contains the uid to use when
locking
Returns:
bool: True if it did get a lock, False otherwise
"""
with lockfile.LockFile(path):
# Prune invalid users
if os.path.exists(_lock_path(path)):
with open(_lock_path(path)) as f:
lock_obj = json.load(f)
else:
lock_obj = {'excl': False, 'users': {}}
for other_key_path in lock_obj['users'].copy():
if not os.path.isfile(other_key_path):
del lock_obj['users'][other_key_path]
continue
with open(other_key_path) as f:
key = f.read()
if key != lock_obj['users'][other_key_path]:
del lock_obj['users'][other_key_path]
if (
(excl and len(lock_obj['users']) != 0)
or (not excl and lock_obj['excl'] and len(lock_obj['users']) != 0)
):
success = False
else:
lock_obj['excl'] = excl
with open(key_path) as f:
lock_obj['users'][key_path] = f.read()
success = True
# Update lock object file
with open(_lock_path(path), 'w') as f:
utils.json_dump(lock_obj, f)
return success
[docs]def lock(path, excl, key_path):
"""
Waits until the given directory can be locked
Args:
path(str): Path of the directory to lock
excl(bool): If the lock should be exclusive
key_path(str): path to the file that contains the uid to use when
locking
Returns:
None
"""
while not trylock(path, excl, key_path):
time.sleep(0.1)
[docs]def unlock(path, key_path):
"""
Removes the lock of the uid in the given key file
Args:
path(str): Path of the directory to lock
key_path(str): path to the file that contains the uid to remove the
lock of
Returns:
None
"""
with lockfile.LockFile(path):
with open(_lock_path(path)) as f:
lock_obj = json.load(f)
del lock_obj['users'][key_path]
with open(_lock_path(path), 'w') as f:
utils.json_dump(lock_obj, f)