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locking.py
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locking.py
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# Copyright 2024 VyOS maintainers and contributors <maintainers@vyos.io>
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library 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
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library. If not, see <http://www.gnu.org/licenses/>.
import fcntl
import re
import time
from pathlib import Path
class LockTimeoutError(Exception):
"""Custom exception raised when lock acquisition times out."""
pass
class InvalidLockNameError(Exception):
"""Custom exception raised when the lock name is invalid."""
pass
class Lock:
"""Lock class to acquire and release a lock file"""
def __init__(self, lock_name: str) -> None:
"""Lock class constructor
Args:
lock_name (str): Name of the lock file
Raises:
InvalidLockNameError: If the lock name is invalid
"""
# Validate lock name
if not re.match(r'^[a-zA-Z0-9_\-]+$', lock_name):
raise InvalidLockNameError(f'Invalid lock name: {lock_name}')
self.__lock_dir = Path('/run/vyos/lock')
self.__lock_dir.mkdir(parents=True, exist_ok=True)
self.__lock_file_path: Path = self.__lock_dir / f'{lock_name}.lock'
self.__lock_file = None
self._is_locked = False
def __del__(self) -> None:
"""Ensure the lock file is removed when the object is deleted"""
self.release()
@property
def is_locked(self) -> bool:
"""Check if the lock is acquired
Returns:
bool: True if the lock is acquired, False otherwise
"""
return self._is_locked
def __unlink_lockfile(self) -> None:
"""Remove the lock file if it is not currently locked."""
try:
with self.__lock_file_path.open('w') as f:
fcntl.flock(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
self.__lock_file_path.unlink(missing_ok=True)
except IOError:
# If we cannot acquire the lock, it means another process has it, so we do nothing.
pass
def acquire(self, timeout: int = 0) -> None:
"""Acquire a lock file
Args:
timeout (int, optional): A time to wait for lock. Defaults to 0.
Raises:
LockTimeoutError: If lock could not be acquired within timeout
"""
start_time: float = time.time()
while True:
try:
self.__lock_file = self.__lock_file_path.open('w')
fcntl.flock(self.__lock_file, fcntl.LOCK_EX | fcntl.LOCK_NB)
self._is_locked = True
return
except IOError:
if timeout > 0 and (time.time() - start_time) >= timeout:
if self.__lock_file:
self.__lock_file.close()
raise LockTimeoutError(
f'Could not acquire lock within {timeout} seconds'
)
time.sleep(0.1)
def release(self) -> None:
"""Release a lock file"""
if self.__lock_file and self._is_locked:
try:
fcntl.flock(self.__lock_file, fcntl.LOCK_UN)
self._is_locked = False
finally:
self.__lock_file.close()
self.__lock_file = None
self.__unlink_lockfile()

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