import os
import time
import errno
"""
credits: https://github.com/dmfrey/FileLock
"""
[docs]class LockFileException(Exception):
pass
[docs]class LockFile(object):
"""
Locks files.
"""
def __init__(self, file_name, timeout=100, delay=0.05):
"""
Initialises the file locker
"""
if timeout is not None and delay is None:
raise ValueError("If timeout is not None, then delay must not be None.")
self.is_locked = False
self.lockfile = os.path.join(os.getcwd(), f"{file_name}.lock")
self.file_name = file_name
self.timeout = timeout
self.delay = delay
[docs] def acquire(self):
"""
Acquires a lock when possible.
"""
start_time = time.time()
while True:
try:
self.fd = os.open(self.lockfile, os.O_CREAT | os.O_EXCL | os.O_RDWR)
self.is_locked = True
break
except OSError as e:
if e.errno != errno.EEXIST:
raise
if (time.time() - start_time) >= self.timeout:
raise FileLockException(
f"Stuck for more than {self.timeout} seconds waiting to unlock the file {self.filename}."
)
time.sleep(self.delay)
[docs] def release(self):
"""
Releases the lock
"""
if self.is_locked:
os.close(self.fd)
os.unlink(self.lockfile)
self.is_locked = False
def __enter__(self):
"""
Lock gets acquired at the `with` statement.
"""
if not self.is_locked:
self.acquire()
return self
def __exit__(self, type, value, traceback):
"""
Lock get's released at the end of the `with` block
"""
if self.is_locked:
self.release()
def __del__(self):
"""
Releases the lock during deletion.
"""
self.release()