Plik blokady Pythona
import os
import time
import errno
class FileLockException(Exception):
pass
class FileLock(object):
""" A file locking mechanism that has context-manager support so
you can use it in a with statement. This should be relatively cross
compatible as it doesn't rely on msvcrt or fcntl for the locking.
"""
def __init__(self, file_name, timeout=10, delay=.05):
""" Prepare the file locker. Specify the file to lock and optionally
the maximum timeout and the delay between each attempt to lock.
"""
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(), "%s.lock" % file_name)
self.file_name = file_name
self.timeout = timeout
self.delay = delay
def acquire(self):
""" Acquire the lock, if possible. If the lock is in use, it check again
every `wait` seconds. It does this until it either gets the lock or
exceeds `timeout` number of seconds, in which case it throws
an exception.
"""
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 #moved to ensure tag only when locked
break;
except OSError as e:
if e.errno != errno.EEXIST:
raise
if self.timeout is None:
raise FileLockException("Could not acquire lock on {}".format(self.file_name))
if (time.time() - start_time) >= self.timeout:
raise FileLockException("Timeout occured.")
time.sleep(self.delay)
# self.is_locked = True
def release(self):
""" Get rid of the lock by deleting the lockfile.
When working in a `with` statement, this gets automatically
called at the end.
"""
if self.is_locked:
os.close(self.fd)
os.unlink(self.lockfile)
self.is_locked = False
def __enter__(self):
""" Activated when used in the with statement.
Should automatically acquire a lock to be used in the with block.
"""
if not self.is_locked:
self.acquire()
return self
def __exit__(self, type, value, traceback):
""" Activated at the end of the with statement.
It automatically releases the lock if it isn't locked.
"""
if self.is_locked:
self.release()
def __del__(self):
""" Make sure that the FileLock instance doesn't leave a lockfile
lying around.
"""
self.release()
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