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89 lines
2.6 KiB
Python
89 lines
2.6 KiB
Python
# Written by Evan Fosmark
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# see http://www.evanfosmark.com/
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# Released under BSD license
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import os
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import time
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import errno
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class FileLockException(Exception):
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pass
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class FileLock(object):
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"""
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A file locking mechanism that has context-manager support so
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you can use it in a with statement. This should be relatively cross
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compatible as it doesn't rely on msvcrt or fcntl for the locking.
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"""
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def __init__(self, file_name, timeout=10, delay=.05):
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"""
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Prepare the file locker. Specify the file to lock and optionally
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the maximum timeout and the delay between each attempt to lock.
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"""
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self.is_locked = False
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self.lockfile = os.path.join(os.getcwd(), "%s.lock" % file_name)
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self.file_name = file_name
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self.timeout = timeout
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self.delay = delay
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self.handle = None
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def acquire(self):
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"""
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Acquire the lock, if possible. If the lock is in use, it check again
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every `wait` seconds. It does this until it either gets the lock or
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exceeds `timeout` number of seconds, in which case it throws
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an exception.
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"""
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start_time = time.time()
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while True:
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try:
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self.handle = os.open(
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self.lockfile,
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os.O_CREAT | os.O_EXCL | os.O_RDWR
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)
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break
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except OSError as e:
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if e.errno != errno.EEXIST:
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raise
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if (time.time() - start_time) >= self.timeout:
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raise FileLockException("Timeout occured.")
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time.sleep(self.delay)
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self.is_locked = True
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def release(self):
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"""
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Get rid of the lock by deleting the lockfile.
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When working in a `with` statement, this gets automatically
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called at the end.
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"""
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if self.is_locked:
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os.close(self.handle)
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os.unlink(self.lockfile)
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self.is_locked = False
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def __enter__(self):
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"""
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Activated when used in the with statement.
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Should automatically acquire a lock to be used in the with block.
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"""
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if not self.is_locked:
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self.acquire()
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return self
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def __exit__(self, typ, value, traceback):
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"""
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Activated at the end of the with statement.
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It automatically releases the lock if it isn't locked.
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"""
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if self.is_locked:
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self.release()
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def __del__(self):
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"""
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Make sure that the FileLock instance doesn't leave a lockfile
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lying around.
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"""
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self.release()
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