97 lines
3.4 KiB
Python
97 lines
3.4 KiB
Python
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#encoding=utf-8
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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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""" 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, timeout=7200, delay=30):
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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.timeout = timeout
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self.delay = delay
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def _setLockFileName(self, file_name):
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self.lockfile = file_name
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def acquire(self):
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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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if os.path.isfile(self.lockfile):
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try:
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mark_file_mtime = os.path.getmtime(self.lockfile)
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if (start_time - mark_file_mtime > self.timeout):
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os.remove(self.lockfile)
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except Exception as e:
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print("the lock file is locked by other process")
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while True:
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try:
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#open file , other application can't open it
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self.fd = os.open(self.lockfile, os.O_CREAT|os.O_EXCL|os.O_RDWR)
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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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""" 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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#
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if self.is_locked :
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os.close(self.fd)
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os.unlink(self.lockfile)
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self.is_locked = False
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def lockFile(self, file_name):
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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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self._setLockFileName(file_name)
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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 releaseFile(self):
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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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""" 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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#用法比较有意思，使用with关键字。对with关键字来说，FileLock类先执行__enter__函数，然后，执行with块里的那些代码，执行完了之后，再执行__exit__函数，等价于相当于如下形式：
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#try:
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# 执行 __enter__的内容
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# 执行 with_block.
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#finally:
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# 执行 __exit__内容
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#FileLock在__enter__函数独占式创建或打开一个文件，这个文件不会被其他程序或者进程再次创建或者打开，由此形成lock，执行完代码，在__exit__里，关闭并删除文件
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