A custom-file-lock wrapper for fcntl in python

file_lock.py

#coding: utf-8
import os
import time
import fcntl
import contextlib
import logging

@contextlib.contextmanager
def open_file(filename, pattern = 'r', timeout = 5):
    """ 以加锁的方式读取文件，尝试timeout * 10 次，每次sleep 1秒钟.
 
    Keyword arguments:
    filename -- file to open
    pattern: 文件打开方式,'r' or 'w'
    timeout: try times (default 5)
    """

    fd = open(filename, pattern)
    if pattern == 'r' or pattern == 'rb':
        lock_type = fcntl.LOCK_SH
    elif pattern == 'w' or pattern == 'wb':
        lock_type = fcntl.LOCK_EX
    else:
        raise Exception('Wrong pattern!')
    # try to acquire the lock
    get_lock = False
    try:
        for i in xrange(int(timeout * 10)):
            fcntl.flock(fd, lock_type | fcntl.LOCK_NB)
            get_lock = True
            logging.debug('Acquire lock of file %s success!' % filename)
            break
    except IOError:
        time.sleep(1)
    if not get_lock:
        # close file
        fd.close()
        raise IOError('Unable to acquire lock for %s' % filename)

    yield fd

    # unlock
    fcntl.flock(fd, fcntl.LOCK_UN)
    logging.debug('Release lock of file %s success!' % filename)

    # close file
    fd.close()


if __name__ == '__main__':
    with open_file('./test', 'r') as fin:
        for line in fin:
            print line