utils.py 文件源码

def lockfile(name, shared=False, retry=True, block=False):
    """
    Use the specified file as a lock file, return when the lock has
    been acquired. Returns a variable to pass to unlockfile().
    Parameters:
        retry: True to re-try locking if it fails, False otherwise
        block: True to block until the lock succeeds, False otherwise
    The retry and block parameters are kind of equivalent unless you
    consider the possibility of sending a signal to the process to break
    out - at which point you want block=True rather than retry=True.
    """
    dirname = os.path.dirname(name)
    mkdirhier(dirname)

    if not os.access(dirname, os.W_OK):
        logger.error("Unable to acquire lock '%s', directory is not writable",
                     name)
        sys.exit(1)

    op = fcntl.LOCK_EX
    if shared:
        op = fcntl.LOCK_SH
    if not retry and not block:
        op = op | fcntl.LOCK_NB

    while True:
        # If we leave the lockfiles lying around there is no problem
        # but we should clean up after ourselves. This gives potential
        # for races though. To work around this, when we acquire the lock
        # we check the file we locked was still the lock file on disk.
        # by comparing inode numbers. If they don't match or the lockfile
        # no longer exists, we start again.

        # This implementation is unfair since the last person to request the
        # lock is the most likely to win it.

        try:
            lf = open(name, 'a+')
            fileno = lf.fileno()
            fcntl.flock(fileno, op)
            statinfo = os.fstat(fileno)
            if os.path.exists(lf.name):
                statinfo2 = os.stat(lf.name)
                if statinfo.st_ino == statinfo2.st_ino:
                    return lf
            lf.close()
        except Exception:
            try:
                lf.close()
            except Exception:
                pass
            pass
        if not retry:
            return None