storage.py 文件源码

def __lock(self, *, write: bool=True):
        """
        A context manager to lock the storage for reading or writing.

        If no processes hold the lock for writing, then several
        processes can simultaneously lock the storage for reading.

        If a process holds the lock for writing, then no other process
        can take the lock (either for reading or writing).

        If the lock cannot be obtained, the process is paused until
        the situation allows to take it.

        Args:
            write -- (bool) if False, the storage is locked for
              reading. If True, the storage is locked for writing.
        """
        assert not self.__locked, 'Nested lock'
        if self.__lockable:
            flags = fcntl.LOCK_SH if not write else fcntl.LOCK_EX
            fcntl.lockf(self.__file, flags, 1)
            self.__locked = True
            try:
                yield
            finally:
                fcntl.lockf(self.__file, fcntl.LOCK_UN, 1)
                self.__locked = False
        else:
            yield