Timeout a specific future

def _timeout_future(self, tag, matcher, future):
        '''
        Timeout a specific future
        '''
        if (tag, matcher) not in self.tag_map:
            return
        if not future.done():
            future.set_exception(TimeoutException())
            self.tag_map[(tag, matcher)].remove(future)
        if not self.tag_map[(tag, matcher)]:
            del self.tag_map[(tag, matcher)]