Add watching dog to extend TTL

[TsingJyujing]

Add watching dog to extend TTL

[eedalong]

@TsingJyujing check this out https://zhuanlan.zhihu.com/p/101913195

[eedalong]

@TsingJyujing

1. if u want to use watchdog feature, u can just use redission with java
2. I've been thinking about this problem this morning, and I came to a rough conclusion that, if we dont want write a new redis client, maybe multithread can be one of the solutions to this problem.I mean use another thread to check and extend the lock for N secs. This can ensure that
   a) if the server goes down, the thread also dies, and the lock will not be extended, so the lock can be auto released by redis
   however, this solution may have some bad effect on the performance of the worker thread.

[TsingJyujing]

@eedalong
Thank you for reply!!!!

I can't use Java because I'm writing a server with Python (the deep reason is PIL is convient in Python and Java do not have a such useful lib).

And I think it's also tricky to stop/kill the thread, I think we should use context manager to make a high level API to manage these troublism things like we described in #25 .

If you have intention to make this high level API, I'd like to make a PR, how about you idea?

[brainix]

Pottery’s implementation of Redlock has an .extend() method that does what you’re looking for. Disclaimer: I develop/maintain Pottery. Good luck!