[Feature]: Improve timeout mechanism in Curp

[markcty]

Description about the issue

Currently, our code uses a real system time timeout mechanism, which is straight forward and easy to understand. However, obtaining system time is not efficient. We need to update last_rpc_time every time we receive a new append_entries, which could lead to performance issue when the server is busy.

Etcd offers a more clever timeout detection mechanism based on tick. A task is spawned to periodically perform tick operation. Every tick is 1 heartbeat interval. A tick will increase election_timeout and heartbeat_timeout by 1. A broadcast of heartbeats(for leader) or a new round of election(for follower) will be performed when timeout.

I believe adopting this method will improve curp’s performance as well as readability(since all periodically executed operations will be in one place).

Approach

• Remove last_rpc_time. Add heartbeat_timeout and election_timeout tick count.
• Merge timeout logic inside bg_election and bg_heartbeat.
• Add tick logic and relevant tests.

Code of Conduct

• I agree to follow this project's Code of Conduct