tree 7db6cd31d2c828b0de20170d87d7c4c6fb2485b2
parent 41d1d6ecb9b03c1cecadd9222b82d3f197e4c9b6
author 4onni <chinababy.sino@gmail.com> 1600931039 +0800
committer Jia Zhai <zhaijia@apache.org> 1600934726 +0800

[Issue 8093]Fix client lookup hangs when broker restarts (#8101)

Fixes #8093

Client hangs forever when all brokers stop and then restart.
There are several steps need to be finished before the broker can be fully started, as illustrated in the pseudo code below:

```
PulsarService#start():
    broker.start(); // Step 1
    webService.start(); // Step 2
    leaderElectionService.start(); //Step 3
```
If a lookup request gets in between Step 2 and Step 3, a NPE would be thrown, which will block all other coming requests from getting processed properly.

Client can only connect to the broker after the election service started successfully

This change added tests and can be verified as follows:
 - * Added 2 test cases under `LeaderElectionServiceTest`
(cherry picked from commit 65cf9c095ea20c0a546e77458274848094131163)