NullPointerException in NodeImpl#handleRequestVoteRequest

[alievmirza]

Describe the bug

Sometimes NPE happens in NodeImpl#handleRequestVoteRequest on the line

                final boolean logIsOk = new LogId(request.getLastLogIndex(), request.getLastLogTerm())
                    .compareTo(lastLogId) >= 0;

It happens when we call o.getTerm() in

final int c = Long.compare(getTerm(), o.getTerm());

in com.alipay.sofa.jraft.entity.LogId#compareTo, because o is null. It happens because

final LogId lastLogId = this.logManager.getLastLogId(true);

return null.

The reason of that is because when we

offerEvent(c, EventType.LAST_LOG_ID);

in com.alipay.sofa.jraft.storage.impl.LogManagerImpl#getLastLogId, we are in the situation when node is stopping, so this code is called

        if (this.stopped) {
            ThreadPoolsFactory.runClosureInThread(this.groupId, done, new Status(RaftError.ESTOP, "Log manager is stopped."));
            return;
        }

in com.alipay.sofa.jraft.storage.impl.LogManagerImpl#offerEvent. That leads to the situation that we count down latch in com.alipay.sofa.jraft.storage.impl.LogManagerImpl.LastLogIdClosure#latch, but do not set com.alipay.sofa.jraft.storage.impl.LogManagerImpl.LastLogIdClosure#lastLogId

Let's discuss a way how to fix it properly. The problem could happen everywhere when we call com.alipay.sofa.jraft.storage.impl.LogManagerImpl#getLastLogId or com.alipay.sofa.jraft.storage.impl.LogManagerImpl#getLastLogIndex(boolean)

[alievmirza]

what do you think about such fix? #1153 @killme2008 @fengjiachun