RATIS-1125. Fix TestDataStream

[amaliujia]

What changes were proposed in this pull request?

TestDataStream no long tests right state machine after RATIS-1124. It is because RaftServer uses its own map to keep state machine so the original state machines used to test server's writes no long work.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/RATIS-1125

How was this patch tested?

UT

[amaliujia]

R: @szetszwo @runzhiwang

[runzhiwang]

LGTM

[szetszwo]

+1 thanks for fixing it.

[runzhiwang]

@amaliujia Thanks the patch. @szetszwo Thanks for review. I have merged it.

[szetszwo]

Oops, just find that the fix does not work since there are multiple servers. Each server should have its own map. Let me fix it in RATIS-1127.

[amaliujia]

@szetszwo

hmm I have thought about that. For current test setup it is ok. Because the data structure is ConcurrentMap<RaftGroupId, MultiDataStreamStateMachine> and currently each client uses a random group id, so sharing the same map among servers does not overwrite each other thus it is still working.

For the multiple group change, I will need to update this test because in that change, servers will share the same group id so they cannot share the same map anymore.

[szetszwo]

... Because the data structure is ConcurrentMap<RaftGroupId, MultiDataStreamStateMachine> and currently each client uses a random group id ...

I see. It would work but it is confusing. Please put some comments on the code for work around like this. :)