Till Rohrmann created FLINK-7387:
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Summary: Let RpcEndpoint directly implement RpcGateways
Key: FLINK-7387
URL: https://issues.apache.org/jira/browse/FLINK-7387
Project: Flink
Issue Type: Sub-task
Components: Distributed Coordination
Affects Versions: 1.4.0
Reporter: Till Rohrmann
Assignee: Till Rohrmann
Right now, a {{RpcGateway}} is only implicitly coupled to a {{RpcEndpoint}} by
specifying it a s type argument and having the {{RpcCompletenessTest}} watching
that the endpoint implements all methods of the gateway.
This makes it possible that the endpoint and the gateway can have slightly
different interfaces. E.g. the gateway defines a method which returns a
{{Future<Integer>}} whereas this method is implemented by the endpoint as a
method which returns {{Integer}}. This underlines the fact that the endpoint
method call is synchronous whereas the gateway issues an asynchronous call.
The downside is that it is very cumbersome to establish type hierarchies among
{{RpcEndpoints}}. Thus, it is not easily possible to extend a specific
{{RcpEndpoint}} to add testing RPCs, for example. Moreover, you rely on the
{{RpcCompletenessTest}} to catch all not implemented methods instead of relying
on the compiler.
I think in the long run, it would be better to let the {{RpcEndpoints}}
directly implement the {{RpcGateways}} because the benefits of being able to
extend {{RpcEndpoints}} outweigh the benefits of the current approach.
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