Document CallStreamObserver.request() thread-safety

What version of gRPC are you using?

1.5.0

The javadoc for CallStreamObserver.request() makes no statement about thread safety. I see that the applicable implementations call request() methods that are documented as thread-safe, and that CallStreamObserver.request() is called as if it were thread-safe. I assume that this is meant to be a contract, as otherwise usage would be oddly complicated.

[ejona86]

To be useful, request() must be thread-safe. Yes, we need to update the documentation.

ClientCall specifies for request():

This method is safe to call from multiple threads without external synchronizaton.

We should include something similar in CallStreamObserver.

[ejona86]

To round it out, isReady() and setMessageCompression() - those actually sound thread-compatible.

Correct. They are not thread-safe.

We should probably just copy the same “Implementations are expected to be thread-compatible” doc to CallStreamObserver (and children). Then we just call out in request()'s documentation that it is thread-safe. Same approach as in ClientCall.