Allow to override prefetch on client and server side

[koldat]

Default Flowable behavior on Client and Server sending side is to send messages into the queue with length 512. When there is too many concurrent calls and when messages are quite big it can cause OOM. This pull requests allows to override these for such RPC calls.

Client example:

        RxNassStub api = RxNassGrpc.newRxStub(channel)
            .withOption(ClientCalls.CALL_OPTIONS_PREFETCH, 16)
            .withOption(ClientCalls.CALL_OPTIONS_LOW_TIDE, 4);

Server example:

public class TestingService extends NassImplBase {

    @Override
    public int getLowTide(int methodId) {
        return 4;
    }

    @Override
    public int getPrefetch(int methodId) {
        return 8;
    }

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @koldat to sign the Salesforce.com Contributor License Agreement.

[rmichela]

This is a great contribution! Just a few small changes/questions before merging.

[rmichela]

I really like where this is going.

Can you refactor the CallOptions and default constants out into their own public ...stub.CallOptions class? That way the ServerCalls class doesn't have to reference the internals of the ClientCalls class. This is also an opportunity to split out a getLowTide(CallOptions options) and getPrefetch(CallOptions options) function.

The last thing it needs is updated documentation explaining how and why to use the new call options.

[rmichela]

Hi @koldat
It's been a while for this PR. Do you have a chance to follow up? I'd really like to release your change. 😁

[koldat]

I have it in my queue, sorry. I will do next week as here are holidays now, ok? But feel free to modify the way you like if you want.

[rmichela]

There is no hurry. 😁

[koldat]

@rmichela, I have pushed another set. please review.

[koldat]

BTW I am trying the same change in Reactor

[koldat]

I have pushed Reactor support as well. Let me know if you like the changes and if you want to squash changesets to a big one.

[rmichela]

These changes look great! Thanks so much for the contribution.

[koldat]

Do you plan to make a release sometimes? I would like to reference official build instead of custom we are using :)

[rmichela]

Yes. I'll comment here when released.

[rmichela]

v1.0.1 is released https://github.com/salesforce/reactive-grpc/releases/tag/v1.0.1

Thank you so much for driving this change!

[koldat]

Thank you very much! Works great :)