Batch sending of RPC Requests

[joeljfischer]

Fixes #723

This PR is ready for review.

Risk

This PR makes minor API changes.

Testing Plan

Unit tests will be added

Summary

Add support for batch sending RPCs sequentially. Either one right after another, or waiting for the last to return before sending the next.

Changelog

Enhancements

• Add support for batch sending RPCs sequentially. Either one right after another, or waiting for the last to return before sending the next.

Tasks Remaining:

• Testing
• Add sequential RPC operation
• Hook up operations to SDLLifecycleManager

CLA

• I have signed the CLA

[NicoleYarroch]

I tested with Livio Music player and Core 4.4.1. Sending multipleCreateInteractionChoiceSets and SubscribeButtons sequentially and simultaneously worked correctly.

Known issue: On both SYNC 3 and Manticore, sending multiple requests simultaneously usually failed after first 2-5.

[joeljfischer]

@NicoleYarroch

Known issue: On both SYNC 3 and Manticore, sending multiple requests simultaneously usually failed after first 2-5.

What do you mean by "sending multiple requests simultaneously"? And does it recover?

[NicoleYarroch]

@joeljfischer

To test this PR, I sent 13 CreateInteractionChoiceSets at once. If I send them one-by-one, so the next one is only sent after a response is received from Core, everything works fine. If I send them all at once, without waiting for a response, the first 2-5 will succeed but the rest will fail with GENERIC_ERROR. The latter error is true for both Manticore (v. 4.4.1) and SYNC 3 (v. 3.0). Both sends work when testing with SDL_Core (v. 4.4.1) and the Generic HMI (v. 0.3.1).

This error has been reported to the Manticore team. Due to more pressing issues, they will not be able to investigate immediately.