Optimize the case of a master communicating with an in-process worker.

This change modifies the GrpcWorkerCache so that, when a master
attempts to communicate with the worker in the same process, it does
so by direct method calls on a `WorkerInterface*`, without making a
loopback RPC call.

This change is another incremental step towards addressing issue
#6256. There are further improvements possible, and we will continue
to investigate them, including:

* Avoiding the protobuf encoding/decoding for request/response objects
  where this affects performance. The zero-copy `TensorResponse` class
  is an example of how we could improve performance here, for
  `RunGraphRequest` and `RunGraphResponse` objects.
* Profiling the closure creation/context switch overhead for
  interactions with the local worker.
Change: 142793965

0 files changed, 0 insertions, 0 deletions