Concurrency Guarantees

[hongchaodeng]

At this early development stage, we only support two operations in example state machine -- read and write.

If you run "-race" and detect that races are coming from the read & write conflicts, it's not a race at all. The state machine will guarantee that:

1. No write & write race condition. Conflicted write operations are Async-Linearizable to each other.
2. Read and write concurrency is expected. It's stale read.