Supporting async workload in worker threads without race conditions

[tysonrm]

FIrst of all, can anyone confirm the following is accurate:

Allowing async workload (multiple requests) to run in a thread leads to a potential race condition. Because the order in which requests are submitted isn't necessarily the order in which they complete, there's nothing to ensure a requester won't receive the output of a different concurrent request. In the case of a single request, where we run synchronous workload only, there is no issue, because there's only one listener to call when the thread posts back. Or rather the listeners will be called in the order they are submitted. Given we process one request at a time in the thread, this works. But what happens when we allow multiple async requests to be submitted. There's no expectation they will complete in FIFO order. Presumably async tracking can solve this by restoring the original context.