Async backlog

[mgravell]

See also #1574; rather than buffering (which helps, but just kicks the problem down a little), this moves ProcessBacklog to be truly async; it also checks for work before attempting to acquire the lock, to short-circuit high contention scenarios

[NickCraver]

👍 Much cleaner too

[ghost]

@mgravell Just for curiosity, why are you using lock inside an async method instead of an async-friendly construct?

[IgorIgorevich94]

@mgravell Just for curiosity, why are you using lock inside an async method instead of an async-friendly construct?

I would assume that there is no point in introducing additional async overhead here, since there is no IO or Network stuff happening inside the lock code block.