Update the blocking threadpool so that threads that are idle are shut down.

[jnicholls]

Update the blocking threadpool so that threads that are idle for KEEP_ALIVE seconds without any queued work will be shutdown. As of now, KEEP_ALIVE does nothing of consequence and threads that are spawned into the pool will never be shutdown during runtime.

[DoumanAsh]

I think ideally before we could do something like that, keep-alive should be configurable...
Not sure to be honest.
Keeping idle threads is bad, but if user will constantly use it with some interval bigger than current keep-alive he gonna get to re-create these threads

[carllerche]

I think ideally before we could do something like that, keep-alive should be configurable...

100%... before 0.2 final I would like the threadpool implementation to be configurable as part of the runtime. I am punting on this initially though as I think it will be easier to polish all this stuff off once Tokio 0.2 is "feature complete.

[carllerche]

This is a great next step. Thanks 👍