Feature request: optionally kill thread when its Async goes out of scope

[jberryman]

I wanted to play with an API that cleans up a thread automatically when its handle goes out of scope. This would probably be an error condition (or bug) and so we'd usually want to log when this happens. The idea being to protect from leaks, while not being restricted to withAsync.

I thought I could do this myself with a weak reference and finalizer on the ThreadId from the Async, but this isn't safe since I also don't want the thread to be killed until the _asyncWait action becomes unreachable too.

I suppose that STM action would have to touch the ThreadId in some way, rather than just being readTMVar, and then the finalizer could be safely attached to the ThreadId?

[simonmar]

Firstly, if the thread is running then it won't be considered dead by the GC because the run queue is a source of roots, so this would only work for blocked threads.

If this is OK, then I guess your idea of touching the ThreadId from the _asyncWait action would be one way to do it, I can't think of a better way off hand.