Hi,
the same thread might be schedule immediately again, and again, ... Or do we have some specification of the scheduler?
My working assumption is that the scheduler tries to be fair. So all strange behaviour could be explained with the scheduler not running at all, because threads weren't yielding.
The question where scheduling can actually happen is a totally different issue, and I don't know of a specification here, either. In GHC, this seems to be tied to allocations, but this is a bit brittle and unintuitive. Yes, especially if the compiler might (re)move allocations due to some code transformations.
Given that, it now feels strange that the following *does* work: main = do forkIO $ do threadDelay 1000000 ; putStrLn "foo" forever $ putStr "" I am seeing the "foo" output. I expect the last line to be non-allocating. But it does still yield? Why? - J.W.