On Fri, Aug 13, 2010 at 4:53 AM, Simon Marlow
Ah yes, that works too. But other similar versions don't, like this one:
process :: String -> String process _ = let x = x in x
Hence why I added the "tail" in my version.
Without "-O", this version doesn't work, but with "-O" it does. Why?
So what happens is this:
- the recursive definition causes the main thread to block on itself (known as a "black hole")
- the program is deadlocked (no threads to run), so the runtime invokes the GC to see if any threads are unreachable
- the GC finds that (a) the main thread is unreachable and blocked on a blackhole, so it gets a NonTermination exception (b) the Handle is unreachable, so its finalizer is started
- the finalizer runs first, and closes the Handle
- the main thread runs next, and the exception handler for writeFile tries to close the Handle, which has already been finalized
Really hClose shouldn't complain about a finalized handle, I'll see if I can fix that.
Cheers, Simon