Simon Marlow wrote:
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
Why is the Handle found unreachable? There seems to be a pointer to the Handle somewhere, which is later passed to the exception handler and used there. Why is that pointer not regarded by GC? Is that situation Handle-specific, or could step (b) above free memory the exception handler is going to acess?
Really hClose shouldn't complain about a finalized handle, I'll see if I can fix that.
That sounds like a work-around to me, not a fix, because it would not fix more complicated exception handlers. Tillmann