Hello all, I recently ran into a rather reproduceable bug where I would get this error from the event manager: /dev/null: hClose: user error (Pattern match failure in do expression at libraries/base/System/Event/Thread.hs:83:3-10) The program was doing some rather strange things: - It was running the Haskell RTS inside another system (Urweb) which was making use of pthreads, sockets, etc. - The Haskell portion was linked against the threaded RTS, and doing communication with a process. and is rather complicated (two compilers are involved). But the gist of the matter is that if I added a quick call to ensureIOManagerIsRunning after hs_init, the error went away. So, if the IO manager is not eagerly loaded at the call to hs_init, how do we decided when it should be loaded? It seems probably that we missed a case. Edward P.S. I tried reproducing on a simple test case but couldn't manage it.