Invariants for GHC.Event ensureIOManagerIsRunning
Edward Z. Yang
ezyang at MIT.EDU
Sat Apr 14 05:53:32 CEST 2012
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.
P.S. I tried reproducing on a simple test case but couldn't manage it.
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