[Haskell-cafe] Stack overflow
bertram.felgenhauer at googlemail.com
Wed May 27 14:59:31 EDT 2009
> Krzysztof Skrzętnicki wrote:
>> The code for modifying the counter:
>> (\ msg -> atomicModifyIORef ioref (\ cnt -> (cntMsg cnt msg,())))
> atomicModifyIORef does not force the new value of the IORef.
> If the previous contents of the IORef is x, the new contents
> will be a thunk,
> (\ cnt -> (cntMsg cnt msg,())) x
Sorry, it's slightly worse than that. The contents becomes
sel_0 (\ cnt -> (cntMsg cnt msg, ())) x
where sel_0 is basically an RTS internal version of fst.
Instead of reading the new value of the IORef, you could also force the
atomicModifyIORef ioref (\ cnt -> (cntMsg cnt msg, msg)) >>= (return $!)
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