[Haskell-cafe] Stack overflow
gtener at gmail.com
Wed May 27 15:36:07 EDT 2009
2009/5/27 Bertram Felgenhauer <bertram.felgenhauer at googlemail.com>:
> I wrote:
>> 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
> old one:
> atomicModifyIORef ioref (\ cnt -> (cntMsg cnt msg, msg)) >>= (return $!)
Thanks for the tip, although it seems tricky to get it right. I wonder
why there is no strict version of atomicModifyIORef?
Dually there might be a strict version of IORef datatype.
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