Is this a concurrency bug in base?

[Jean-Marie Gaillourdet]

On 09.10.2011, at 18:13, Daniel Fischer wrote:

> On Sunday 09 October 2011, 17:51:06, Jean-Marie Gaillourdet wrote:
>>> That sounds plausible. Do you see any workaround? Perhaps repeatedly
>>> evaluating typeOf?
>> 
>> typeOf' seems to be a working workaround: 
>> 
>> typeOf' val
>>    | t1 == t2 = t1
>>    | otherwise = typeOf' val
>>  where
>>    t1 = typeOf'' val
>>    t2 = typeOf''' val
>> {-# NOINLINE typeOf' #-}
>> 
>> 
>> typeOf'' x = typeOf x
>> {-# NOINLINE typeOf'' #-}
>> typeOf''' x = typeOf x
>> {-# NOINLINE typeOf''' #-}
> 
> That'll make it very improbable to get bad results, but not impossible.
> 
> Thread1: typeOf' (); typeOf'' (), lookup, not there
> Thread2: typeOf' (); typeOf'' (), lookup, not there
> Thread1: create and insert; typeOf''' (), entry present, use ~> Key 0
> Thread2: create and insert, overwites entry with Key 0,
>         new entry has Key 1; typeOf''' (), entry present, use ~> Key 1
> 
> It will probably take a long time until it bites, but when it does, it will 
> hurt.
> A proper fix would need a lock to ensure only one thread at a time can 
> access the cache.
Ok, you're right. I tried to avoid the IO monad, but there seems to be no way around it.