Is this a concurrency bug in base?

[Jean-Marie Gaillourdet]

Hi Daniel,

On 09.10.2011, at 14:45, Daniel Fischer wrote:

> On Sunday 09 October 2011, 13:52:47, Jean-Marie Gaillourdet wrote:
>> This seems to be a Heisenbug as it is extremely fragile, when adding a
>> "| grep 1" to the while loop it seems to disappears. At least on my
>> computers. 
> 
> Still produces 1s here with a grep.

Well, it may have been bad luck on my site.

> 
>> 
>> All this was done on several Macs running the latest OS X Lion with ghc
>> 7.0.3 from the binary distribution on the GHC download page. 
> 
> linux x86_64, ghc-7.0.4, 7.0.2 and 6.12.3.
> Indeed 6.12.3 goes so far to sometimes produce
> 0
> 0
> ---
> 10
> 
> ---
> 0
> 0
> ---
> 01
> 
> ---
> 
> i.e. it switches threads during print.
Thanks, for reproducing it. I failed to see it on Linux so far. So I guess a bug report is in order? Or are bug reports to old versions not welcome? 

Jean