[Haskell-cafe] How to ensure code executes in the context of a specific OS thread?

[Jason Dagit]

On Thu, Jul 7, 2011 at 12:41 AM, Simon Marlow <marlowsd at gmail.com> wrote:
> On 06/07/2011 21:19, Jason Dagit wrote:
>>
>> On Wed, Jul 6, 2011 at 12:52 PM, Simon Marlow<marlowsd at gmail.com>  wrote:
>>>
>>> On 06/07/11 17:14, David Barbour wrote:
>>>>
>>>>
>>>> On Wed, Jul 6, 2011 at 8:09 AM, Simon Marlow<marlowsd at gmail.com
>>>> <mailto:marlowsd at gmail.com>>  wrote:
>>>>
>>>>    On 06/07/2011 15:42, Jason Dagit wrote:
>>>>
>>>>        How can I make sure my library works from GHC (with arbitrary
>>>>
>>>>        user threads) and from GHCI?
>>>>
>>>>    Right, but usually the way this is implemented is with some
>>>>    cooperation from the main thread. [...] So you can't just do this
>>>>    from a library - the main thread has to be in on the game. I suppose
>>>>    you might wonder whether the GHC RTS could implement runInMainThread
>>>>    by preempting the main thread and running some different code on it.
>>>>      [...]
>>>>
>>>>
>>>> I think the real issue is that GHC has a different behavior than GHCi,
>>>> and I think this causes a lot of difficulties for people working on GUI
>>>> and other FFI integration.
>>>>
>>>> Perhaps it would be possible to reverse the default roles of threads in
>>>> GHCi: the main thread run user commands, and a second bound thread will
>>>> process user interrupts and such.
>>>
>>> Well, GHCi has no main, so it doesn't seem surprising (to me) that it's
>>> different.
>>>
>>> However, if -fno-ghci-sandbox doesn't have any drawbacks we could just
>>> make
>>> it the default.  I don't actually remember why we run each statement in a
>>> new thread, I think it just seemed like a prudent thing to do.
>>
>> +1 for this change.  I'm not sure how we would know if there are
>> drawbacks.
>
> Now that I think about it, the original reason may have been that if the
> computation grows a large stack, having it in a separate thread means GHCi
> can recover the memory.  However we have been able to recover stack memory
> for some time now, so that is no longer an issue.

Then by all means, please make -fno-ghci-sandbox the default! :)

Thanks
Jason