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

[Jason Dagit]

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.

Jason