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

On 06/07/11 17:14, David Barbour wrote:

On Wed, Jul 6, 2011 at 8:09 AM, Simon Marlow mailto:marlowsd@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. Cheers, Simon