On 07/07/2011 08:41, Simon Marlow wrote:
On 06/07/2011 21:19, Jason Dagit wrote:
On Wed, Jul 6, 2011 at 12:52 PM, Simon Marlow<marlo...@gmail.com> wrote:
On 06/07/11 17:14, David Barbour wrote:
On Wed, Jul 6, 2011 at 8:09 AM, Simon Marlow<marlo...@gmail.com
<mailto:marlo...@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.
I discovered the real reason we run statements in a separate thread: the
GHCi debugger. If the computation stops at a breakpoint, then we have
to save the context and resume GHCi, which can only be done if the
computation was running in a separate thread.
The way things are arranged right now, each stopped computation gets a
different thread. What you want is for all these to be on the main
thread. It might be possible to arrange this, but it would require some
non-trivial reorganisation in the implementation of interactive
evaluation (compiler/main/InteractiveEval.hs). I'm going to have to
leave this for now, sorry. In the meantime you'll still be able to use
-fno-ghci-sandbox, but the debugging features in GHCi will be disabled.
Cheers,
Simon
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