On 06/07/2011 07:37, Jason Dagit wrote:
On Jul 5, 2011 1:04 PM, "Jason Dagit" <dag...@gmail.com
<mailto:dag...@gmail.com>> wrote:
>
> On Tue, Jul 5, 2011 at 12:33 PM, Ian Lynagh <ig...@earth.li
<mailto:ig...@earth.li>> wrote:
> > On Tue, Jul 05, 2011 at 08:11:21PM +0100, Simon Marlow wrote:
> >>
> >> In GHCi it's a different matter, because the main thread is running
> >> GHCi itself, and all the expressions/statements typed at the prompt
> >> are run in forkIO'd threads (a new one for each statement, in fact).
> >> If you want a way to run command-line operations in the main thread,
> >> please submit a feature request. I'm not sure it can be done, but
> >> I'll look into it.
> >
> > We already have a way: -fno-ghci-sandbox
>
> I've removed all my explicit attempts to forkIO/forkOS and passed the
> command line flag you mention. I just tried this but it doesn't
> change the behavior in my example.
I tried it again and discovered that due to an argument parsing bug in
cabal-dev that the flag was not passed correctly. I explicitly passed it
and verified that it works. Thanks for the workaround. By the way, I did
look at the user guide for options like this and didn't see it. Which
part of the manual is it in?
Can I still make a feature request for a function to make code run on
the original thread? My reasoning is that the code which needs to run on
the main thread may appear in a library in which case the developer has
no control over how ghc is invoked.
I'm not sure how that would work. The programmer is in control of what
the main thread does, not GHC. So in order to implement some mechanism
to run code on the main thread, we would need some cooperation from the
main thread itself. For example, in gtk2hs the main thread runs an
event handler loop which occasionally checks a queue for requests from
other threads (at least, I think that's how it works).
Cheers,
Simon
The alternative appears to be context specific workarounds. I think that
a general solution, if possible, will make gui libraries easier to
develop for Ghc. I'm hooping it's as simple as exposing a pthreads call.
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