On Wed, Nov 16, 2005 at 10:53:17AM -0800, Andrew Pimlott wrote:
On Wed, Nov 16, 2005 at 07:20:48PM +0100, Tomasz Zielonka wrote:
I think it wouldn't be possible using only methods in MonadIO.
Here's what I had in mind for forkProcess. Recall that the fork syscall returns 0 to the child and a pid to the parent.
forkProcess :: MonadIO m => m () -> m ProcessID forkProcess io = do pid <- liftIO forkSyscall if (pid == 0) then io >> exit else return pid
Well, yes, I haven't thought about it. I don't know forkSyscall and I can't say if it's a good idea or not.
But maybe the primitives used by forkIO do not allow this approach. I'm not sure.
I'm pretty sure they don't, but I may be wrong again. They could probably be extended to allow this. However, I'm not sure I would like this, because it would be too easy to break abstraction.
Besides, what should be the semantics of forkIO for (StateT s IO)? I can't think of anything reasonable.
I don't see the problem--they would each get a copy of the state. Although I could be missing something, as I use System.Posix.Process more than Control.Concurrent.
Yes, but the changes made in the child thread would be ignored in the parent. Best regards Tomasz