On Wed, Nov 16, 2005 at 07:20:48PM +0100, Tomasz Zielonka wrote:
On Wed, Nov 16, 2005 at 09:45:17AM -0800, Andrew Pimlott wrote:
On Wed, Nov 16, 2005 at 11:51:19AM -0500, Kurt Hutchinson wrote:
I have to perform another runReaderT when forking? Or is there a way to get the ReaderT environment automatically carried over to the newly created Set B thread?
This is an unavoidable pain as far as I know. It would be nice if forkIO were defined in terms of MonadIO:
forkIO :: MonadIO m => m () -> m ThreadId
(Same with forkProcess.) I haven't thought too hard about it, but it seems that it should be possible.
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 But maybe the primitives used by forkIO do not allow this approach. I'm not sure.
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. Andrew