On 18 May 2005 14:47, Frederik Eaton wrote:

When I run the following line in ghci:

Prelude System.Process Control.Concurrent System.IO> do { (inp, out, err, ph) <- runInteractiveProcess "cat" [] Nothing Nothing; forkIO (do hPutStr inp "this\nis\na\ntest\n"; hClose inp); waitForProcess ph }

... it doesn't terminate. I'm following the example in the System.Process documentation. But I would think that since I close 'inp', "cat" would terminate. Also, I don't see the expected output.

This example won't work inside GHCi, because GHCi isn't compiled with -threaded: the -threaded option is required to get a version of waitForProcess that doesn't block other threads in a multithreaded program. The only reason GHCi isn't compiled with -threaded is because I'm being conservative; the threaded RTS introduces a lot more complexity and hasn't been shaken down as much as the single-threaded RTS. If you compile GHC up yourself you can fix it by adding "GhcStage2HcOpts += -threaded" to mk/build.mk before building. In a future release of GHC we'll do this by default. Cheers, Simon