In local.glasgow-haskell-users, you wrote:

Suppose I have a program with two (ghc-)threads, one that does execute some `system' commands, and another one that accepts socket connections. While the system thread waits (for the system call to finish), will the other thread be awake (and accept new connections)?

As Simon already stated: no. If you decide to use fork() in any way, be sure to implement some kind of locking as *all* threads (including the thread for the socket!) will be clowned, e.g.: giant <- newMVar () ... takeMVar giant pid <- fork case pid of Nothing -> do -- Child systen(...) Just p -> do -- Parent putMVar giant () and placing locks on 'giant' in the essential parts in every other threads, e.g. before hGetLine. Ugly, but necessary for the worst case: threadWaitRead fd takeMVar giant hGetLine h putMVar giant () However, waiting on the system command to finish requires that you use a sigCHLD signal handler which invokes get[Any]ProcessStatus as you can't invoke waitpid in the parent. -- Volker Stolz * stolz@i2.informatik.rwth-aachen.de * PGP + S/MIME