I have an application that uses multiple processes and multiple threads together. What's the best way to detect child process terminations?
The initial thread in the inital process serves as driver of the application. It creates child processes and threads to carry out portions of the computation. A natural way to have the driver detect termination of these child processes and threads would be to have the driver "listen" on a single MVar to which termination notices are "posted". Child threads would simply post their termination notices directly. For child processes, I'd like to have a single thread in the initial process execute (getAnyProcessStatus True False) repeatedly, posting a termination notice each time such a call returns. However, with the current implementation of Concurrent Haskell, when the thread pends on the getAnyProcessStatus call, the entire initial process pends. The best solution I've come up with so far, which is unsatisfying, is to have this thread poll periodically (that is, loop over (getAnyProcessStatus False False) and (threadDelay)). Is there a better way?
One (possibly better) way is to listen for SIGCLD. This has been discussed a couple of times before, threads here: http://www.haskell.org/pipermail/glasgow-haskell-users/2001-July/002079.html http://www.haskell.org/pipermail/glasgow-haskell-users/2001-September/002276... The upshot is the GHC *should* provide a better mechanism than it does currently, but it doesn't, sorry :-) Cheers, Simon