[Xmonad] darcs patch: zombie_children

[Don Stewart]

dbenbenn:
> On 10/24/07, Don Stewart <dons at galois.com> wrote:
> > Also, I'd like to know what impact, if any, waiting before every
> > X event has.
> 
> I haven't noticed any impact on my Linux box.  I assume that the
> wait() system call is implemented efficiently.
> 
> Though now that I think about it, it should be better to just set
> SIGCHLD to SIG_IGN.  Perhaps that would work on BSD too?  I'll send
> another patch ...

Strangely, getGroupProcessStatus is implemented as:

    getGroupProcessStatus :: Bool
                          -> Bool
                          -> ProcessGroupID
                          -> IO (Maybe (ProcessID, ProcessStatus))
    getGroupProcessStatus block stopped pgid =
      alloca $ \wstatp -> do
        pid <- throwErrnoIfMinus1Retry "getGroupProcessStatus"
            (c_waitpid (-pgid) wstatp (waitOptions block stopped))
        case pid of
          0  -> return Nothing
          _  -> do ps <- decipherWaitStatus wstatp
               return (Just (pid, ps))

so we get Just/Nothing distinction, *and* a possible exception that 
needs to be handles. How un-Haskelly.

-- Don