Edit: if you're just coming to this issue, then this comment has a good overview of what there is to do: #4 (comment)

Original description

Lots of annoying and fiddly details, but important!

I think for waiting, the best plan is to just give up on SIGCHLD (seriously, SIGCHLD is the worst) and park a thread in waitpid for each child process. Threads are lighter weight than processes so one thread-per-process shouldn't be a big deal. At least on Linux - if we're feeling ambitious we can do better on kqueue platforms. On Windows, it depends on what the state of our WaitFor{Multiple,Single}Object-fu is.