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I checked libevent, and it doesn't support wait() events. It would be great if it did...

You can catch sigCHLD in the main event-loop and then invoke wait(). [This could even be possible in the current RTS by applying another incarnation of Wolfgang's pipe-hack]

Why another incarnation? The "first incarnation" should do the job, too. What's wrong with just safe-foreign-calling wait and relying on the threaded RTS to do the job?

Sure, we could do that - and we could do it for the I/O library too and remove all the select() stuff entirely. But that would impose a performance penalty on applications with large numbers of I/O-bound threads, so we like to keep the lightweight mechanism too. The same argument applies to process waiting, although you could argue that it is less convincing there, because there are probably not that many applications which need to wait on thousands of processes. Cheers, Simon