Thanks for the patch sbt.
I think this is indeed useful, but I'm tempted to go further and say we should make this the default - and only - behavior. This will probably break existing code that accidentaly relied the fact that the implementation uses a bare fork(), but i'd say it's worth it:
- it's cleaner
- it will make it possible to remove all the ad-hoc handlers called after fork()
- it will remove the only place in the whole stdlib where fork() isn't followed by exec(): people who get bitten by issue #6721 will thus only be people calling explicitely fork(), in which case they're the sole responsibles for their misery ;-)

Another - although less common - advantage over the current implementation is that now one can run out of memory pretty easily if the operating system doesn't do overcommitting if you work with a large dataset. If fork() is followed by an exec, no problem.

Thoughts?