I'm constantly told simultaneous emerging is bad, even emerge on one terminal and emerge --fetch on another screws up (but see bug 1661 and bug 33098). Is there any good reason emerge should *let* users do parallel emerges? Why not stop them using some simple lockfile system? Sure, some people want to risk it occasionally and emerge one small tiny unrelated thing alongside their big, time consuming xfree emerge, but there could be ways around that (a get-around var in /etc/make.conf, another command line option, a big red warning message when simultaneous emerge is attempted, but without actually preventing the user from doing it). Of course, if this were actually implemented you'd have to be careful to allow emerge -s, emerge -S and emerge -p. Any thoughts?
It should be ok in current stable portages as lockfiles are now employed on the database. Worst thing that will happen is deletion of the source code being compiled. It's being worked on.
*** Bug 354419 has been marked as a duplicate of this bug. ***