I've created 2 tasks <Wait> and <Notify>.
The use case is where you have parallel ants running (on some server) doing
builds, but 1 part of the build (in our case, some JFCUnit) needs to be single
threaded. By this I mean that each of the build/validates that we are doing can
run in parallel, with the exception of the JFCUnit portion due to focus
issues.

So, wrap the JFCUnit portion of the validate in the <Wait> <Notify> tasks. What
wait does is create a lock file, check for other locks, of none exist, it goes
forward. If other locks exist, it removes its lock file and does a random wait
(based on parameters) and tries again. <Notify> simply removes the lock.

I have a test build file and the working tasks if anyone wants to see and play
around.