Threads must wait to be ready

[sbordet]

Performing work in N threads must ensure that the N threads are really all started and ready to perform the work.

Currently, Runnable tasks are created and submitted to the Executor in a loop, which may cause the first task to run to completion before the second task is even submitted.

The code should use a barrier that waits for all the threads to be ready, and only then release the barrier to make all the threads perform the work.

[olamy]

done