
Barrier

Here are the options:

-b<num>		how many iterations
		default: 10

-p<num>		how many processors
		default: 1

-q<num>		preemption quantum in milliseconds
		default: no time slicing

-s<num>		how many slave threads
		default: 1

Barrier demonstrates another discipline for combining
synchronous and asynchronous computation.

A master thread grabs an exclusive lock and then starts a cycle
where it arrives at the barrier, waits for the slaves to arrive,
then grabs a lock for the next iteration, and releases
the lock for the current iteration.

The slave threads run in a cycle where they arrive at the barrier,
check to see if they should wake up the master thread, and then try to
get and release the exclusive lock.
