Rather then lock/unlock the work queue ring for every item, save
tons of pthread lock manipulation by allocating to the producer
in batches. Over the long run, this doesn't change the CPU balance
or hold up either thread, but it eliminates almost 3/4 of the
lock/unlock episodes.
The time change is usually a trivial operation, so instead carry
a timestamp on all the work items and let the work thread decide
on its own when to do a SET_TIME operation. This reduces some
pthread overhead and thus gets us some better performance.
Stephen Williams