[jetty-dev] SelectSet optimization

[Greg Wilkins <gregw@xxxxxxxxxxx>]

Simone,

I instrumented the select manager and ran the StressTest class with
-DSTRESS=true and got results like:

selected=488481
cleared= 146416

This says that from 488k scheduled endpoint, 146k of them were already
dispatched, so the interested ops were cleared.
So  for 195k events, we avoided clearing the interestedOps AND avoided
a second dispatch, but for 146k events, we ended up dispatching twice
and clearing the interested ops.
So the question is, which is more expensive:  195k setting/clearing of
the interested ops, or 146k unnecessary schedules (note these are done
in selector thread and really just cost another synchronisation.

But more worryingly, the StressTest itself is currently failing
frequently with -DSTRESS=true -  so I'm going to investigate that
first.