PARTIAL DEV-43869: LLMediaDataClient now uses two queues

This is a fairly major change that addresses the issue of an object
with constantly-updating media.  Before, that object would be put
into our single queue and sorted to a particular spot, and since it
continuously updates, it would "always be there".  That means that
nothing "behind" it would ever get serviced.

This change introduces two queues for each MDC: one is the same
"sorted" queue as before, and the other is unsorted, and
"round-robins".  New objects go into the sorted queue, objects
whose media we already know about get put into the unsorted queue.
The two queues are interleaved when serviced (one then the other is
serviced -- if one is empty we try the other -- until they are both
drained).

The round-robin queue works a little differently: after an item is
fetched from that queue (remember this would be an item we already
know about), that request is marked and put back at the end of the
queue.  If that object gets a UDP update while in the queue, that mark
is "cleared".  When it gets to the front of the queue again, if it
still marked, it is thrown away.  If it is not marked, it is fetched,
and again marked and put at the end.  This makes the queue
self-limiting in how big it can get.

I have also made some other changes:
- The sorting comparator now just delegates to the object for its
"interest" calculation.  A higher value = more interesting.
LLVOVolume now uses its PixelArea for its "interest" calculation,
which seems apparently better (the prior distance calculation was
wrong anyway).
- The score is cached before the sort operation is performed, so that
it won't be expensive to sort
- Now, the media version that is fetched is saved in the LLVOVolume,
and we do not update if it is not newer (this is not very
useful...yet.)
- I've introduced hard limits (settable by debug settings) on the size
of the queues.  The sorted queue will be culled (after sort) to that
count. NOTE: this will probably get removed in a later checkin, as
I've already gotten feedback that this is not desirable
- I've reorganized LLMediaDataClient so it makes more sense.
- I've made the request object a little smaller, so the queue won't take up so
much memory (more work could be done here)
- Added a unit test for the two-queue case (though more tests are needed!)

0 files changed, 0 insertions, 0 deletions