AAShapePipe concurrency & memory waste

[Laurent Bourgès]

Dear java2d members,

I figured out some troubles in java2d.pipe.AAShapePipe related to both
concurrency & memory usage:
- concurrency issue related to static theTile field: only 1 tile is cached
so a new byte[] is created for other threads at each call to renderTile()
- excessive memory usage (byte[] for tile, int[] and rectangle): at each
call to renderPath / renderTiles, several small objects are created (never
cached) that leads to hundreds megabytes that GC must deal with

Here are profiling screenshots:
- 4 threads drawing on their own buffered image (MapBench test):
http://jmmc.fr/~bourgesl/share/AAShapePipe/AAShapePipe_byte_tile.png

- excessive int[] / Rectangle creation:
http://jmmc.fr/~bourgesl/share/AAShapePipe/AAShapePipe_int_bbox.png
http://jmmc.fr/~bourgesl/share/AAShapePipe/AAShapePipe_rectangle_bbox.png

Here is the proposed patch:
http://jmmc.fr/~bourgesl/share/AAShapePipe/webrev-1/

I applied a simple solution = use a ThreadLocal or ConcurrentLinkedQueue
(see useThreadLocal flag) to cache one AAShapePipeContext per thread (2K
max).
As its memory footprint is very small, I recommend using ThreadLocal.

Is it necessary to use Soft/Weak reference to avoid excessive memory usage
for such cache ?

Is there any class dedicated to such cache (ThreadLocal with cache eviction
or ConcurrentLinkedQueue using WeakReference ?) ?
I think it could be very useful at the JDK level to have such feature (ie a
generic "GC friendly"cache )

Regards,
Laurent