[OpenJDK 2D-Dev] RFR: 8147443: Use Common Cleaner in Marlin OffHeapArray

[Laurent Bourgès]

Dear all,

Sorry, I need to restart properly the review thread that occured in another
topic:
<http://cr.openjdk.java.net/%7Elbourges/marlin/marlin-Cleaner.1/>
http://mail.openjdk.java.net/pipermail/2d-dev/2016-January/006145.html


Please review this webrev refactoring Marlin OffHeapArray to use the new
jdk.internal.ref.CleanerFactory (new Cleaner API) instead of my own
solution (ReferenceQueue + PhantomReference + Thread):
http://cr.openjdk.java.net/~lbourges/marlin/marlin-Cleaner.1/

bug: https://bugs.openjdk.java.net/browse/JDK-8147443

The new API is really great as it just needs 1 line:

+        // Register a cleaning function to ensure freeing off-heap
memory:+        CleanerFactory.cleaner().register(parent, () ->
this.free());


I added a qualified export in modules.xml:

     <export>+      <name>jdk.internal.ref</name>+
<to>java.desktop</to>+    </export>+    <export>


FYI there is no performance issue as all off-heap arrays are belonging
to a Marlin's RendererContext (parent reference).
The RendererContext instances are stored as thread-local variables
using a SoftReference (or a WeakReference) to maximize the potential
reuse (like a  buffer) but avoid OOME.


Finally I tested the patch using the following settings to use weak
references to
RendererContexts and enable logging all allocations / free operations in
OffHeapArray:

-Dsun.java2d.renderer.log=true
-Dsun.java2d.renderer.logUnsafeMalloc=true
-Dsun.java2d.renderer.useRef=weak

INFO: 1452703097931: OffHeapArray.allocateMemory = 65536 to addr =
140642864899472
INFO: 1452703097931: OffHeapArray.allocateMemory = 98304 to addr =
140642864965024
...
INFO: 1452703103321: OffHeapEdgeArray.free = 98304 at addr = 140642864965024
INFO: 1452703103321: OffHeapEdgeArray.free = 65536 at addr = 140642864899472
...
INFO: 1452703103827: OffHeapArray.allocateMemory = 65536 to addr =
140642864910240
INFO: 1452703103827: OffHeapArray.allocateMemory = 98304 to addr =
140642864975792
...
INFO: 1452703113822: OffHeapEdgeArray.free = 98304 at addr = 140642864975792
INFO: 1452703113822: OffHeapEdgeArray.free = 65536 at addr = 140642864910240
...

As mentioned by Phil, other Java2D classes (like Disposer) may use the new
Cleaner approach in the future and potentially need a dedicated Cleaner
instance (Thread) for performance sensitive code.

Best regards,
Laurent
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