[OpenJDK 2D-Dev] [10] Review Request: 8185093 Expensive multi-core choke point when any graphics objects are created

[Sergey Bylokhov]

Hello,
Please review the fix for jdk10.

Bug: https://bugs.openjdk.java.net/browse/JDK-8185093
Webrev can be found at: http://cr.openjdk.java.net/~serb/8185093/webrev.00
jmh test: http://cr.openjdk.java.net/~serb/8185093/LocalGEproblem.java

While working on some other bug I found a performance issue in our 
java2d pipeline in multi-threaded environment. We have a "hot spot" in 
the "GraphicsEnvironment.getLocalGraphicsEnvironment()". This method is 
executed every time the graphics object is created, for example 
BufferedImage.java:

     public Graphics2D createGraphics() {
         GraphicsEnvironment env =
             GraphicsEnvironment.getLocalGraphicsEnvironment();
         return env.createGraphics(this);
     }

So even if the application will draw to a different Images it will be 
blocked for some time in this method.
I created a jmh test case which shows that implementing this method via 
holder will speedup the next code:
       Graphics2D graphics = bi.createGraphics();
       graphics.drawLine(0, 0, 100, 100);

  4 Threads:
  - Before the fix:  8922 ops/ms
  - After the fix :  9442 ops/ms
  8 Threads:
  - Before the fix:  4511 ops/ms
  - After the fix : 11899 ops/ms

The main issue which I would like to clarify is it possible to remove 
synchronize keyword from the getLocalGraphicsEnvironment(), possibly 
with updating a specification? We have similar issues in other parts of 
code which I would like to update later after this one.

-- 
Best regards, Sergey.