RFR: 8060130: Simplify the synchronization of defining and getting java.lang.Package

[Claes Redestad]

Hi all,

please review this patch which attempts to clean up synchronization and 
improve scalability when
defining and getting java.lang.Package objects.

webrev: http://cr.openjdk.java.net/~redestad/8060130/webrev.02/
bug: https://bugs.openjdk.java.net/browse/JDK-8060130

Testing: jtreg, UTE vm.parallel_class_loading.testlist, various benchmarks

Torturing the retrieval code with a simple microbenchmark[1] shows that 
the existing code
could cause bottlenecks, but also that the proposed patch works slightly 
faster even in
uncontended cases:

Benchmark                           Mode  Samples   Score Score error   
Units
baseline, 1 thread:
o.s.SimpleBench.getClassPackage    thrpt       10 11.621        0.618  
ops/us
o.s.SimpleBench.getPackage         thrpt       10 41.754        3.381  
ops/us
o.s.SimpleBench.getPackages        thrpt       10 0.009        0.000  ops/us

baseline, 2 threads:
o.s.SimpleBench.getClassPackage    thrpt       10 7.884        1.977  ops/us
o.s.SimpleBench.getPackage         thrpt       10 17.013        8.079  
ops/us
o.s.SimpleBench.getPackages        thrpt       10 0.004        0.001  ops/us

patch applied, 1 thread:
o.s.SimpleBench.getClassPackage    thrpt       10 13.519        0.170  
ops/us
o.s.SimpleBench.getPackage         thrpt       10 59.999        0.988  
ops/us
o.s.SimpleBench.getPackages        thrpt       10 0.019        0.001  ops/us

patch applied, 2 threads:
o.s.SimpleBench.getClassPackage    thrpt       10 19.181        3.688  
ops/us
o.s.SimpleBench.getPackage         thrpt       10 79.708       31.220  
ops/us
o.s.SimpleBench.getPackages        thrpt       10 0.025        0.006  ops/us

/Claes

[1]
package org.sample;

import org.openjdk.jmh.annotations.*;

@State(Scope.Thread)
public class SimpleBench {

     @Benchmark
     public Package[] getPackages() {
         return Package.getPackages();
     }

     @Benchmark
     public Package getClassPackage() {
         return this.getClass().getPackage();
     }

     @Benchmark
     public Package getPackage() {
         return Package.getPackage("java.util.zip");
     }
}