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

[Stanimir Simeonoff]

The commented annotation in ClassLoader.java must be removed (line 268)
// @GuardedBy("itself")

Stanimir


On Fri, Oct 10, 2014 at 6:10 PM, Claes Redestad <claes.redestad at oracle.com>
wrote:

> 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");
>     }
> }
>
>