Avoid allocations in Executable.getAllGenericParameterTypes

[Claes Redestad]

Hi Christoph,

I agree this might not be called super often, but the refactoring is
straightforward and I think it clarifies the intent of the code, so
seems like a reasonable enhancement to make.

I've already volunteered to sponsor another patch of yours, so I might
as well pick this up too and test them together.

/Claes

On 2020-05-23 09:53, Christoph Dreis wrote:
> Hi,
> 
> I was looking through the code and found a relatively straight-forward optimization in Executable.getAllGenericParameterTypes (attached below).
> The idea is to simply move some code around to avoid unnecessary allocations from getParameters() or array initializations when working with generics and no "real" parameter data is available.
> 
> I used the following benchmark:
> 
> @BenchmarkMode(Mode.AverageTime)
> @OutputTimeUnit(TimeUnit.NANOSECONDS)
> public class MyBenchmark {
> 
>      @State(Scope.Benchmark)
>      public static class ThreadState {
>          
>          private Parameter parameter;
> 
>          public ThreadState() {
>              try {
>                  this.parameter = Test1.class.getDeclaredConstructor(Set.class).getParameters()[0];
>              } catch (NoSuchMethodException e) {
>                  // Do nothing
>              }
>          }
> 
>      }
> 
>      @Benchmark
>      public AnnotatedType test(ThreadState threadState) {
>          return threadState.parameter.getAnnotatedType();
>      }
> 
> }
> 
> public class Test1 {
>        public Test1(Set<?> names) {}
> }
> 
> With the attached patch and the benchmark above I get the following results.
> 
> Old
> Benchmark                                                  Mode  Cnt    Score     Error   Units
> MyBenchmark.test                                       avgt   10  358,103 ±  58,098   ns/op
> MyBenchmark.test:·gc.alloc.rate.norm    avgt   10  248,021 ±   0,003    B/op
> 
> Patched
> MyBenchmark.test                                       avgt   10  309,133 ±  6,319   ns/op
> MyBenchmark.test:·gc.alloc.rate.norm    avgt   10  200,016 ±  0,001    B/op
> 
> 
> I don't think the particular method is called super often, but it seems to be used in ByteBuddy & JUnit as far as I can see.
> In case you think this is worthwhile, I would appreciate it if someone can sponsor this patch.
> 
> Cheers,
> Christoph
> 
> ========= PATCH ==========
> --- a/src/java.base/share/classes/java/lang/reflect/Executable.java     Wed May 13 16:18:16 2020 +0200
> +++ b/src/java.base/share/classes/java/lang/reflect/Executable.java     Sat May 23 08:31:23 2020 +0200
> @@ -307,12 +307,12 @@
>               final boolean realParamData = hasRealParameterData();
>               final Type[] genericParamTypes = getGenericParameterTypes();
>               final Type[] nonGenericParamTypes = getParameterTypes();
> -            final Type[] out = new Type[nonGenericParamTypes.length];
> -            final Parameter[] params = getParameters();
> -            int fromidx = 0;
>               // If we have real parameter data, then we use the
>               // synthetic and mandate flags to our advantage.
>               if (realParamData) {
> +                final Type[] out = new Type[nonGenericParamTypes.length];
> +                final Parameter[] params = getParameters();
> +                int fromidx = 0;
>                   for (int i = 0; i < out.length; i++) {
>                       final Parameter param = params[i];
>                       if (param.isSynthetic() || param.isImplicit()) {
> @@ -325,6 +325,7 @@
>                           fromidx++;
>                       }
>                   }
> +                return out;
>               } else {
>                   // Otherwise, use the non-generic parameter data.
>                   // Without method parameter reflection data, we have
> @@ -334,7 +335,6 @@
>                   return genericParamTypes.length == nonGenericParamTypes.length ?
>                       genericParamTypes : nonGenericParamTypes;
>               }
> -            return out;
>           }
> 
>