RFR: 8288327: Executable.hasRealParameterData should not be volatile [v7]

[Сергей Цыпанов]

On Fri, 1 Jul 2022 18:32:18 GMT, Peter Levart <plevart at openjdk.org> wrote:

>> @plevart I've checked it with and without `@stable`, it's the same:
>> 
>> with
>> Benchmark                            Mode  Cnt  Score   Error  Units
>> AccessParamsBenchmark.getParameter0  avgt   50  6,196 ± 0,142  ns/op
>> AccessParamsBenchmark.getParameters  avgt   50  4,636 ± 0,075  ns/op
>> 
>> without
>> Benchmark                            Mode  Cnt  Score   Error  Units
>> AccessParamsBenchmark.getParameter0  avgt   50  6,196 ± 0,142  ns/op
>> AccessParamsBenchmark.getParameters  avgt   50  4,636 ± 0,075  ns/op
>> 
>> This seems logical as effects of `@Stable` aren not propagated into cloned array.
>> This is the benchmark I used:
>> 
>> @State(Scope.Thread)
>> @BenchmarkMode(Mode.AverageTime)
>> @OutputTimeUnit(TimeUnit.NANOSECONDS)
>> @Fork(jvmArgsAppend = {"-Xms1g", "-Xmx1g"})
>> public class AccessParamsBenchmark {
>> 
>>   private final Method method;
>> 
>>   public AccessParamsBenchmark() {
>>     try {
>>       method = getClass().getMethod("foo", int.class, String.class);
>>     } catch (NoSuchMethodException e) {
>>       throw new RuntimeException(e);
>>     }
>>   }
>> 
>>   @Benchmark
>>   public Object getParameters() {
>>     return method.getParameters();
>>   }
>> 
>>   @Benchmark
>>   public Object getParameter0() {
>>     return method.getParameters()[0];
>>   }
>> 
>>   public void foo(int parameter1, String parameter2) {
>>   }
>> }
>> 
>> 
>> So, should we rid the annotation from `parameters` field?
>
> @Stable is only effective if the path leading to @Stable value can be constant-folded by JIT. In above test, you have an instance field Method method. This can not be constant-folded, so neither can @stable fiels in the Field object, nor array elements of a @stable array. You should replace that with "static final Method method = ..." and re-run the test.

With `static` and without `@Stable` the benchmark yields

Benchmark                            Mode  Cnt  Score   Error  Units
AccessParamsBenchmark.getParameter0  avgt   10  1,212 ± 0,083  ns/op
AccessParamsBenchmark.getParameters  avgt   10  2,493 ± 0,076  ns/op

and with `@Stable`

Benchmark                            Mode  Cnt  Score   Error  Units
AccessParamsBenchmark.getParameter0  avgt   40  0,427 ± 0,007  ns/op
AccessParamsBenchmark.getParameters  avgt   40  2,123 ± 0,052  ns/op

so the annotation is useful.

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PR: https://git.openjdk.org/jdk/pull/9143