fast way to infer caller

[Kasper Nielsen]

>
> MethodHandles.lookup().lookupClass() looks very promising except that
> there is no way to specify the depth.
>
> I am looking for a method to obtain the Nth caller at a cost of around
> 100 to 200 nanoseconds of CPU time.  Do you think the JDK could cater
> for this use case?
>

Hi Ceki,

I don't think you will find the numbers you are looking for with
StackWalker.
Compared to something like Reflection.getCallerClass() which
MethodHandles.lookup() uses.
There is still a very large (>100x) performance gap between the two.

public class StackWalkerPerf {

    static final StackWalker sw =
StackWalker.getInstance(Option.RETAIN_CLASS_REFERENCE);

    @Benchmark
    public Class<?> stackWalkerCallerClass() {
        return sw.getCallerClass();
    }

    @Benchmark
    public Class<?> reflectionCallerClass() {
        return MethodHandles.lookup().lookupClass();
    }
}

Benchmark                               Mode  Cnt     Score    Error  Units
StackWalkerPerf.reflectionCallerClass   avgt   10    2,927 ± 0,012  ns/op
StackWalkerPerf.stackWalkerCallerClass  avgt   10  915,287 ± 9,565  ns/op

/Kasper