> From: "Kasper Nielsen" <kaspe...@gmail.com> > To: "Remi Forax" <fo...@univ-mlv.fr> > Cc: "Ceki Gülcü" <c...@qos.ch>, "core-libs-dev" > <core-libs-dev@openjdk.java.net> > Sent: Thursday, April 7, 2022 2:42:46 PM > Subject: Re: fast way to infer caller
> On Thu, 7 Apr 2022 at 13:33, Remi Forax < [ mailto:fo...@univ-mlv.fr | > fo...@univ-mlv.fr ] > wrote: >> ----- Original Message ----- >> > From: "Kasper Nielsen" < [ mailto:kaspe...@gmail.com | kaspe...@gmail.com >> > ] > >> > To: "Ceki Gülcü" < [ mailto:c...@qos.ch | c...@qos.ch ] > >>> Cc: "core-libs-dev" < [ mailto:core-libs-dev@openjdk.java.net | >> > core-libs-dev@openjdk.java.net ] > >> > Sent: Thursday, April 7, 2022 1:53:33 PM >> > Subject: Re: fast way to infer caller >> >> 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 >>> The resulting class is not the same, so comparing the performance of two >>> codes >> > that does not do the same thing is dubious, no ? > I think it is a fair test. MethodHandles.lookup() is basically just wrapping > Reflection.getCallerClass(). So if anything > calling Reflection.getCallerClass() directly would be even faster than calling > MethodHandles.lookup().lookupClass(); nope, see my previous mail to Ceki, the VM is cheating here if it can inline the call to MethodHandles.lookup(). > /Kasper Rémi
