fast way to infer caller

[Michael Kuhlmann]

On 4/7/22 19:27, Kasper Nielsen wrote:
>>
>> nope, see my previous mail to Ceki, the VM is cheating here if it can
>> inline the call to MethodHandles.lookup()
>>
> 
> Does how the VM cheats really matter? The fact is that the code in the JDK
> can
> get the calling class and implement something like MethodHandles.lookup() so
> it takes ~3 ns. If you implemented something like a lookup class as a normal
> user your best bet would be StackWalker.GetCallingClass() and you would end
> up with something that is at least 2 magnitudes slower. That is probably not
> an issue for most use cases. But for some, it might be a bit of a steep
> cost.
> 
> /Kasper

Hi Kasper,

sorry to jump in here as an uninvolved onlooker, but I can't resist.
I really don't see why this should matter. Getting the caller class is a 
rare edge case that you just do in exceptional situations; most often 
it's more for debugging or something.

What users really are interested in is high performance for standard 
cases. Implementing a specific optimization into Hotspot to gain few 
milliseconds is the least thing I expect from the JVM developers.

I also don't understand why someone should instantiate a logger during 
performance critical procedures. In more than 20 years of Java 
development, I've never seen the need to create a logger on the fly. 
They are *always* assigned to final static variables, or at least to 
predefined pools. Everything else would be just wrong: To instantiate a 
logger, you have to fetch at least the log level definition from some 
configuration source, and this can never be fast. At least not that 
we're talking about nanoseconds here.

All logging implementations I know of (and all that make sense) are 
highly optimized on log throughput; this can only be achieved by 
preprocessing during initialization, why this is slow. But that doesn't 
matter, because, as said, you should anyway create logger instances 
beforehand.

Sorry for the rant, but I really don't see the use case here.