MethodHandle.invoke* performance

[Cédric Champeau]

Hi guys,

First of all, sorry if my question looks stupid, but I have difficulties 
explaining what I see. I made a small benchmark for various 
MethodHandle.invoke* combinations. Of course, micro-benchmarks are evil, 
but in that case, I find the figures quite interesting. Note that I'm 
not using invokedynamic instructions anywhere, I'm just "testing" the 
API from plain Java. As MethodHandles are promoted as "faster than 
reflection", I expected very different results.

So first, the link: https://gist.github.com/melix/5291792

The results I obtain here with openjdk-8-lambda b83 are not good:

|Classic for loop[-1] 166ms||
||InvokeExact[-1] 170ms||
||InvokeExact (local method handle)[-1] 3410ms||
||bindTo+invokeExact[-1] 6905ms||
||insertArgument+invokeExact[-1] 6254ms||
||invoke[-1] 60118ms||
||bindTo+invoke[-1] 80072ms||
||insertArgument+invoke[-1] 78337ms||
||Reflect[-1] 1219ms||
|
I added the "static final field" version as a suggestion from Jochen 
Theodorou, and it does make things much faster, but it's the *only* case 
that comes close to regular Java performance. Any other combination is 
much slower. I know that invoke() is supposed to perform type 
conversions, but is it supposed to be that slow as compared to 
invokeExact? What explains the difference between the local method 
handle and the static field version? In theory, using invokedynamic 
instruction, the method handle would come from a boostrap method so I 
could expect the same performance as the static field version, but if 
any other combination than direct invokeExact calls are slower, then 
it's not good. So, basically, I'd like to know what I'm missing here :)

Thanks for your explanations!

P.S: Note that order of tests do not matter here, I know I should not 
mix things, but I tested with different test execution order without 
more success.

-- 
Cédric Champeau
SpringSource - A Division Of VMware
http://www.springsource.com/
http://twitter.com/CedricChampeau

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