MH customization doesn't help here. The benchmark measures the cost of MH type check + MH.invokeBasic() call.

For MH.invokeExact(), type check is ptr comparison of MH.type against MethodType associated with the call site.


MH.invokeBasic() involves the following steps:
  MethodHandle        --form-->
  LambdaForm          --vmentry-->
  MemberName          --method-->
  (ResolvedMemberName --vmtarget--> // since jdk11 [1])
  JVM_Method*         --_from_compiled_entry-->
  entry address

The only optimization I see is to remove LambdaForm step and access MemberName (ResolvedMemberName since jdk11) directly from MethodHandle.
But there'll be still 3 dereferences involved:
  MethodHandle         --form-->
  [Resolved]MemberName --vmtarget-->
  JVM_Method*          --_from_compiled_entry-->
  entry address

The downside of such removal would be inability to rewrite individual LambdaForms (e.g., to eliminate redundant class initialization check) w/o tracking all MethodHandles which use particular LambdaForm. Probably, we can live without that (especially in JIT-compiled code).

In total, it ends up as 4 indirect loads (3 selection steps + 1 load from MH.type for type check) and I don't see a way to cut it down further.

For example, MemberName is a sort of handle for JVM internal Method*. JVM keeps a table of all MemberName instances and iterates over them when, for example, class redefinition happens. If MemberName indirection is eliminated, then MethodHandle would point directly to JVM_Method and JVM has to track all MethodHandle instances instead.

JVM_Method* is required due to similar reasons.

Type check on MH can't be further optimized as well.

So, I'm quite pessimistic about the prospects of speeding up invocations on non-constant MethodHandles.

Best regards,
Vladimir Ivanov

[1] https://bugs.openjdk.java.net/browse/JDK-8174749

On 2/2/18 3:33 PM, John Rose wrote:
Vladimir Ivanov did some work a few years ago on MH customization for hot MH 
instances. It’s in the system. That should get better results than what you 
show. I wonder why it isn’t kicking in. You are using invokeExact right?

On Feb 2, 2018, at 1:26 PM, Charles Oliver Nutter <head...@headius.com> wrote:

Hey folks!

I'm running some simple benchmarks for my FOSDEM handles talk and wanted to 
reopen discussion about the performance of non-static-final method handles.

In my test, I just try to call a method that adds given argument to a static 
long. The numbers for reflection and static final handle are what I'd expect, 
with the latter basically being equivalent to a direct call:

Direct: 0.05ns/call
Reflected: 3ns/call
static final Handle: 0.05ns/call

If the handle is coming from an instance field or local variable, however, 
performance is only slightly faster than reflection. I assume the only real 
improvement in this case is that it doesn't box the long value I pass in.

local var Handle: 2.7ns/call

What can we do to improve the performance of non-static method handle 
invocation?

- Charlie
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