[9] RFR (M): 8069591: Customize LambdaForms which are invoked using MH.invoke/invokeExact

[Vladimir Ivanov]

Remi, John, thanks for review!

Updated webrev:
http://cr.openjdk.java.net/~vlivanov/8069591/webrev.01/

This time I did additional testing (COMPILE_THRESHOLD > 0) and spotted a 
problem with MethodHandle.copyWith(): a MethodHandle can inherit 
customized LambdaForm this way. I could have added 
LambdaForm::uncustomize() call in evey Species_*::copyWith() method, but 
I decided to add it into MethodHandle constructor. Let me know if you 
think it's too intrusive.

Also, I made DirectMethodHandles a special-case, since I don't see any 
benefit in customizing them.

Best regards,
Vladimir Ivanov

On 1/21/15 10:30 PM, John Rose wrote:
> On Jan 21, 2015, at 9:31 AM, Remi Forax <forax at univ-mlv.fr> wrote:
>>
>> in Invokers.java, I think that checkCustomized should take an Object and not a MethodHandle
>> exactly like getCallSiteTarget takes an Object and not a CallSite.
>
> The use of erased types (any ref => Object) in the MH runtime is an artifact of bootstrapping difficulties, early in the project.  I hope it is not necessary any more.  That said, I agree that the pattern should be consistent.
>
> Vladimir, would you please file a tracking bug for this cleanup, to change MH library functions to use stronger types instead of Object?
>
>> in MethodHandle.java, customizationCount is declared as a byte and there is no check that
>> the CUSTOMIZE_THRESHOLD is not greater than 127.
>
> Yes.  Also, the maybeCustomize method has a race condition that could cause the counter to wrap.  It shouldn't use "+=1" to increment; it should load the old counter value, test it, increment it (in a local), and then store the updated value.  That is also one possible place to deal with jumbo CUSTOMIZE_THRESHOLD values.
>
> — John
>