[11] RFR: 8198418: Invoke LambdaMetafactory::metafactory exactly from the BootstrapMethodInvoker

Claes Redestad claes.redestad at oracle.com
Tue Feb 20 12:07:29 UTC 2018

Hi Rémi,

sure, MethodType.equals will do a fast == check, but then checks the 
param types. It sure looks cleaner, though:




On 2018-02-20 12:38, Remi Forax wrote:
> Hi Claes,
> instead of checking each parameter of the bsmType(), why not allocating the corresponding MethodType and storing it in a static final, so you can check if the MethodType are equals using equals (as far as i remember MethodType.equals is a == in the OpenJDK implementation).
> in term of name why not isLambdaMetafactoryIndyBootstrapMethod and isLambdaMetafactoryCondyBoostrapMethod instead of isLambdaMetafactoryCallSite and isLambdaMetafactoryFunction ?
> and you can remove <T> in the signature of isLambdaMetafactoryCallSite() and replace Class<T> by Class<?>.
> cheers,
> Rémi
> ----- Mail original -----
>> De: "Claes Redestad" <claes.redestad at oracle.com>
>> À: "core-libs-dev" <core-libs-dev at openjdk.java.net>
>> Envoyé: Mardi 20 Février 2018 11:51:15
>> Objet: [11] RFR: 8198418: Invoke LambdaMetafactory::metafactory exactly from the BootstrapMethodInvoker
>> Hi,
>> a small regression to lambda bootstrapping came in with the recent
>> condy merge, and it took me a while to figure out why.
>> Before condy, the first three parameters of calls from the BSM invoker
>> to the six parameter LambdaMetafactory::metafactory were statically
>> known, so only the fourth through sixth param were dynamically bound
>> to enforce runtime type checks (MH.invoke -> MH.checkGenericInvoker
>> -> MH.asType(MT) -> MHI.makePairwiseConvertByEditor -> generates a
>> slew of filterArguments, rebinds, casting MHs etc).
>> With condy, the third parameter is now an Object (in reality either a
>> Class or a MethodType), thus not statically known. This means the
>> MethodType sent to checkGenericInvoker will have to add a cast for
>> this param too, thus in makePairwiseConvertByEditor we see an
>> additional rebind, some additional time spent spinning classes etc.
>> Effectively increasing the cost of first lambda initialization by a small
>> amount (a couple of ms).
>> Here came the realization that much of the static overhead of the
>> lambda bootstrapping could be avoided altogether since we can
>> determine and cast arguments statically for the special-but-common
>> case of LambdaMetafactory::metafactory. By using exact type
>> information, and even bootstrapMethod.invokeExact, no dynamic
>> runtime checking is needed, so the time spent in
>> makePairwiseConvertByEditor is avoided entirely.
>> This might be a hack, but a hack that removes a large chunk of the
>> code executed (~75% less bytecode) for the initial lambda bootstrap.
>> Startup tests exercising lambdas show a 10-15ms improvement - the
>> static overhead of using lambdas is now just a few milliseconds in total.
>> Webrev: http://cr.openjdk.java.net/~redestad/8198418/jdk.00/
>> RFE: https://bugs.openjdk.java.net/browse/JDK-8198418
>> The patch includes a test for an experimental new metafactory method
>> that exists only in the amber condy-folding branch. I can easily break it
>> out and push that directly to amber once this patch syncs up there, but
>> have tested that keeping it in here does no harm.
>> Thanks!
>> /Claes

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