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

Claes Redestad claes.redestad at oracle.com
Tue Feb 20 15:46:47 UTC 2018

Would injecting this before the LMF::metafactory do? Or should this be 
an @implNote?

diff -r d8e1eab41853 
Tue Feb 20 14:40:53 2018 +0100
Tue Feb 20 16:50:27 2018 +0100
@@ -242,6 +242,12 @@
      private static final Class<?>[] EMPTY_CLASS_ARRAY = new Class<?>[0];
      private static final MethodType[] EMPTY_MT_ARRAY = new MethodType[0];

+    // LambdaMetafactory bootstrap methods are startup sensitive, and 
may be
+    // special cased in java.lang.invokeBootstrapMethodInvoker to ensure
+    // methods are invoked with exact type information to avoid generating
+    // code for runtime checks. Take care any changes or additions here are
+    // reflected there as appropriate.
       * Facilitates the creation of simple "function objects" that 
implement one
       * or more interfaces by delegation to a provided {@link 


On 2018-02-20 16:05, Brian Goetz wrote:
> Add a comment to LMF to remember to update the hack if additional sigs are added.
> Sent from my iPad
>> On Feb 20, 2018, at 4:27 AM, Claes Redestad <claes.redestad at oracle.com> wrote:
>> You also pointed out that if the params or return types doesn't match, we'd get a CCE sooner or later, making the return and argument checks superfluous. This all simplifies into this, then:
>> http://cr.openjdk.java.net/~redestad/8198418/jdk.02/
>> Thanks!
>> /Claes
>>> On 2018-02-20 13:20, Vladimir Ivanov wrote:
>>> No need in MT.equals. Pointer comparison should work as well: MethodType instances are interned and all exact type checks on MethodHandles are implemented using == on their MTs.
>>> Best regards,
>>> Vladimir Ivanov
>>>> On 2/20/18 3:07 PM, Claes Redestad wrote:
>>>> Hi Rémi,
>>>> sure, MethodType.equals will do a fast == check, but then checks the param types. It sure looks cleaner, though:
>>>> http://cr.openjdk.java.net/~redestad/8198418/jdk.01/
>>>> Thanks!
>>>> /Claes
>>>>> 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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