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

[Brian Goetz]

That’s great.  Anyone maintaining this file should see it.


> On Feb 20, 2018, at 7:46 AM, Claes Redestad <claes.redestad at oracle.com> wrote:
> 
> Would injecting this before the LMF::metafactory do? Or should this be an @implNote?
> 
> diff -r d8e1eab41853 src/java.base/share/classes/java/lang/invoke/LambdaMetafactory.java
> --- a/src/java.base/share/classes/java/lang/invoke/LambdaMetafactory.java Tue Feb 20 14:40:53 2018 +0100
> +++ b/src/java.base/share/classes/java/lang/invoke/LambdaMetafactory.java 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 MethodHandle},
> 
> /Claes
> 
> 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
>