RFR: 8291065: Creating a VarHandle for a static field triggers class initialization [v14]

[Paul Sandoz]

On Tue, 27 Jun 2023 13:57:31 GMT, Chen Liang <liach at openjdk.org> wrote:

>> This patch implements lazy initialization for VarHandle working on static fields. It has a good initial call performance.
>> 
>> We introduce a new internal API, `target()` to unpack a lazy VarHandle in VH implementation methods. If called via MethodHandle, a barrier is added in the MethodHandle instead.
>> 
>> The new test ensures the correctness of Lazy VH for both direct and indirect invocation; the performance of MethodHandle version of lazy VH is not yet tested.
>> 
>> 
>> Benchmark                                            Mode  Cnt    Score    Error  Units
>> LazyStaticColdStart.methodHandleCreateEager            ss   10   41.490 ± 12.331  us/op
>> LazyStaticColdStart.methodHandleCreateLazy             ss   10   21.810 ± 16.964  us/op
>> LazyStaticColdStart.methodHandleInitializeCallEager    ss   10   57.860 ± 13.738  us/op
>> LazyStaticColdStart.methodHandleInitializeCallLazy     ss   10   93.300 ± 18.858  us/op
>> LazyStaticColdStart.varHandleCreateEager               ss   10   39.860 ±  9.362  us/op
>> LazyStaticColdStart.varHandleCreateLazy                ss   10   17.630 ±  1.111  us/op
>> LazyStaticColdStart.varHandleInitializeCallEager       ss   10  123.170 ± 62.468  us/op
>> LazyStaticColdStart.varHandleInitializeCallLazy        ss   10  105.390 ± 41.815  us/op
>
> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Rollback VHG changes

src/java.base/share/classes/java/lang/invoke/LazyInitializingVarHandle.java line 63:

> 61:     }
> 62: 
> 63:     @ForceInline

Suggestion:

    @Override
    @ForceInline

src/java.base/share/classes/java/lang/invoke/VarHandle.java line 2210:

> 2208: 
> 2209:     /**
> 2210:      * Computes a method handle that can be passed the {@linkplain #target() direct}

Suggestion:

     * Computes a method handle that can be passed the {@linkplain #asDirect() direct}

?

test/jdk/java/lang/invoke/VarHandles/LazyInitializingTest.java line 85:

> 83: 
> 84:     @Test
> 85:     public void testInitializationOnVarHandleUse() {

I think we will need to expand this to also test operating on a MH to a VH, an indirect VH, and on a MH to indirect VH. We could do this separately.

test/micro/org/openjdk/bench/java/lang/invoke/LazyStaticColdStart.java line 92:

> 90:             });
> 91: 
> 92:             static {

Is this static block required?

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PR Review Comment: https://git.openjdk.org/jdk/pull/13821#discussion_r1244336226
PR Review Comment: https://git.openjdk.org/jdk/pull/13821#discussion_r1244362027
PR Review Comment: https://git.openjdk.org/jdk/pull/13821#discussion_r1244367651
PR Review Comment: https://git.openjdk.org/jdk/pull/13821#discussion_r1244367889