RFR: 8291065: Creating a VarHandle for a static field triggers class initialization [v7]

[Chen Liang]

On Sat, 3 Jun 2023 03:47:40 GMT, Chen Liang <liach at openjdk.org> wrote:

>> src/java.base/share/classes/java/lang/invoke/LazyInitializingVarHandle.java line 106:
>> 
>>> 104:         UNSAFE.ensureClassInitialized(refc);
>>> 105:         this.initialized = true;
>>> 106:     }
>> 
>> This should probably have a fast‑path when `this.initialized` is `true`, so that it can be better constant folded by the **JIT**:
>> Suggestion:
>> 
>>     private void ensureInitialized() {
>>         if (this.initialized) {
>>             return;
>>         }
>>         UNSAFE.ensureClassInitialized(refc);
>>         this.initialized = true;
>>     }
>
> I think I should probably update the MH lambda form as well, to skip the ensure call entirely if JVM has not constant-fold the inefficient form yet.

Indeed, updating lambda form and cached mh works: the average invocation performance becomes ~0.8ns/op, equal to the direct version, compared to the original ~1ms/op. See the updated benchmark results in the main PR body.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13821#discussion_r1216694641