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

[Maurizio Cimadamore]

On Fri, 5 May 2023 13:01:09 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Also fixed the bug with NPE in `IndirectVarHandle::isAccessModeSupported`.
>> 
>> A few implementation-detail methods in VarHandle are now documented with the implied constraints to avoid subtle problems in the future. Changed `IndirectVarHandle` to call `asDirect` lazily to accomodate the lazy VarHandle changes. Also changed VarHandleBaseTest to report the whole incorrect type of exception caught than swallow it and leaving only a message.
>> 
>> Current problems:
>> - [ ] The lazy var handle is quite slow on the first invocation.
>>    - As seen in the benchmark, users can first call `Lookup::ensureInitialized` to create an eager handle.
>>    - After that, the lazy handle has a performance on par with the regular var handle.
>> - [ ] The class-loading-based test is not in a unit test
>>    - The test frameworks don't seem to offer fine-grained control for class-loading detection or reliable unloading
>> 
>> 
>> Benchmark                                            Mode  Cnt       Score        Error  Units
>> VarHandleLazyStaticInvocation.initializedInvocation  avgt   30       0.769 ±      0.003  ns/op
>> VarHandleLazyStaticInvocation.lazyInvocation         avgt   30       0.767 ±      0.002  ns/op
>> VarHandleLazyStaticCreation.eagerInitialize            ss   10  348580.000 ± 115234.161  ns/op
>> VarHandleLazyStaticCreation.lazyInitialize             ss   10  961670.000 ± 154813.238  ns/op
>
> src/java.base/share/classes/java/lang/invoke/VarHandles.java line 110:
> 
>> 108:         }
>> 109:         else {
>> 110:             if (UNSAFE.shouldBeInitialized(refc)) {
> 
> This seems unrelated to the issue this PR is really about (if I understand correctly). Would it make sense to address this as part of another PR?

Also, perhaps @PaulSandoz knows more history on this one (I believe this code predates FFM).

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PR Review Comment: https://git.openjdk.org/jdk/pull/13821#discussion_r1186069095