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

[Chen Liang]

> 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  12.668 ± 0.069  ns/op
> VarHandleLazyStaticInvocation.lazyInvocation         avgt   30  12.683 ± 0.069  ns/op
> 
> 
> Benchmark                                            Mode  Cnt     Score     Error  Units
> LazyStaticColdStart.methodHandleCreateEager            ss   10    50.980 ±   9.454  us/op
> LazyStaticColdStart.methodHandleCreateLazy             ss   10    24.350 ±   6.701  us/op
> LazyStaticColdStart.methodHandleInitializeCallEager    ss   10    65.140 ±   7.552  us/op
> LazyStaticColdStart.methodHandleInitializeCallLazy     ss   10   118.360 ±  20.320  us/op
> LazyStaticColdStart.varHandleCreateEager               ss   10    49.500 ±   4.277  us/op
> LazyStaticColdStart.varHandleCreateLazy                ss   10    26.690 ±   5.157  us/op
> LazyStaticColdStart.varHandleInitializeCallEager       ss   10    87.930 ±  12.643  us/op
> LazyStaticColdStart.varHandleInitializeCallLazy        ss   10  1057.120 ± 189.810  us/op

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  Remove lazy init of MH, for all invocation of the Lazy VH needs this MH

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/13821/files
  - new: https://git.openjdk.org/jdk/pull/13821/files/e21733c1..0d44a0d3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13821&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13821&range=05-06

  Stats: 24 lines in 1 file changed: 10 ins; 13 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13821.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13821/head:pull/13821

PR: https://git.openjdk.org/jdk/pull/13821