RFR: 8291065: Creating a VarHandle for a static field triggers class initialization [v4]

[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       0.769 ±      0.003  ns/op
> VarHandleLazyStaticInvocation.lazyInvocation         avgt   30       0.767 ±      0.002  ns/op
> 
> 
> Benchmark                                            Mode  Cnt       Score        Error  Units
> LazyStaticColdStart.methodHandleCreateEager            ss   10   73140.100 ±   7735.276  ns/op
> LazyStaticColdStart.methodHandleCreateLazy             ss   10   50000.000 ±   8482.883  ns/op
> LazyStaticColdStart.methodHandleInitializeCallEager    ss   10   91350.100 ±   9776.343  ns/op
> LazyStaticColdStart.methodHandleInitializeCallLazy     ss   10  145540.200 ±  72894.865  ns/op
> LazyStaticColdStart.varHandleCreateEager               ss   10   47069.900 ±   3513.909  ns/op
> LazyStaticColdStart.varHandleCreateLazy                ss   10   24780.300 ±   5144.540  ns/op
> LazyStaticColdStart.varHandleInitializeCallEager       ss   10   85479.700 ±  10816.983  ns/op
> LazyStaticColdStart.varHandleInitializeCallLazy        ss   10  413630.100 ± 189370.448  ns/op

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

  Fix exact swap
  
  Co-authored-by: Mandy Chung <mandy.chung at oracle.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13821/files
  - new: https://git.openjdk.org/jdk/pull/13821/files/6ed6b805..d347ee7e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13821&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13821&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 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