RFR: 8255883: Avoid multiple GeneratedMethodAccessor for same NativeMethod… [v2]

[Hui Shi]

> …AccessorImpl object
> 
> We met real problem when using protobuf with option optimized for code size, detail in JBS https://bugs.openjdk.java.net/browse/JDK-8255883
> 
> Optimize solution is adding a new boolean field to detect concurrent method accessor generation in same NativeMethodAccessorImpl object, only one thread is allowed to generate accessor, other threads still invoke in jni way until parent's delegator is updated from NativeMethodAccessorImpl  to generated accessor.
> 
> In common case, extra overhead is an atomic operation, compared with method accessor generate, this cost is trivial.

Hui Shi has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  8255883: Avoid multiple GeneratedAccessor for same NativeMethod/ConstructorAccessorImpl object

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1070/files
  - new: https://git.openjdk.java.net/jdk/pull/1070/files/94390613..8f65047e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1070&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1070&range=00-01

  Stats: 43 lines in 2 files changed: 15 ins; 9 del; 19 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1070.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1070/head:pull/1070

PR: https://git.openjdk.java.net/jdk/pull/1070