RFR: 8307298: JFR: Ensure jdk.jfr.internal.TypeLibrary is initialized only once [v4]

[Robert Toyonaga]

> Hello, may I have a review of a small change that enforces that `jdk.jfr.internal.TypeLibrary` only gets initialized once?
> Previously, it was the case that `TypeLibrary` was only initialized once, but since [this change](https://github.com/openjdk/jdk/pull/12884/files) it can now be initialized multiple times. This can be a problem because re-initialization [results in attempting to add elements to `jdk.jfr.internal.Type#fields`](https://github.com/openjdk/jdk/blob/master/src/jdk.jfr/share/classes/jdk/jfr/internal/MetadataLoader.java#L264) which may have already been changed to an unmodifiableList after the initial initialization of `TypeLibrary`.
> 
> This is of concern for JFR support in GraalVM Native Image. Specifically, multiple initializations of TypeLibrary breaks the ability to use JFR at native image built time. This is because, if JFR is used at image build time, the data of a few of the JFR singletons such as MetadataRepository must be re-initialized for runtime recordings to start with a "clean-slate". However, re-initializing MetadataRepository, also has the effect of calling `TypeLibrary#initialize()` which now unconditionally attempts to initialize TypeRepository, resulting in errors.
> 
> Example of exception upon second initialization of `TypeRepository`: 
> 
> Caused by: java.lang.InternalError: java.lang.UnsupportedOperationException
> 	at jdk.jfr/jdk.jfr.internal.MetadataLoader.createTypes(MetadataLoader.java:195)
> 	at jdk.jfr/jdk.jfr.internal.TypeLibrary.initialize(TypeLibrary.java:103)
> 	at jdk.jfr/jdk.jfr.internal.MetadataRepository.initializeJVMEventTypes(MetadataRepository.java:72)
> 	at jdk.jfr/jdk.jfr.internal.MetadataRepository.<init>(MetadataRepository.java:68)
> 	at org.graalvm.nativeimage.builder/com.oracle.svm.core.jfr.Target_jdk_jfr_internal_MetadataRepository.<clinit>(Target_jdk_jfr_internal_MetadataRepository.java:42)
> 	at java.base/jdk.internal.misc.Unsafe.ensureClassInitialized0(Native Method)
> 	at java.base/jdk.internal.misc.Unsafe.ensureClassInitialized(Unsafe.java:1160)
> 	at org.graalvm.nativeimage.builder/com.oracle.svm.hosted.classinitialization.ClassInitializationSupport.ensureClassInitialized(ClassInitializationSupport.java:168)
> 	... 11 more
> Caused by: java.lang.UnsupportedOperationException
> 	at java.base/java.util.Collections$UnmodifiableCollection.add(Collections.java:1085)
> 	at jdk.jfr/jdk.jfr.internal.Type.add(Type.java:227)
> 	at jdk.jfr/jdk.jfr.internal.MetadataLoader.addFields(MetadataLoader.java:264)
> 	at jdk.j...

Robert Toyonaga has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'master' of github.com:roberttoyonaga/jdk into initialize-TypeLibrary-once
 - add comment
 - Merge branch 'master' of github.com:openjdk/jdk into initialize-TypeLibrary-once
 - Only init TypeLibrary once

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13760/files
  - new: https://git.openjdk.org/jdk/pull/13760/files/d659cbe9..2f239b2d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13760&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13760&range=02-03

  Stats: 12805 lines in 297 files changed: 10061 ins; 328 del; 2416 mod
  Patch: https://git.openjdk.org/jdk/pull/13760.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13760/head:pull/13760

PR: https://git.openjdk.org/jdk/pull/13760