RFR: 8260589: Crash in JfrTraceIdLoadBarrier::load(_jclass*)

[Denghui Dong]

hi,

Could I have a review of this fix?

If we run the following code snippet, will get a crash
class JFRDemo {
    public static void main(String[] args) {
        Recording r = new Recording();
        r.enable("MyEvent");
        r.start();

        MyEvent event = new MyEvent();
        event.begin();
        event.clazz = long.class;
        event.commit();
    }
}

@Enabled(true)
@StackTrace(true)
@Registered(true)
@Name("MyEvent")
class MyEvent extends Event {

    @Label("Class")
    public Class clazz;
}

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

Commit messages:
 - 8260589: Crash in JfrTraceIdLoadBarrier::load(_jclass*)

Changes: https://git.openjdk.java.net/jdk/pull/2295/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2295&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260589
  Stats: 138 lines in 3 files changed: 138 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2295.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2295/head:pull/2295

PR: https://git.openjdk.java.net/jdk/pull/2295