The suspend handshake code tests if the JavaThread->is_exiting or that the threadObj() is null. Ever since JDK-8244997, once the JavaThread is running, the _threadObj won't be null until JavaThread is destroyed. So testing is_exiting is all you need to do.

To get the JavaThread, the suspend code uses the field in the already created threadObj.

JvmtiExport::cv_external_thread_to_JavaThread(ThreadsList * t_list, jthread thread
...
  oop thread_oop = JNIHandles::resolve_external_guard(thread);
  if (thread_oop == NULL) {
    // NULL jthread, GC'ed jthread or a bad JNI handle.
    return JVMTI_ERROR_INVALID_THREAD;
  }
...
  JavaThread * java_thread = java_lang_Thread::thread(thread_oop);
  if (java_thread == NULL) {
    // The java.lang.Thread does not contain a JavaThread * so it has
    // not yet run or it has died.
    return JVMTI_ERROR_THREAD_NOT_ALIVE;
  }

We detach C++ JavaThread from threadOop when the thread joins in ensure_join but we don't detach threadObj from JavaThread until the JavaThread is destroyed.

In gtest, the test JavaThread doesn't create a _threadObj JDK-8215948 so removing this unnecessary test allows writing gtests for suspend handshakes.