8307068: store a JavaThread* in the java.lang.Thread object after the JavaThread* is added to the main ThreadsList

Reviewed-by: dholmes, rehn, apangin

src/hotspot/share/classfile/javaClasses.cpp

@@ -1570,10 +1570,18 @@ JavaThread* java_lang_Thread::thread(oop java_thread) {
   return reinterpret_cast<JavaThread*>(java_thread->address_field(_eetop_offset));
 }
 
+JavaThread* java_lang_Thread::thread_acquire(oop java_thread) {
+  return reinterpret_cast<JavaThread*>(java_thread->address_field_acquire(_eetop_offset));
+}
+
 void java_lang_Thread::set_thread(oop java_thread, JavaThread* thread) {
   java_thread->address_field_put(_eetop_offset, (address)thread);
 }
 
+void java_lang_Thread::release_set_thread(oop java_thread, JavaThread* thread) {
+  java_thread->release_address_field_put(_eetop_offset, (address)thread);
+}
+
 JvmtiThreadState* java_lang_Thread::jvmti_thread_state(oop java_thread) {
   return (JvmtiThreadState*)java_thread->address_field(_jvmti_thread_state_offset);
 }

src/hotspot/share/classfile/javaClasses.hpp

@@ -366,8 +366,10 @@ class java_lang_Thread : AllStatic {
 
   // Returns the JavaThread associated with the thread obj
   static JavaThread* thread(oop java_thread);
+  static JavaThread* thread_acquire(oop java_thread);
   // Set JavaThread for instance
   static void set_thread(oop java_thread, JavaThread* thread);
+  static void release_set_thread(oop java_thread, JavaThread* thread);
   // FieldHolder
   static oop holder(oop java_thread);
   // Interrupted status

src/hotspot/share/runtime/javaThread.cpp

@@ -743,8 +743,7 @@ static void ensure_join(JavaThread* thread) {
   // Clear the native thread instance - this makes isAlive return false and allows the join()
   // to complete once we've done the notify_all below. Needs a release() to obey Java Memory Model
   // requirements.
-  OrderAccess::release();
+  java_lang_Thread::release_set_thread(threadObj(), nullptr);
-  java_lang_Thread::set_thread(threadObj(), nullptr);
   lock.notify_all(thread);
   // Ignore pending exception, since we are exiting anyway
   thread->clear_pending_exception();
@@ -1668,7 +1667,6 @@ void JavaThread::prepare(jobject jni_thread, ThreadPriority prio) {
   assert(InstanceKlass::cast(thread_oop->klass())->is_linked(),
          "must be initialized");
   set_threadOopHandles(thread_oop());
-  java_lang_Thread::set_thread(thread_oop(), this);
 
   if (prio == NoPriority) {
     prio = java_lang_Thread::priority(thread_oop());
@@ -1684,6 +1682,11 @@ void JavaThread::prepare(jobject jni_thread, ThreadPriority prio) {
   // added to the Threads list for if a GC happens, then the java_thread oop
   // will not be visited by GC.
   Threads::add(this);
+  // Publish the JavaThread* in java.lang.Thread after the JavaThread* is
+  // on a ThreadsList. We don't want to wait for the release when the
+  // Theads_lock is dropped somewhere in the caller since the JavaThread*
+  // is already visible to JVM/TI via the ThreadsList.
+  java_lang_Thread::release_set_thread(thread_oop(), this);
 }
 
 oop JavaThread::current_park_blocker() {
@@ -2121,9 +2124,6 @@ void JavaThread::start_internal_daemon(JavaThread* current, JavaThread* target,
   MutexLocker mu(current, Threads_lock);
 
   // Initialize the fields of the thread_oop first.
-
-  java_lang_Thread::set_thread(thread_oop(), target); // isAlive == true now
-
   if (prio != NoPriority) {
     java_lang_Thread::set_priority(thread_oop(), prio);
     // Note: we don't call os::set_priority here. Possibly we should,
@@ -2136,6 +2136,11 @@ void JavaThread::start_internal_daemon(JavaThread* current, JavaThread* target,
   target->set_threadOopHandles(thread_oop());
 
   Threads::add(target); // target is now visible for safepoint/handshake
+  // Publish the JavaThread* in java.lang.Thread after the JavaThread* is
+  // on a ThreadsList. We don't want to wait for the release when the
+  // Theads_lock is dropped when the 'mu' destructor is run since the
+  // JavaThread* is already visible to JVM/TI via the ThreadsList.
+  java_lang_Thread::release_set_thread(thread_oop(), target); // isAlive == true now
   Thread::start(target);
 }
 

src/hotspot/share/runtime/threadSMR.cpp

@@ -815,10 +815,11 @@ bool ThreadsListHandle::cv_internal_thread_to_JavaThread(jobject jthread,
     *thread_oop_p = thread_oop;
   }
 
-  JavaThread *java_thread = java_lang_Thread::thread(thread_oop);
+  JavaThread *java_thread = java_lang_Thread::thread_acquire(thread_oop);
   if (java_thread == nullptr) {
-    // The java.lang.Thread does not contain a JavaThread * so it has
+    // The java.lang.Thread does not contain a JavaThread* so it has not
-    // not yet run or it has died.
+    // run enough to be put on a ThreadsList or it has exited enough to
+    // make it past ensure_join() where the JavaThread* is cleared.
     return false;
   }
   // Looks like a live JavaThread at this point.