8289003: JavaThread::check_is_terminated() implementation should rely…

… on Thread-SMR

Reviewed-by: dholmes, pchilanomate

src/hotspot/share/runtime/javaThread.cpp

@@ -564,9 +564,10 @@ bool JavaThread::is_interrupted(bool clear_interrupted) {
 void JavaThread::block_if_vm_exited() {
   if (_terminated == _vm_exited) {
     // _vm_exited is set at safepoint, and Threads_lock is never released
-    // we will block here forever.
+    // so we will block here forever.
     // Here we can be doing a jump from a safe state to an unsafe state without
-    // proper transition, but it happens after the final safepoint has begun.
+    // proper transition, but it happens after the final safepoint has begun so
+    // this jump won't cause any safepoint problems.
     set_thread_state(_thread_in_vm);
     Threads_lock->lock();
     ShouldNotReachHere();

src/hotspot/share/runtime/javaThread.hpp

@@ -567,12 +567,10 @@ class JavaThread: public Thread {
   bool is_exiting() const;
   // thread's GC barrier is NOT detached and thread is NOT terminated
   bool is_oop_safe() const;
-  // thread is terminated (no longer on the threads list); we compare
-  // against the three non-terminated values so that a freed JavaThread
-  // will also be considered terminated.
+  // thread is terminated (no longer on the threads list); the thread must
+  // be protected by a ThreadsListHandle to avoid potential crashes.
   bool check_is_terminated(TerminatedTypes l_terminated) const {
-    return l_terminated != _not_terminated && l_terminated != _thread_exiting &&
-           l_terminated != _thread_gc_barrier_detached;
+    return l_terminated == _thread_terminated || l_terminated == _vm_exited;
   }
   bool is_terminated() const;
   void set_terminated(TerminatedTypes t);

src/hotspot/share/runtime/vmOperations.cpp

@@ -367,7 +367,7 @@ int VM_Exit::set_vm_exited() {
   _shutdown_thread = thr_cur;
   _vm_exited = true;                                // global flag
   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
-    if (thr!=thr_cur && thr->thread_state() == _thread_in_native) {
+    if (thr != thr_cur && thr->thread_state() == _thread_in_native) {
       ++num_active;
       thr->set_terminated(JavaThread::_vm_exited);  // per-thread flag
     }
@@ -495,7 +495,7 @@ void VM_Exit::wait_if_vm_exited() {
   if (_vm_exited &&
       Thread::current_or_null() != _shutdown_thread) {
     // _vm_exited is set at safepoint, and the Threads_lock is never released
-    // we will block here until the process dies
+    // so we will block here until the process dies.
     Threads_lock->lock();
     ShouldNotReachHere();
   }