8332360: JVM hangs at exit when running on a uniprocessor

Reviewed-by: dholmes, dcubed, shade

src/hotspot/share/runtime/objectMonitor.cpp

@@ -987,6 +987,13 @@ void ObjectMonitor::ReenterI(JavaThread* current, ObjectWaiter* currentNode) {
     guarantee(v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant");
     assert(owner_raw() != current, "invariant");
 
+    // This thread has been notified so try to reacquire the lock.
+    if (TryLock(current) == TryLockResult::Success) {
+      break;
+    }
+
+    // If that fails, spin again.  Note that spin count may be zero so the above TryLock
+    // is necessary.
     if (TrySpin(current)) {
         break;
     }