diff -r 3198179d97fa -r 56309b1b9d9b src/hotspot/share/runtime/thread.cpp
--- a/src/hotspot/share/runtime/thread.cpp	Thu Aug 30 16:33:14 2018 -0400
+++ b/src/hotspot/share/runtime/thread.cpp	Thu Aug 30 17:03:46 2018 -0400
@@ -307,13 +307,15 @@
   }
 #endif // ASSERT
 
-  // Notify the barrier set that a thread is being created. Note that the
-  // main thread is created before a barrier set is available. The call to
-  // BarrierSet::on_thread_create() for the main thread is therefore deferred
-  // until it calls BarrierSet::set_barrier_set().
+  // Notify the barrier set that a thread is being created. Note that some
+  // threads are created before a barrier set is available. The call to
+  // BarrierSet::on_thread_create() for these threads is therefore deferred
+  // to BarrierSet::set_barrier_set().
   BarrierSet* const barrier_set = BarrierSet::barrier_set();
   if (barrier_set != NULL) {
     barrier_set->on_thread_create(this);
+  } else {
+    DEBUG_ONLY(Threads::inc_threads_before_barrier_set();)
   }
 }
 
@@ -3397,6 +3399,7 @@
 
 #ifdef ASSERT
 bool        Threads::_vm_complete = false;
+size_t      Threads::_threads_before_barrier_set = 0;
 #endif
 
 static inline void *prefetch_and_load_ptr(void **addr, intx prefetch_interval) {