6770608: G1: Mutator thread can flush barrier and satb queues during safepoint

6660573: G1: BigApps Failure : guarantee(satb_mq_set.completed_buffers_num() == 0,"invariant")

When exiting a mutator thread is removed from the thread list before it has a chance to flush its SATB and barrier queues. If GC happens at this moment the objects that are refererred from these queues can be moved, which will case a crash. The fix is simply to flush the buffers before removing a thread from the list.

Reviewed-by: jcoomes, tonyp

hotspot/src/share/vm/runtime/thread.hpp

@@ -793,6 +793,8 @@ class JavaThread: public Thread {
   DirtyCardQueue _dirty_card_queue;      // Thread-local log for dirty cards.
   // Set of all such queues.
   static DirtyCardQueueSet _dirty_card_queue_set;
+
+  void flush_barrier_queues();
 #endif // !SERIALGC
 
   friend class VMThread;