523   {

   524     // Given that a concurrent operation might be adding regions to

   525     // the secondary free list we have to take the lock before

   526     // verifying it.

   527     MutexLockerEx x(SecondaryFreeList_lock, Mutex::_no_safepoint_check_flag);

   528     _g1h->_secondary_free_list.verify_list();

   529   }

   530 

   531   // If a concurrent region freeing operation is in progress it will

   532   // be difficult to correctly attributed any free regions we come

   533   // across to the correct free list given that they might belong to

   534   // one of several (free_list, secondary_free_list, any local lists,

   535   // etc.). So, if that's the case we will skip the rest of the

   536   // verification operation. Alternatively, waiting for the concurrent

   537   // operation to complete will have a non-trivial effect on the GC's

   538   // operation (no concurrent operation will last longer than the

   539   // interval between two calls to verification) and it might hide

   540   // any issues that we would like to catch during testing.

   541   if (_g1h->free_regions_coming()) {

   542     return;

   543   }

   544 

   545   // Make sure we append the secondary_free_list on the free_list so

   546   // that all free regions we will come across can be safely

   547   // attributed to the free_list.

   548   _g1h->append_secondary_free_list_if_not_empty_with_lock();