264 void HeapRegionLinkedList::add_as_head(HeapRegionLinkedList* from_list) {

   265   hrs_assert_mt_safety_ok(this);

   266   hrs_assert_mt_safety_ok(from_list);

   267 

   268   verify_optional();

   269   from_list->verify_optional();

   270 

   271   if (from_list->is_empty()) return;

   272 

   273 #ifdef ASSERT

   274   HeapRegionLinkedListIterator iter(from_list);

   275   while (iter.more_available()) {

   276     HeapRegion* hr = iter.get_next();

   277     // In set_containing_set() we check that we either set the value

   278     // from NULL to non-NULL or vice versa to catch bugs. So, we have

   279     // to NULL it first before setting it to the value.

   280     hr->set_containing_set(NULL);

   281     hr->set_containing_set(this);

   282   }

   283 #endif // ASSERT

   284 

   285   if (_head != NULL) {

   286     assert(length() >  0 && _tail != NULL, hrs_ext_msg(this, "invariant"));

   287     from_list->_tail->set_next(_head);

   288   } else {

   289     assert(length() == 0 && _head == NULL, hrs_ext_msg(this, "invariant"));

   290     _tail = from_list->_tail;

   291   }

   292   _head = from_list->_head;

   293 

   294   _length           += from_list->length();

   295   _region_num       += from_list->region_num();

   296   _total_used_bytes += from_list->total_used_bytes();

   297   from_list->clear();

   298 

   299   verify_optional();

   300   from_list->verify_optional();

   301 }

   302