8272231: G1: Refactor G1CardSet::get_card_set to return G1CardSetHash…

…TableValue*

Reviewed-by: tschatzl, kbarrett

src/hotspot/share/gc/g1/g1CardSet.cpp

@@ -194,6 +194,8 @@ class G1CardSetHashTable : public CHeapObj<mtGCCardSet> {
   class G1CardSetHashTableFound : public StackObj {
     G1CardSetHashTableValue* _value;
   public:
+    G1CardSetHashTableFound() : _value(nullptr) { }
+
     void operator()(G1CardSetHashTableValue* value) {
       _value = value;
     }
@@ -247,14 +249,12 @@ class G1CardSetHashTable : public CHeapObj<mtGCCardSet> {
     return found.value();
   }
 
-  CardSetPtr get(uint region_idx) {
+  G1CardSetHashTableValue* get(uint region_idx) {
     G1CardSetHashTableLookUp lookup(region_idx);
     G1CardSetHashTableFound found;
 
-    if (_table.get(Thread::current(), lookup, found)) {
-      return found.value()->_card_set;
-    }
-    return nullptr;
+    _table.get(Thread::current(), lookup, found);
+    return found.value();
   }
 
   void iterate_safepoint(G1CardSet::G1CardSetPtrIterator* cl2) {
@@ -611,8 +611,9 @@ void G1CardSet::transfer_cards_in_howl(CardSetPtr parent_card_set,
     G1CardSetHowl* howling_array = card_set_ptr<G1CardSetHowl>(parent_card_set);
     Atomic::add(&howling_array->_num_entries, diff, memory_order_relaxed);
 
-    bool should_grow_table = false;
-    G1CardSetHashTableValue* table_entry = get_or_add_card_set(card_region, &should_grow_table);
+    G1CardSetHashTableValue* table_entry = get_card_set(card_region);
+    assert(table_entry != nullptr, "Table entry not found for transferred cards");
+
     Atomic::add(&table_entry->_num_occupied, diff, memory_order_relaxed);
 
     Atomic::add(&_num_occupied, diff, memory_order_relaxed);
@@ -656,7 +657,7 @@ G1CardSetHashTableValue* G1CardSet::get_or_add_card_set(uint card_region, bool*
   return _table->get_or_add(card_region, should_grow_table);
 }
 
-G1CardSet::CardSetPtr G1CardSet::get_card_set(uint card_region) {
+G1CardSetHashTableValue* G1CardSet::get_card_set(uint card_region) {
   return _table->get(card_region);
 }
 
@@ -709,10 +710,13 @@ bool G1CardSet::contains_card(uint card_region, uint card_in_region) {
 
   // Protect the card set from reclamation.
   GlobalCounter::CriticalSection cs(Thread::current());
-  CardSetPtr card_set = get_card_set(card_region);
-  if (card_set == nullptr) {
+  G1CardSetHashTableValue* table_entry = get_card_set(card_region);
+  if (table_entry == nullptr) {
     return false;
-  } else if (card_set == FullCardSet) {
+  }
+
+  CardSetPtr card_set = table_entry->_card_set;
+  if (card_set == FullCardSet) {
     // contains_card() is not a performance critical method so we do not hide that
     // case in the switch below.
     return true;
@@ -736,11 +740,14 @@ bool G1CardSet::contains_card(uint card_region, uint card_in_region) {
 }
 
 void G1CardSet::print_info(outputStream* st, uint card_region, uint card_in_region) {
-  CardSetPtr card_set = get_card_set(card_region);
-  if (card_set == nullptr) {
+  G1CardSetHashTableValue* table_entry = get_card_set(card_region);
+  if (table_entry == nullptr) {
     st->print("NULL card set");
     return;
-  } else if (card_set == FullCardSet) {
+  }
+
+  CardSetPtr card_set = table_entry->_card_set;
+  if (card_set == FullCardSet) {
     st->print("FULL card set)");
     return;
   }

src/hotspot/share/gc/g1/g1CardSet.hpp

@@ -257,7 +257,7 @@ class G1CardSet : public CHeapObj<mtGCCardSet> {
   G1AddCardResult add_to_howl(CardSetPtr parent_card_set, uint card_region, uint card_in_region, bool increment_total = true);
 
   G1CardSetHashTableValue* get_or_add_card_set(uint card_region, bool* should_grow_table);
-  CardSetPtr get_card_set(uint card_region);
+  G1CardSetHashTableValue* get_card_set(uint card_region);
 
   // Iterate over cards of a card set container during transfer of the cards from
   // one container to another. Executes