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Correctly size the map/list from the builder to avoid re-allocation or over-allocation. #24231

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Correctly size the map/list from the builder to avoid re-allocation or over-allocation. #24231

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15 changes: 13 additions & 2 deletions java/core/src/main/java/com/google/protobuf/MapField.java
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Original file line number Diff line number Diff line change
Expand Up @@ -123,6 +123,11 @@ public static <K, V> MapField<K, V> newMapField(MapEntry<K, V> defaultEntry) {
return new MapField<K, V>(defaultEntry, StorageMode.MAP, new LinkedHashMap<K, V>());
}

public static <K, V> MapField<K, V> newMapField(MapEntry<K, V> defaultEntry, int entries) {
int mapCapacity = calculateInitialCapacity(entries);
return new MapField<K, V>(defaultEntry, StorageMode.MAP, new LinkedHashMap<K, V>(mapCapacity));
}

private Message convertKeyAndValueToMessage(K key, V value) {
return converter.convertKeyAndValueToMessage(key, value);
}
Expand All @@ -132,15 +137,21 @@ private void convertMessageToKeyAndValue(Message message, Map<K, V> map) {
}

private List<Message> convertMapToList(MutabilityAwareMap<K, V> mapData) {
List<Message> listData = new ArrayList<Message>();
List<Message> listData = new ArrayList<Message>(mapData.size());
for (Map.Entry<K, V> entry : mapData.entrySet()) {
listData.add(convertKeyAndValueToMessage(entry.getKey(), entry.getValue()));
}
return listData;
}

private static int calculateInitialCapacity(int entries) {
// Map's default load factor is 0.75. Add 1 to round up.
return (int) Math.ceil(entries / (double) 0.75) + 1;
}

private MutabilityAwareMap<K, V> convertListToMap(List<Message> listData) {
Map<K, V> mapData = new LinkedHashMap<K, V>();
int mapCapacity = calculateInitialCapacity(listData.size());
Map<K, V> mapData = new LinkedHashMap<K, V>(mapCapacity);
for (Message item : listData) {
convertMessageToKeyAndValue(item, mapData);
}
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5 changes: 3 additions & 2 deletions java/core/src/main/java/com/google/protobuf/MapFieldBuilder.java
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Expand Up @@ -189,9 +189,10 @@ public MapFieldBuilder<KeyT, MessageOrBuilderT, MessageT, BuilderT> copy() {

/** Converts this MapFieldBuilder to a MapField. */
public MapField<KeyT, MessageT> build(MapEntry<KeyT, MessageT> defaultEntry) {
MapField<KeyT, MessageT> mapField = MapField.newMapField(defaultEntry);
Map<KeyT, MessageOrBuilderT> builderMap = ensureBuilderMap();
MapField<KeyT, MessageT> mapField = MapField.newMapField(defaultEntry, builderMap.size());
Map<KeyT, MessageT> map = mapField.getMutableMap();
for (Map.Entry<KeyT, MessageOrBuilderT> entry : ensureBuilderMap().entrySet()) {
for (Map.Entry<KeyT, MessageOrBuilderT> entry : builderMap.entrySet()) {
map.put(entry.getKey(), converter.build(entry.getValue()));
}
mapField.makeImmutable();
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