avoid unnecessary locking in ConcurrentReferenceHashMap's implementation of computeIfAbsent and computeIfPresent

Author: chschu

spring-core/src/main/java/org/springframework/util/ConcurrentReferenceHashMap.java

@@ -371,6 +371,12 @@ protected Boolean execute(@Nullable Reference<K, V> ref, @Nullable Entry<K, V> e
 
 	@Override
 	public @Nullable V computeIfAbsent(@Nullable K key, Function<@Nullable ? super K, @Nullable ? extends V> mappingFunction) {
+		// avoid locking if entry is present
+		Reference<K, V> ref = getReference(key, Restructure.NEVER);
+		Entry<K, V> entry = (ref != null ? ref.get() : null);
+		if (entry != null) {
+			return entry.getValue();
+		}
 		return doTask(key, new Task<V>(TaskOption.RESTRUCTURE_BEFORE, TaskOption.RESIZE) {
 			@Override
 			protected @Nullable V execute(@Nullable Reference<K, V> ref, @Nullable Entry<K, V> entry, @Nullable Entries<V> entries) {
@@ -390,6 +396,12 @@ protected Boolean execute(@Nullable Reference<K, V> ref, @Nullable Entry<K, V> e
 
 	@Override
 	public @Nullable V computeIfPresent(@Nullable K key, BiFunction<@Nullable ? super K, @Nullable ? super V, @Nullable ? extends V> remappingFunction) {
+		// avoid locking if entry is absent
+		Reference<K, V> ref = getReference(key, Restructure.NEVER);
+		Entry<K, V> entry = (ref != null ? ref.get() : null);
+		if (entry == null) {
+			return null;
+		}
 		return doTask(key, new Task<V>(TaskOption.RESTRUCTURE_BEFORE, TaskOption.RESIZE) {
 			@Override
 			protected @Nullable V execute(@Nullable Reference<K, V> ref, @Nullable Entry<K, V> entry, @Nullable Entries<V> entries) {