reschke commented on code in PR #2457: URL: https://github.com/apache/jackrabbit-oak/pull/2457#discussion_r2287706178
########## oak-commons/src/main/java/org/apache/jackrabbit/oak/commons/function/Suppliers.java: ########## @@ -0,0 +1,62 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, + * software distributed under the License is distributed on an + * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + * KIND, either express or implied. See the License for the + * specific language governing permissions and limitations + * under the License. + */ +package org.apache.jackrabbit.oak.commons.function; + +import org.jetbrains.annotations.Nullable; + +import java.util.function.Supplier; + +/** + * Utility methods for {@link java.util.function.Supplier} handling. + */ +public class Suppliers { + + private Suppliers() { + } + + /** + * Transforms a {@link Supplier} based on a wrapper that evaluates + * the given {@code Supplier} at most one time. + * @param <T> return type + * @return Supplier based on the given Supplier + */ + public static <T> Supplier<@Nullable T> memoize(final Supplier<@Nullable T> computeOnce) { + return new Supplier<>() { + volatile boolean initialized = false; + @Nullable T result = null; + + @Override + public @Nullable T get() { + if (!initialized) { + synchronized (this) { + if (!initialized) { + result = computeOnce.get(); + // only set initialized once value is computed and assigned + initialized = true; + // return from inside the synchronized block in order to + // avoid concurrency problems + return result; Review Comment: I'm currently double-checking. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: oak-dev-unsubscr...@jackrabbit.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
