/* * 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.commons.lang3.concurrent; import java.util.concurrent.atomic.AtomicReference; /** * A specialized {@link ConcurrentInitializer} implementation which is similar * to {@link AtomicInitializer}, but ensures that the {@link #initialize()} * method is called only once. * *
* As {@link AtomicInitializer} this class is based on atomic variables, so it * can create an object under concurrent access without synchronization. * However, it implements an additional check to guarantee that the * {@link #initialize()} method which actually creates the object cannot be * called multiple times. *
** Because of this additional check this implementation is slightly less * efficient than {@link AtomicInitializer}, but if the object creation in the * {@code initialize()} method is expensive or if multiple invocations of * {@code initialize()} are problematic, it is the better alternative. *
** From its semantics this class has the same properties as * {@link LazyInitializer}. It is a "save" implementation of the lazy * initializer pattern. Comparing both classes in terms of efficiency is * difficult because which one is faster depends on multiple factors. Because * {@link AtomicSafeInitializer} does not use synchronization at all it probably * outruns {@link LazyInitializer}, at least under low or moderate concurrent * access. Developers should run their own benchmarks on the expected target * platform to decide which implementation is suitable for their specific use * case. *
* * @since 3.0 * @param