Coverage Report - org.apache.commons.lang3.concurrent.AtomicSafeInitializer
 
Classes in this File Line Coverage Branch Coverage Complexity
AtomicSafeInitializer
100%
7/7
100%
4/4
2
 
 1  
 /*
 2  
  * Licensed to the Apache Software Foundation (ASF) under one or more
 3  
  * contributor license agreements.  See the NOTICE file distributed with
 4  
  * this work for additional information regarding copyright ownership.
 5  
  * The ASF licenses this file to You under the Apache License, Version 2.0
 6  
  * (the "License"); you may not use this file except in compliance with
 7  
  * the License.  You may obtain a copy of the License at
 8  
  *
 9  
  *      http://www.apache.org/licenses/LICENSE-2.0
 10  
  *
 11  
  * Unless required by applicable law or agreed to in writing, software
 12  
  * distributed under the License is distributed on an "AS IS" BASIS,
 13  
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 14  
  * See the License for the specific language governing permissions and
 15  
  * limitations under the License.
 16  
  */
 17  
 package org.apache.commons.lang3.concurrent;
 18  
 
 19  
 import java.util.concurrent.atomic.AtomicReference;
 20  
 
 21  
 /**
 22  
  * <p>
 23  
  * A specialized {@code ConcurrentInitializer} implementation which is similar
 24  
  * to {@link AtomicInitializer}, but ensures that the {@link #initialize()}
 25  
  * method is called only once.
 26  
  * </p>
 27  
  * <p>
 28  
  * As {@link AtomicInitializer} this class is based on atomic variables, so it
 29  
  * can create an object under concurrent access without synchronization.
 30  
  * However, it implements an additional check to guarantee that the
 31  
  * {@link #initialize()} method which actually creates the object cannot be
 32  
  * called multiple times.
 33  
  * </p>
 34  
  * <p>
 35  
  * Because of this additional check this implementation is slightly less
 36  
  * efficient than {@link AtomicInitializer}, but if the object creation in the
 37  
  * {@code initialize()} method is expensive or if multiple invocations of
 38  
  * {@code initialize()} are problematic, it is the better alternative.
 39  
  * </p>
 40  
  * <p>
 41  
  * From its semantics this class has the same properties as
 42  
  * {@link LazyInitializer}. It is a &quot;save&quot; implementation of the lazy
 43  
  * initializer pattern. Comparing both classes in terms of efficiency is
 44  
  * difficult because which one is faster depends on multiple factors. Because
 45  
  * {@code AtomicSafeInitializer} does not use synchronization at all it probably
 46  
  * outruns {@link LazyInitializer}, at least under low or moderate concurrent
 47  
  * access. Developers should run their own benchmarks on the expected target
 48  
  * platform to decide which implementation is suitable for their specific use
 49  
  * case.
 50  
  * </p>
 51  
  *
 52  
  * @since 3.0
 53  
  * @version $Id: AtomicSafeInitializer.java 1309977 2012-04-05 17:53:39Z ggregory $
 54  
  * @param <T> the type of the object managed by this initializer class
 55  
  */
 56  4
 public abstract class AtomicSafeInitializer<T> implements
 57  
         ConcurrentInitializer<T> {
 58  
     /** A guard which ensures that initialize() is called only once. */
 59  4
     private final AtomicReference<AtomicSafeInitializer<T>> factory =
 60  
             new AtomicReference<AtomicSafeInitializer<T>>();
 61  
 
 62  
     /** Holds the reference to the managed object. */
 63  4
     private final AtomicReference<T> reference = new AtomicReference<T>();
 64  
 
 65  
     /**
 66  
      * Get (and initialize, if not initialized yet) the required object
 67  
      *
 68  
      * @return lazily initialized object
 69  
      * @throws ConcurrentException if the initialization of the object causes an
 70  
      * exception
 71  
      */
 72  
     @Override
 73  
     public final T get() throws ConcurrentException {
 74  
         T result;
 75  
 
 76  78
         while ((result = reference.get()) == null) {
 77  24
             if (factory.compareAndSet(null, this)) {
 78  4
                 reference.set(initialize());
 79  
             }
 80  
         }
 81  
 
 82  54
         return result;
 83  
     }
 84  
 
 85  
     /**
 86  
      * Creates and initializes the object managed by this
 87  
      * {@code AtomicInitializer}. This method is called by {@link #get()} when
 88  
      * the managed object is not available yet. An implementation can focus on
 89  
      * the creation of the object. No synchronization is needed, as this is
 90  
      * already handled by {@code get()}. This method is guaranteed to be called
 91  
      * only once.
 92  
      *
 93  
      * @return the managed data object
 94  
      * @throws ConcurrentException if an error occurs during object creation
 95  
      */
 96  
     protected abstract T initialize() throws ConcurrentException;
 97  
 }