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 * https://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.CancellationException;
20 import java.util.concurrent.ConcurrentHashMap;
21 import java.util.concurrent.ConcurrentMap;
22 import java.util.concurrent.ExecutionException;
23 import java.util.concurrent.Future;
24 import java.util.function.Function;
25
26 import org.apache.commons.lang3.exception.ExceptionUtils;
27
28 /**
29 * Definition of an interface for a wrapper around a calculation that takes a single parameter and returns a result. The
30 * results for the calculation will be cached for future requests.
31 *
32 * <p>
33 * This is not a fully functional cache, there is no way of limiting or removing results once they have been generated.
34 * However, it is possible to get the implementation to regenerate the result for a given parameter, if an error was
35 * thrown during the previous calculation, by setting the option during the construction of the class. If this is not
36 * set the class will return the cached exception.
37 * </p>
38 * <p>
39 * Thanks go to Brian Goetz, Tim Peierls and the members of JCP JSR-166 Expert Group for coming up with the
40 * original implementation of the class. It was also published within Java Concurrency in Practice as a sample.
41 * </p>
42 *
43 * @param <I> the type of the input to the calculation
44 * @param <O> the type of the output of the calculation
45 * @since 3.6
46 */
47 public class Memoizer<I, O> implements Computable<I, O> {
48
49 private final ConcurrentMap<I, Future<O>> cache = new ConcurrentHashMap<>();
50 private final Function<? super I, ? extends Future<O>> mappingFunction;
51 private final boolean recalculate;
52
53 /**
54 * Constructs a Memoizer for the provided Computable calculation.
55 *
56 * <p>
57 * If a calculation throws an exception for any reason, this exception will be cached and returned for all future
58 * calls with the provided parameter.
59 * </p>
60 *
61 * @param computable the computation whose results should be memorized
62 */
63 public Memoizer(final Computable<I, O> computable) {
64 this(computable, false);
65 }
66
67 /**
68 * Constructs a Memoizer for the provided Computable calculation, with the option of whether a Computation that
69 * experiences an error should recalculate on subsequent calls or return the same cached exception.
70 *
71 * @param computable the computation whose results should be memorized
72 * @param recalculate determines whether the computation should be recalculated on subsequent calls if the previous call
73 * failed
74 */
75 public Memoizer(final Computable<I, O> computable, final boolean recalculate) {
76 this.recalculate = recalculate;
77 this.mappingFunction = k -> FutureTasks.run(() -> computable.compute(k));
78 }
79
80 /**
81 * Constructs a Memoizer for the provided Function calculation.
82 *
83 * <p>
84 * If a calculation throws an exception for any reason, this exception will be cached and returned for all future
85 * calls with the provided parameter.
86 * </p>
87 *
88 * @param function the function whose results should be memorized
89 * @since 2.13.0
90 */
91 public Memoizer(final Function<I, O> function) {
92 this(function, false);
93 }
94
95 /**
96 * Constructs a Memoizer for the provided Function calculation, with the option of whether a Function that
97 * experiences an error should recalculate on subsequent calls or return the same cached exception.
98 *
99 * @param function the computation whose results should be memorized
100 * @param recalculate determines whether the computation should be recalculated on subsequent calls if the previous call
101 * failed
102 * @since 2.13.0
103 */
104 public Memoizer(final Function<I, O> function, final boolean recalculate) {
105 this.recalculate = recalculate;
106 this.mappingFunction = k -> FutureTasks.run(() -> function.apply(k));
107 }
108
109 /**
110 * This method will return the result of the calculation and cache it, if it has not previously been calculated.
111 *
112 * <p>
113 * This cache will also cache exceptions that occur during the computation if the {@code recalculate} parameter in the
114 * constructor was set to {@code false}, or not set. Otherwise, if an exception happened on the previous calculation,
115 * the method will attempt again to generate a value.
116 * </p>
117 *
118 * @param arg the argument for the calculation
119 * @return the result of the calculation
120 * @throws InterruptedException thrown if the calculation is interrupted
121 */
122 @Override
123 public O compute(final I arg) throws InterruptedException {
124 while (true) {
125 final Future<O> future = cache.computeIfAbsent(arg, mappingFunction);
126 try {
127 return future.get();
128 } catch (final CancellationException e) {
129 cache.remove(arg, future);
130 } catch (final ExecutionException e) {
131 if (recalculate) {
132 cache.remove(arg, future);
133 }
134 throw launderException(e.getCause());
135 }
136 }
137 }
138
139 /**
140 * This method launders a Throwable to either a RuntimeException, Error or any other Exception wrapped in an
141 * IllegalStateException.
142 *
143 * @param throwable the throwable to laundered
144 * @return a RuntimeException, Error or an IllegalStateException
145 */
146 private RuntimeException launderException(final Throwable throwable) {
147 throw new IllegalStateException("Unchecked exception", ExceptionUtils.throwUnchecked(throwable));
148 }
149 }