1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19 package org.apache.maven.impl.cache;
20
21 import java.util.function.Function;
22
23 /**
24 * A caching supplier wrapper that caches results and exceptions from the underlying supplier.
25 * Used internally to cache expensive computations in the session.
26 *
27 * @param <REQ> The request type
28 * @param <REP> The response type
29 */
30 public class CachingSupplier<REQ, REP> implements Function<REQ, REP> {
31 protected final Function<REQ, REP> supplier;
32 protected volatile Object value;
33
34 public CachingSupplier(Function<REQ, REP> supplier) {
35 this.supplier = supplier;
36 }
37
38 public Object getValue() {
39 return value;
40 }
41
42 @Override
43 @SuppressWarnings({"unchecked", "checkstyle:InnerAssignment"})
44 public REP apply(REQ req) {
45 Object v;
46 if ((v = value) == null) {
47 synchronized (this) {
48 if ((v = value) == null) {
49 try {
50 v = value = supplier.apply(req);
51 } catch (Exception e) {
52 v = value = new AltRes(e);
53 }
54 }
55 }
56 }
57 if (v instanceof AltRes altRes) {
58 DefaultRequestCache.uncheckedThrow(altRes.throwable);
59 }
60 return (REP) v;
61 }
62
63 /**
64 * Special holder class for exceptions that occur during supplier execution.
65 * Allows caching and re-throwing of exceptions on subsequent calls.
66 */
67 public static class AltRes {
68 protected final Throwable throwable;
69
70 /**
71 * Creates a new AltRes with the given throwable.
72 *
73 * @param throwable The throwable to store
74 */
75 public AltRes(Throwable throwable) {
76 this.throwable = throwable;
77 }
78
79 public Throwable getThrowable() {
80 return throwable;
81 }
82 }
83 }