1 /*
2 * Copyright 2013 The Netty Project
3 *
4 * The Netty Project licenses this file to you under the Apache License,
5 * version 2.0 (the "License"); you may not use this file except in compliance
6 * with the License. You may obtain a copy of the License at:
7 *
8 * https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13 * License for the specific language governing permissions and limitations
14 * under the License.
15 */
16
17 package io.netty.util;
18
19 import static io.netty.util.internal.ObjectUtil.checkNotNull;
20 import static io.netty.util.internal.ObjectUtil.checkNonEmpty;
21
22 import io.netty.util.internal.PlatformDependent;
23
24 import java.util.concurrent.ConcurrentMap;
25 import java.util.concurrent.atomic.AtomicInteger;
26
27 /**
28 * A pool of {@link Constant}s.
29 *
30 * @param <T> the type of the constant
31 */
32 public abstract class ConstantPool<T extends Constant<T>> {
33
34 private final ConcurrentMap<String, T> constants = PlatformDependent.newConcurrentHashMap();
35
36 private final AtomicInteger nextId = new AtomicInteger(1);
37
38 /**
39 * Shortcut of {@link #valueOf(String) valueOf(firstNameComponent.getName() + "#" + secondNameComponent)}.
40 */
41 public T valueOf(Class<?> firstNameComponent, String secondNameComponent) {
42 return valueOf(
43 checkNotNull(firstNameComponent, "firstNameComponent").getName() +
44 '#' +
45 checkNotNull(secondNameComponent, "secondNameComponent"));
46 }
47
48 /**
49 * Returns the {@link Constant} which is assigned to the specified {@code name}.
50 * If there's no such {@link Constant}, a new one will be created and returned.
51 * Once created, the subsequent calls with the same {@code name} will always return the previously created one
52 * (i.e. singleton.)
53 *
54 * @param name the name of the {@link Constant}
55 */
56 public T valueOf(String name) {
57 return getOrCreate(checkNonEmpty(name, "name"));
58 }
59
60 /**
61 * Get existing constant by name or creates new one if not exists. Threadsafe
62 *
63 * @param name the name of the {@link Constant}
64 */
65 private T getOrCreate(String name) {
66 T constant = constants.get(name);
67 if (constant == null) {
68 final T tempConstant = newConstant(nextId(), name);
69 constant = constants.putIfAbsent(name, tempConstant);
70 if (constant == null) {
71 return tempConstant;
72 }
73 }
74
75 return constant;
76 }
77
78 /**
79 * Returns {@code true} if a {@link AttributeKey} exists for the given {@code name}.
80 */
81 public boolean exists(String name) {
82 return constants.containsKey(checkNonEmpty(name, "name"));
83 }
84
85 /**
86 * Creates a new {@link Constant} for the given {@code name} or fail with an
87 * {@link IllegalArgumentException} if a {@link Constant} for the given {@code name} exists.
88 */
89 public T newInstance(String name) {
90 return createOrThrow(checkNonEmpty(name, "name"));
91 }
92
93 /**
94 * Creates constant by name or throws exception. Threadsafe
95 *
96 * @param name the name of the {@link Constant}
97 */
98 private T createOrThrow(String name) {
99 T constant = constants.get(name);
100 if (constant == null) {
101 final T tempConstant = newConstant(nextId(), name);
102 constant = constants.putIfAbsent(name, tempConstant);
103 if (constant == null) {
104 return tempConstant;
105 }
106 }
107
108 throw new IllegalArgumentException(String.format("'%s' is already in use", name));
109 }
110
111 protected abstract T newConstant(int id, String name);
112
113 @Deprecated
114 public final int nextId() {
115 return nextId.getAndIncrement();
116 }
117 }
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