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1   /*
2    * Copyright 2012 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    *   http://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  package io.netty.util;
17  
18  
19  /**
20   * A special {@link Error} which is used to signal some state or request by throwing it.
21   * {@link Signal} has an empty stack trace and has no cause to save the instantiation overhead.
22   */
23  public final class Signal extends Error implements Constant<Signal> {
24  
25      private static final long serialVersionUID = -221145131122459977L;
26  
27      private static final ConstantPool<Signal> pool = new ConstantPool<Signal>() {
28          @Override
29          protected Signal newConstant(int id, String name) {
30              return new Signal(id, name);
31          }
32      };
33  
34      /**
35       * Returns the {@link Signal} of the specified name.
36       */
37      public static Signal valueOf(String name) {
38          return pool.valueOf(name);
39      }
40  
41      /**
42       * Shortcut of {@link #valueOf(String) valueOf(firstNameComponent.getName() + "#" + secondNameComponent)}.
43       */
44      public static Signal valueOf(Class<?> firstNameComponent, String secondNameComponent) {
45          return pool.valueOf(firstNameComponent, secondNameComponent);
46      }
47  
48      private final SignalConstant constant;
49  
50      /**
51       * Creates a new {@link Signal} with the specified {@code name}.
52       */
53      private Signal(int id, String name) {
54          constant = new SignalConstant(id, name);
55      }
56  
57      /**
58       * Check if the given {@link Signal} is the same as this instance. If not an {@link IllegalStateException} will
59       * be thrown.
60       */
61      public void expect(Signal signal) {
62          if (this != signal) {
63              throw new IllegalStateException("unexpected signal: " + signal);
64          }
65      }
66  
67      @Override
68      public Throwable initCause(Throwable cause) {
69          return this;
70      }
71  
72      @Override
73      public Throwable fillInStackTrace() {
74          return this;
75      }
76  
77      @Override
78      public int id() {
79          return constant.id();
80      }
81  
82      @Override
83      public String name() {
84          return constant.name();
85      }
86  
87      @Override
88      public boolean equals(Object obj) {
89          return this == obj;
90      }
91  
92      @Override
93      public int hashCode() {
94          return System.identityHashCode(this);
95      }
96  
97      @Override
98      public int compareTo(Signal other) {
99          if (this == other) {
100             return 0;
101         }
102 
103         return constant.compareTo(other.constant);
104     }
105 
106     @Override
107     public String toString() {
108         return name();
109     }
110 
111     private static final class SignalConstant extends AbstractConstant<SignalConstant> {
112         SignalConstant(int id, String name) {
113             super(id, name);
114         }
115     }
116 }