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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  import io.netty.util.internal.PlatformDependent;
20  
21  import java.util.concurrent.ConcurrentMap;
22  
23  /**
24   * A special {@link Error} which is used to signal some state or request by throwing it.
25   * {@link Signal} has an empty stack trace and has no cause to save the instantiation overhead.
26   */
27  public final class Signal extends Error {
28  
29      private static final long serialVersionUID = -221145131122459977L;
30  
31      private static final ConcurrentMap<String, Boolean> map = PlatformDependent.newConcurrentHashMap();
32  
33      @SuppressWarnings("deprecation")
34      private final UniqueName uname;
35  
36      /**
37       * Creates a new {@link Signal} with the specified {@code name}.
38       */
39      @SuppressWarnings("deprecation")
40      public static Signal valueOf(String name) {
41          return new Signal(name);
42      }
43  
44      /**
45       * @deprecated Use {@link #valueOf(String)} instead.
46       */
47      @Deprecated
48      public Signal(String name) {
49          super(name);
50          uname = new UniqueName(map, name);
51      }
52  
53      /**
54       * Check if the given {@link Signal} is the same as this instance. If not an {@link IllegalStateException} will
55       * be thrown.
56       */
57      public void expect(Signal signal) {
58          if (this != signal) {
59              throw new IllegalStateException("unexpected signal: " + signal);
60          }
61      }
62  
63      @Override
64      public Throwable initCause(Throwable cause) {
65          return this;
66      }
67  
68      @Override
69      public Throwable fillInStackTrace() {
70          return this;
71      }
72  
73      @Override
74      public String toString() {
75          return uname.name();
76      }
77  }