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   /*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty.util;
  
  
  /**
   * A special {@link Error} which is used to signal some state or request by throwing it.
   * {@link Signal} has an empty stack trace and has no cause to save the instantiation overhead.
   */
  public final class Signal extends Error implements Constant<Signal> {
  
      private static final long serialVersionUID = -221145131122459977L;
  
      private static final ConstantPool<Signal> pool = new ConstantPool<Signal>() {
          @Override
          protected Signal newConstant(int id, String name) {
              return new Signal(id, name);
          }
      };
  
      /**
       * Returns the {@link Signal} of the specified name.
       */
      public static Signal valueOf(String name) {
          return pool.valueOf(name);
      }
  
      /**
       * Shortcut of {@link #valueOf(String) valueOf(firstNameComponent.getName() + "#" + secondNameComponent)}.
       */
      public static Signal valueOf(Class<?> firstNameComponent, String secondNameComponent) {
          return pool.valueOf(firstNameComponent, secondNameComponent);
      }
  
      private final SignalConstant constant;
  
      /**
       * Creates a new {@link Signal} with the specified {@code name}.
       */
      private Signal(int id, String name) {
          constant = new SignalConstant(id, name);
      }
  
      /**
       * Check if the given {@link Signal} is the same as this instance. If not an {@link IllegalStateException} will
       * be thrown.
       */
      public void expect(Signal signal) {
          if (this != signal) {
              throw new IllegalStateException("unexpected signal: " + signal);
          }
      }
  
      // Suppress a warning since the method doesn't need synchronization
      @Override
      public Throwable initCause(Throwable cause) {
          return this;
      }
  
      // Suppress a warning since the method doesn't need synchronization
      @Override
      public Throwable fillInStackTrace() {
          return this;
      }
  
      @Override
      public int id() {
          return constant.id();
      }
  
      @Override
      public String name() {
          return constant.name();
      }
  
      @Override
      public boolean equals(Object obj) {
          return this == obj;
      }
  
      @Override
      public int hashCode() {
          return System.identityHashCode(this);
      }
  
      @Override
     public int compareTo(Signal other) {
         if (this == other) {
             return 0;
         }
 
         return constant.compareTo(other.constant);
     }
 
     @Override
     public String toString() {
         return name();
     }
 
     private static final class SignalConstant extends AbstractConstant<SignalConstant> {
         SignalConstant(int id, String name) {
             super(id, name);
         }
     }
 }