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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:
    *
    *   http://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;
  
  
  import io.netty.util.internal.PlatformDependent;
  
  import java.util.concurrent.ConcurrentMap;
  
  /**
   * 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 {
  
      private static final long serialVersionUID = -221145131122459977L;
  
      private static final ConcurrentMap<String, Boolean> map = PlatformDependent.newConcurrentHashMap();
  
      @SuppressWarnings("deprecation")
      private final UniqueName uname;
  
      /**
       * Creates a new {@link Signal} with the specified {@code name}.
       */
      @SuppressWarnings("deprecation")
      public static Signal valueOf(String name) {
          return new Signal(name);
      }
  
      /**
       * @deprecated Use {@link #valueOf(String)} instead.
       */
      @Deprecated
      public Signal(String name) {
          super(name);
          uname = new UniqueName(map, 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);
          }
      }
  
      @Override
      public Throwable initCause(Throwable cause) {
          return this;
      }
  
      @Override
      public Throwable fillInStackTrace() {
          return this;
      }
  
      @Override
      public String toString() {
          return uname.name();
      }
  }