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   /*
    * Copyright 2016 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.concurrent;
  
  import io.netty.util.internal.ObjectUtil;
  
  import java.util.concurrent.RejectedExecutionException;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.locks.LockSupport;
  
  /**
   * Expose helper methods which create different {@link RejectedExecutionHandler}s.
   */
  public final class RejectedExecutionHandlers {
      private static final RejectedExecutionHandler REJECT = new RejectedExecutionHandler() {
          @Override
          public void rejected(Runnable task, SingleThreadEventExecutor executor) {
              throw new RejectedExecutionException();
          }
      };
  
      private RejectedExecutionHandlers() { }
  
      /**
       * Returns a {@link RejectedExecutionHandler} that will always just throw a {@link RejectedExecutionException}.
       */
      public static RejectedExecutionHandler reject() {
          return REJECT;
      }
  
      /**
       * Tries to backoff when the task can not be added due restrictions for an configured amount of time. This
       * is only done if the task was added from outside of the event loop which means
       * {@link EventExecutor#inEventLoop()} returns {@code false}.
       */
      public static RejectedExecutionHandler backoff(final int retries, long backoffAmount, TimeUnit unit) {
          ObjectUtil.checkPositive(retries, "retries");
          final long backOffNanos = unit.toNanos(backoffAmount);
          return new RejectedExecutionHandler() {
              @Override
              public void rejected(Runnable task, SingleThreadEventExecutor executor) {
                  if (!executor.inEventLoop()) {
                      for (int i = 0; i < retries; i++) {
                          // Try to wake up the executor so it will empty its task queue.
                          executor.wakeup(false);
  
                          LockSupport.parkNanos(backOffNanos);
                          if (executor.offerTask(task)) {
                              return;
                          }
                      }
                  }
                  // Either we tried to add the task from within the EventLoop or we was not able to add it even with
                  // backoff.
                  throw new RejectedExecutionException();
              }
          };
      }
  }