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1   /*
2    * Copyright 2016 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.concurrent;
17  
18  import io.netty.util.internal.ObjectUtil;
19  
20  import java.util.concurrent.RejectedExecutionException;
21  import java.util.concurrent.TimeUnit;
22  import java.util.concurrent.locks.LockSupport;
23  
24  /**
25   * Expose helper methods which create different {@link RejectedExecutionHandler}s.
26   */
27  public final class RejectedExecutionHandlers {
28      private static final RejectedExecutionHandler REJECT = new RejectedExecutionHandler() {
29          @Override
30          public void rejected(Runnable task, SingleThreadEventExecutor executor) {
31              throw new RejectedExecutionException();
32          }
33      };
34  
35      private RejectedExecutionHandlers() { }
36  
37      /**
38       * Returns a {@link RejectedExecutionHandler} that will always just throw a {@link RejectedExecutionException}.
39       */
40      public static RejectedExecutionHandler reject() {
41          return REJECT;
42      }
43  
44      /**
45       * Tries to backoff when the task can not be added due restrictions for an configured amount of time. This
46       * is only done if the task was added from outside of the event loop which means
47       * {@link EventExecutor#inEventLoop()} returns {@code false}.
48       */
49      public static RejectedExecutionHandler backoff(final int retries, long backoffAmount, TimeUnit unit) {
50          ObjectUtil.checkPositive(retries, "retries");
51          final long backOffNanos = unit.toNanos(backoffAmount);
52          return new RejectedExecutionHandler() {
53              @Override
54              public void rejected(Runnable task, SingleThreadEventExecutor executor) {
55                  if (!executor.inEventLoop()) {
56                      for (int i = 0; i < retries; i++) {
57                          // Try to wake up the executor so it will empty its task queue.
58                          executor.wakeup(false);
59  
60                          LockSupport.parkNanos(backOffNanos);
61                          if (executor.offerTask(task)) {
62                              return;
63                          }
64                      }
65                  }
66                  // Either we tried to add the task from within the EventLoop or we was not able to add it even with
67                  // backoff.
68                  throw new RejectedExecutionException();
69              }
70          };
71      }
72  }