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   /*
    * Copyright 2015 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.concurrent;
  
  import io.netty.util.internal.ObjectUtil;
  
  import java.util.PriorityQueue;
  import java.util.Queue;
  import java.util.concurrent.Callable;
  import java.util.concurrent.Executors;
  import java.util.concurrent.TimeUnit;
  
  /**
   * Abstract base class for {@link EventExecutor}s that want to support scheduling.
   */
  public abstract class AbstractScheduledEventExecutor extends AbstractEventExecutor {
  
      Queue<ScheduledFutureTask<?>> scheduledTaskQueue;
  
      protected static long nanoTime() {
          return ScheduledFutureTask.nanoTime();
      }
  
      Queue<ScheduledFutureTask<?>> scheduledTaskQueue() {
          if (scheduledTaskQueue == null) {
              scheduledTaskQueue = new PriorityQueue<ScheduledFutureTask<?>>();
          }
          return scheduledTaskQueue;
      }
  
      private static  boolean isNullOrEmpty(Queue<ScheduledFutureTask<?>> queue) {
          return queue == null || queue.isEmpty();
      }
  
      /**
       * Cancel all scheduled tasks.
       *
       * This method MUST be called only when {@link #inEventLoop()} is {@code true}.
       */
      protected void cancelScheduledTasks() {
          assert inEventLoop();
          Queue<ScheduledFutureTask<?>> scheduledTaskQueue = this.scheduledTaskQueue;
          if (isNullOrEmpty(scheduledTaskQueue)) {
              return;
          }
  
          final ScheduledFutureTask<?>[] scheduledTasks =
                  scheduledTaskQueue.toArray(new ScheduledFutureTask<?>[scheduledTaskQueue.size()]);
  
          for (ScheduledFutureTask<?> task: scheduledTasks) {
              task.cancelWithoutRemove(false);
          }
  
          scheduledTaskQueue.clear();
      }
  
      /**
       * @see #pollScheduledTask(long)
       */
      protected final Runnable pollScheduledTask() {
          return pollScheduledTask(nanoTime());
      }
  
      /**
       * Return the {@link Runnable} which is ready to be executed with the given {@code nanoTime}.
       * You should use {@link #nanoTime()} to retrieve the the correct {@code nanoTime}.
       */
      protected final Runnable pollScheduledTask(long nanoTime) {
          assert inEventLoop();
  
          Queue<ScheduledFutureTask<?>> scheduledTaskQueue = this.scheduledTaskQueue;
          ScheduledFutureTask<?> scheduledTask = scheduledTaskQueue == null ? null : scheduledTaskQueue.peek();
          if (scheduledTask == null) {
              return null;
          }
  
          if (scheduledTask.deadlineNanos() <= nanoTime) {
              scheduledTaskQueue.remove();
              return scheduledTask;
          }
          return null;
      }
  
      /**
       * Return the nanoseconds when the next scheduled task is ready to be run or {@code -1} if no task is scheduled.
       */
     protected final long nextScheduledTaskNano() {
         Queue<ScheduledFutureTask<?>> scheduledTaskQueue = this.scheduledTaskQueue;
         ScheduledFutureTask<?> scheduledTask = scheduledTaskQueue == null ? null : scheduledTaskQueue.peek();
         if (scheduledTask == null) {
             return -1;
         }
         return Math.max(0, scheduledTask.deadlineNanos() - nanoTime());
     }
 
     final ScheduledFutureTask<?> peekScheduledTask() {
         Queue<ScheduledFutureTask<?>> scheduledTaskQueue = this.scheduledTaskQueue;
         if (scheduledTaskQueue == null) {
             return null;
         }
         return scheduledTaskQueue.peek();
     }
 
     /**
      * Returns {@code true} if a scheduled task is ready for processing.
      */
     protected final boolean hasScheduledTasks() {
         Queue<ScheduledFutureTask<?>> scheduledTaskQueue = this.scheduledTaskQueue;
         ScheduledFutureTask<?> scheduledTask = scheduledTaskQueue == null ? null : scheduledTaskQueue.peek();
         return scheduledTask != null && scheduledTask.deadlineNanos() <= nanoTime();
     }
 
     @Override
     public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
         ObjectUtil.checkNotNull(command, "command");
         ObjectUtil.checkNotNull(unit, "unit");
         if (delay < 0) {
             delay = 0;
         }
         return schedule(new ScheduledFutureTask<Void>(
                 this, command, null, ScheduledFutureTask.deadlineNanos(unit.toNanos(delay))));
     }
 
     @Override
     public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
         ObjectUtil.checkNotNull(callable, "callable");
         ObjectUtil.checkNotNull(unit, "unit");
         if (delay < 0) {
             delay = 0;
         }
         return schedule(new ScheduledFutureTask<V>(
                 this, callable, ScheduledFutureTask.deadlineNanos(unit.toNanos(delay))));
     }
 
     @Override
     public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
         ObjectUtil.checkNotNull(command, "command");
         ObjectUtil.checkNotNull(unit, "unit");
         if (initialDelay < 0) {
             throw new IllegalArgumentException(
                     String.format("initialDelay: %d (expected: >= 0)", initialDelay));
         }
         if (period <= 0) {
             throw new IllegalArgumentException(
                     String.format("period: %d (expected: > 0)", period));
         }
 
         return schedule(new ScheduledFutureTask<Void>(
                 this, Executors.<Void>callable(command, null),
                 ScheduledFutureTask.deadlineNanos(unit.toNanos(initialDelay)), unit.toNanos(period)));
     }
 
     @Override
     public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) {
         ObjectUtil.checkNotNull(command, "command");
         ObjectUtil.checkNotNull(unit, "unit");
         if (initialDelay < 0) {
             throw new IllegalArgumentException(
                     String.format("initialDelay: %d (expected: >= 0)", initialDelay));
         }
         if (delay <= 0) {
             throw new IllegalArgumentException(
                     String.format("delay: %d (expected: > 0)", delay));
         }
 
         return schedule(new ScheduledFutureTask<Void>(
                 this, Executors.<Void>callable(command, null),
                 ScheduledFutureTask.deadlineNanos(unit.toNanos(initialDelay)), -unit.toNanos(delay)));
     }
 
     <V> ScheduledFuture<V> schedule(final ScheduledFutureTask<V> task) {
         if (inEventLoop()) {
             scheduledTaskQueue().add(task);
         } else {
             execute(new Runnable() {
                 @Override
                 public void run() {
                     scheduledTaskQueue().add(task);
                 }
             });
         }
 
         return task;
     }
 
     final void removeScheduled(final ScheduledFutureTask<?> task) {
         if (inEventLoop()) {
             scheduledTaskQueue().remove(task);
         } else {
             execute(new Runnable() {
                 @Override
                 public void run() {
                     removeScheduled(task);
                 }
             });
         }
     }
 }