Task核心调度器[TaskScheduler]

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字数统计: 322

一：TaskScheduler

问：TaskScheduler是做什么的？

答：我们发现任务执行要经过Scheduler。Task的核心就是这个Scheduler，因为他把要执行任务安排在线程或者线程池中。TaskScheduler由Thread和ThreadPool组成。

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二：在.net FrameWork中有两种TaskScheduler

1.ThreadPoolTaskScheduler

也就是Task的默认是调用ThreadPool

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protected internal override void QueueTask(Task task)
		{
			if ((task.Options & TaskCreationOptions.LongRunning) != TaskCreationOptions.None)
			{
				new Thread(ThreadPoolTaskScheduler.s_longRunningThreadWork)
				{
					IsBackground = true
				}.Start(task);
				return;
			}
			bool forceGlobal = (task.Options & TaskCreationOptions.PreferFairness) > TaskCreationOptions.None;
			ThreadPool.UnsafeQueueCustomWorkItem(task, forceGlobal);
		}

2.SynchronizationContextTaskScheduler

1.同步上下文

Task task = new Task(() =>
{
    try
    {
        label1.Text = "das";
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
});
task.Start(TaskScheduler.FromCurrentSynchronizationContext());

2.操作耗时线程

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var task = Task.Factory.StartNew(() =>
           {
               Thread.Sleep(10000);
           });
           task.ContinueWith(t =>
           {
               label1.Text = "你好!";
           }, TaskScheduler.FromCurrentSynchronizationContext());

ContinueWith等待执行完耗时线程，在同步上下文

三：如何自定义Scheduler？

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public class PerThreadTaskScheduler : TaskScheduler
   {
       /// <summary>
       /// 给debug
       /// </summary>
       /// <returns></returns>
       protected override IEnumerable<Task> GetScheduledTasks()
       {
           return Enumerable.Empty<Task>();
       }
       /// <summary>
       /// 执行Task
       /// </summary>
       /// <param name="task"></param>
       protected override void QueueTask(Task task)
       {
           var thread = new Thread(()=> {
               TryExecuteTask(task);
           });
           thread.Start();
       }
       /// <summary>
       /// 同步执行
       /// </summary>
       /// <param name="task"></param>
       /// <param name="taskWasPreviouslyQueued"></param>
       /// <returns></returns>
       protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
       {
           return true;
       }
   }