C# Task详解

双手一摊 發表於 2019-6-25 14:45:00

<h2 id="1task产生背景">1、Task产生背景</h2>
<p><code>Task</code>出现之前，微软的多线程处理方式有：<code>Thread→ThreadPool→委托的异步调用</code>，虽然也可以基本业务需要的多线程场景，但它们在多个线程的等待处理方面、资源占用方面、线程延续和阻塞方面、线程的取消方面等都显得比较笨拙，在面对复杂的业务场景下，显得有点捉襟见肘了。</p>
<p><code>ThreadPool</code>相比<code>Thread</code>来说具备了很多优势，但是<code>ThreadPool</code>却又存在一些使用上的不方便。比如：</p>
<ul>
<li><code>ThreadPool</code>不支持线程的取消、完成、失败通知等交互性操作；</li>
<li><code>ThreadPool</code>不支持线程执行的先后次序；</li>
</ul>
<p>正是在这种背景下，<code>Task</code>应运而生。Task是微软在<code>.Net 4.0</code>时代推出来的，也是微软极力推荐的一种多线程的处理方式，<code>Task</code>看起来像一个<code>Thread</code>，实际上，它是在<code>ThreadPool</code>的基础上进行的封装，<code>Task</code>的控制和扩展性很强，在线程的延续、阻塞、取消、超时等方面远胜于<code>Thread</code>和<code>ThreadPool</code>。以下是一个简单的任务示例：</p>
<pre><code class="language-C#">static void Main(string[] args)
{
Task t = new Task(() =>
{
   Console.WriteLine("任务开始工作……");
   Thread.Sleep(5000);//模拟工作过程
});
t.Start();
t.ContinueWith(task =>
{
   Console.WriteLine("任务完成，完成时候的状态为：");
   Console.WriteLine("IsCanceled={0}\tIsCompleted={1}\tIsFaulted={2}",
                     task.IsCanceled, task.IsCompleted, task.IsFaulted);
});
Console.ReadKey();
}
</code></pre>
<h2 id="2task使用方法">2、Task使用方法</h2>
<h3 id="21创建和启动任务">2.1　创建和启动任务</h3>
<h4 id="211-无返回值的方式">2.1.1 无返回值的方式</h4>
<h5 id="方式1调用start方法">方式1:调用Start方法</h5>
<pre><code class="language-C#">var t1 = new Task(() => TaskMethod("Task 1"));
t1.Start();
Task.WaitAll(t1);//等待所有任务结束
</code></pre>
<p>任务的状态：<code>Start</code>之前为<code>Created</code>，之后为<code>WaitingToRun</code></p>
<h5 id="方式2静态方法run">方式2:静态方法Run</h5>
<pre><code class="language-C#">Task.Run(() => TaskMethod("Task 2"));
</code></pre>
<h5 id="方式3taskfactory工厂">方式3:TaskFactory工厂</h5>
<pre><code class="language-C#">// 方法1. TaskFactory工厂
TaskFactory taskFactory = new TaskFactory() ;
taskFactory.StartNew(() => TaskMethod("Task 3"));
// 方法2. Task.Factory属性
Task.Factory.StartNew(() => TaskMethod("Task 3"));
//或者
var t3=Task.Factory.StartNew(() => TaskMethod("Task 3"));
Task.WaitAll(t3);
</code></pre>
<p>任务的状态：<code>Start</code>之前为<code>Running</code>，之后为<code>Running</code></p>
<pre><code class="language-C#">static void Main(string[] args)
{
var t1 = new Task(() => TaskMethod("Task 1"));
var t2 = new Task(() => TaskMethod("Task 2"));
t2.Start();
t1.Start();
Task.WaitAll(t1, t2);
Task.Run(() => TaskMethod("Task 3"));
Task.Factory.StartNew(() => TaskMethod("Task 4"));
//标记为长时间运行任务,则任务不会使用线程池,而在单独的线程中运行。
Task.Factory.StartNew(() => TaskMethod("Task 5"), TaskCreationOptions.LongRunning);

#region 常规的使用方式
Console.WriteLine("主线程执行业务处理.");
//创建任务
Task task = new Task(() =>
                     {
                        Console.WriteLine("使用`System.Threading.Tasks.Task`执行异步操作.");
                        for (int i = 0; i < 10; i++)
                        {
                              Console.WriteLine(i);
                        }
                     });
//启动任务,并安排到当前任务队列线程中执行任务(System.Threading.Tasks.TaskScheduler)
task.Start();
Console.WriteLine("主线程执行其他处理");
task.Wait();
#endregion

Thread.Sleep(TimeSpan.FromSeconds(1));
Console.ReadLine();
}

static void TaskMethod(string name)
{
Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
                  name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
}
</code></pre>
<h5 id="方式4runsynchronously同步启动">方式4:RunSynchronously同步启动</h5>
<p><code>Task</code>实例化后调用同步方法<code>RunSynchronously</code>，进行线程启动。(PS: 类似委托开启线程，<code>BeginInvoke</code>是异步，而<code>Invoke</code>是同步)</p>
<pre><code class="language-C#">var task = new Task(() => TaskMethod("Task 1"));
task.RunSynchronously();
</code></pre>
<h5 id="asyncawait的实现方式">async/await的实现方式</h5>
<pre><code>using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
class Program
{
   async static void AsyncFunction()
   {
         await Task.Delay(1);
         Console.WriteLine("使用`System.Threading.Tasks.Task`执行异步操作.");
         for (int i = 0; i < 10; i++)
         {
            Console.WriteLine(string.Format("AsyncFunction:i={0}", i));
         }
   }

   public static void Main()
   {
         Console.WriteLine("主线程执行业务处理.");
         AsyncFunction();
         Console.WriteLine("主线程执行其他处理");
         for (int i = 0; i < 10; i++)
         {
            Console.WriteLine(string.Format("Main:i={0}", i));
         }
         Console.ReadLine();
   }
}
}
</code></pre>
<h4 id="212-带返回值的方式">2.1.2 带返回值的方式</h4>
<h5 id="方式4">方式4:</h5>
<pre><code class="language-C#">Task<int> task = CreateTask("Task 1");
task.Start();
int result = task.Result;
</code></pre>
<pre><code class="language-c#">using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
class Program
{
   static Task<int> CreateTask(string name)
   {
         return new Task<int>(() => TaskMethod(name));
   }

   static void Main(string[] args)
   {
         TaskMethod("Main Thread Task");
         Task<int> task = CreateTask("Task 1");
         task.Start();
         int result = task.Result;
         Console.WriteLine("Task 1 Result is: {0}", result);

         task = CreateTask("Task 2");
         task.RunSynchronously(); //该任务会运行在主线程中
         result = task.Result;
         Console.WriteLine("Task 2 Result is: {0}", result);

         task = CreateTask("Task 3");
         Console.WriteLine(task.Status);
         task.Start();

         while (!task.IsCompleted)
         {
            Console.WriteLine(task.Status);
            Thread.Sleep(TimeSpan.FromSeconds(0.5));
         }

         Console.WriteLine(task.Status);
         result = task.Result;
         Console.WriteLine("Task 3 Result is: {0}", result);

         #region 常规使用方式
         //创建任务
         Task<int> getsumtask = new Task<int>(() => Getsum());
         //启动任务,并安排到当前任务队列线程中执行任务(System.Threading.Tasks.TaskScheduler)
         getsumtask.Start();
         Console.WriteLine("主线程执行其他处理");
         getsumtask.Wait(); //等待任务的完成执行过程
         Console.WriteLine("任务执行结果：{0}", getsumtask.Result.ToString());//获得任务的执行结果
         #endregion
   }

   static int TaskMethod(string name)
   {
         Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
            name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
         Thread.Sleep(TimeSpan.FromSeconds(2));
         return 42;
   }

   static int Getsum()
   {
         int sum = 0;
         Console.WriteLine("使用`Task`执行异步操作.");
         for (int i = 0; i < 100; i++)
         {
            sum += i;
         }
         return sum;
   }
}
}
</code></pre>
<pre><code>using System;
using System.Threading.Tasks;

namespace ConsoleApp1
{
class Program
{
   public static void Main()
   {
         var ret1 = AsyncGetsum();
         Console.WriteLine("主线程执行其他处理");
         for (int i = 1; i <= 3; i++)
            Console.WriteLine("Call Main()");
         int result = ret1.Result; //阻塞主线程
         Console.WriteLine("任务执行结果：{0}", result);
   }

   async static Task<int> AsyncGetsum()
   {
         await Task.Delay(1);
         int sum = 0;
         Console.WriteLine("使用`Task`执行异步操作.");
         for (int i = 0; i < 100; i++)
         {
            sum += i;
         }
         return sum;
   }
}
}
</code></pre>
<h3 id="22线程等待延续和组合">2.2　线程等待、延续和组合</h3>
<h4 id="221-task的线程等待和延续主要以下几类">2.2.1 Task的线程等待和延续主要以下几类：</h4>
<ul>
<li>Wait：针对单个Task的实例，可以task1.wait进行线程等待</li>
<li>WaitAny：线程列表中任何一个线程执行完毕即可执行（阻塞主线程）</li>
<li>WaitAll：线程列表中所有线程执行完毕方可执行（阻塞主线程）</li>
<li>WhenAny：与ContinueWith配合,线程列表中任何一个执行完毕，则继续ContinueWith中的任务（开启新线程，不阻塞主线程）</li>
<li>WhenAll：与ContinueWith配合,线程列表中所有线程执行完毕，则继续ContinueWith中的任务（开启新线程，不阻塞主线程）</li>
<li>ContinueWith：与WhenAny或WhenAll配合使用</li>
<li>ContinueWhenAny：等价于Task的WhenAny+ContinueWith</li>
<li>ContinueWhenAll：等价于Task的WhenAll+ContinueWith</li>
</ul>
<pre><code class="language-c#">public static void Main()
{
//创建一个任务
Task<int> task = new Task<int>(() =>
{
   int sum = 0;
   Console.WriteLine("使用`Task`执行异步操作.");
   for (int i = 0; i < 100; i++)
   {
         sum += i;
   }
   return sum;
});
//启动任务,并安排到当前任务队列线程中执行任务(System.Threading.Tasks.TaskScheduler)
task.Start();
Console.WriteLine("主线程执行其他处理");
//任务完成时执行处理。
Task cwt = task.ContinueWith(t =>
{
   Console.WriteLine("任务完成后的执行结果：{0}", t.Result.ToString());
});
task.Wait();
cwt.Wait();

Action<string,int> log = (name,time) =>
{
   Console.WriteLine($"{name}任务开始...");
   Thread.Sleep(time);
   Console.WriteLine($"{name}任务结束!");
};
List<Task> tasks = new List<Task>
{
   Task.Run(() => log("张三",3000)),
   Task.Run(() => log("李四",1000)),
   Task.Run(() => log("王五",2000))
};
//以下语句逐个测试效果
Task.WaitAny(tasks.ToArray());
Task.WaitAll(tasks.ToArray());
Task.WhenAny(tasks.ToArray()).ContinueWith(x => Console.WriteLine("某个Task执行完毕"));
Task.WhenAll(tasks.ToArray()).ContinueWith(x => Console.WriteLine("所有Task执行完毕"));
Task.Factory.ContinueWhenAny(tasks.ToArray(), x => Console.WriteLine("某个Task执行完毕"));
Task.Factory.ContinueWhenAll(tasks.ToArray(), x => Console.WriteLine("所有Task执行完毕"));
Console.Read();
}
</code></pre>
<h4 id="222-任务的串行">2.2.2 任务的串行</h4>
<pre><code class="language-c#">static void Main(string[] args)
{
ConcurrentStack<int> stack = new ConcurrentStack<int>();

//t1先串行
var t1 = Task.Factory.StartNew(() =>
{
   stack.Push(1);
   stack.Push(2);
});

//t2,t3并行执行
var t2 = t1.ContinueWith(t =>
{
   int result;
   stack.TryPop(out result);
   Console.WriteLine("Task t2 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
});

//t2,t3并行执行
var t3 = t1.ContinueWith(t =>
{
   int result;
   stack.TryPop(out result);
   Console.WriteLine("Task t3 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
});

//等待t2和t3执行完
Task.WaitAll(t2, t3);

//t4串行执行
var t4 = Task.Factory.StartNew(() =>
{
   Console.WriteLine("当前集合元素个数：{0},Thread id {1}", stack.Count, Thread.CurrentThread.ManagedThreadId);
});
t4.Wait();
}
</code></pre>
<h4 id="223-子任务">2.2.3 子任务</h4>
<pre><code class="language-c#">public static void Main()
{
Task<string[]> parent = new Task<string[]>(state =>
{
   Console.WriteLine(state);
   string[] result = new string;
   //创建并启动子任务
   new Task(() => { result = "我是子任务1"; }, TaskCreationOptions.AttachedToParent).Start();
   new Task(() => { result = "我是子任务2"; }, TaskCreationOptions.AttachedToParent).Start();
   return result;
}, "我是父任务，并在我的处理过程中创建多个子任务，所有子任务完成以后我才会结束执行");
//任务完成后执行
parent.ContinueWith(t =>
{
   Array.ForEach(t.Result, r => Console.WriteLine(r));
});
parent.Start(); //启动父任务
parent.Wait();//等待任务结束Wait只能等待父线程结束,没办法等到父线程的ContinueWith结束
Console.ReadLine();
}
</code></pre>
<h4 id="224-动态并行">2.2.4 动态并行</h4>
<p><code>TaskCreationOptions.AttachedToParent</code>父任务等待所有子任务完成后整个任务才算完成</p>
<pre><code class="language-c#">class Node
{
public Node Left { get; set; }
public Node Right { get; set; }
public string Text { get; set; }
}

class Program
{
static Node GetNode()
{
   Node root = new Node
   {
         Left = new Node
         {
            Left = new Node{ Text = "L-L" },
            Right = new Node{ Text = "L-R" },
            Text = "L"
         },
         Right = new Node
         {
            Left = new Node{ Text = "R-L" },
            Right = new Node{ Text = "R-R" },
            Text = "R"
         },
         Text = "Root"
   };
   return root;
}

static void Main(string[] args)
{
   Node root = GetNode();
   DisplayTree(root);
}

static void DisplayTree(Node root)
{
   var task = Task.Factory.StartNew(() => DisplayNode(root),
                                    CancellationToken.None,
                                    TaskCreationOptions.None,
                                    TaskScheduler.Default);
   task.Wait();
}

static void DisplayNode(Node current)
{

   if (current.Left != null)
         Task.Factory.StartNew(() => DisplayNode(current.Left),
                                    CancellationToken.None,
                                    TaskCreationOptions.AttachedToParent,
                                    TaskScheduler.Default);
   if (current.Right != null)
         Task.Factory.StartNew(() => DisplayNode(current.Right),
                                    CancellationToken.None,
                                    TaskCreationOptions.AttachedToParent,
                                    TaskScheduler.Default);
   Console.WriteLine("当前节点的值为{0};处理的ThreadId={1}", current.Text, Thread.CurrentThread.ManagedThreadId);
}
}
</code></pre>
<h3 id="23取消任务">2.3　取消任务</h3>
<pre><code class="language-c#">private static int TaskMethod(string name, int seconds, CancellationToken token)
{
Console.WriteLine("Task {0} 正在运行,当前线程id {1}. Is thread pool thread: {2}",
   name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
for (int i = 0; i < seconds; i++)
{
   Thread.Sleep(TimeSpan.FromSeconds(1));
   if (token.IsCancellationRequested) return -1;
}
return 42 * seconds;
}

private static void Main(string[] args)
{
var cts = new CancellationTokenSource();
var longTask = new Task<int>(() => TaskMethod("Task 1", 10, cts.Token), cts.Token);
Console.WriteLine(longTask.Status);
cts.Cancel();
Console.WriteLine(longTask.Status);
Console.WriteLine("第一个任务在执行前已被取消");
cts = new CancellationTokenSource();
longTask = new Task<int>(() => TaskMethod("Task 2", 10, cts.Token), cts.Token);
longTask.Start();
for (int i = 0; i < 5; i++)
{
   Thread.Sleep(TimeSpan.FromSeconds(0.5));
   Console.WriteLine(longTask.Status);
}
cts.Cancel();
for (int i = 0; i < 5; i++)
{
   Thread.Sleep(TimeSpan.FromSeconds(0.5));
   Console.WriteLine(longTask.Status);
}

Console.WriteLine("任务已完成,结果为 {0}.", longTask.Result);
}
</code></pre>
<h3 id="24处理异常">2.4　处理异常</h3>
<h4 id="241-单个任务">2.4.1 单个任务</h4>
<pre><code class="language-c#">static int TaskMethod(string name, int seconds)
{
Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
   name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
Thread.Sleep(TimeSpan.FromSeconds(seconds));
throw new Exception("Boom!");
return 42 * seconds;
}

static void Main(string[] args)
{
try
{
   Task<int> task = Task.Run(() => TaskMethod("Task 2", 2));
   int result = task.GetAwaiter().GetResult();
   Console.WriteLine("Result: {0}", result);
}
catch (Exception ex)
{
   Console.WriteLine("Task 2 Exception caught: {0}", ex.Message);
}
Console.WriteLine("----------------------------------------------");
Console.ReadLine();
}
</code></pre>
<h4 id="242-多个任务">2.4.2 多个任务</h4>
<pre><code class="language-c#">static int TaskMethod(string name, int seconds)
{
Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
   name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
Thread.Sleep(TimeSpan.FromSeconds(seconds));
throw new Exception(string.Format("Task {0} Boom!", name));
return 42 * seconds;
}

public static void Main(string[] args)
{
try
{
   var t1 = new Task<int>(() => TaskMethod("Task 3", 3));
   var t2 = new Task<int>(() => TaskMethod("Task 4", 2));
   var complexTask = Task.WhenAll(t1, t2);
   var exceptionHandler = complexTask.ContinueWith(t =>
            Console.WriteLine("Result: {0}", t.Result),
            TaskContinuationOptions.OnlyOnFaulted
         );
   t1.Start();
   t2.Start();
   Task.WaitAll(t1, t2);
}
catch (AggregateException ex)
{
   ex.Handle(exception =>
   {
         Console.WriteLine(exception.Message);
         return true;
   });
}
}
</code></pre>
<h4 id="243-asyncawait的方式">2.4.3 async/await的方式</h4>
<pre><code class="language-c#">class Program
{
static async Task ThrowNotImplementedExceptionAsync()
{
   throw new NotImplementedException();
}

static async Task ThrowInvalidOperationExceptionAsync()
{
   throw new InvalidOperationException();
}

static async Task Normal()
{
   await Fun();
}

static Task Fun()
{
   return Task.Run(() =>
   {
         for (int i = 1; i <= 10; i++)
         {
            Console.WriteLine("i={0}", i);
            Thread.Sleep(200);
         }
   });
}

static async Task ObserveOneExceptionAsync()
{
   var task1 = ThrowNotImplementedExceptionAsync();
   var task2 = ThrowInvalidOperationExceptionAsync();
   var task3 = Normal();
   try
   {
         Task allTasks = Task.WhenAll(task1, task2, task3); //异步的方式
         await allTasks;
         //Task.WaitAll(task1, task2, task3); //同步的方式
   }
   catch (NotImplementedException ex)
   {
         Console.WriteLine("task1 任务报错!");
   }
   catch (InvalidOperationException ex)
   {
         Console.WriteLine("task2 任务报错!");
   }
   catch (Exception ex)
   {
         Console.WriteLine("任务报错!");
   }
}

public static void Main()
{
   Task task = ObserveOneExceptionAsync();
   Console.WriteLine("主线程继续运行........");
   task.Wait();
}
}
</code></pre>
<h3 id="25taskfromresult">2.5　Task.FromResult</h3>
<p>此方法创建一个<code>Task<TResult></code>对象，该对象的<code>Task<TResult>.Result</code>属性为<code>result</code>，其<code>Status</code>属性为<code>RanToCompletion</code>。当立即知道任务的返回值而不执行更长的代码路径时，通常使用方法。</p>
<pre><code class="language-c#">class Program
{
static IDictionary<string, string> cache = new Dictionary<string, string>()
{
   {"0001","A"}, {"0002","B"}, {"0003","C"},
   {"0004","D"}, {"0005","E"}, {"0006","F"}
};

public static void Main()
{
   Task<string> task = GetValueFromCache("0006");
   Console.WriteLine("主程序继续执行。。。。");
   string result = task.Result;
   Console.WriteLine("result={0}", result);
}

private static Task<string> GetValueFromCache(string key)
{
   Console.WriteLine("GetValueFromCache开始执行。。。。");
   string result = string.Empty;
   //Task.Delay(5000);
   Thread.Sleep(5000);
   Console.WriteLine("GetValueFromCache继续执行。。。。");
   if (cache.TryGetValue(key, out result))
   {
         return Task.FromResult(result);
   }
   return Task.FromResult("");
}
}
</code></pre>
<h3 id="26factoryfromasync">2.6　Factory.FromAsync</h3>
<p>简<code>APM</code>模式（委托）转换为任务，<code>BeginXXX</code>和<code>EndXXX</code></p>
<h4 id="261-带回调方式的">2.6.1 带回调方式的</h4>
<pre><code class="language-c#">class Program
{
private delegate string AsynchronousTask(string threadName);
private static string Test(string threadName)
{
   Console.WriteLine("开始...");
   Console.WriteLine("线程池是线程吗: {0}", Thread.CurrentThread.IsThreadPoolThread);
   Thread.Sleep(TimeSpan.FromSeconds(2));
   Thread.CurrentThread.Name = threadName;
   return string.Format("线程名称: {0}", Thread.CurrentThread.Name);
}

private static void Callback(IAsyncResult ar)
{
   Console.WriteLine("开始一个回调...");
   Console.WriteLine("传递给callbak的状态: {0}", ar.AsyncState);
   Console.WriteLine("线程池是线程吗: {0}", Thread.CurrentThread.IsThreadPoolThread);
   Console.WriteLine("线程池工作线程id: {0}", Thread.CurrentThread.ManagedThreadId);
}

//执行的流程是:先执行Test--->Callback--->task.ContinueWith
static void Main(string[] args)
{
   AsynchronousTask d = Test;
   Console.WriteLine("Option 1");
   Task<string> task = Task<string>.Factory.FromAsync(
         d.BeginInvoke("AsyncTaskThread", Callback, "委托异步调用"), d.EndInvoke);
   task.ContinueWith(t => Console.WriteLine("完成回调, 现在继续! Result: {0}", t.Result));
   while (!task.IsCompleted)
   {
         Console.WriteLine(task.Status);
         Thread.Sleep(TimeSpan.FromSeconds(0.5));
   }
   Console.WriteLine(task.Status);
}
}
</code></pre>
<h4 id="262-不带回调方式的">2.6.2 不带回调方式的</h4>
<pre><code class="language-c#">class Program
{
private delegate string AsynchronousTask(string threadName);
private static string Test(string threadName)
{
   Console.WriteLine("开始...");
   Console.WriteLine("线程池是线程吗: {0}", Thread.CurrentThread.IsThreadPoolThread);
   Thread.Sleep(TimeSpan.FromSeconds(2));
   Thread.CurrentThread.Name = threadName;
   return string.Format("线程名称: {0}", Thread.CurrentThread.Name);
}

//执行的流程是:先执行Test--->task.ContinueWith
static void Main(string[] args)
{
   AsynchronousTask d = Test;
   Task<string> task = Task<string>.Factory.FromAsync(
         d.BeginInvoke, d.EndInvoke, "AsyncTaskThread", "委托异步调用");
   task.ContinueWith(t => Console.WriteLine("任务完成，现在运行一个延续! Result: {0}", t.Result));
   while (!task.IsCompleted)
   {
         Console.WriteLine(task.Status);
         Thread.Sleep(TimeSpan.FromSeconds(0.5));
   }
   Console.WriteLine(task.Status);
}
}
</code></pre>
<h4 id="263-task启动带参数和返回值的函数任务">2.6.3 Task启动带参数和返回值的函数任务</h4>
<h5 id="方法1">方法1</h5>
<pre><code class="language-c#">private int MyTest(object i)
{
this.Invoke(new Action(() =>
{
   pictureBox1.Visible = true;
}));
System.Threading.Thread.Sleep(3000);
MessageBox.Show("hello:" + i);
this.Invoke(new Action(() =>
{
   pictureBox1.Visible = false;
}));
return 0;
}

private void Call()
{
//Func<string, string> funcOne = delegate(string s){ return "fff"; };
object i = 55;
var t = Task<int>.Factory.StartNew(new Func<object, int>(MyTest), i);
}
</code></pre>
<h5 id="方法2">方法2</h5>
<pre><code class="language-c#">private async Task<int> MyTest(object i)
{
this.Invoke(new Action(() =>
{
   pictureBox1.Visible = true;
}));

HttpClient client = new HttpClient();
var a = await client.GetAsync("http://www.baidu.com");
Task<string> s = a.Content.ReadAsStringAsync();
MessageBox.Show (s.Result);
this.Invoke(new Action(() =>
{
   pictureBox1.Visible = false;
}));
return 0;
}

async private void Call()
{
object i = 55;
var t = Task<Task<int>>.Factory.StartNew(new Func<object, Task<int>>(MyTest), i);
}
</code></pre>
<h5 id="方法3">方法3</h5>
<pre><code class="language-c#">private async void MyTest()
{
this.Invoke(new Action(() =>
{
   pictureBox1.Visible = true;
}));
HttpClient client = new HttpClient();
var a = await client.GetAsync("http://www.baidu.com");
Task<string> s = a.Content.ReadAsStringAsync();
MessageBox.Show (s.Result);
this.Invoke(new Action(() =>
{
   pictureBox1.Visible = false;
}));
}

private void Call()
{
var t = Task.Run(new Action(MyTest));
//相当于
//Thread th= new Thread(new ThreadStart(MyTest));
//th.Start();
}
</code></pre>
<h3 id="27使用iprogress">2.7　使用IProgress</h3>
<p><code>IProgress<in T></code>只提供了一个方法<code>void Report(T value)</code>，通过<code>Report</code>方法把一个<code>T</code>类型的值报告给<code>IProgress</code>，然后<code>IProgress<in T></code>的实现类<code>Progress<in T></code>的构造函数接收类型为<code>Action<T></code>的形参，通过这个委托让进度显示在<code>UI</code>界面中。</p>
<pre><code class="language-c#">class Program
{
static void DoProcessing(IProgress<int> progress)
{
   for (int i = 0; i <= 100; ++i)
   {
         Thread.Sleep(100);
         if (progress != null)
         {
            progress.Report(i);
         }
   }
}

static async Task Display()
{
   //当前线程
   var progress = new Progress<int>(percent =>
   {
         Console.Clear();
         Console.Write("{0}%", percent);
   });
   //线程池线程
   await Task.Run(() => DoProcessing(progress));
   Console.WriteLine("");
   Console.WriteLine("结束");
}

public static void Main()
{
   Task task = Display();
   task.Wait();
}
}
</code></pre><br><br>
来源：https://www.cnblogs.com/zhaoshujie/p/11082753.html

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C# Task详解