C#中处理耗时任务的几种方式

0、准备

首先，我们先创建几个耗时任务：

public class TestTasks
{
    //无参、无返回值任务
    public void Task1()
    {
        Console.WriteLine("task1.");
        Thread.Sleep(5000);
        Console.WriteLine("task1 completed.");
    }

    //有参数、无返回值任务
    public void Task2(int x)
    {
        if (x < 2000)
        {
            x += 2000;
        }
        Console.WriteLine("task2.");
        Thread.Sleep(x);
        Console.WriteLine("task2 completed.");
    }

    //有参数，有返回值任务
    public int Task3(int x)
    {
        if (x < 2000)
        {
            x += 2000;
        }
        Console.WriteLine("task3.");
        Thread.Sleep(x);
        Console.WriteLine("task3 completed.");
        return x;
    }
}

1、创建新线程执行方法

var tt = new TestTasks();

new Thread(tt.Task1).Start();

//针对有参数的任务，需要用Lambda进行包装或者使用ParameterizedThreadStart对象
new Thread(x=>tt.Task2((int)x)).Start((object)1000);

//使用ParameterizedThreadStart，要求要执行的方法参数必须为object，同时无返回值。
//new Thread(new ParameterizedThreadStart(tt.Task2)).Start((object)1000);

注意：使用该方式无法执行带返回值的方法。

推荐指数：★★

2、使用异步调用方式执行方法

var tt = new TestTasks();

Action ac = tt.Task1;
Action<int> ac2 = tt.Task2;
ac.BeginInvoke(null, null);
ac2.BeginInvoke(1000, null, null);

//以下是调用有参数，有返回值的方法
//代码一
private delegate int AsyncCaller(int x); //该代码放在方法体外部

AsyncCaller ac = new AsyncCaller(tt.Task3);
var asyncResult =  ac.BeginInvoke(1000,null,null);
int result = ac.EndInvoke(asyncResult); //接收返回值

//代码二，使用Func简化代码
Func<int,int> ac = tt.Task3;
var asyncResult =  ac.BeginInvoke(1000,null,null);
int result = ac.EndInvoke(asyncResult);

注意：通过这种方式生成新线程是运行在后台的（background）,优先级为normal

推荐指数：★★

3、通过ThreadPool（线程池）执行方法

var tt = new TestTasks();

ThreadPool.QueueUserWorkItem(o => tt.Task1());
ThreadPool.QueueUserWorkItem(o => tt.Task2(1000));

注意：该方式不支持返回值，可以将返回值保存在引入类型的参数上，然后进行迂回实现

推荐指数：★★★

4、通过BackgroundWorker（后台Worker）执行方法

var tt = new TestTasks();

var bw = new BackgroundWorker();
bw.DoWork += (sender, e) => tt.Task1();
bw.DoWork += (sender, e) => tt.Task2(1000); 

//要接收返回值，必须将返回值赋值给Result。
bw.DoWork += (sender, e) => e.Result = tt.Task3(1000);

bw.RunWorkerAsync();

//注册事件使用返回值
bw.RunWorkerCompleted += (sender, e) => Console.WriteLine(e.Result);

注意：使用BackgroundWorker注册DoWork事件的任务只能挨个执行，如果要同时执行多个任务，需要多个BackgroundWorker。要使用返回值，一定要记得赋值给Result。

推荐指数：★★

5、同时Task执行方法

var tt = new TestTasks();

var t1 = Task.Factory.StartNew(tt.Task1);
var t2 = Task.Factory.StartNew(() => tt.Task2(1000));
var t3 =Task.Factory.StartNew(() => tt.Task3(1000));

//等待t1,t2,t3执行完成
Task.WaitAll(t1,t2,t3);
Console.WriteLine(t3.Result);

注意：Task具有灵活的控制能力，同时可以单个等待，多个等待。

推荐指数：★★★★★

6、使用async/await执行方法

private async void AsyncRunTask()
{
    var tt = new TestTasks();
    await Task.Factory.StartNew(tt.Task1);
    await Task.Factory.StartNew(() => tt.Task2(1000));
    var result = await Task.Factory.StartNew(() => tt.Task3(1000));
    Console.WriteLine(result);
}

AsyncRunTask();
Console.WriteLine("不用等待，我先执行了。");

注意：需要Framework4.5的支持

推荐指数：★★★★

The End

没有原理，没有言语，相信以大家聪明的大脑，已经学会如何在C#中执行耗时任务和使用多线程了。

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