异步编程(二)

3.TAP 基于任务的异步编程

1..NET4.0 引入了Task任务，Task的使用

Task task = new Task(()=> {
                for (int i = 0; i < 1000; i++)
                {
                    Console.WriteLine("task run");
                }               
            });
            task.Start();

这是简单的启动任务：下面是task的一些版本

public Task(Action action);
      
        public Task(Action action, CancellationToken cancellationToken);
      
        public Task(Action action, TaskCreationOptions creationOptions);
        
        public Task(Action<object> action, object state);
        
        public Task(Action action, CancellationToken cancellationToken, TaskCreationOptions creationOptions);
      
        public Task(Action<object> action, object state, CancellationToken cancellationToken);
       
        public Task(Action<object> action, object state, TaskCreationOptions creationOptions);
       
        public Task(Action<object> action, object state, CancellationToken cancellationToken, TaskCreationOptions creationOptions);

2.创建一个带取消功能的Task

CancellationTokenSource tokenSource = new CancellationTokenSource();
Task task = new Task(() => {
                for (int i = 0; i < 1000000; i++)
                {
                    Console.WriteLine("task run");
                }

            }, tokenSource.Token);
           task.Start();

这里使用Task的task 将会观察CancellationToken，当调用

tokenSource.Cancel() 便可终止任务

 

3.使用TaskFactory来建立任务

Task.Factory.StartNew(() => {
                Console.WriteLine("task is running");
            });

 

4.任务的管理

1.WaitAny

var task1= Task.Factory.StartNew(() => {
                for (int i = 0; i < 20; i++)
                {
                    Console.WriteLine("task1 is running");
                }                
            });

            var task2= Task.Factory.StartNew(() => {
                Console.WriteLine("task2 is running");
            });

            var taskid= Task.WaitAny(task1, task2);
            Console.WriteLine(taskid);

Task.WaitAny(task1, task2) 返回的是完成任务的id，表示只要有一个任务完成就返回完成任务的Id 不然一直阻塞；

 

2.WaitAll

var task1= Task.Factory.StartNew(() => {
                for (int i = 0; i < 20; i++)
                {
                    Console.WriteLine("task1 is running");
                }                
            });

            var task2= Task.Factory.StartNew(() => {
                Console.WriteLine("task2 is running");
            });

            Task.WaitAll(task1, task2);
            Console.WriteLine("All Task Completed");

WaitAll 将等待全部任务的完成，不然将一直阻塞；

 

3.ContinueWith

这个最有意思，在传统的同步编程模式下，咱们喜欢程序串行执行，而后获得结果，可是在多线程编程中，任务都是并发的，很难再使用同步的方法来编程多线程，可是Task提供了这个ContinueWith，当异步任务完成的时候，接着执行这个ContinueWith，任务执行有返回结果，则使用相应版本的ContinueWith来执行，而后总体的执行就想同步编程那样，很方便；

var task1= Task.Factory.StartNew(() => {
                for (int i = 0; i < 20; i++)
                {
                    Console.WriteLine("task1 is running");
                }                
            });
            task1.ContinueWith((ta)=> {
                Console.WriteLine("task1 continuewith");
            });

 

带返回值版本：

 

var task1= Task.Factory.StartNew(() => {
                for (int i = 0; i < 20; i++)
                {
                    Console.WriteLine("task1 is running");
                }

                return "Hello,world";
            });
            task1.ContinueWith((ta)=> {
                Console.WriteLine("task1 continuewith reulst"+ta.Result);
            });

 

4.任务的阻塞

var task1= Task.Factory.StartNew(() => {
                for (int i = 0; i < 20; i++)
                {
                    Console.WriteLine("task1 is running");
                }

                return "Hello,world";
            });
            task1.Wait();
            Console.WriteLine("task1 completed");

waite 将阻塞线程，知道task的完成