Task class example

 

一、Task class example - 任務無需取得結果

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Action<object> action = (object obj) =>
            {
                Console.WriteLine("obj = {0}, Task.CurrentId = {1}, Thread.CurrentThread.ManagedThreadId = {2}",
                obj, Task.CurrentId,
                Thread.CurrentThread.ManagedThreadId);
            };
            // .NET framework 4.0 開始提供 Task 類別。
            Task alpha = new Task(action, "alpha");
            alpha.Start();

            //---------------------------------------------------------------
            Task beta = new Task(
                (object obj) =>
                {
                    Console.WriteLine("obj = {0}, Task.CurrentId = {1}, Thread.CurrentThread.ManagedThreadId = {2}",
                        obj,
                        Task.CurrentId,
                        Thread.CurrentThread.ManagedThreadId);
                }, "beta");
            beta.Start();

            //---------------------------------------------------------------
            // 已不需要固定呼叫 Start(); 了
            Task delta = Task.Factory.StartNew(action, "delta");

            //---------------------------------------------------------------
            // .NET framework 4.5 的 Task 類別新增了靜態方法 Run。
            // 已不需要固定呼叫 Start(); 了
            Task gamma = Task.Run(() =>
            {
                Console.WriteLine("obj = {0}, Task.CurrentId = {1}, Thread.CurrentThread.ManagedThreadId = {2}",
                    "gamma",
                    Task.CurrentId, Thread.CurrentThread.ManagedThreadId);
            });

            Console.ReadKey();
        }
    }
}

使用 Task 類別有三種寫法

1、Task.Start();

2、Task.Factory.StartNew

3、Task.Run(() =>{});

 

二、Task<TResult> - 任務需要取得結果

1、使用 Task.Result 屬性來取得函式執行結果

a、Task<string>.Run(() =>{}); 型式

using System;
using System.Threading.Tasks;


namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Task<string> t = Task<string>.Run(() =>
            {
                return "test";
            });

            Console.WriteLine(t.Result);

            Console.ReadKey();
        }
    }
}

 

b、Task.Start 型式

using System;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            string mission = "Landing Mars";
            Task<string> task = new Task<string>(execute, mission);    // 建立工作。

            task.Start();   // 起始工作。

            task.Wait();    // 等待工作。

            // 取得結果。
            Console.WriteLine(task.Result);

            Console.ReadKey();
        }

        static string execute(object state)
        {
            return (string)state + " was mission complete!";
        }
    }
}

 

c、使用 GetAwaiter、GetResult 方法

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Task<string> task = Task.Run(() =>
            {
                Console.WriteLine("processing...");
                Thread.Sleep(2000);
                return "complete";
            });

            System.Runtime.CompilerServices.TaskAwaiter<string> awaiter = task.GetAwaiter();
            awaiter.OnCompleted(() =>
            {
                string result = awaiter.GetResult();
                Console.WriteLine("the result is " + result);
            });

            Console.ReadKey();
        }
    }
}

 

三、其他範例

1、示範 IsCompleted 屬性與 Wait 方法的使用

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Task task = Task.Run(() =>
            {
                Console.WriteLine("processing...");
                Thread.Sleep(2000);
            });

            Console.WriteLine("task is complete? " + task.IsCompleted);

            task.Wait();
            Console.WriteLine("task is complete? " + task.IsCompleted);

            Console.ReadKey();
        }
    }
}

IsCompleted 屬性用來判斷 Task 的委派方法是否已經執行完畢。(不管結果是否會跳出 exception)

Wait 方法用來確保 Task 的委派方法會執行完畢。

 

參考資料：

Task Class

Task<TResult> Class

Start may not be called on a promise-style task.