Task.Run()方法总结

一、从异步方法的声明说起

无返回值的类型异步方法

（1）public async Task MethodName()

带返回值类型的异步方法

（2）public async Task<TResult> MethodName()

注意有无返回值只是相对于同步方法来说的，其实直接执行异步方法（不与await结合使用）是有返回值的，分别返回 Task、Task<TResult>

要注意的是 异步 lambda表达式 与 异步方法 一样，使用 Func委托 直接调用也有相应的返回值 Task 或 Task<TResult>，自然也可以 结合 await 使用

无返回值的类型异步方法对应的 lambda

（1）async () => {}

对应于Func委托：Func<Task>

带返回值类型的异步方法对应的 lambda

（2）async () => { return TResult; }

对应于Func委托：Func<Task<TResult>>

接下来简单演示一下上述问题

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class TaskSummary
    {
        public static async void RunTaskSummary()
        {
            AsyncMethodDemo();
            AsyncLambdaDemo();
        }

        public static async void AsyncLambdaDemo()
        {
            Func<Task> asyncLambda = async () => { Console.WriteLine("[AsyncLambda] Hello, Lambda"); };
            Task task = asyncLambda();
            Console.WriteLine($"[AsyncLambdaDemo] AsyncLambda()返回值为 {task}");

            Func<Task<string>> asyncParamLambda = async () => 
            {
                Console.WriteLine("[AsyncParamLambda] Hello, Param Lambda");
                return "AsyncParamLambda Return Value";
            };

            Task<string> task2 = asyncParamLambda();
            Console.WriteLine($"[AsyncLambdaDemo] AsyncParamLambda()返回值为 {task2}");
            Console.WriteLine($"[AsyncLambdaDemo] AsyncParamLambda()返回值参数为 {task2.Result}");
        }

        public static async Task AsyncMethodDemo()
        {
            Task task = AsyncMethod();
            Console.WriteLine($"[AsyncMethodDemo] AsyncMethod()返回值为 {task}");

            Task<string> task2 = AsyncParamMethod();
            Console.WriteLine($"[AsyncMethodDemo] AsyncParamMethod()返回值为 {task2}");
            Console.WriteLine($"[AsyncMethodDemo] AsyncParamMethod()返回值参数为 {task2.Result}");
        }

        private static async Task<string> AsyncParamMethod()
        {
            Console.WriteLine("[AsyncMethod] Hello, Param AsyncMethod");
            return "AsyncParamMethod Return Value";
        }

        public static async Task AsyncMethod()
        {
            Console.WriteLine("[AsyncMethod] Hello, AsyncMethod");
        }
    }
}
[AsyncMethod] Hello, AsyncMethod
[AsyncMethodDemo] AsyncMethod()返回值为 System.Threading.Tasks.Task`1[System.Threading.Tasks.VoidTaskResult]
[AsyncMethod] Hello, Param AsyncMethod
[AsyncMethodDemo] AsyncParamMethod()返回值为 System.Threading.Tasks.Task`1[System.String]
[AsyncMethodDemo] AsyncParamMethod()返回值参数为 AsyncParamMethod Return Value
[AsyncLambda] Hello, Lambda
[AsyncLambdaDemo] AsyncLambda()返回值为 System.Threading.Tasks.Task`1[System.Threading.Tasks.VoidTaskResult]
[AsyncParamLambda] Hello, Param Lambda
[AsyncLambdaDemo] AsyncParamLambda()返回值为 System.Threading.Tasks.Task`1[System.String]
[AsyncLambdaDemo] AsyncParamLambda()返回值参数为 AsyncParamLambda Return Value

二、Task.Run()

Task.Run()
参数可以为：(1)Action委托

表示无参无返回值的方法
同步方法：public void MethodName()

Lambda： () => {}
(2)Func<Task>委托        
表示无参无返回值的方法
异步方法：public async Task MethodName()

Lambda： async () => {}

此处注意一种用法

符合Func<Task>委托

Task task2 = Task.Run(() => ParamteredAsyncFunc("param"));

public async Task ParamteredAsyncFunc(string param)


Task.Run<TResult>()

带返回值版本的Run()

参数可以为：(1)Func<TResult>
表示无参且具有一个 TResult类型 返回值的方法
应该是表示同步方法

同步方法：public TResult MethodName()
Lambda： ()=>TResult
(2)Func<Task<TResult>>
表示无参且具有一个 Task<TResult>类型 返回值的方法
应该用于异步方法

异步方法：public async Task<TResult> MethodName() 
Lambda： async()=> TResult

 示例如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class TaskRunSummary
    {
        public static async void RunTaskSummary()
        {
            //Task.Run()    Action  Lambda
            Task t1 = Task.Run(() => { Console.WriteLine("Task.Run()    Action  Lambda"); });
            await t1;

            //Task.Run()    Func<Task>  Lambda  Async
            Task t2 = Task.Run(async () => { Console.WriteLine("Task.Run()    Func<Task>  Lambda  Async"); });
            await t2;

            //Task.Run()    Func<Task>  Method  Async
            Task t3 = Task.Run(MethodAsync);
            await t3;

            //Task.Run<TResult>()    Func<TResult>  Lambda
            Task<string> t4 = Task.Run<string>(() => { Console.WriteLine("Task.Run<TResult>()    Func<TResult>  Lambda"); return "Task.Run<TResult>()    Func<TResult>  Lambda Return Value"; });
            Console.WriteLine(await t4);

            //Task.Run<TResult>()    Func<Task<TResult>>  Lambda  Async
            Task<string> t5 = Task.Run<string>(async () => { Console.WriteLine("Task.Run<TResult>()    Func<Task<TResult>>  Lambda  Async"); return "Task.Run<TResult>()    Func<Task<TResult>>  Lambda Async  Return Value"; });
            Console.WriteLine(await t5);

            //Task.Run<TResult>()    Func<Task<TResult>>  Method  Async
            Task<string> t6 = Task.Run<string>(new Func<Task<string>>(ParameteredMethodAsync));
            Console.WriteLine(await t6);
        }

        public static async Task MethodAsync()
        {
            Console.WriteLine("Task.Run()    Func<Task>  Method  Async");
        }

        public static async Task<string> ParameteredMethodAsync()
        {
            Console.WriteLine("Task.Run<TResult>()    Func<Task<TResult>>  Method  Async"); 
            return "Task.Run<TResult>()    Func<Task<TResult>>  Method Async  Return Value";
        }
    }
}

三、注意一点

Task<TResult>.Start()会异步执行，而对TResult的引用会阻塞直到Task执行完毕

转载于:https://www.cnblogs.com/liupy/p/10822816.html