C ＃ basic 5-asynchronous

asynchronous

Official document - Asynchronous model

Asynchrony is a very important concept in programming , C# The principle of implementing asynchrony is that the compiler converts the code into a state machine , Trace code execution to await Pause when and continue when the background job is completed .

if necessary I/O binding （ For example, request data from the network 、 Access the database or read and write to the file system ）, You need to use asynchronous programming . You can also use CPU Binding code （ For example, perform costly calculations ）, For writing asynchronous code , This is a good plan .

The following example CPU Binding code Asynchronous case of ：

The main thread ： Trigger the key to execute the background task -> count down -> Press any key to exit the program

Background thread ： Get into -> count down -> sign out

Task class

Create an asynchronous task and execute

	public static async Task SimpleWriteAsync()
    {
    
        string filePath = "simple.txt";
        string text = $"Hello World!";

        await File.WriteAllTextAsync(filePath, text);
    }
    static void Main()
    {
    
        SimpleWriteAsync().Wait();
    }

about I/O Binding code , Waiting for one in async Return in method Task or Task The operation of .

about CPU Binding code , Wait for a use Task.Run Method to start the operation in the background thread .

using System;
using System.Threading.Tasks;
using System.Threading;
// 1  Declaration delegation 
public delegate void onCountTime();
class Program
{
    
    //  Simulate some time-consuming and complex operations 
    static string CountTimer(string s, int start, int dt)
    {
    
        int counter = start;
        while (counter > 0)
        {
    
            Console.WriteLine(s + counter);
            Thread.Sleep(dt);
            counter--;
        }
        return s + " End of the timing ";
    }
    // 4  Asynchronous event handler 
    static async void OnClicked()
    {
    
        string result = "";
        Console.WriteLine("async OnClicked start");
        // 4.1  Wait for asynchronous task   Until the end of the mission 
        await Task.Run(() => {
     result = CountTimer("task:", 3, 2000); });
        // 4.2  Print the results 
        Console.WriteLine(result);
        Console.WriteLine("async OnClicked end");
    }
    static void Main()
    {
    
        //  Instantiate an instance of a button class 
        Button btn = new Button();
        // 5  Bind the event handler for the click of the button 
        btn.Clicked += OnClicked;
        // 6 ( Simulate the user pressing the key ) Manual call event 
        btn.CallClicked();
        // 7  Process the task of pressing keys in the background   The current thread continues execution 
        Console.WriteLine(CountTimer("main:", 3, 500));
        Console.WriteLine("pressed any key to exit");
        //  Press any key to exit the program 
        Console.ReadKey();
    }
    //  Button class 
    class Button
    {
    
        // 2  Claim event 
        public event onCountTime Clicked;
        // 3  Call the event that the user presses the key 
        public void CallClicked()
        {
    
            Clicked?.Invoke();
        }
    }
}

//  Print the results :
async OnClicked start
task:3
main:3
main:2
main:1
main: End of the timing 
pressed any key to exit
task:2
task:1
task: End of the timing 
async OnClicked end