Event-driven asynchronous mode

Event-driven asynchronous mode

Objective

What do you mean, events ? What do you mean drive? ? What's the asynchronous thing? ? I know all these words, one by one. , but I don't know what it means to practice. , Don't worry . , look down . .

In the next article , I'll specialize in concurrency , synchronization , asynchronous, and event-driven technology .

event-based Asynchronous (EAP)provides a simple way of handling in a multithreaded environment.

It has several features:

1. Support Cancellation

2. The WPF or windows Form space can be updated safely

3. The exception information can be queried in the completion event .

4. "In the background" performs time-consuming tasks ( such as downloads and database Operations ), but does not end your application

5. Perform multiple operations at the same time and receive a notification when each operation completes .

6. Wait for the resource to become available but not stop ("hang") you have to the application

7. Communicating with a pending asynchronous operation using a familiar event and delegate model

EAP is just a pattern , So these features must all be implemented by the implementation . in the . NET There are a few classes that support this pattern , The most famous is BackgroundWorker and the System.Net.WebClient the .

The essence of this pattern is that each class provides a number of similar members to manage multithreading , For example :

   Public byte[] Downloaddata (Uri address);        public void DownloadDataAsync (Uri address);        public void DownloadDataAsync (Uri address, Object usertoken);        public event Downloaddatacompletedeventhandler downloaddatacompleted;         public void CancelAsync (); Cancels the operation public        bool IsBusy {get;}//Gets whether the information is running.

Here's an example of using WebClient :

    Class program    {        static void Main (string[] argss)        {            var WC = new WebClient ();            Wc. downloadstringcompleted + = (sender, args) =                {                    if (args. Cancelled)                    {                        Console.WriteLine ("Canceled");                    }                    else if (args. Error! = null)                    {                        Console.WriteLine ("Exception:" + args. error.message);                    }                    else                    {                        Console.WriteLine (args. Result.length + "chars were downloaded");                    }                 ;            Wc. DownloadStringAsync (New Uri ("http://www.cnblogs.com/LoveJenny/"));             Console.ReadLine ();        }      

Analysis : Although a WebClient has multiple async methods , they all share the same cancelasyc and the IsBusy Properties , so there can only be one asynchronous operation at a time .

BackgroundWorker

BackgroundWorker is A helper class for managing worker threads under System.ComponentModel , which provides the following features .

1. Support Cancellation

2. The WPF or Windows Forms controls can be updated safely

3. The exception information can be queried in the completion event .

4. Progress can be reported

5. Because the IComponent interface is implemented , It can be used by the designer .

6.BackgroundWorker uses a thread pool , which means you can never call on a backgroundworker thread Abort Method .

    Class program    {        static BackgroundWorker _BW = new BackgroundWorker ();        public static void Mainthread ()        {            _BW. DoWork + = new Doworkeventhandler (_bw_dowork);            _BW. RunWorkerAsync ("Message to Worker");            Console.ReadLine ();        }        static void _bw_dowork (object sender, DoWorkEventArgs e)        {            Console.WriteLine (e.argument);            Do some time-consuming things for            (int i = 0; i < 100000; i++)            {                Console.WriteLine (i);            }        }        static void Main (string[] argss)        {            mainthread ();            Console.ReadLine ();        }      

The following example implements the progress report

Using system;using system.collections.generic;using system.componentmodel;using system.linq;using System.Text;using System.threading;using System.Threading.Tasks; Namespace Event Async {class Program {static void Main (string[] args) {threadbackgroundworker.ma            Inthread ();        Console.ReadLine ();        }} class Threadbackgroundworker {static BackgroundWorker _bw; public static void Mainthread () {_BW = new BackgroundWorker {WORKERREPORTSPR             ogress=true,//Allow report progress workersupportscancellation =true//allow cancellation}; _BW.            DoWork + = new Doworkeventhandler (_bw_dowork); _BW.            ProgressChanged + = new Progresschangedeventhandler (_bw_progresschanged); _BW.            runworkercompleted + = new Runworkercompletedeventhandler (_bw_runworkercompleted); _BW.            RunWorkerAsync ("Hello to Worker"); Console.WriteLine ("Press Enter in the next 5 seconds to canCel. ");             Console.ReadLine (); if (_BW. IsBusy) {_BW.            CancelAsync ();        } console.readline (); } static void _bw_runworkercompleted (Object Sender,runworkercompletedeventargs e) {if (E.cancell            ED)//whether to cancel {Console.WriteLine ("You canceled!");             } else if (E.error!=null) {Console.WriteLine ("Worker Exception" +e.error.tostring ());            } else {Console.WriteLine ("Completed" +e.result);              }} static void _bw_progresschanged (object sender, ProgressChangedEventArgs e) {//Output progress report        Console.WriteLine ("Reacher" +e.progresspercentage+ "%");            } static void _bw_dowork (object sender, DoWorkEventArgs e) {for (int i = 0; I <=100; i+=20) {if (_BW.    cancellationpending) {                E.cancel = true;                Return } _BW.             ReportProgress (i);//Report Progress Thread.Sleep (1000);        } E.result = 123;  }    }}

Analysis:I don't know what this is, though.,What do you want?,but looking at the output, it feels so cool.,It's gorgeous.,if it's used somewhere else ,,like when you're at home on a Web page.,prompt you to load the situation,How much do you suggest when you're on the next piece?,It's cool if you use a good feeling.,Ben Caishuxueqian No learning .,don't know how to apply,wait till you take it slow..

A little knot, please.

Tell the truth.,These things are beyond my personal understanding.,I don't know what that means.,but it was just a bite to finish.,because I think it's like when I was a kid, the teacher let me carry Zi Jing.,that's when I was in elementary school.1Grade,The words are not recognized,let alone understand what Zi Jing means.,but I was carrying it.,as we grow older,,I'm going to understand what it means.,I believe that scholarship is similar .,now because I'm not,Don't understand,you don't learn .,that must be the future .!

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Event-driven asynchronous mode