async-await

问题 I created following code: using System; using System.Threading.Tasks; namespace ConsoleApplication2 { class Program { static void Main() { Console.WriteLine("M Start"); MyMethodAsync(); Console.WriteLine("M end"); Console.Read(); } static async Task MyMethodAsync() { await Task.Yield(); Task<int> longRunningTask = LongRunningOperationAsync(); Console.WriteLine("M3"); //and now we call await on the task int result = await longRunningTask; //use the result Console.WriteLine(result); } static

问题 let x = 0; async function test() { x += await 5; console.log('x :', x); } test(); x += 1; console.log('x :', x); The values of x logged are 1 and 5 . My question is: why is the value of x 5 on second log? If the test is executed after x += 1 (since it is an async function) then the value of x is 1 by the time test is executed, so x += await 5 should make the value of x 6 . 回答1: TL;DR: Because += reads x before, but writes it after it has changed, due to await . async functions run

问题 I have some code of the following form: static async Task DoSomething(int n) { ... } static void RunThreads(int totalThreads, int throttle) { var tasks = new List<Task>(); for (var n = 0; n < totalThreads; n++) { var task = DoSomething(n); tasks.Add(task); } Task.WhenAll(tasks).Wait(); // all threads must complete } Trouble is, if I don't throttle the threads, things start falling apart. Now, I want to launch a maximum of throttle threads, and only start the new thread when an old one is

问题 I have some code of the following form: static async Task DoSomething(int n) { ... } static void RunThreads(int totalThreads, int throttle) { var tasks = new List<Task>(); for (var n = 0; n < totalThreads; n++) { var task = DoSomething(n); tasks.Add(task); } Task.WhenAll(tasks).Wait(); // all threads must complete } Trouble is, if I don't throttle the threads, things start falling apart. Now, I want to launch a maximum of throttle threads, and only start the new thread when an old one is

问题 I want to run a processing loop on a separate thread: _processingThread = new Thread(new ThreadStart(DoWork))); But DoWork needs to be async: private async Task QueueProcessorDoWork() { while (true) { await something(); } } How can I connect the two together? When I add async Task , it doesn't match the parameter of ThreadStart. It is possible to make the method that sets up the thread async Task , I think, but I am not sure if that would help. What's the best solution here? I need my thread

问题 I want to iterate over a CSV file in node, and for each row, call an asynchronous function and wait for it to complete. How can I do this? I have: const getFile = async function(url) { const response = await page.goto(url, { waitUntil: 'networkidle2' }); await page.waitFor(3000); const ad = await page.waitForSelector('div.chart'); await ad.screenshot({ path: path }); }; fs.createReadStream(fname) .pipe(csv()) .on('data', (row) => { let id = row.ad_id; let url = 'xxxx' + id; await getFile(path

问题 Trying to get stored data by SharedPreferences But does not work .. my main.dart : Widget build(BuildContext context) { return StreamProvider<User>.value( value: AuthService().user, child: FutureBuilder<String>( future: SaadConstants.setValueFromLocal('app_lang','ar'), builder: (BuildContext context, AsyncSnapshot<String> snapshot){ return MaterialApp( debugShowCheckedModeBanner: false, home: Scaffold( body:Wrapper(), ), ); } ), ); } my wrapper : @override Widget build(BuildContext context) {

问题 Trying to get stored data by SharedPreferences But does not work .. my main.dart : Widget build(BuildContext context) { return StreamProvider<User>.value( value: AuthService().user, child: FutureBuilder<String>( future: SaadConstants.setValueFromLocal('app_lang','ar'), builder: (BuildContext context, AsyncSnapshot<String> snapshot){ return MaterialApp( debugShowCheckedModeBanner: false, home: Scaffold( body:Wrapper(), ), ); } ), ); } my wrapper : @override Widget build(BuildContext context) {

问题 I have a custom user manager class (ASP .NET Identity). I want to override the FindByIdMethod, so that it automatically loads the role names for the user model. This is the only method I am overriding. I am using Microsoft.Identity nuget packages version 2.2.1, Asp.Net Framework. However, the code below throws a StackOverflow exception - at await base.FindByIdAsync(userId); public class MyUserManager : UserManager<MyUser>, IMyUserManager { public override async Task<MyUser> FindByIdAsync

问题 I have gotten it through my head (perhaps incorrectly) that library methods that take some time should generally be made async. Is that true, and if so, how should that be done when there is nothing to await within the library method? I am designing my own library with the method: public Dictionary<FunctionEnum, double> Evaluate(Func<uint,uint> algorithm, IList<double> suggestedList) It takes in a method that takes a uint and returns a uint and uses that method many times over. In brief, I'm