Tutorial by Examples: await

It is possible to use await expression to apply await operator to Tasks or Task(Of TResult) in the catch and finally blocks in C#6. It was not possible to use the await expression in the catch and finally blocks in earlier versions due to compiler limitations. C#6 makes awaiting async tasks a lot e...

When ASP.NET handles a request, a thread is assigned from the thread pool and a request context is created. The request context contains information about the current request which can be accessed through the static HttpContext.Current property. The request context for the request is then assigned t...

You have to keep the operator precedence in mind when using await keyword. Imagine that we have an asynchronous function which calls another asynchronous function, getUnicorn() which returns a Promise that resolves to an instance of class Unicorn. Now we want to get the size of the unicorn using th...

The await keyword was added as part of C# 5.0 release which is supported from Visual Studio 2012 onwards. It leverages Task Parallel Library (TPL) which made the multi-threading relatively easier. The async and await keywords are used in pair in the same function as shown below. The await keyword is...

await operator and async keyword come together: The asynchronous method in which await is used must be modified by the async keyword. The opposite is not always true: you can mark a method as async without using await in its body. What await actually does is to suspend execution of the code ...

When using async await in loops, you might encounter some of these problems. If you just try to use await inside forEach, this will throw an Unexpected token error. (async() => { data = [1, 2, 3, 4, 5]; data.forEach(e => { const i = await somePromiseFn(e); console.log(i); }); ...

import 'dart:async'; Future main() async { var value = await _waitForValue(); print("Here is the value: $value"); //since _waitForValue() returns immediately if you un it without await you won't get the result var errorValue = "not finished yet"; _waitForValue()...

You can start some slow process in parallel and then collect the results when they are done: Public Sub Main() Dim results = Task.WhenAll(SlowCalculation, AnotherSlowCalculation).Result For Each result In results Console.WriteLine(result) Next End Sub Async Functio...

If we try to change an object on the UI thread from a different thread we will get a cross-thread operation exception: Private Sub Button_Click(sender As Object, e As EventArgs) Handles MyButton.Click ' Cross thread-operation exception as the assignment is executed on a different thread '...

See below for a simple example of how to use async/await to do some time intensive stuff in a background process while maintaining the option of doing some other stuff that do not need to wait on the time intensive stuff to complete. However, if you need to work with the result of the time intensiv...

async and await are two operators that are intended to improve performance by freeing up Threads and waiting for operations to complete before moving forward. Here's an example of getting a string before returning it's length: //This method is async because: //1. It has async and Task or Task<...

Methods that perform asynchronous operations don't need to use await if: There is only one asynchronous call inside the method The asynchronous call is at the end of the method Catching/handling exception that may happen within the Task is not necessary Consider this method that returns a Ta...

The same example above, Image loading, can be written using async functions. This also allows using the common try/catch method for exception handling. Note: as of April 2017, the current releases of all browsers but Internet Explorer supports async functions. function loadImage(url) { return...

You can use async methods to handle asynchronous executions. For example POST and GET requests. Let say below is your get data method. Task<List> GetDataFromServer(int type); You can call that method as shown below var result = await GetDataFromServer(1); However, in real day practic...

Consider a simple asynchronous method: async Task Foo() { Bar(); await Baz(); Qux(); } Simplifying, we can say that this code actually means the following: Task Foo() { Bar(); Task t = Baz(); var context = SynchronizationContext.Current; t.ContinueWith(task...

Consider the following code: public async Task MethodA() { await MethodB(); // Do other work } public async Task MethodB() { await MethodC(); // Do other work } public async Task MethodC() { // Or await some other async work await Task.Delay(100); } ...

Function using promises: function myAsyncFunction() { return aFunctionThatReturnsAPromise() // doSomething is a sync function .then(result => doSomething(result)) .catch(handleError); } So here is when Async/Await enter in action in order to get clean...

const { expect } = require('chai') describe('Suite Name', function() { describe('#method()', function() { it('should run without an error', async function() { const result = await answerToTheUltimateQuestion() expect(result).to.be.equal(42) }) }) })

If the promise doesn't return anything, the async task can be completed using await. try{ await User.findByIdAndUpdate(user._id, { $push: { tokens: token } }).exec() }catch(e){ handleError(e) }