Skip to main content

Task.Yield(...), Task.Delay(...)

I think that a lot of person already heard about these new methods. In this post I want to clarify some things about these new methods that I saw that are not very clear.
We will start with Task.Yield(). The book definition of this method is: “Creates an awaitable that asynchronously yields back to the current context when awaited”. Let see what does it means in reality.
Yield gives us the possibility to leave the current async code (method or lambda expression) and allow other code to run in the underlying thread. Usually this is used when we have long running code that is executed in events (on main UI thread for example). In this case we want to allow other code to be executed on the UI thread. For this purpose the Yield method can be called. The rest of the function that need to be executed is posted back and will be executed after other messages that were waiting were executed.
For example we can have a for in an event handler that process items for a list. To permit the UI to execute not only our code we can use Yield.
public async void StartButton_Click(...)
    for( int i=0; i < list.Count; i++)
        await Task.Yield();
We use await in front of the Yield() because we want to wait until the other messages are processed. On the other side, we can use this method when our application uses threads from ThreadPool. If an action execute for long time, you don’t want other thread to block and wait for that current action. In this situation, using Yield() can permit other actions from the queue to be executed. In this way all the actions will be executed.
In background this method resumes the current action. We can compare this method to be something similar to a pause. When Yield() is called, the remaining action is posted back to the current context (it can be the TaskScheduler.Default or SynchronizationContext). After the rest of the code is executed, the rest of our action is resumed.
When you are working with tasks, especially when you want to simulate some behavior you will need a method to put a task to sleep. Thread.Sleep cannot be found anymore (for Metro style app). This method would put the thread on sleep, but we don’t want to freeze the UI thread or block another thread. Other actions could be executed on this thread.
For this purpose Task.Delay(…) was introduce. We can specify a delay time when the task will be suspended. Other tasks will be able to be executed on that read. In this way all the resources will be used at maximum. Optionally, you can specify a cancelation token that will be used if the task is canceled and stop the delay.


  1. Do not rely on await Task.Yield() to keep a UI responsive!


Post a Comment

Popular posts from this blog

How to check in AngularJS if a service was register or not

There are cases when you need to check in a service or a controller was register in AngularJS.
For example a valid use case is when you have the same implementation running on multiple application. In this case, you may want to intercept the HTTP provider and add a custom step there. This step don’t needs to run on all the application, only in the one where the service exist and register.
A solution for this case would be to have a flag in the configuration that specify this. In the core you would have an IF that would check the value of this flag.
Another solution is to check if a specific service was register in AngularJS or not. If the service was register that you would execute your own logic.
To check if a service was register or not in AngularJS container you need to call the ‘has’ method of ‘inhector’. It will return TRUE if the service was register.
if ($injector.has('httpInterceptorService')) { $httpProvider.interceptors.push('httpInterceptorService&#…

ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

Today blog post will be started with the following error when running DB tests on the CI machine:
threw exception: System.InvalidOperationException: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See for more information. at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName) This error happened only on the Continuous Integration machine. On the devs machines, everything has fine. The classic problem – on my machine it’s working. The CI has the following configuration:

TeamCity.NET 4.51EF 6.0.2VS2013
It seems that there …

Run native .NET application in Docker (.NET Framework 4.6.2)

The main scope of this post is to see how we can run a legacy application written in .NET Framework in Docker.

First of all, let’s define what is a legacy application in our context. By a legacy application we understand an application that runs .NET Framework 3.5 or higher in a production environment where we don’t have any more the people or documentation that would help us to understand what is happening behind the scene.
In this scenarios, you might want to migrate the current solution from a standard environment to Docker. There are many advantages for such a migration, like:

Continuous DeploymentTestingIsolationSecurity at container levelVersioning ControlEnvironment Standardization
Until now, we didn’t had the possibility to run a .NET application in Docker. With .NET Core, there was support for .NET Core in Docker, but migration from a full .NET framework to .NET Core can be costly and even impossible. Not only because of lack of features, but also because once you…