Creating and aborting a low-priority background thread

The reason we want to have a look at a background thread specifically is because by default, all threads created by the main app thread or Thread class constructor are foreground threads. So, what exactly separates a foreground thread from a background thread? Well, background threads are identical to foreground threads with the exception that if all foreground threads are terminated, the background threads are stopped too. This is useful if you have a process in your application that must not stop the application from terminating. In other words, while your application is running, the background thread must continue to run.

Getting ready

We will create a simple application that defines the thread created as a background thread. It will then suspend, resume, and abort the thread.

How to do it…

  1. Create a new class library by right-clicking on your solution and selecting Add and then New Project from the context menu:
    How to do it…
  2. From the Add New Project dialog screen, select Class Library from the installed templates and call your class Chapter7:
    How to do it…
  3. Your new class library will be added to your solution with a default name Class1.cs, which we renamed to Recipes.cs in order to distinguish the code properly. You can, however, rename your class to whatever you like if that makes more sense to you.
  4. To rename your class, simply click on the class name in Solution Explorer and select Rename from the context menu:
    How to do it…
  5. Visual Studio will ask you to confirm a rename of all references to the code element Class1 in the project. Just click on Yes:
    How to do it…
  6. The following class is added to your Chapter7 library project:
    namespace Chapter7
{
    public class Recipes
    {
        
    }
}
  7. Inside the Recipes class, add a method called DoBackgroundTask() with the public void modifiers, and add the following console output to it:
    public void DoBackgroundTask()
        {
            WriteLine($"Thread {Thread.CurrentThread.ManagedThreadId} has a threadstate of {Thread.CurrentThread.ThreadState} with {Thread.CurrentThread.Priority} priority");
            WriteLine($"Start thread sleep at {DateTime.Now.Second} seconds");
            Thread.Sleep(3000);
            WriteLine($"End thread sleep at {DateTime.Now.Second} seconds");
        }

    Note

    Make sure that you have added the using statements for System.Threading and static System.Console to your using statements.

  8. Inside the console application called CodeSamples, added previously, add a reference to the Chapter7 class library by right-clicking on References under the CodeSamples project and selecting Add Reference from the context menu:
    How to do it…
  9. In the Reference Manager window, select the Chapter7 solution by going to Projects | Solutions. This will allow you to use the classes we just created in your console application:
    How to do it…
  10. In the void Main method, create a new instance of your Recipes class and add it to a new thread called backgroundThread. Define this newly created thread to be a background thread and then start it. Finally, set the thread to sleep for five seconds. We need to do this because we have created a background thread that is set to sleep for three seconds. Background threads do not prohibit foreground threads from terminating. Therefore, if the main application thread (which is by default a foreground thread) terminates before the background thread completes, the application will terminate and also terminate the background thread:
    static void Main(string[] args)
{
    Chapter7.Recipes oRecipe = new Chapter7.Recipes();
    var backgroundThread = new Thread(oRecipe.DoBackgroundTask);
    backgroundThread.IsBackground = true;
    backgroundThread.Start();
    Thread.Sleep(5000);
}

    Note

    Please note that you might need to add the using System.Threading; directive.

  11. Run your console application by pressing F5. You will see that we have created a background thread with a normal priority:
    How to do it…
  12. Let's modify our thread and set its priority down to low. Add this line of code to your console application: backgroundThread.Priority = ThreadPriority.Lowest;. This line will downgrade the thread priority:
    Chapter7.Recipes oRecipe = new Chapter7.Recipes();
var backgroundThread = new Thread(oRecipe.DoBackgroundTask);
backgroundThread.IsBackground = true;
backgroundThread.Priority = ThreadPriority.Lowest;
backgroundThread.Start();
Thread.Sleep(5000);
  13. Run your console application again. This time, you will see that the thread priority has been set to the lowest priority:
    How to do it…
  14. Go back to your DoBackgroundTask() method and add Thread.CurrentThread.Abort(); right before Thread.Sleep(3000); is called. This line will prematurely kill the background thread. Your code should look like this:
    public void DoBackgroundTask()
{
    WriteLine($"Thread {Thread.CurrentThread.ManagedThreadId} has a threadstate of {Thread.CurrentThread.ThreadState} with {Thread.CurrentThread.Priority} priority");
    WriteLine($"Start thread sleep at {DateTime.Now.Second} seconds");
    Thread.CurrentThread.Abort();
    Thread.Sleep(3000);
    WriteLine($"End thread sleep at {DateTime.Now.Second} seconds");
}
  15. When you run your console application, you will see that the thread is aborted before the Thread.Sleep method is called. Aborting a thread in this way, however, is generally not recommended:
    How to do it…

How it works…

Being able to create a background thread is a great way to work on a different thread from the main thread while not interfering with the process of the main application thread. Another added benefit is that the background thread is terminated as soon as the main application thread is completed. This process ensures that your application will terminate gracefully.

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