[C#] Multithreading in C# 3 [3] – Foreground and Background Threads

What is a foreground thread and a background thread? What are the differences? Let’s find out.

1. Foreground Threads and Background Threads

Let’s summarize what they are and how they differ:

  • Foreground Threads : The foreground tasks cannot be ignored and must be completed. CLR will not shut down an application until all foreground threads have ended.
  • Background Threads : The background tasks can be terminated at any time. When all foreground threads have terminated, any background threads can be aborted.

2. IsBackground Property

The “Thread” class provides the “IsBackground” property to set or set a value indicating whether or not a thread is a background thread.

public sealed class Thread
  public bool IsBackground { get; set; } // default is false

3. Creating Background Threads

It is easy to create a background thread. You just need to set the “IsBackground” property to true before starting the thread.

public static void Test1()
  Thread printPlus = new Thread(() =>
      for (int i = 0; i < 1000; i++)
        Console.Write("+ ");

  printPlus.IsBackground = true;

  for (int j = 0; j < 20; j++)
    Console.Write("- ");


Note that the “Join()” method is commented out. The result will be quite surprising. As soon as “- ” is printed 20 times, the application is terminated. It does not wait until “+ ” is printed 1000 times.

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