What are Foreground and Background Threads?

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Threads are means to parallelize the work being done so that a given task can be accomplished quickly. There exists two broad classification of threads they are called as Foreground and Background Threads. Let us look at them one by one with the help of some examples. Here we will be seeing some examples from the c# context.


Foreground Thread

  • These are the threads which are created by default.
  • These Threads run until its task gets finished and is not dependent on other threads such as other foreground threads.
  • In other words it can be said that an application is kept alive until all its Foreground thread completes its execution and terminates.
  • Foreground Threads are mainly used to perform Application critical tasks such as processing the application data which is required to be shown in the User Interface.
  • Syntax for creating a Foreground Thread:

Creating a Foreground Thread
Creating a Foreground Thread



Background Thread

  • Background Threads are the threads whose lifetime depends on the Foreground Thread of the application which is running.
  • If all the Foreground Thread of an application exits then the application kills all the background threads which are running.
  • Background thread is mainly used to perform support operations or book keeping operations such as logging the application activity which are not run in a high priority.
  • Syntax for creating a Background thread:

Creating a Background Thread
Creating a Background Thread


There is a property called IsBackground which determines whether the given thread should run as a Foreground Thread or Background Thread. By default value of this property is false. 

Having understood the basics of Foreground and Background Threads lets look at them in Operation:

Scenario 1:

We will create one Foreground Thread and One Background Thread with identical tasks and observe the output in the console.

Foreground and Background Thread Program
One Foreground and One Background Thread Code

Foreground and Background thread result
Output for One Foreground and One Background Thread


As you can see from the output both the foreground and background thread executed its job and exited even though Main Thread had exited long ago.

Its because we had one foreground thread which was running when the Main thread exited, therefore background thread can run with the foreground thread to complete its operation.

Scenario 2:

In this case we will have two threads configured as background threads and start them parallelly and observe the output.

Code for Background Thread
Method Handlers for the two Background Threads

  
Starting Background Threads
Configuring and starting two background threads


OUTPUT for two background threads
Output for two background threads


Conclusion 

As its evident from the output obtained in Scenario-2 The Background threads were unable to perform its task of printing to the console 5 times and the application exited as soon as the Main thread exited.
Therefore the lifetime of the background thread depends on the Foreground threads running in the current application context.

I hope this was useful, If you know of some other interesting cases related to Foreground and Background Threads do leave a comment below.

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