Background Worker Queue in C#

Sometimes it is required to run multimple tasks in the background, while one task can only start after another has finished. In this case a simple background queue based on the C# TPL can be used.

Most of the time a simple Task.Run() can be used to do work on the background thread pool. But when one has to process multiple tasks one after the other this does not work any more since using Task.Run() does not guarantee any order for the processed tasks.

In this case the following code can be used to have a background queue and execute tasks one after the other.

var queue = new BackgroundQueue();
queue.QueueTask(() => { /* Do some work */ });
queue.QueueTask(() => { /* Do some more work */ });
var result = await queue.QueueTask(() => { return result; });

Here is the code for the background queue class:

public class BackgroundQueue
{
  private Task previousTask = Task.FromResult(true);
  private object key = new object();

  public Task QueueTask(Action action)
  {
    lock (key)
    {
      previousTask = previousTask.ContinueWith(
        t => action(),
        CancellationToken.None,
        TaskContinuationOptions.None,
        TaskScheduler.Default);
      return previousTask;
    }
  }

  public Task<T> QueueTask<T>(Func<T> work)
  {
    lock (key)
    {
      var task = previousTask.ContinueWith(
        t => work(), 
        CancellationToken.None,
        TaskContinuationOptions.None,
        TaskScheduler.Default);
      previousTask = task;
      return task;
    }
  }
}

Twitter  facebook  Google+