How to implement multi-threading and parallel execute several tasks?

Question

I am new to threaded programming. I have to run few tasks in PARALLEL and in Background (so that main UI execution thread remain responsive to user actions) and wait for eac

Answer 1

You can use Task library to complete:

 string[] urls = ...;
 var tasks = urls.Select(url => Task.Factory.StartNew(() => DoSomething(url)));

To avoid locking UI Thread, you can use ContinueWhenAll in .NET 4.0:

Task.Factory.ContinueWhenAll(tasks.ToArray(), _ => 
    Console.Write("All tasks Completed. Now we can do further processing");
);

If you are in the latest version of .NET, you can use Task.WhenAll instead

Answer 2

If you use Net 4.0 or up, refer to the Parallel class and Task class. Joseph Albahari wrote very clear book about that: http://www.albahari.com/threading/part5.aspx#_Creating_and_Starting_Tasks

Answer 3

To me it would seem like you want Parallel.ForEach

Parallel.ForEach(myTasks, t => t.DoSomethingInBackground());

Console.Write("All tasks Completed. Now we can do further processing");

You can also perform multiple tasks within a single loop

List<string> results = new List<string>(myTasks.Count);
Parallel.ForEach(myTasks, t =>
{
    string result = t.DoSomethingInBackground();
    lock (results)
    { // lock the list to avoid race conditions
        results.Add(result);
    }
});

In order for the main UI thread to remain responsive, you will want to use a BackgroundWorker and subscribe to its DoWork and RunWorkerCompleted events and then call

worker.RunWorkerAsync();
worker.RunWorkerAsync(argument); // argument is an object