Threaded simultaneous jobs

Question

There is a string array myDownloadList containing 100 string URIs. I want to start 5 thread jobs that will pop next URI from myDownloadList (like a stack) and do something with it (download it), until there is no URIs left on a stack (myDownloadList).

What would be the best practice to do this?

Answer 1

Use the ThreadPool, and just setup all of your requests. The ThreadPool will automatically schedule them appropriately.

This will get easier with .NET 4, using the Task Parallel Library. Setting up each request as a Task is very efficient and easy.

Answer 2

Make sure each thread locks the myDownloadList when accessing it. You could use recursion to keep getting the latest one, then when the list is 0 it can just stop the function.

See the example below.

public static List<string> MyList { get; set; }
public static object LockObject { get; set; }

static void Main(string[] args)
{
    Console.Clear();

    Program.LockObject = new object();

    // Create the list
    Program.MyList = new List<string>();

    // Add 100 items to it
    for (int i = 0; i < 100; i++)
    {
        Program.MyList.Add(string.Format("Item Number = {0}", i));
    }

    // Start Threads
    for (int i = 0; i < 5; i++)
    {
        Thread thread = new Thread(new ThreadStart(Program.PopItemFromStackAndPrint));

        thread.Name = string.Format("Thread # {0}", i);

        thread.Start();
    }
} 


public static void PopItemFromStackAndPrint()
{
    if (Program.MyList.Count == 0)
    {
        return;
    }

    string item = string.Empty;

    lock (Program.LockObject)
    {
        // Get first Item
        item = Program.MyList[0];

        Program.MyList.RemoveAt(0);
    }

    Console.WriteLine("{0}:{1}", System.Threading.Thread.CurrentThread.Name, item);

    // Sleep to show other processing for examples only
    System.Threading.Thread.Sleep(10);

    Program.PopItemFromStackAndPrint();
}