C#

class Program
{
    static Service1[] clients = null;

    public delegate void AsyncMethodCaller(int index);

    static void ThreadJob (int index)
    {
        // query 100 times
        for (int i = 0; i < 100; i++)
        {
            clients[index].HelloWorld();
        }
    }

    static void Main(string[] args)
    {
        Console.WriteLine("Specify number of threads: ");
        int number = Int32.Parse(Console.ReadLine());
        //note: this doesn't actually specify the number of threads
        //the number of threads will be something like "at most 15 time the number of available cores"
        //which means that it will only specify the number of threads that are used if
        //the number if small. And any number of threads may exists - but they wouldn't be used.

        clients = new Service1[number];
        IAsyncResult[] results = new IAsyncResult[number];

        AsyncMethodCaller TJ = new AsyncMethodCaller(ThreadJob)
        for (int i = 0; i < number; i++)
        {
            clients[i] = new Service1();
            clients[i].EnableDecompression = true;
            results[i] = TJ.BeginInvoke(i, null, null);
        }

        DateTime begin = DateTime.Now;

        foreach (IAsyncResult res in results)
            TJ.EndInvoke(res);

        Console.WriteLine("Total elapsed time (s): " + (DateTime.Now - begin).TotalSeconds);

        Console.ReadLine();

        return;
    }
}

/// <summary>
/// Summary description for Service1
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.ComponentModel.ToolboxItem(false)]
public class Service1 : System.Web.Services.WebService
{

    [WebMethod]
    public double HelloWorld()
    {
        return new Random().NextDouble();
    }
}

/// <summary>
/// Summary description for Service1
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.ComponentModel.ToolboxItem(false)]
public class Service1 : System.Web.Services.WebService
{

    [WebMethod]
    public double HelloWorld()
    {
        Thread.Sleep(500);
        return new Random().NextDouble();
    }
}