Wait for threads to complete

Question

    private void button1_Click(object sender, EventArgs e)
    {
        for (int i = 0; i < 15; i++)
        {
            Thread nova = new Thread(Method);
            nova.Start();
        }
        listBox1.Items.Add("Some text");
    }

    private void Method()
    {
        for (int i = 0; i < 15; i++)
        {
            Console.WriteLine(i);
        }

    }

This code does write: Some text and then numbers 111222333..... I would like that it writes 111122223333.... and then on the end Some text. is it possible to do that with threads (parent thread wait for child threads)? or do i have to use something else?

Answer 1

You need to keep track of all the threads, and use Thread.Join on each one. This waits until the specified thread terminates, and then continues executing. Like this:

var threads = new List<Thread>();
for (int i = 0; i < 15; i++)
{
    Thread nova = new Thread(Method);
    nova.Start();
    threads.Add(nova);
}
foreach (var thread in threads)
    thread.Join();
listBox1.Items.Add("Some text");

Answer 2

I suggest to use TPL to get this done. You won't need to spawn so many threads. By default TPL will use thread pool for that:

using System;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        private const int TaskCount = 15;

        static void Main(string[] args)
        {
            var tasks = new Task[TaskCount];
            for (var index = 0; index < TaskCount; index++)
            {
                tasks[index] = Task.Factory.StartNew(Method);
            }
            Task.WaitAll(tasks);

            Console.WriteLine("Some text");
        }

        private static void Method()
        {
            for (int i = 0; i < 15; i++)
            {
                Console.WriteLine(i);
            }
        }
    }
}