Thread myThread = new Thread(PrintNumbers);
myThread.Start();
myThread.Join();   // wait for it to finish

Thread pingThread = new Thread(Ping);
Thread pongThread = new Thread(Pong);
pingThread.IsBackground = true;
pongThread.IsBackground = true;
pingThread.Start();
pongThread.Start();
pingThread.Join();
pongThread.Join();

static void IncrementCounter(object state)
{
    // WITHOUT LOCK - race condition can occur
    for (int i = 0; i < 100; i++) counter++;
}

static object lockObject = new object();

lock (lockObject)
{
    for (int i = 0; i < 100; i++) counter++;
}

ThreadPool.SetMaxThreads(50, 50);
ThreadPool.QueueUserWorkItem(IncrementCounter);

long partialSum = 0;
for (int i = start; i <= end; i++) partialSum += i;
lock (lockObject) { totalSum += partialSum; }