Thread.Sleep（0）和Join（）的使用

Question

I am reading a book about multithreading programs and I found this small example :

public static class Program
    {
        public static void ThreadMethod()
        {
            for (int i = 0; i < 10; i++)
            {
                Console.WriteLine(“ThreadProc: {0}”, i);
                Thread.Sleep(0);
            }
        }
        public static void Main()
        {
            Thread t = new Thread(new ThreadStart(ThreadMethod));
            t.Start();
            for (int i = 0; i < 4; i++)
            {
                Console.WriteLine(“Main thread: Do some work.”);
                Thread.Sleep(0);
            }
            t.Join();
        }
    }

I've got too many questions in mind:

1) What's the use of Thread.Sleep(0) , I mean, I've tried the two cases : with or without Thread.Sleep(0) , no big difference in runtime

2) Is t.Join() really usefull here, since it is in the end of the Main method ?

Answer 1

Thread.Sleep(0) will yield to other threads that don't have lower priority then yours:

If the value of the millisecondsTimeout argument is zero, the thread relinquishes the remainder of its time slice to any thread of equal priority that is ready to run. If there are no other threads of equal priority that are ready to run, execution of the current thread is not suspended.

So in case of this example it is something that tries to make threads run at approximately equal pace.

The Thread.Join usage suggests that it is needed not to end your program before your threads finish their work. However, as Scott Chamberlain points out, by default IsBackground property is false so your threads are foreground threads, and will keep the program running by themselves until they've finished their work. If your program had something more to do, and usually has, that needs the results of threads' work then the Join call would really be essential.

Try setting the IsBackground property to different values, and experiment with removing the Join call to see what happens.