Question

I am trying to understand threading concepts in .Net.
I am unable to use Yield() method. I want the control to go to a parallel thread when i becomes divisible by 10.

Please help.

Below is my sample code:

class ThreadTest
{
    //Index i is declared as static so that both the threads have only one copy
    static int i;


    static void Main(string[] args)
    {
        Thread t = new Thread(WriteY);          
        i = 0;

        //Start thread Y    
        t.Start();                              
        //Do something on the main thread.
        for (; i < 100; i++)
        {
            if (i % 10 == 0)
            {
                //Simulate Yield() function
                Thread.Sleep(0);
                Console.WriteLine("The X thread");
            }
            Console.Write(i + ":X ");
        }
        Console.ReadKey(true);
    }

    static void WriteY()
    {
        for (; i < 100; i++)
        {
            if (i % 10 == 0)
            {
                //Simulate Yield() function
                Thread.Sleep(0);
                Console.WriteLine("The Y thread");
            }
            Console.Write(i + ":Y ");
        }
    }
}

I get the compile time error:

System.Threading.Thread does not contain a definition for ‘Yield’

Answered by Tudor. This method will only work on .Net 4.0 and upwards.

Ideally I would want one thread to start and want each thread to execute for 10 incremented of i each. With my current method, I either get all ‘X’ or all ‘Y’.

Edit:
With inputs from Tudor and TheHe – I have been able to get alternate X and Y. The crux of the problem was usage of lock object. But the output of this code is not predictable.

Answer 1

Thread.Yield will simply enable the scheduler to select a different thread that is ready to run:

Causes the calling thread to yield execution to another thread that is
ready to run on the current processor. The operating system selects
the thread to yield to.

If other threads in your application are also waiting on that lock, you can yield all you want, they won’t get a chance to run.

Btw, Yield is a .NET 4.0+ method. Make sure you’re not targeting an earlier version.

Edit: IMO, to do what you want you should use events:

class Test
{
    //Index i is declared as static so that both the threads have only one copy
    static int i;

    static AutoResetEvent parentEvent = new AutoResetEvent(true);
    static AutoResetEvent childEvent = new AutoResetEvent(false);

    static void Main(string[] args)
    {
        Thread t = new Thread(WriteY);

        i = 0;

        //Start thread Y
        t.Start();
        // Print X on the main thread
        parentEvent.WaitOne();
        while (i < 100)
        {                
            if (i % 10 == 0)
            {
                childEvent.Set();
                parentEvent.WaitOne();
            }
            Console.Write(i + ":Y ");
            i++;
        }
        t.Join();
    }

    static void WriteY()
    {
        childEvent.WaitOne();
        while (i < 100)
        {
            if (i % 10 == 0)
            {
                parentEvent.Set();
                childEvent.WaitOne();
            }
            Console.Write(i + ":X ");
            i++;
        }
    }
}