C＃问题中的多线程返回值

Question

I think I'm doing something incredibly wrong, but I don't know what. When I run this code, the two thread (thread1 and thread2) result immediately not alive, but the value in val1 and val2 are not correctly set.

The part of the code not in the thread works, if I call Process with level = 0, I get the two correct results in val1 and val2.

public int Process(int left, int right, List<int> array, int level)
    {

        int val1, val2;
        val1 = 0;
        val2 = 0;

        int val = array[left] + array[right] + (right - left);

        if (level > 0)
        {
            if ((right - left) > 1)
            {
                var thread1 = new Thread(() => { val1 = Process(left, right - 1, array, level - 1); });

                var thread2 = new Thread(() => { val2 = Process(left - 1, right, array, level - 1); });

                while (thread1.IsAlive)
                {
                    System.Threading.Thread.Sleep(100);
                }

                while (thread2.IsAlive)
                {
                    System.Threading.Thread.Sleep(100);
                }

                val = Math.Max(Math.Max(val1, val2), val);
            }
        }
        else
        {

            if ((right - left) > 1)
            {
                val1 = Process(left, right - 1, array, level);
                val2 = Process(left + 1, right, array, level);
                val = Math.Max(Math.Max(val1, val2), val);
            }
        }

        return val;
    }

Answer 1

You created threads, but didn't start them. Call Thread.Start() after creation.

var thread1 = new Thread(() => { val1 = Process(left, right - 1, array, level - 1); });
var thread2 = new Thread(() => { val2 = Process(left - 1, right, array, level - 1); });
thread1.Start();
thread2.Start();