Question

i have this code:

    Thread[] threadsArray = new Thread[4];
        for (int i = 0; i < 4; i++)
        {
            threadsArray[i] = new Thread(() => c1.k(i));
        }
        for (int i = 0; i < 4; i++)
        {
            threadsArray[i].Start();
        }
        for (int i = 0; i < 4; i++)
        {
            threadsArray[i].Join();
        }

the function k is this:

void k(int i)
{
    while(true)
      Console.WriteLine(i);
}

for some reason just the last thread is running and printing 4444444….
why aren’t all the threads running?

Answer 1

All of the threads are printing the same variable.

Your lambda expression (() => c1.k(i)) captures the i variable by reference.
Therefore, when the lambda expression runs after i++, it picks up the new value of i.

To fix this, you need to declare a separate variable inside the loop so that each lambda gets its own variable, like this:

    for (int i = 0; i < 4; i++)
    {
        int localNum = i;
        threadsArray[i] = new Thread(() => c1.k(localNum));
    }