How to kill all threads immediately

Question

I made a little example program that counts numbers using two threads. It also prints a second number next to the count so I can see which thread printed which number.

Now my goal is to make both threads immediately stop once one of them counted 7. I don't know how to go about it. I thought about passing a thread array as a parameter to Counter and then use a foreach loop to abort both threads. The problem is that t0 might be executing it and calls t0.Abort()and thus t1.Abort() won't be called anymore.

public static int count = 0;
private static object lockObject = new object();

static void Main(string[] args) {
    Thread t0 = new Thread(() => Counter(1, 10));
    Thread t1 = new Thread(() => Counter(10, 20));

    t0.Start();
    t1.Start();

    t0.Join();
    t1.Join();

    Console.ReadLine();
}

public static void Counter(int k, int m) {
    for(int i = k; i < m; i++) {
        lock (lockObject) {
            count++;
            Console.WriteLine(count + " " + i);
            if (i == 7) {
                /* 
                 * Code that will kill thread t0 and t1
                 */
            }
        }
    }
}

The output should be something like

1 1
2 2
3 10
4 11
5 12
6 13
7 14

Does someone have suggestions how to kill both t0 and t1?

Answer 1

Have a look at ManualResetEvent. You should create one and inside the for-loop of the Counter-method you should check if the event is set and if so, break the for-loop and return. If you reach 7, simply set the event. The event is thread-safe.

By the way, seems to be a university homework ;) next time, try it yourself.

public static int count = 0;
private static object lockObject = new object();
private ManualResetEvent finish = new ManualResetEvent(false);

static void Main(string[] args) {
    Thread t0 = new Thread(() => Counter(1, 10));
    Thread t1 = new Thread(() => Counter(10, 20));

    t0.Start();
    t1.Start();

    t0.Join();
    t1.Join();

    Console.ReadLine();
}

public static void Counter(int k, int m) {
    for(int i = k; i < m; i++) {

        lock (lockObject) {
            if (finish.waitOne(0))
                break;

            count++;
            Console.WriteLine(count + " " + i);
            if (i == 7)
                finish.set()
        }
    }
}

Answer 2

MSDN Doesn't know what is ManualResetEvent.isset(), but Matthias's answer looks correct. If replace isset() to WaitOne(0), code works fine.

private static int count = 0;
private static ManualResetEvent finish = new ManualResetEvent(false);
private static int stopValue = 7;
private static int syncInterval = 0; //0ms
private static object lockObject = new object();
static void Main(string[] args)
{
    Thread t0 = new Thread(() => Counter(1, 10));
    Thread t1 = new Thread(() => Counter(10, 20));
    t0.Name = "Thread 1";
    t1.Name = "Thread 2";

    t0.Start();
    t1.Start();

    t0.Join();
    t1.Join();

    Console.ReadKey();
}
public static void Counter(int k, int m)
{
    for (int i = k; i < m; i++)
    {
        lock (lockObject)
        {
            if (finish.WaitOne(syncInterval))
                break;
            count++;
            Console.WriteLine($"{count} {i}");
            if (count == stopValue)
            {
                finish.Set();
            }
        }
    }
}

Answer 3

Use a flag, in this case "run".

public static int count = 0;
private static object lockObject = new object();
static bool run = true;

static void Main(string[] args) {
    Thread t0 = new Thread(() => Counter(1, 10));
    Thread t1 = new Thread(() => Counter(10, 20));        

    t0.Start();
    t1.Start();

    t0.Join();
    t1.Join();

    Console.ReadLine();
}

public static void Counter(int k, int m) {
    for(int i = k; i < m && run; i++) {
        lock (lockObject) {
            count++;
            Console.WriteLine(count + " " + i);
            if (i == 7) {
                run = false;
            }
        }
    }
}