Google Interview Question for SDE-3s


Country: United States




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class MonitorTest
{
    public static int m_counter = 0;
    Random rnd = new Random();
    object key = new object();
    const int m_upperLimit = 3;
    const int m_lowerLimit = -1;

    private void addCounter()
    {
        lock (key)
        {
            while (m_counter >= m_upperLimit)
            {
                Console.WriteLine("add waiting");
                Monitor.Wait(key);
            }
            Thread.Sleep(rnd.Next() % 200);
            ++m_counter;
            Console.WriteLine(m_counter);
            Monitor.PulseAll(key);
        }
        addCounter();
    }

    private void subtractCounter()
    {
        lock (key)
        {
            while (m_counter <= m_lowerLimit)
            {
                Console.WriteLine("subtract waiting");
                Monitor.Wait(key);
            }
            Thread.Sleep(rnd.Next() % 200);
            --m_counter;
            Console.WriteLine(m_counter);
            Monitor.PulseAll(key);
        }
        subtractCounter();
    }

    public void startAllThreads()
    {
        Thread thAdd = new Thread(new ThreadStart(addCounter));
        Thread thSub = new Thread(new ThreadStart(subtractCounter));

        thAdd.Start();
        thSub.Start();

        thAdd.Join();
        thSub.Join();
    }
}

class Program
{
    static void Main(string[] args)
    {
        MonitorTest mt = new MonitorTest();
        mt.startAllThreads();
    }
}

- Student November 28, 2016 | Flag Reply


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