using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;

static class MM
{
  public static void MulSeq(int size, int[,] m1, int[,] m2, int[,] result)
  {
    for (int i = 0; i < size; i++)
    {
      for (int j = 0; j < size; j++)
      {
        int tmp = 0;
        for (int k = 0; k < size; k++)
        {
          tmp += m1[i, k] * m2[k, j];
        }
        result[i, j] = tmp;
      }
    }
  }
  public static void MulPFor(int size, int[,] m1, int[,] m2, int[,] result)
  {
      Parallel.For(0, size, (int i) =>
      {
        for (int j = 0; j < size; j++)
        {
          int tmp = 0;
          for (int k = 0; k < size; k++)
          {
            tmp += m1[i, k] * m2[k, j];
          }
          result[i, j] = tmp;
        }
      });
  }

  public static void MulTask(int size, int[,] m1, int[,] m2, int[,] result)
  {
    Task[] tasks = new Task[size];
    for (int n = 0; n < size; n++)
    {
      int i = n;
      tasks[n] = Task.Factory.StartNew(() =>
      {
        for (int j = 0; j < size; j++)
        {
          int tmp = 0;
          for (int k = 0; k < size; k++)
          {
            tmp += m1[i, k] * m2[k, j];
          }
          result[i, j] = tmp;
        }
        Debug.WriteLine("done " + Task.CurrentId.ToString());
      });
    }
    Task.WaitAll(tasks);
  }

  public static void MulPool(int size, int[,] m1, int[,] m2, int[,] result)
  {
    ManualResetEvent signal = new ManualResetEvent(false);
    long iters = size;
    for (int n = 0; n < size; n++)
    {
      int i = n;
      ThreadPool.QueueUserWorkItem(_ =>
      {
        for (int j = 0; j < size; j++)
        {
          int tmp = 0;
          for (int k = 0; k < size; k++)
          {
            tmp += m1[i, k] * m2[k, j];
          }
          result[i, j] = tmp;
        }

        if (Interlocked.Decrement(ref iters) == 0)
          signal.Set();
      });
    }
    signal.WaitOne();
  }
}