Question

I’m new to threading and parallelism. I have this method for a game in C# and need to use parallel iteration. How could I use this on the for loops in the below method?

public int[,] GetLegalMoves()
{
    int[,] legalMoves = new int[8, 8];

    for (int i = 0; i < 8; i++)
        for (int j = 0; j < 8; j++)
            if (IsMoveLegal(i, j)) legalMoves[i, j] = 1;
            else legalMoves[i, j] = 0;

    return legalMoves;
}

Answer 1

This could be parallelized by parallelizing your outer loop:

public int[,] GetLegalMoves()
{
    int[,] legalMoves = new int[8, 8];

    Parallel.For(0, 8, i =>
    {
        for (int j = 0; j < 8; j++)
            if (IsMoveLegal(i, j)) legalMoves[i, j] = 1;
            else legalMoves[i, j] = 0;
    });

    return legalMoves;
}

That being said, this will likely cause this to run slower, as an 8×8 matrix is such a small value that the overhead of scheduling the parallel work is likely higher than the gains made, unless IsMoveLegal is a fairly expensive operation.

This will also require that IsMoveLegal be safe to use from multiple threads.