Unity job system and multi dimensional arrays

Question

I have a IJobParallelFor where each job creates an array of data

I have tried using NativeArray<float[]> but that doesn't work because it is a reference type and I have tried NativeArray<NativeArray<float>> but that doesn't work because

...However, a type that contains a variable array of blittable types is not itself blittable.

Source: MSDN blittable types

Is there any way to get around this without using a giant one dimensional array and calculating the index's by hand? This is not nice since you have to use [NativeDisableParallelForRestriction] to access the array outside each jobs range.

My job:

public struct DistanceJob : IJobParallelFor
{
    [NativeDisableParallelForRestriction] public NativeArray<float> distance;
    [ReadOnly] public NativeArray<Vector2> position;

    public void Execute(int i)
    {
        for (int j = 0; j < position.Length; j++)
            distance[i * position.Length + j] = Vector2.Distance(position[i], position[j]);
    }
}

I know there are other algorithms that are not n^2 to do this but this is just a toy example of a real problem.

Answer 1

If I understand the question correctly, the Unity NativeMultiHashMap could help you. You can try something like:

public NativeMultiHashMap<float, NativeArray<float>> FooBar 
             = new NativeMultiHashMap<float, NativeArray<float>>();

At any point you can now use the key to add a value as a NativeArray.

Answer 2

Based on Raph_Wa awnser i used a

NativeHashMap<int, NativeList<Vector3>> distance;

Then each job gets a list each

public void Execute(int i)
{
    NativeList<Vector3> a;
    distance.TryGet(i, out a);

    for (int j = 0; j < position.Length; j++)
        a[j] = Vector2.Distance(position[i], position[j]);

    distance.TryAdd(i, a);
}

Answer 3

You can also, in addition, get your NativeArray pointer, store it in an IntPtr, and add it, instead of the array itself, to your array (it's a way of circumventing the nesting limitation of arrays). So, when using arrays in code, just convert them back to the array (I usually use the UnsafeUtility and UnsafeUtilityEx methods).