FindNearestJob.cs

using Unity.Burst;
using Unity.Collections;
using Unity.Jobs;

// We'll use Unity.Mathematics.float3 instead of Vector3,
// and we'll use Unity.Mathematics.math.distancesq instead of Vector3.sqrMagnitude.
using Unity.Mathematics;

// Include the BurstCompile attribute to Burst compile the job.
[BurstCompile]
public struct FindNearestJob : IJob
{
    // All of the data which a job will access should 
    // be included in its fields. In this case, the job needs
    // three arrays of float3.

    // Array and collection fields that are only read in
    // the job should be marked with the ReadOnly attribute.
    // Although not strictly necessary in this case, marking data  
    // as ReadOnly may allow the job scheduler to safely run 
    // more jobs concurrently with each other.
    // (See the "Intro to jobs" for more detail.)

    [ReadOnly] public NativeArray<float3> TargetPositions;
    [ReadOnly] public NativeArray<float3> SeekerPositions;

    // For SeekerPositions[i], we will assign the nearest 
    // target position to NearestTargetPositions[i].
    public NativeArray<float3> NearestTargetPositions;

    // 'Execute' is the only method of the IJob interface.
    // When a worker thread executes the job, it calls this method.
    public void Execute()
    {
        // Compute the square distance from each seeker to every target.
        for (int i = 0; i < SeekerPositions.Length; i++)
        {
            float3 seekerPos = SeekerPositions[i];
            float nearestDistSq = float.MaxValue;
            for (int j = 0; j < TargetPositions.Length; j++)
            {
                float3 targetPos = TargetPositions[j];
                float distSq = math.distancesq(seekerPos, targetPos);
                if (distSq < nearestDistSq)
                {
                    nearestDistSq = distSq;
                    NearestTargetPositions[i] = targetPos;
                }
            }
        }
    }
}