How to handle expensive and frequent functions without blocking the main thread?

Questions & Answers
1

I have an A* algorithm that I want to run a lot.

public static event Action<List<Position>> FoundPath = delegate { };

public void A*(List<Vector3> path)
{
    while(!IsSorted(path) || !end)
    {
        bogosort(path)
    }
    if(IsSorted(path))
    {
        FoundPath(path)
    }
}

Bogosort is expensive, doesn’t always have a solution and can run for so long that by the time it has a solution I don’t need it anymore. What is the simplest and most consistent way to handle this use case?

  • I have tried coroutines but I want such a large and arbitrary amount of attempts that yielding is awkward
  • I have tried jobs but have found updating a parameter on a job to be inconsistent and whimsical (I haven’t gotten locks, volatile or Interlock to work effectively)

Any help would be appreciated thanks.

2

You can run the code asynchronously. This will take the same amount of time, however the code will run on a separate thread, meaning your application won’t hang whilst it is running.

Setting up a thread/task is still a costly process, so I would try not to create threads every frame, instead, put delays.

For example:
The A* function will be written as:

 public async void A*(List<Vector3> path)
 {
     while(!IsSorted(path) || !end)
     {
         await bogosort(path)
     }
     if(IsSorted(path))
     {
         FoundPath(path)
     }
 }

instead. Notice the async keyword before void.

Now, you’ll also need to make bogosort an async method too. E.g:

async void bogosort()
{
     await Task.Run(() =>
     {
          // Put all code inside this block..
     });
}

The await block allows you to wait till the code has finished execution, and the Task.Run block allows you to offload some code to another thread.

Be careful when threading code, as most of the Unity API isn’t allowed to be called from another thread.

@DeanShea

3

For context my current solution is

public class PathScheduler
{
    	public JobHandle current_job;
    	public FindPath path;
    	public Guid path_id;
    
    	public void ScheduleFindPath((List<Vector3> m_list)
    	{
    		path = new Map.FindPath(m_list);
    		path_id = path.m_id;
    		current_job = path.Schedule();
    		Map.FindPath.current.Add( path_id);
    	}
    	public void EndJob()
        {
    		Map.FindPath<T>.current.Remove(path_id);
         }
}
public struct FindPath: IJob
{
            public static event Action<List<Vector3>> FoundPath = delegate { };
            public static HashSet<Guid> current = new HashSet<Guid>();
            public Guid m_id;
            public FindPath(List<Vector3> given_list)
            {
                m_id = Guid.NewGuid();
                m_list = given_list;
            }
    
            public void Execute()
            {
                 while(!IsSorted(path) && current.Contains(m_id) )
                 {
                     bogosort(path)
                 }
                 if(IsSorted(path))
                 {
                     FoundPath(path)
                 }
            }
    }

I realise my solution isn’t thread safe/best practice (using static variables in multiple threads). So far I’ve had no runtime errors, all the functionality and consistency that I want, no alternatives and better things to do. So if there is a solution that is thread safe, killable, doesn’t block main and allows a loop to run a lot/arbitrary amount of times each frame, let me know.