Can I write values to a Transform via main thread and jobs simultaneously?

[coldlogic]

@Joachim_Ante_1

How the TransformAccess actually transform game objects from jobs?

In IJobParallelForTransform is the change being queued up in parallel but the real change in position happen in the main thread later like how entity command buffer works? Or can the worker thread work together to change the transform for real? That is, is it wise to make a job which its only task is to transform given that all the required float3/quaternion required are already calculated (no more benefit to gain from parallel calculation), the only thing left is to set local position/rotatio…

TransformAccess writes to the transform component directly. This is only safe in the context of this job since it needs to make sure that other jobs in the engine don’t read / write at the same time. Hence we give you no access to TransformAccess directly only as a parameter in that job.

I read your answer in this thread and have a further question.

Is it thread safe when I write to a Transform via Update() on the main thread and Execute() in jobs simultaneously or should I move code in Update to a new job?

Transform cubeTransform;

void Update()
{
    cubeTransform.position = new Vector3(0,0,0);
}

// ...

public struct TransformJob : IJobParallelForTransform
{
    // transform is passed from cubeTransform     
    public void Execute(int index, TransformAccess transform)
    {
        transform.position = new Vector3(1,1,1);
    }
}

[xVergilx]

Its safe, but you shouldn’t. Because that will cause jobs to complete & main thread will wait until their completion.

Anything “unsafe” with jobs is usually caught by safety system.

Better solution is to run main thread logic when jobs aren’t running.
E.g. when jobs are complete and new ones aren’t scheduled yet. Its fairly simple to implement with Entities, harder with MonoBehaviours a bit, cause you’d have to control execution order manually.

[coldlogic]

@Joachim_Ante_1

Jobs Performance questions.

IJobParallelForTransform runs asynchronous to the main thread until anyone else needs to access it from another job. This alone is a huge optimization opportunity. Jobs going wide is far from the only reason to use jobs… If you really want to get to next level performace in terms for Transform Components then the upcoming preview of the Entity Component System is the safety best.

Internally when there is a root game object, we create a dedicated hierarchy. Each hierarchy owns its own JobHandle. Thus further jobs are scheduled against it. Grabbing position of a single transform on the main thread waits on all jobs against that specific hierarchy.

Even if I write a position rather than grabbing to a single transform on the main thread(a MonoBehaviour), does it also wait for all jobs against that hierarchy to complete?

I’m confused as to whether it’s safe to write to a transform on the main thread and jobs competitively.
All the documents and forum threads say it’s safe to access among jobs, but I don’t know if it’s safe to access it from the main thread simultaneously either.

Would you mind telling me “it’s okay” or “don’t do that accessing from the main thread and jobs together”?