Thread problem when moving kinematic rigidbody with coroutine, using Leap Motion

[PLjubarskij]

Hello everyone!
First some context: I am trying to make kinematic rigidbodys collide with certain colliders.
Here is some code to start getting to my problem.

private void FixedUpdate()
{
AvoidCollision();
}

in the AvoidCollision function i am checking some stuff, but the relevant part is that i am checking the distance between a grasped kinematic object and a collider it is supposed to collide with. When a certain minDistance is reached i call a coroutine which does the following:

private IEnumerator WaitForAction()
{
currentSphere.GetComponent().constraints = RigidbodyConstraints.FreezePosition;
yield return new WaitUntil(() => currentSphere.GetComponent().isGrasped == false);
UnfreezeAndMove();
}

and

private void UnfreezeAndMove()
{
currentSphere.GetComponent().constraints = RigidbodyConstraints.None;
currentSphere.GetComponent().MovePosition(currentSphere.GetComponent().gameObject.transform.position + (Vector3.back * setBackMultiplier));
Debug.Log("hello");
}

The problem is, that when i have the Debug.Log everything works fine. Just as the code is dictating it to.
When i remove the Debug.Log tho, the object which is supposed to be set back on release, is just set back for like one frame(you can see it glitch to its destined position) and then its back at the collider and not able to move when i grab it because of the code. Also the Debug.Log is called 150 times.
I am suspecting some kind of thread problem where the Leap motion update is interfering with the update position of the rigidbody.

i have also tried the following:

void Start(){
InteractionManager.instance.OnPrePhysicsUpdate += UnfreezeAndMove;
}

where

private void UnfreezeAndMove()
{
if (!nowExecute) return;
currentSphere.GetComponentInParent().constraints = RigidbodyConstraints.None;
currentSphere.GetComponentInParent().MovePosition(
currentSphere.GetComponentInParent().gameObject.transform.position + (Vector3.back * setBack));

    nowExecute = false;
}

with yield

yield return new WaitUntil(() => currentSphere.GetComponentInParent().isGrasped == false);

nowExecute = true;

But updating it in prePhysics didnt help either.
Does anyone maybe have a suggestion where the problem lies?

[jselstad]

Hrm, so an important thing to understand is that there is no threading happening with Fixed Update and coroutines.

When you set up a “WaitUntil()” yield, it just checks the condition once per frame (sometime between update and late update).

Another thing to note: FixedUpdate is not threaded either. It just happens before Update (and before the physics simulation has updated the rigidbodies’ positions).

And the last thing to note: both Unity and the Interaction Engine move the transforms separately from the rigidbodies. This is to compensate for the temporal offset between the two update rates, and to keep the visuals smooth. You can get the rigidbody’s actual/physics position/rotation by accessing them from the rigidbody directly.

Since WaitUntil() happens after both the physics simulation and update, but your coroutine/checks are initialized before the physics, I expect you’re running into some unanticipated behavior regarding pre-/post-update object states.

I would also recommend doing your collision checks directly on the rigidbody’s parameters as well.