Hashtable.Enumerator: snapshot out of sync

Questions & Answers
1

Hi all,
I’ve been getting the following exception: Hashtable.Enumerator: snapshot out of sync
which I believe is being caused by attempting to read and write to a hashtable at the same time.

Can someone give me some advice on the best way of handling read/writing for hashtables at the same time?

Here’s the code I’m using in case I’ve got this wrong:

#pragma strict
private var targetPosition: Vector3;
private var forceDirection: Vector3;
private var distanceFromCentre: float = 0.0;
private var targetMass: float = 0.0;
private var gravitationalForce: float;
private var localBodyTable = new Hashtable();
private var localMassTable = new Hashtable();

function Start () {
 	if(!StellarIndex.bodyTable.Contains(transform.parent.name))
	{
		StellarIndex.bodyTable.Add(transform.parent.name, transform.position);
	}	
	if(!StellarIndex.massTable.Contains(transform.parent.name))
	{
		StellarIndex.massTable.Add(transform.parent.name, rigidbody.mass);
	}
}

function FixedUpdate () {
	
	// If this hashtable is populated (implicitly the hashtable for mass is also populated)
	if(StellarIndex.bodyTable.Count > 0)
	{
		// Cycle through the hash table keys and find the associated mass / vector3 values for each object
		for each(var i: String in StellarIndex.bodyTable.Keys)
		{	
				targetPosition = StellarIndex.bodyTable*;*

  •  		forceDirection = targetPosition - transform.position;*

_ targetMass = StellarIndex.massTable*;_
_ distanceFromCentre = Vector3.Distance(targetPosition, transform.position);_
_ gravitationalForce = GameLogic.gravitationalConstant * ((rigidbody.mass * targetMass) / distanceFromCentre);
rigidbody.AddForce(forceDirection * gravitationalForce * Time.deltaTime);_
_ }_
_ }_
_}*_

function LateUpdate () {

* //Update every hashtable entry with new data *
* for (var i: String in StellarIndex.bodyTable.Keys)*
* { *
* StellarIndex.bodyTable[transform.parent.name] = transform.position;*
* } *
* for(var p: String in StellarIndex.massTable.Keys)*
* { *
* StellarIndex.massTable[transform.parent.name] = rigidbody.mass; *
* } *

*} *

Any help with this would be greatly appreciated :slight_smile:
Thanks

2

So I managed to solve this. It seems that the loops in the LateUpdate function were to blame. My LateUpdate function now looks as such:

 function LateUpdate () {
     
     //Update every hashtable entry with new data      
     StellarIndex.bodyTable[transform.parent.name] = transform.position;
     StellarIndex.massTable[transform.parent.name] = rigidbody.mass;            
 }

As a side note my gravitational force variable was occasionally outputting values of Nan or Infinity which I have clamped with an if loop like so:

		if(!float.IsNaN(gravitationalForce) && !float.IsNaN(forceDirection.x) && !float.IsNaN(forceDirection.y) && !float.IsNaN(forceDirection.z))
		{ 
			if(!float.IsInfinity(gravitationalForce) && !float.IsInfinity(forceDirection.x) && !float.IsInfinity(forceDirection.y) && !float.IsInfinity(forceDirection.z))
			{
				rigidbody.AddForce(forceDirection * gravitationalForce * Time.deltaTime);
				//Debug.Log(transform.parent.name + " is pulled towards" + i + " by " + gravitationalForce);
			}
		}