Parent component and Unity crash

Unity Engine
,
1

What is the correct way to handle these components?

I’ve written a system that adds and removes the Parent and LocalToParent components to objects that are being picked up by an agent.

Adding the component works fine, the object is now attached to the agent and follows him around.

When the agent places the item into a container, I modify the Parent component using an entity command buffer to attach it to the container Entity.

Doing this results in Unity hanging, requiring a Ctrl-Alt-Del.

Checking the editor.log file I found this:

Am I doing this wrong?

I’ve tried deleting the Parent and LocalToParent components instead of setting it, and get the exact same result.

1 Like
2

Problem solved…
Turns out I was passing the wrong ID value and trying to stick the item inside itself.

Doing that causes a crash apparently.

EDIT:

Looks like there was two problems. The first was the above, however I still get the below error.

 CommandBuffer.SetComponent(index, entity, new Parent {Value = newParent});
3

I’ve fixed the problem. In the Transforms package in ParentSystem.cs it sets the size of the UniqueParents hashmap to the count of existing parents. However in the code of the job using this hash map it can actually add to this hashmap twice. The error always triggers for me when I have one entity with a parent and swap parents around, but only sometimes triggers when more parents are being changed. Details below.

var count = m_ExistingParentsGroup.CalculateEntityCount();
if (count == 0)
    return;

// 1. Get (Parent,Child) to remove
// 2. Get (Parent,Child) to add
// 3. Get unique Parent change list
// 4. Set PreviousParent to new Parent
var parentChildrenToAdd = new NativeMultiHashMap<Entity, Entity>(count, Allocator.TempJob);
var parentChildrenToRemove = new NativeMultiHashMap<Entity, Entity>(count, Allocator.TempJob);
var uniqueParents = new NativeHashMap<Entity, int>(count, Allocator.TempJob);
var gatherChangedParentsJob = new GatherChangedParents
{
    ParentChildrenToAdd = parentChildrenToAdd.AsParallelWriter(),
    ParentChildrenToRemove = parentChildrenToRemove.AsParallelWriter(),
    UniqueParents = uniqueParents.AsParallelWriter(),
    PreviousParentType = GetArchetypeChunkComponentType<PreviousParent>(false),
    ParentType = GetArchetypeChunkComponentType<Parent>(true),
    EntityType = GetArchetypeChunkEntityType(),
    LastSystemVersion = LastSystemVersion
};
var gatherChangedParentsJobHandle = gatherChangedParentsJob.Schedule(m_ExistingParentsGroup);
gatherChangedParentsJobHandle.Complete();

The actual job itself has this loop in it:

 public void Execute(ArchetypeChunk chunk, int chunkIndex, int firstEntityIndex)
            {
                if (chunk.DidChange(ParentType, LastSystemVersion))
                {
                    var chunkPreviousParents = chunk.GetNativeArray(PreviousParentType);
                    var chunkParents = chunk.GetNativeArray(ParentType);
                    var chunkEntities = chunk.GetNativeArray(EntityType);

                    for (int j = 0; j < chunk.Count; j++)
                    {
                        if (chunkParents[j].Value != chunkPreviousParents[j].Value)
                        {
                            var childEntity = chunkEntities[j];
                            var parentEntity = chunkParents[j].Value;
                            var previousParentEntity = chunkPreviousParents[j].Value;

                            ParentChildrenToAdd.Add(parentEntity,childEntity);
                            UniqueParents.TryAdd(parentEntity, 0);

                            if (previousParentEntity != Entity.Null)
                            {
                                ParentChildrenToRemove.Add(previousParentEntity, childEntity);
                                UniqueParents.TryAdd(previousParentEntity, 0);
                            }

                            chunkPreviousParents[j] = new PreviousParent
                            {
                                Value = parentEntity
                            };
                        }
                    }
                }
            }

I can reproduce the bug every time if there is only one Entity with a parent being changed. It is a little more chance based after that.

var count = m_ExistingParentsGroup.CalculateEntityCount();

If this returns a count of 1, then the UniqueParents hashmap is set to a size of 1. However the code of the job allows for adding two entities to UniqueParents here:

UniqueParents.TryAdd(parentEntity, 0);

                            if (previousParentEntity != Entity.Null)
                            {
                                ParentChildrenToRemove.Add(previousParentEntity, childEntity);
                                UniqueParents.TryAdd(previousParentEntity, 0);
                            }

If i double the size of the UniqueParents hashmap I don’t get the error any more.