Job System and minecraft like mesh generation question.

The examples on the github are all about changing the existing vertices. How to make a vertices list with Job System? After I check posts in forum, it seems that NativeList is not thread safe. Then the indices may be changed over time.

 

Anyone helps? How to create a collection instead of modify the collection. The examples in Job System Cookbook is modifying the data.

 

You could probably use a NativeQueue for assembly and use an IJob to put into a NativeList if the order isn't important.

You could split the work amongst smaller native lists (safe on IJob) and reassemble them into a master on another IJob (the AddRange function can take a NativeArray, and NativeList has an implicit operator for that sort of thing.

If you need to assemble with a specific ordering and know the max index count you can use a NativeHashMap (which has a concurrent writer) for assembly with the intended index number as the key, then iterate through on an IJob to add to a list.

 

Thank you.
The exception below is reported if I make it readonly.

Code (CSharp):

1.  
2.         [ReadOnly]
3.         public NativeHashMap<int, NativeList<Vector3>> verticesHashMap;
4.  

The exception below is reported if I make it without readonly.

 

First off, most containers are paralell-write restricted for good reason, you can disable this safety check if you know what you're doing with the attribute

NativeDisableParallelForRestriction

, this can be useful for writing to certain structures if you ARE ABSOLUTELY CERTAIN UNIQUE VALUES WILL BE WRITTEN TO UNIQUE TARGET LOCATIONS.

What I recommend for your case is this alternative, which maintains safety:

NativeHashMap and NativeMultiHashMap both have a .Concurrent helper structure that supports parallel/cross-job writes (but no reads).

You can then read from them in other threads AFTER you've finished writing to them.

Try using NativeHashMap<int, NativeList<Vector3>>.Concurrent, and if it rejects having a container type as a value (it probably will), you can use a NativeMultiHashMap<int, Vector3> which is similar to a HashMap but it supports multiple values per key.

You can then iterate like so:

Code (CSharp):

1. [ComputeJobOptimization]
2. struct LinearizeMeshDataJob : IJob
3. {
4.     public int numParts;
5.     [ReadOnly] public NativeMultiHashMap<int, Vector3> input;
6.  
7.     public NativeList<Vector3> output;
8.  
9.     public void Execute()
10.     {
11.         for(int i = 0; i < NumParts; ++i)
12.         {
13.             NativeMultiHashMapIterator<int> iterator;
14.             Vector3 data;
15.             var found = input.TryGetFirstValue(i, out data, out iterator);
16.             while(found)
17.             {
18.                 output.Add(data);
19.                 found = input.TryGetNextValue(out data, ref iterator);
20.             }
21.         }
22.     }
23. }

If you dig into the Unity.Entities.Transforms package sources you can find TransformSystem.cs that builds and then updates the entire transform hierarchy. I wholeheartedly recommend it.

I do something similar in an object dependency lifecycle management system I'm building.