Bug Deferred Job arrays (from NativeList) don't work when cast to a NativeSlice

Case number: IN-21886

Description of the bug:
I have two jobs that work in succession. Both are scheduled at the same time.
Job 1 modifies a NativeList.
Job 2 operates on said list's results.
I use the

NativeList<>.AsDeferredJobArray

method to get a NativeArray for Job 2, as mentioned in the documentation.
Job 2 has a field of type NativeArray, for which it behaves expectedly. If this is changed to a NativeSlice, the slice will be empty when the job executes.

Expected behaviour:
Given that

NativeArray<T>

can implicitly cast to

NativeSlice<T>

, I would expect that the job should operate on the correct data in either situation.

Reproduction:
1. Run the project and observe the resulting log message stating that the WorkerJob operated on a valid number of elements.
2. Change the type of the

WorkerJob.values

field from NativeArray to NativeSlice (comment/uncomment the two lines there).
3. Run the project again and observe that the WorkerJob now operates on zero elements.

Sample code:

Code (CSharp):

1. using Unity.Burst;
2. using Unity.Collections;
3. using Unity.Jobs;
4. using UnityEngine;
5.  
6. namespace DeferredNativeSliceRepro
7. {
8.     public class EntryPoint : MonoBehaviour
9.     {
10.         private void Start()
11.         {
12.             int count = 100;
13.  
14.             // Populate a native list with the same values duplicated many times
15.             var nativeList = new NativeList<int>(count * 5, Allocator.TempJob);
16.             for (int i = 0; i < count; i++)
17.             {
18.                 nativeList.Add(1);
19.                 nativeList.Add(2);
20.                 nativeList.Add(3);
21.                 nativeList.Add(4);
22.                 nativeList.Add(5);
23.             }
24.  
25.             // Start a job to get a distinct set (remove the duplicates)
26.             var distinctJob = new DistinctValuesJob()
27.             {
28.                 values = nativeList
29.             };
30.             var distinctHandle = distinctJob.Schedule();
31.  
32.             // Get deferred array, will have results after distinct job finishes
33.             var deferredData = nativeList.AsDeferredJobArray();
34.  
35.             var result = new NativeArray<int>(1, Allocator.TempJob);
36.             var workerJob = new WorkerJob()
37.             {
38.                 // If 'values' is a NativeSlice, this will implicitly cast but will not work.
39.                 values = deferredData,
40.                 result = result
41.             };
42.             var handle = workerJob.Schedule(dependsOn: distinctHandle);
43.             handle.Complete();
44.  
45.             Debug.Log($"Worker job operated on {workerJob.result[0]} elements.");
46.  
47.             // Resource clean up
48.             nativeList.Dispose();
49.             result.Dispose();
50.         }
51.     }
52.  
53.     [BurstCompile]
54.     public struct DistinctValuesJob : IJob
55.     {
56.         public NativeList<int> values;
57.  
58.         public void Execute()
59.         {
60.             var set = new NativeParallelHashSet<int>(capacity: values.Length, Allocator.Temp);
61.  
62.             for (int i = 0; i < values.Length; ++i)
63.             {
64.                 int value = values[i];
65.                 if (!set.Add(value))
66.                 {
67.                     values.RemoveAt(i);
68.                     --i;
69.                 }
70.             }
71.  
72.             set.Dispose();
73.         }
74.     }
75.  
76.     [BurstCompile]
77.     public struct WorkerJob : IJob
78.     {
79.         public NativeArray<int> values;
80.         //public NativeSlice<int> values;
81.  
82.         public NativeArray<int> result;
83.  
84.         public void Execute()
85.         {
86.             result[0] = values.Length;
87.         }
88.     }
89. }
90.  

 

Update: Unity has now confirmed this is a bug & has transferred it to the team to be fixed

 

Unity has updated the bug report with the following info

Fix version/s: Pending
Resolution Notes: *Bug is fixed in:
2020.3.26f1.1459_a93835ac10a1