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  "contentMarkdown": "# Unity Jobsystem问题\n\n> [!note] 我的 UWA 问答\n> 本文收录我在 UWA 问答发表的公开回答。问题内容归原提问者；回答保留当时语境，技术结论可能受 Unity 版本、平台和项目条件限制。\n\n## 问题\n\n```\nusing CSharp;\n\nusing Unity.Burst;\n\nusing Unity.Collections.LowLevel.Unsafe;\n\nusing UnityEngine;\n\nusing UnityEngine.Jobs;\n\nusing Unity.Collections;\n\nusing Unity.Jobs;\n\npublic class JobTest : MonoBehaviour\n\n{\n\n    // Start is called before the first frame update\n\n    public Transform t1;\n\n    public Transform t2;\n\n    public TransformAccessArray TransformAccessArray;\n\n    void Start()\n\n    {\n\n        TransformAccessArray = new TransformAccessArray(50000,64);\n\n    }\n\n    private JobHandle handle;\n\n    // Update is called once per frame\n\n    void Update()\n\n    {\n\n        if (!handle.IsCompleted)\n\n        {\n\n            return;\n\n        }\n\n        if (TransformAccessArray.length == 0)\n\n        {\n\n            TransformAccessArray.Add(t1);\n\n            TransformAccessArray.Add(t2);\n\n        }\n\n        float t = Time.time;\n\n        Debug.Log(\"time:\" + t);\n\n        NativeList<int> end_list = new NativeList<int>(TransformAccessArray.length,Allocator.TempJob);\n\n        NativeList<int> end_id_list = new NativeList<int>(TransformAccessArray.length,Allocator.TempJob);\n\n        UpdateJob job = new UpdateJob\n\n        {\n\n            time = t,\n\n            end_list = end_list,\n\n            end_id_list = end_id_list,\n\n        };\n\n        handle = job.Schedule(TransformAccessArray);\n\n        handle.Complete();\n\n        if (end_id_list.Length != end_list.Length)\n\n        {\n\n            Debug.LogError(\"error time:\" + t);\n\n        }\n\n        else\n\n        {\n\n            Debug.LogWarning(\"right time:\" + t);\n\n        }\n\n        end_list.Dispose();\n\n        end_id_list.Dispose();\n\n    }\n\n}\n\nusing System;\n\nusing Unity.Burst;\n\nusing Unity.Collections;\n\nusing Unity.Collections.LowLevel.Unsafe;\n\nusing UnityEngine;\n\nusing UnityEngine.Jobs;\n\nnamespace CSharp\n\n{\n\n    [BurstCompile]\n\n    public struct UpdateJob : IJobParallelForTransform\n\n    {\n\n        [NativeDisableContainerSafetyRestriction] public NativeList<int> end_list;\n\n        [NativeDisableContainerSafetyRestriction] public NativeList<int> end_id_list;\n\n        [ReadOnly] public float time;\n\n        public void Execute(int index, TransformAccess transform)\n\n        {\n\n            end_list.Add(index);\n\n            end_id_list.Add(index);\n\n            int a = end_list.Length;\n\n            int b = end_id_list.Length;\n\n        }\n\n    }\n\n}\n```\n\n执行多线程之后发现，end*id*list.Length和 end_list.Length的长度有时候不一样，谁能解答一下\n\n- 提问者：hardy\n- 提问时间：2021-03-09 22:55:15\n\n## 我的回答\n\n这样写的话，两个线程是并行的，并且是线程不安全的：\n\n![image.png](assets/60471bd3cfa35d5b536699e8/01.png)\n\n两个线程对指令的执行的先后顺序是不确定的。\n\n如果两个线程依次对end*list进行Add的话，end*list就会加入两个元素。\n\n如果两个线程同时取得end_list，同时进行Add，就会产生错误——两个线程都执行完后，某个List只添加了一个元素。\n\n可以用如下方法进行验证：\n\n![image.png](assets/60471bd3cfa35d5b536699e8/02.png)\n\n![image.png](assets/60471bd3cfa35d5b536699e8/03.png)\n\n如果对数据的访问进行加锁，保证一个线程访问list时，另外一个线程无法访问，就不会出现题主所述的问题。**不过这多线程执行就没有意义了，相当于顺序执行。**\n\n- 回答时间：2021-03-10 02:06:15\n- 最后更新：2021-03-10 02:07:28\n- 采纳状态：未采纳\n\n## 来源与关系\n\n- 上位集合：[[10-计算机、信息技术与工程/05-游戏图形与运行时/我的UWA问答/我的UWA问答|我的 UWA 问答]]\n- UWA 标签：C#编程\n- 原始问题：[Unity Jobsystem问题](https://answer.uwa4d.com/question/60471bd3cfa35d5b536699e8)\n- 源页最后更新：2021-03-10 02:06:15\n"
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