Question

我正在Unity（2017.1.1f1）内的.NET Next()实例上调用System.Random。它从受保护的函数Sample()中抛出一个IndexOutOfRangeException，该函数不接受任何参数，并返回0到1之间的双精度值。

这里是例外情况

System.IndexOutOfRangeException：数组索引超出范围。

在System.Random.Sample（）[0x0003e]中   /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Random.cs:91
     在System.Random.Next（Int32 maxValue）[0x00017]中的
  /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Random.cs:112
     在Quicksilver.SysIRand.RandInt（Int32 max_exclusive）[0x00008]中位于
  F：\ SVNHome \ gemrush \ GemRush \ Assets \ Source \ Shared \ Utility \ IRand.cs：38
     在Quicksilver.IEnumerableExt.SelectRandom [Skill]（IEnumerable`1   集合，IRand兰特，Int32计数）[0x00070]在   F：\ SVNHome \ gemrush \ GemRush \ Assets \ Source \ Shared \ Utility \ IEnumerableExt.cs：61

（在此之上还有13层调用栈）

这是一个多线程环境，但是每个线程都有其自己的System.Random专用实例。从下面的代码中可以看到，传递给Next（）的参数必须为1或更高。

此错误在复杂的自动化测试脚本中投入了大约1个小时，因此多次运行以测试理论是昂贵的，并且任何更改RNG调用方式的修改都将阻止复制。（如果错误某种程度上涉及线程之间的意外交互，则可能根本无法再现。）

由于它已经进入测试脚本一个小时了，因此该方法的绝大多数调用都不得抛出错误。

直接使用随机数的函数在这里：

    // Chooses count items at random from the enumeration and returns them in an array
    // The order of selected items within the array is also random
    // If the collection is smaller than count, the entire collection is returned (in random order)
    public static T[] SelectRandom<T>(this IEnumerable<T> collection, IRand rand, int count = 1)
    {
        if (count <= 0) return new T[0];    // Optimization for trivial case

        T[] keep = new T[count];
        int found = 0;
        foreach (T item in collection)
        {
            if (found < count)
            {
                // Take the first #count items, in case that's all there are

                // Move a random item of those found so far (including the new one)
                // to the end of the array, and insert the new one in its place
                int r = rand.RandInt(found + 1);
                keep[found++] = keep[r];
                keep[r] = item;
            }
            else
            {
                // Random chance to replace one of our previously-selected elements
                ++found;
                if (rand.RandInt(found) < count)    // probability desired/found
                {
                    // Replace a random previously-selected element
                    int r = rand.RandInt(count);
                    keep[r] = item;
                }
            }
        }
        if (found < count)
        {
            // The collection was too small to get everything requested;
            // Make a new, smaller array containing everything in the collection
            T[] all = new T[found];
            Array.Copy(keep, all, found);
            return all;
        }
        return keep;
    }

此行抛出错误：

                if (rand.RandInt(found) < count)    // probability desired/found

IRand是围绕System.Random的非常薄的包装程序的接口； IRand.RandInt（）仅返回Random.Next（）。

编辑

以下是创建和分发随机实例的方式：

   private void Start()
    {
        SysIRand[] rngs = new SysIRand[parallelTesters];
        if (parallelTesters > 0) rngs[0] = new SysIRand(new System.Random(548913));
        if (parallelTesters > 1) rngs[1] = new SysIRand(new System.Random(138498));
        if (parallelTesters > 2) rngs[2] = new SysIRand(new System.Random(976336));
        if (parallelTesters > 3) rngs[3] = new SysIRand(new System.Random(793461));
        if (parallelTesters > 4) rngs[4] = new SysIRand(new System.Random(648791));
        if (parallelTesters > 5) rngs[5] = new SysIRand(new System.Random(348916));
        if (parallelTesters > 6) rngs[6] = new SysIRand(new System.Random(8467168));
        if (parallelTesters > 7) rngs[7] = new SysIRand(new System.Random(6183569));
        for (int i = 8; i < parallelTesters; ++i)
        {
            rngs[i] = new SysIRand(new System.Random(7 * i * i + 8961 * i + 129786));
        }

        for (int t = 0; t < parallelTesters; ++t)
        {
            SysIRand rand = rngs[t];

            IBot bot = BotFactory.DrawBot(rand);

            BotTester tester = new BotTester(rand, bot);
            tester.testerID = t + 1;
            tester.OnMessage += (str) => UponMessage(tester.testerID + " ~ " + str);
            tester.OnError += (str) => UponError(tester.testerID + " ~ " + str);
            tester.OnGameAborted += UponGameAborted;
            tester.OnDebugMoment += UponDebugMoment;

            testers.Add(tester);
        }

（在此运行中，parallelTesters的值为3）

每个BotTester仅使用传递给其构造函数的Random实例。每个线程对一个单独的BotTester都是私有的，从BotTester.RunGame()开始：

    public bool RunGame(GameMode mode, int maxGames = 1, long maxMilliSeconds = 100000000, int maxRetries = 5000)
    {
        if (threadRunning) return false;
        thread = new Thread(() => ThreadedRunGame(mode, maxGames, maxMilliSeconds, maxRetries));
        thread.Start();
        return true;
    }

Answer 1

唯一有意义的解释是，您认为自己访问Random()实例线程安全，每个线程都有自己的Random()实例，但看起来您正在访问相同的{ {1}}实例仍在计算中间。这是Unity中的实现。 Random()只需调用Sample()

InternalSample()

如您所见，您可以获得private int InternalSample() { int inext = this.inext; int inextp = this.inextp; int index1; if ((index1 = inext + 1) >= 56) index1 = 1; int index2; if ((index2 = inextp + 1) >= 56) index2 = 1; int num = this.SeedArray[index1] - this.SeedArray[index2]; if (num < 0) num += int.MaxValue; this.SeedArray[index1] = num; this.inext = index1; this.inextp = index2; return num; }的位置是有限的，即当您访问IndexOutOfRangeException时。这是SeedArray的定义。

this.SeedArray

它已经分配给56个元素，在执行public class Random { private int[] SeedArray = new int[56]; .... }方法时，您可以看到每次调用InternalSample和index1始终被限制为最多{{1} }，除非多次调用index2方法。

为什么System.Random.Sample抛出IndexOutOfRangeException？

1 个答案: