c#SortedList <string,TValue> .ContainsKey表示成功添加的键返回false

Question

检查下面的更新3 我发现我遇到的问题与.Net 4.0,4.0客户端和4.5的c#字符串比较器的已知严重问题有关,这将导致字符串列表的排序顺序不一致(导致输出依赖在输入的顺序和使用的排序算法).该问题于2012年12月向微软报告,并以"不会修复"结束.可以使用一种解决方法,但速度慢得多,对于大型集合来说几乎不实用.

在实现不可变的PatriciaTrie时,我想将其性能与System.Collections.Generic.SortedList进行比较.我使用以下文件https://github.com/rkapsi/patricia-trie/blob/master/src/test/resources/org/ardverk/collection/hamlet.txt来创建用于测试的输入词表.

当使用Comparer<string>.Default或StringComparer.InvariantCulture作为密钥比较器插入c#SortedList中的每个单词时,使用常规搜索方法无法检索成功插入的多个条目(例如,ContainsKey返回false),但密钥在列表中显示为通过迭代列表观察.

更奇怪的是,比较器在将从排序列表中检索到的密钥与无法找到的搜索密钥进行比较时返回值"0" ContainsKey.

下面的完整示例演示了我的系统上的这个问题.

using System;
using System.IO;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        // the problem is possibly related to comparison.
        var fail = true;
        var comparer = fail ? StringComparer.InvariantCulture : StringComparer.Ordinal;

        // read hamlet (contains duplicate words)
        var words = File
            .ReadAllLines("hamlet.txt")
            .SelectMany(l => l.Split(new[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries))
            .Select(w => w.Trim())
            .Where(w => !string.IsNullOrEmpty(w))
            .Distinct(comparer)
            .ToArray();

        // insert hamlet's words in the sorted list.
        var list = new SortedList<string, int>(comparer);
        var ndx = 0;
        foreach (var word in words)
            list[word] = ndx++;

        // search for each of the added words.
        foreach (var keyToSearch in words)
        {
            if (!list.ContainsKey(keyToSearch))
            {
                // was inserted, but cannot be retrieved.
                Console.WriteLine("Error - Key not found: \"{0}\"", keyToSearch);
                // however when we iterate over the list, we see that the entry is present
                var prefix = keyToSearch.Substring(0, Math.Min(keyToSearch.Length, 3));
                foreach (var wordCloseToSearchKey in list.Keys.Where(s => s.StartsWith(prefix)))
                {
                    // and using the SortedList's supplied comparison returns 0, signaling equality
                    var comparisonResult = list.Comparer.Compare(wordCloseToSearchKey, keyToSearch);
                    Console.WriteLine("{0} - comparison result = {1}", wordCloseToSearchKey, comparisonResult);
                }
            }
        }

        // Check that sort order of List.Keys is correct 
        var keys = list.Keys.ToArray();
        BinarySearchAll("list.Keys", keys, list.Comparer);
        CheckCorrectSortOrder("list.Keys", keys, list.Comparer);

        // Check that sort order of Array.Sort(List.Keys) is correct 
        var arraySortedKeys = CopySortSearchAndCheck("Array.Sort(List.Keys)", keys, list.Comparer);

        // Check that sort order of the Array.Sort(input words) is correct 
        var sortedInput = CopySortSearchAndCheck("Array.Sort(input words)", words, list.Comparer);

        Console.ReadLine();
    }

    static string[] CopySortSearchAndCheck(string arrayDesc, string[] input, IComparer<string> comparer)
    {
        // copy input
        var sortedInput = new string[input.Length];
        Array.Copy(input, sortedInput, sortedInput.Length);

        // sort it
        Array.Sort(sortedInput, comparer);

        // check that we can actually find the keys in the array using bin. search
        BinarySearchAll(arrayDesc, sortedInput, comparer);

        // check that sort order is correct
        CheckCorrectSortOrder(arrayDesc, sortedInput, comparer);

        return sortedInput;
    }

    static void BinarySearchAll(string arrayDesc, string[] sortedInput, IComparer<string> comparer)
    {
        // check that each key in the input can be found using bin. search
        foreach (var word in sortedInput)
        {
            var ix = Array.BinarySearch(sortedInput, word, comparer);
            if (ix < 0)
                // and it appears it cannot!
                Console.WriteLine("Error - {0} - Key not found: \"{1}\"", arrayDesc, word);
        }
    }

    static void CheckCorrectSortOrder(string arrayDesc, string[] sortedKeys, IComparer<string> comparer)
    {
        for (int n = 0; n < sortedKeys.Length; n++)
        {
            for (int up = n + 1; up < sortedKeys.Length; up++)
            {
                var cmp = comparer.Compare(sortedKeys[n], sortedKeys[up]);
                if (cmp >= 0)
                {
                    Console.WriteLine(
                        "{0}[{1}] = \"{2}\" not < than {0}[{3}] = \"{4}\"  - cmp = {5}",
                        arrayDesc, n, sortedKeys[n], up, sortedKeys[up], cmp);
                }
            }
            for (int down = n - 1; down > 0; down--)
            {
                var cmp = comparer.Compare(sortedKeys[n], sortedKeys[down]);
                if (cmp <= 0)
                {
                    Console.WriteLine(
                        "{0}[{1}] = \"{2}\" not > than {0}[{3}] = \"{4}\"  - cmp = {5}",
                        arrayDesc, n, sortedKeys[n], down, sortedKeys[down], cmp);
                }
            }
        }
    }
}

有没有人对这种意外和奇怪的行为有解释？

当将SortedList使用的比较器更改为StringComparer.Ordinal(通过例如更改fail为false上例中)问题消失时,这似乎指向比较问题,但我不太明白为什么.

更新 如Sébastien所述,此处描述的问题未显示在.Net 3.5和3.5客户端配置文件上.它适用于.Net 4.0,4.0客户端和4.5.

经过一些挖掘后,我注意到如果我从列表中取出排序的键并运行Array.BinarySearch这些键,它也会返回未找到的相同键的负值(未找到)值SortedList.ContainsKey.因此,这表明密钥的排序顺序不正确.

如果我从列表中取出已经排序的键并使用Array.Sort输出的排序顺序对它们进行排序,则对于有问题的键是不同的.

所以我添加了一个函数来检查(使用列表的比较器),如果给定数组的排序顺序正确(即前一个键总是更小,后续键总是更大)并将输入限制为根据不同的单词.比较器.我在3个不同的输入上应用了这个功能(全部使用相同的比较器):

1. SortedList的Keys集合.
2. 这些键上的Array.Sort输出.
3. Array.Sort的输出来自文件的输入.

(2)和(3)的输出与(1)相同且不同.但是,在(2)和(3)的Array.Sort输出上执行Array.BinarySearch再次无法找到相同的键(返回<0).此外,检查正确排序顺序的函数表明,对于所有3种情况,涉及的有问题键的排序顺序不正确.

在这一点上,我只是希望我做了一些非常愚蠢的事情并且有一个简单的解释.希望有人可以指出这一点.

示例代码通过我的其他故障排除实验进行更新,输出的屏幕截图可在此处找到http://imgur.com/DU8SCsA.

更新2 好的,我把这个问题缩小到了我认为是一个非常严重的问题,因为.Net 4.0引入了c#字符串比较器.

总之,假设我们有3个值:a1,a2和a3.为了使任何类型的排序正常工作,我们希望if a1 < a2和a2 < a3that为了进行比较是一致的,因此以下内容也是如此:a1 < a3.

然而,c#字符串比较器不是这种情况(至少对于Comparer<string>.Default和StringComparer.InvariantCulture).

下面的小程序说明了这个确切的问题:

class Program
{
    static void Main(string[] args)
    {
        var comparer = StringComparer.InvariantCulture;
        var a1 = "A";
        var a2 = "a\'";
        var a3 = "\'a";
        PrintComparison("a1", a1, "a2", a2, comparer);
        PrintComparison("a2", a2, "a3", a3, comparer);
        PrintComparison("a1", a1, "a3", a3, comparer);
        Console.ReadLine();
    }
    public static void PrintComparison(string firstSymbol, string first, string secondSymbol, string second, IComparer<string> comparer)
    {
        var cmp = comparer.Compare(first, second);
        var result = cmp == 0 ? "=" : cmp < 0 ? "<" : ">";
        Console.WriteLine("{0} {1} {2}   ({3} {1} {4})", firstSymbol, result, secondSymbol, first, second);
    }
}

这是它的输出:

a1 < a2   (A < a')
a2 < a3   (a' < 'a)
a1 > a3   (A > 'a)

结论似乎是依赖使用c#字符串编译器确定的排序顺序是不安全的,还是我错过了什么？

更新3 此问题似乎已于2012年12月向MS报告,并以"不会修复"状态结束,这是相当令人失望的; 请参阅以下评论中发布的链接(由于我的声誉点数有限,我似乎无法在此发布).这也列出了一个解决方法,我已经实现并用于验证这确实解决了标准比较器观察到的问题.

public class WorkAroundStringComparer : StringComparer
{
    private static readonly Func<CompareInfo, string, CompareOptions, int> _getHashCodeOfString;
    private readonly CompareInfo _compareInfo;
    private readonly CompareOptions _compareOptions;

    static WorkAroundStringComparer()
    {
        // Need this internal method to compute hashcode
        // as an IEqualityComparer implementation.
        _getHashCodeOfString = BuildGetHashCodeOfStringDelegate();
    }

    static Func<CompareInfo, string, CompareOptions, int> BuildGetHashCodeOfStringDelegate()
    {
        var compareInfoType = typeof(CompareInfo);
        var argTypes = new[] { typeof(string), typeof(CompareOptions) };
        var flags = BindingFlags.NonPublic | BindingFlags.Instance;
        var methods = compareInfoType.GetMethods(flags).ToArray(); ;
        var method = compareInfoType.GetMethod("GetHashCodeOfString", flags, null, argTypes, null);

        var instance = Expression.Parameter(compareInfoType, "instance");
        var stringArg = Expression.Parameter(typeof(string), "string");
        var optionsArg = Expression.Parameter(typeof(CompareOptions), "options");
        var methodCall = Expression.Call(instance, method, stringArg, optionsArg);
        var expr = Expression.Lambda<Func<CompareInfo, string, CompareOptions, int>>(methodCall, instance, stringArg, optionsArg);
        return expr.Compile();
    }

    public WorkAroundStringComparer()
        : this(CultureInfo.InvariantCulture)
    {
    }

    public WorkAroundStringComparer(CultureInfo cultureInfo, CompareOptions compareOptions = CompareOptions.None)
    {
        if (cultureInfo == null)
            throw new ArgumentNullException("cultureInfo");
        this._compareInfo = cultureInfo.CompareInfo;
        this._compareOptions = compareOptions;
    }

    public override int Compare(string x, string y)
    {
        if (ReferenceEquals(x, y))
            return 0;
        if (ReferenceEquals(x, null))
            return -1;
        if (ReferenceEquals(y, null))
            return 1;

        var sortKeyFor_x = _compareInfo.GetSortKey(x, _compareOptions);
        var sortKeyFor_y = _compareInfo.GetSortKey(y, _compareOptions);
        return SortKey.Compare(sortKeyFor_x, sortKeyFor_y);
    }

    public override bool Equals(string x, string y)
    {
        return Compare(x, y) == 0;
    }

    public override int GetHashCode(string obj)
    {
        return _getHashCodeOfString(_compareInfo, obj, _compareOptions);
    }
}

这种解决方法的问题在于它对于大型集合来说几乎不实用,因为它比例如慢一个数量级StringComparer.InvariantCulture.

使用两个比较器对给定单词列表进行1000次排序所花费的时间:

StringComparer.InvariantCulture : 00:00:15.3120013
WorkAroundStringComparer        : 00:01:35.8322409

所以我仍然希望微软重新考虑或者有人知道一个可行的替代方案.否则剩下的唯一选择是重新使用StringComparer.Ordinal.

Answer 1

是否与.Net Framework 4/4.5有关？我已将您的示例改编为 .Net 3.5，如下所示：

var words = ReadFile("hamlet.txt");

//...

private static string[] ReadFile(string path)
{
    List<string> lines = new List<string>();
    using (StreamReader sr = new StreamReader(path))
    {
        string text = sr.ReadToEnd();
        lines.Add(text);
    }

    return lines.SelectMany(l => l.Split(new[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries).Select(w => w.Trim()))
        .Where(w => !(w.ToCharArray().All(c => c == ' ')))
        .ToArray();
}

两个比较器在使用 .Net 3.5 的 XP 上运行良好。