构建线程安全的 GUID 增量器

Question

在我下面的代码中，我锁定了 guid，以尝试使其线程安全。在我的示例应用程序中，大约每 10 次我运行程序就会得到一个 "duplicate key"。 Aka，我得到了一个副本，这不是我需要的。

有没有办法使“.NextGuid”线程安全？

using System;    
namespace MyConsoleOne.BAL
{
    public class GuidStore
    {
        private static object objectlock = new object();    
        private Guid StartingGuid { get; set; }    
        private Guid? LastGuidHolder { get; set; }    
        public GuidStore(Guid startingGuid)
        {
            this.StartingGuid = startingGuid;
        }

        public Guid? GetNextGuid()
        {
            lock (objectlock)
            {
                if (this.LastGuidHolder.HasValue)
                {
                    this.LastGuidHolder = Increment(this.LastGuidHolder.Value);
                }
                else
                {
                    this.LastGuidHolder = Increment(this.StartingGuid);
                }
            }    
            return this.LastGuidHolder;
        }

        private Guid Increment(Guid guid)
        {    
            byte[] bytes = guid.ToByteArray();    
            byte[] order = { 15, 14, 13, 12, 11, 10, 9, 8, 6, 7, 4, 5, 0, 1, 2, 3 };    
            for (int i = 0; i < 16; i++)
            {
                if (bytes[order[i]] == byte.MaxValue)
                {
                    bytes[order[i]] = 0;
                }
                else
                {
                    bytes[order[i]]++;
                    return new Guid(bytes);
                }
            }    
            throw new OverflowException("Guid.Increment failed.");
        }
    }
}

using MyConsoleOne.BAL;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MyConsoleOne
{
    class Program
    {
        static void Main(string[] args)
        {
            GuidStore gs = new GuidStore(Guid.NewGuid());

            for (int i = 0; i < 1000; i++)
            {
                Console.WriteLine(i);
                Dictionary<Guid, int> guids = new Dictionary<Guid, int>();
                Parallel.For(0, 1000, j =>
                {
                    Guid? currentGuid = gs.GetNextGuid();
                    guids.Add(currentGuid.Value, j);
                    Console.WriteLine(currentGuid);
                }); // Parallel.For
            }    
            Console.WriteLine("Press ENTER to Exit");
            Console.ReadLine();
        }
    }
}

我的代码是以下组合：

Making Guid properties threadsafe

因为我收到 "Why not use Guid.NewGuid" 个问题，我将在此处提供原因：

我有一个父进程，它有一个由 Guid.NewGuid() 创建的唯一标识符。我将其称为 "parent guid"。该父进程将创建 N 个文件。如果我从头开始编写，我会在文件名末尾附加 "N"。例如，如果父 Guid 是“11111111-1111-1111-1111-111111111111”，我会写文件

"11111111-1111-1111-1111-111111111111_1.txt"
"11111111-1111-1111-1111-111111111111_2.txt"
"11111111-1111-1111-1111-111111111111_3.txt"

，等等，等等。但是，通过现有的 "contract" 和客户端 ::: 文件名中必须有一个（唯一的）Guid，而不是 "N" (1,2等）文件名中的值（这个 "contract" 已经存在多年，所以它几乎是固定不变的）。有了这里列出的功能，我将能够保留 "contract"，但文件名与 "parent" Guid 松散相关（同样，父项由 Guid.NewGuid 生成()).冲突不是文件名问题（它们被放在不同的文件夹下以供 'process' 执行）。碰撞是 "parent" Guid 的一个问题。但同样，这已经用 Guid.NewGuid.

处理了

因此，使用“11111111-1111-1111-1111-111111111111”的起始 Guid，我将能够编写如下文件名：

OTHERSTUFF_111111111-1111-1111-1111-111111111112_MORESTUFF.txt
OTHERSTUFF_111111111-1111-1111-1111-111111111113_MORESTUFF.txt
OTHERSTUFF_111111111-1111-1111-1111-111111111114_MORESTUFF.txt
OTHERSTUFF_111111111-1111-1111-1111-111111111115_MORESTUFF.txt
OTHERSTUFF_111111111-1111-1111-1111-111111111116_MORESTUFF.txt
OTHERSTUFF_111111111-1111-1111-1111-111111111117_MORESTUFF.txt
OTHERSTUFF_111111111-1111-1111-1111-111111111118_MORESTUFF.txt
OTHERSTUFF_111111111-1111-1111-1111-111111111119_MORESTUFF.txt
OTHERSTUFF_111111111-1111-1111-1111-11111111111a_MORESTUFF.txt
OTHERSTUFF_111111111-1111-1111-1111-11111111111b_MORESTUFF.txt

所以在我上面的示例中，"parent guid" 由 "this.StartingGuid" 表示......然后我从中得到 "incremented" guid。

还有。我可以编写更好的单元测试，因为现在我可以提前知道文件名。

追加：

最终代码版本：

public class GuidStore
{
    private static object objectlock = new object();

    private static int[] byteOrder = { 15, 14, 13, 12, 11, 10, 9, 8, 6, 7, 4, 5, 0, 1, 2, 3 };

    private Guid StartingGuid { get; set; }

    private Guid? LastGuidHolder { get; set; }

    public GuidStore(Guid startingGuid)
    {
        this.StartingGuid = startingGuid;
    }

    public Guid GetNextGuid()
    {
        return this.GetNextGuid(0);
    }

    public Guid GetNextGuid(int firstGuidOffSet)
    {
        lock (objectlock)
        {
            if (this.LastGuidHolder.HasValue)
            {
                this.LastGuidHolder = Increment(this.LastGuidHolder.Value);
            }
            else
            {
                this.LastGuidHolder = Increment(this.StartingGuid);
                for (int i = 0; i < firstGuidOffSet; i++)
                {
                    this.LastGuidHolder = Increment(this.LastGuidHolder.Value);
                }
            }

            return this.LastGuidHolder.Value;
        }
    }

    private static Guid Increment(Guid guid)
    {
        var bytes = guid.ToByteArray();
        var canIncrement = byteOrder.Any(i => ++bytes[i] != 0);
        return new Guid(canIncrement ? bytes : new byte[16]);
    }
}

和单元测试：

public class GuidStoreUnitTests
{
    [TestMethod]
    public void GetNextGuidSimpleTest()
    {
        Guid startingGuid = new Guid("11111111-1111-1111-1111-111111111111");
        GuidStore gs = new GuidStore(startingGuid);


        List<Guid> guids = new List<Guid>();

        const int GuidCount = 10;

        for (int i = 0; i < GuidCount; i++)
        {
            guids.Add(gs.GetNextGuid());
        }

        Assert.IsNotNull(guids);
        Assert.AreEqual(GuidCount, guids.Count);
        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-111111111112")));
        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-111111111113")));
        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-111111111114")));
        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-111111111115")));
        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-111111111116")));
        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-111111111117")));
        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-111111111118")));
        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-111111111119")));
        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-11111111111a")));
        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-11111111111b")));
    }

    [TestMethod]
    public void GetNextGuidWithOffsetSimpleTest()
    {
        Guid startingGuid = new Guid("11111111-1111-1111-1111-111111111111");
        GuidStore gs = new GuidStore(startingGuid);

        List<Guid> guids = new List<Guid>();

        const int OffSet = 10;

        guids.Add(gs.GetNextGuid(OffSet));

        Assert.IsNotNull(guids);
        Assert.AreEqual(1, guids.Count);

        Assert.IsNotNull(guids.FirstOrDefault(g => g == new Guid("11111111-1111-1111-1111-11111111111c")));
    }

    [TestMethod]
    public void GetNextGuidMaxRolloverTest()
    {
        Guid startingGuid = new Guid("ffffffff-ffff-ffff-ffff-ffffffffffff");
        GuidStore gs = new GuidStore(startingGuid);

        List<Guid> guids = new List<Guid>();

        const int OffSet = 10;

        guids.Add(gs.GetNextGuid(OffSet));

        Assert.IsNotNull(guids);
        Assert.AreEqual(1, guids.Count);

        Assert.IsNotNull(guids.FirstOrDefault(g => g == Guid.Empty));
    }

    [TestMethod]
    public void GetNextGuidThreadSafeTest()
    {
        Guid startingGuid = Guid.NewGuid();
        GuidStore gs = new GuidStore(startingGuid);

        /* The "key" of the ConcurrentDictionary must be unique, so this will catch any duplicates */
        ConcurrentDictionary<Guid, int> guids = new ConcurrentDictionary<Guid, int>();
        Parallel.For(
            0,
            1000,
            j =>
            {
                Guid currentGuid = gs.GetNextGuid();
                if (!guids.TryAdd(currentGuid, j))
                {
                    throw new ArgumentOutOfRangeException("GuidStore.GetNextGuid ThreadSafe Test Failed");
                }
            }); // Parallel.For
    }

    [TestMethod]
    public void GetNextGuidTwoRunsProduceSameResultsTest()
    {
        Guid startingGuid = Guid.NewGuid();

        GuidStore gsOne = new GuidStore(startingGuid);

        /* The "key" of the ConcurrentDictionary must be unique, so this will catch any duplicates */
        ConcurrentDictionary<Guid, int> setOneGuids = new ConcurrentDictionary<Guid, int>();
        Parallel.For(
            0,
            1000,
            j =>
            {
                Guid currentGuid = gsOne.GetNextGuid();
                if (!setOneGuids.TryAdd(currentGuid, j))
                {
                    throw new ArgumentOutOfRangeException("GuidStore.GetNextGuid ThreadSafe Test Failed");
                }
            }); // Parallel.For

        gsOne = null;

        GuidStore gsTwo = new GuidStore(startingGuid);

        /* The "key" of the ConcurrentDictionary must be unique, so this will catch any duplicates */
        ConcurrentDictionary<Guid, int> setTwoGuids = new ConcurrentDictionary<Guid, int>();
        Parallel.For(
                0,
                1000,
                j =>
                {
                    Guid currentGuid = gsTwo.GetNextGuid();
                    if (!setTwoGuids.TryAdd(currentGuid, j))
                    {
                        throw new ArgumentOutOfRangeException("GuidStore.GetNextGuid ThreadSafe Test Failed");
                    }
                }); // Parallel.For

        bool equal = setOneGuids.Select(g => g.Key).OrderBy(i => i).SequenceEqual(
                         setTwoGuids.Select(g => g.Key).OrderBy(i => i), new GuidComparer<Guid>());

        Assert.IsTrue(equal);
    }
}

internal class GuidComparer<Guid> : IEqualityComparer<Guid>
{
    public bool Equals(Guid x, Guid y)
    {
        return x.Equals(y);
    }

    public int GetHashCode(Guid obj)
    {
        return 0;
    }
}

Answer 1

你这里有两个问题：

Dictionary.Add() 不是线程安全的。请改用 ConcurrentDictionary.TryAdd()。
您的 GetNextGuid() 实现存在竞争条件，因为您 returning this.LastGuidHolder 处于锁外，因此它可能会在 [=38] 之前被另一个线程修改=]ed.

一个明显的解决方案是将 return 移到锁内：

public Guid? GetNextGuid()
{
    lock (objectlock)
    {
        if (this.LastGuidHolder.HasValue)
        {
            this.LastGuidHolder = Increment(this.LastGuidHolder.Value);
        }
        else
        {
            this.LastGuidHolder = Increment(this.StartingGuid);
        }

        return this.LastGuidHolder;
    }
}

但是，我会将 return 类型更改为 Guid - 它似乎对 return 和 Guid? 没有任何作用 - 这应该是隐藏在 class:

中

public Guid GetNextGuid()
{
    lock (objectlock)
    {
        if (this.LastGuidHolder.HasValue)
        {
            this.LastGuidHolder = Increment(this.LastGuidHolder.Value);
        }
        else
        {
            this.LastGuidHolder = Increment(this.StartingGuid);
        }

        return this.LastGuidHolder.Value;
    }
}

这是您使用 ConcurrentDictionary 的测试方法的一个版本：

static void Main(string[] args)
{
    GuidStore gs = new GuidStore(Guid.NewGuid());

    for (int i = 0; i < 1000; i++)
    {
        Console.WriteLine(i);
        ConcurrentDictionary<Guid, int> guids = new ConcurrentDictionary<Guid, int>();
        Parallel.For(0, 1000, j =>
        {
            Guid currentGuid = gs.GetNextGuid();
            if (!guids.TryAdd(currentGuid, j))
            {
                Console.WriteLine("Duplicate found!");
            }
        }); // Parallel.For
    }

    Console.WriteLine("Press ENTER to Exit");
    Console.ReadLine();
}

说了这么多，我不明白你为什么不只是使用 Guid.NewGuid()...

构建线程安全的 GUID 增量器

Building a thread-safe GUID increment'er

.net

c#

multithreading

guid