Question

我希望设置一些非常类似于事务范围的东西，它在服务上创建一个版本，并在范围的末尾删除/提交。在事务范围内运行的每个SQL语句在内部查看某个连接池/事务存储，以确定它是否在范围内并做出适当的反应。呼叫者不需要将事务传递给每个呼叫。我正在寻找这个功能。

以下是关于它的更多信息：https://blogs.msdn.microsoft.com/florinlazar/2005/04/19/transaction-current-and-ambient-transactions/

这是基本的一次性课程：

public sealed class VersionScope : IDisposable
{
    private readonly GeodatabaseVersion _version;
    private readonly VersionManager _versionManager;

    public VersionScope(Configuration config)
    {
        _versionManager = new VersionManager(config);
        _version = _versionManager.GenerateTempVersion();
        _versionManager.Create(_version);
        _versionManager.VerifyValidVersion(_version);
        _versionManager.ServiceReconcilePull();
        _versionManager.ReconcilePull(_version);
    }

    public void Dispose()
    {
        _versionManager.Delete(_version);
    }

    public void Complete()
    {
        _versionManager.ReconcilePush(_version);
    }
}

我希望我迄今为止编写的所有代码都不具备任何版本的概念。我只想包含一个简单的

Version = GetCurrentVersionWithinScope()

在代码的最低级别。

如果内存中有多个实例同时运行，那么实现类似内容的最安全方法是什么，几乎没有使用错误版本的风险。

如果有一个进程正在运行的内存块的唯一标识符，我会发现我非常天真的方法。然后将当前工作版本存储到全局数组或并发字典中。然后在我需要当前版本的代码中，我使用其内存标识符块并将其映射到创建的版本。

编辑：

使用示例：

using (var scope = new VersionScope(_config))
{
    AddFeature(); // This has no concept of scope passed to it, and could error out forcing a dispose() without a complete()
    scope.Complete();
}

Answer 1

最直接的方法是使用ThreadStatic或ThreadLocal将当前版本存储在线程本地存储中。这样多线程就不会相互干扰。例如，假设我们版本类：

public class Version {
    public Version(int number) {
        Number = number;
    }
    public int Number { get; }

    public override string ToString() {
        return "Version " + Number;
    }
}

然后VersionScope的实现可以这样：

public sealed class VersionScope : IDisposable {
    private bool _isCompleted;
    private bool _isDisposed;
    // note ThreadStatic attribute
    [ThreadStatic] private static Version _currentVersion;
    public static Version CurrentVersion => _currentVersion;

    public VersionScope(int version) {
        _currentVersion = new Version(version);
    }

    public void Dispose() {
        if (_isCompleted || _isDisposed)
            return;
        var v = _currentVersion;
        if (v != null) {
            DeleteVersion(v);
        }
        _currentVersion = null;
        _isDisposed = true;
    }

    public void Complete() {
        if (_isCompleted || _isDisposed)
            return;
        var v = _currentVersion;
        if (v != null) {
            PushVersion(v);
        }
        _currentVersion = null;
        _isCompleted = true;
    }

    private void DeleteVersion(Version version) {
        Console.WriteLine($"Version {version} deleted");
    }

    private void PushVersion(Version version) {
        Console.WriteLine($"Version {version} pushed");
    }
}

它会起作用，但它不支持嵌套作用域，这不好，所以要修复我们需要在开始新作用时存储以前作用域，并在Complete或Dispose上恢复它：

public sealed class VersionScope : IDisposable {
    private bool _isCompleted;
    private bool _isDisposed;
    private static readonly ThreadLocal<VersionChain> _versions = new ThreadLocal<VersionChain>();

    public static Version CurrentVersion => _versions.Value?.Current;

    public VersionScope(int version) {
        var cur = _versions.Value;
        // remember previous versions if any
        _versions.Value = new VersionChain(new Version(version), cur);
    }

    public void Dispose() {
        if (_isCompleted || _isDisposed)
            return;
        var cur = _versions.Value;
        if (cur != null) {
            DeleteVersion(cur.Current);
            // restore previous
            _versions.Value = cur.Previous;
        }
        _isDisposed = true;
    }

    public void Complete() {
        if (_isCompleted || _isDisposed)
            return;
        var cur = _versions.Value;
        if (cur != null) {
            PushVersion(cur.Current);
            // restore previous
            _versions.Value = cur.Previous;
        }
        _isCompleted = true;
    }

    private void DeleteVersion(Version version) {
        Console.WriteLine($"Version {version} deleted");
    }

    private void PushVersion(Version version) {
        Console.WriteLine($"Version {version} pushed");
    }

    // just a class to store previous versions
    private class VersionChain {
        public VersionChain(Version current, VersionChain previous) {
            Current = current;
            Previous = previous;
        }

        public Version Current { get; }
        public VersionChain Previous { get; }
    }
}

这已经是您可以使用的东西了。示例用法（我使用单线程，但如果有多个线程单独执行此操作 - 它们不会相互干扰）：

static void Main(string[] args) {
    PrintCurrentVersion(); // no version
    using (var s1 = new VersionScope(1)) {
        PrintCurrentVersion(); // version 1
        s1.Complete();
        PrintCurrentVersion(); // no version, 1 is already completed
        using (var s2 = new VersionScope(2)) {
            using (var s3 = new VersionScope(3)) {
                PrintCurrentVersion(); // version 3
            } // version 3 deleted
            PrintCurrentVersion(); // back to version 2
            s2.Complete();
        }
        PrintCurrentVersion(); // no version, all completed or deleted
    }
    Console.ReadKey();
}

private static void PrintCurrentVersion() {
    Console.WriteLine("Current version: " + VersionScope.CurrentVersion);
}

但是当您使用异步调用时，这将无效，因为ThreadLocal与线程绑定，但异步方法可以跨多个线程。但是，有一个名为AsyncLocal的类似构造，该值将通过异步调用流动。所以我们可以将构造函数参数添加到VersionScope，指示我们是否需要异步流。事务范围以类似的方式工作 - 有TransactionScopeAsyncFlowOption传递给TransactionScope构造函数，指示它是否会流经异步调用。

修改后的版本如下所示：

public sealed class VersionScope : IDisposable {
    private bool _isCompleted;
    private bool _isDisposed;
    private readonly bool _asyncFlow;
    // thread local versions
    private static readonly ThreadLocal<VersionChain> _tlVersions = new ThreadLocal<VersionChain>();
    // async local versions
    private static readonly AsyncLocal<VersionChain> _alVersions = new AsyncLocal<VersionChain>();
    // to get current version, first check async local storage, then thread local
    public static Version CurrentVersion => _alVersions.Value?.Current ?? _tlVersions.Value?.Current;
    // helper method
    private VersionChain CurrentVersionChain => _asyncFlow ? _alVersions.Value : _tlVersions.Value;

    public VersionScope(int version, bool asyncFlow = false) {
        _asyncFlow = asyncFlow;

        var cur = CurrentVersionChain;
        // remember previous versions if any
        if (asyncFlow) {
            _alVersions.Value = new VersionChain(new Version(version), cur);
        }
        else {
            _tlVersions.Value = new VersionChain(new Version(version), cur);
        }
    }

    public void Dispose() {
        if (_isCompleted || _isDisposed)
            return;
        var cur = CurrentVersionChain;
        if (cur != null) {
            DeleteVersion(cur.Current);
            // restore previous
            if (_asyncFlow) {
                _alVersions.Value = cur.Previous;
            }
            else {
                _tlVersions.Value = cur.Previous;
            }
        }
        _isDisposed = true;
    }

    public void Complete() {
        if (_isCompleted || _isDisposed)
            return;
        var cur = CurrentVersionChain;
        if (cur != null) {
            PushVersion(cur.Current);
            // restore previous
            if (_asyncFlow) {
                _alVersions.Value = cur.Previous;
            }
            else {
                _tlVersions.Value = cur.Previous;
            }
        }
        _isCompleted = true;
    }

    private void DeleteVersion(Version version) {
        Console.WriteLine($"Version {version} deleted");
    }

    private void PushVersion(Version version) {
        Console.WriteLine($"Version {version} pushed");
    }

    // just a class to store previous versions
    private class VersionChain {
        public VersionChain(Version current, VersionChain previous) {
            Current = current;
            Previous = previous;
        }

        public Version Current { get; }
        public VersionChain Previous { get; }
    }
}

使用异步流的范围的示例用法：

static void Main(string[] args) {
    Test();
    Console.ReadKey();
}

static async void Test() {
    PrintCurrentVersion(); // no version
    using (var s1 = new VersionScope(1, asyncFlow: true)) {
        await Task.Delay(100);
        PrintCurrentVersion(); // version 1
        await Task.Delay(100);
        s1.Complete();
        await Task.Delay(100);
        PrintCurrentVersion(); // no version, 1 is already completed
        using (var s2 = new VersionScope(2, asyncFlow: true)) {
            using (var s3 = new VersionScope(3, asyncFlow: true)) {
                PrintCurrentVersion(); // version 3
            } // version 3 deleted
            await Task.Delay(100);
            PrintCurrentVersion(); // back to version 2
            s2.Complete();
        }
        await Task.Delay(100);
        PrintCurrentVersion(); // no version, all completed or deleted
    }
}

private static void PrintCurrentVersion() {
    Console.WriteLine("Current version: " + VersionScope.CurrentVersion);
}

Answer 2

像这样使用IDisposable有点值得怀疑。（见Is it abusive to use IDisposable and "using" as a means for getting "scoped behavior" for exception safety?）

我，我发现它对某些事情很有用。这是我使用的模式：

class LevelContext
{
    private int _level;

    public int CurrentLevel
    {
        get { return _level; }
        set { _level = value < 0 ? 0 : value; }
    }

    public ILevel NewLevel(int depth = 1)
    {
        return new Level(this, depth);
    }

    /// <summary>
    /// Provides an interface that calling code can use to handle level objects.
    /// </summary>
    public interface ILevel : IDisposable
    {
        LevelContext Owner { get; }
        int Depth { get; }
        void Close();
    }

    /// <summary>
    /// Private class that provides an easy way to scope levels by allowing
    /// them to participate in the "using" construct. Creation of a Level results in an
    /// increase in owner's level, while disposal returns owner's level to what it was before.
    /// </summary>
    class Level : ILevel
    {
        public Level(LevelContext owner, int depth)
        {
            Owner = owner;
            Depth = depth;
            PreviousLevel = owner.CurrentLevel;
            Owner.CurrentLevel += Depth;
        }

        public LevelContext Owner { get; private set; }
        public int Depth { get; private set; }
        public int PreviousLevel { get; private set; }

        public void Close()
        {
            if (Owner != null)
            {
                Owner.CurrentLevel = PreviousLevel;
                Owner = null;
            }
        }

        void IDisposable.Dispose()
        {
            Close();
        }

    }

然后调用代码如下所示：

    static void Main(string[] args)
    {
        var lc = new LevelContext();

        Console.WriteLine(lc.CurrentLevel);

        using (lc.NewLevel())
            Console.WriteLine(lc.CurrentLevel);

        Console.WriteLine(lc.CurrentLevel);
    }

所以在你的情况下，你是对的 - 你需要创建跟踪当前版本的东西。在创建和处理VersionScopes时，应该更新某些内容。

交易范围类似的功能

2 个答案: