易失性 IEnlistmentNotification 和 TransactionScope.AsyncFlowEnabled = true

Question

除了 .NET 4.5.1 之外，TransactionScope 上还有一个新选项，可以使用异步流。这允许编写以下客户端代码

using(var txt = new TransactionScope(..., TransactionScopeAsyncFlowOption.Enabled)
{
   await sender.SendAsync();
}

到目前为止，一切都很好。但是当我需要实现一个易失性的 IEnlistmentNotification 时，我很难做到这一点。让我们想象一下以下场景，假设：我的底层基础设施从下到上完全异步

public class MessageSender : ISendMessages
{
    public async Task SendAsync(TransportMessage message, SendOptions options)
    {
        await sender.SendAsync(message);
    }
}

所以我想要实现的是引入一个像这样的易失性IEnlistmentNotification：

internal class SendResourceManager : IEnlistmentNotification
{
    private readonly Func<Task> onCommit;

    public SendResourceManager(Func<Task> onCommit)
    {
        this.onCommit = onCommit;
    }

    public void Prepare(PreparingEnlistment preparingEnlistment)
    {
        preparingEnlistment.Prepared();
    }

    public void Commit(Enlistment enlistment)
    {
        await this.onCommit();
        enlistment.Done();
    }

    public void Rollback(Enlistment enlistment)
    {
        enlistment.Done();
    }

    public void InDoubt(Enlistment enlistment)
    {
        enlistment.Done();
    }
}

和新的发件人

public class MessageSender : ISendMessages
{
    public async Task SendAsync(TransportMessage message, SendOptions options)
    {
        // Dirty: Let's assume Transaction.Current is never null
        Transaction.Current.EnlistVolatile(new SendResourceManager(async () => { await sender.SendAsync(message) }));
    }
}

注意：当然这段代码不能编译。这需要我将提交方法声明为 async void。这太棒了。

所以我的问题是：如何编写一个可以在内部等待异步操作的登记？

Answer 1

只要EnlistVolatile不是 CPU 密集型耗时操作，您就可以使用Task以下方法创建基于精简的包装器：EnlistVolatileTask.FromResult

public static class TranscationExtensions
{
    public static Task EnlistVolatileAsync(this Transaction transaction, 
                                           IEnlistmentNotification 
                                           enlistmentNotification, 
                                           EnlistmentOptions enlistmentOptions)
    {
        return Task.FromResult(transaction.EnlistVolatile
                                           (enlistmentNotification, 
                                            enlistmentOptions));
    }
}

然后在你的方法中使用它：

public class MessageSender : ISendMessages
{
    public Task SendAsync(TransportMessage message, SendOptions options)
    {
        return Transaction.Current.EnlistVolatileAsync
               (new SendResourceManager(async () => 
                                       { await sender.SendAsync(message) }));
    }
}

可以在您的调用堆栈中等待更高的位置：

MessageSender sender = new MessageSender();
await sender.SendAsync(message, options);