NetTcpBinding和Async/Await WCF阻塞

Question

我们正在创建一个共享WCF通道，用于异步操作：

var channelFactory = new ChannelFactory<IWcfService>(new NetTcpBinding {TransferMode = TransferMode.Buffered});

channelFactory.Endpoint.Behaviors.Add(new DispatcherSynchronizationBehavior(true, 25));
var channel = channelFactory.CreateChannel(new EndpointAddress(new Uri("net.tcp://localhost:80/Service").AbsoluteUri + "/Test"));

这将调用以下服务：

[ServiceContract]
public interface IWcfService
{
    [OperationContract]
    Task<MyClass> DoSomethingAsync();
}

[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Multiple, InstanceContextMode = InstanceContextMode.PerCall)]
public class WcfServiceImpl : IWcfService
{
    public Task<MyClass> DoSomethingAsync()
    {
        Thread.Sleep(4000);

        return Task.FromResult(new MyClass());
    }
}

[Serializable]
public class MyClass
{
    public string SomeString { get; set; }      
    public MyClass Related { get; set; }        
    public int[] Numbers { get; set; }
}

如果我们一次启动3个请求，并在响应上模拟一个长时间运行的任务：

        using ((IDisposable)channel)
        {
            var task1 = Task.Run(async () => await DoStuffAsync(channel));
            var task2 = Task.Run(async () => await DoStuffAsync(channel));
            var task3 = Task.Run(async () => await DoStuffAsync(channel));

            Task.WaitAll(task1, task2, task3);
        }
    }

    public static async Task DoStuffAsync(IWcfService channel)
    {
        await channel.DoSomethingAsync();

        Console.WriteLine("Response");

        // Simulate long running CPU bound operation
        Thread.Sleep(5000);

        Console.WriteLine("Wait completed");
    }

Response
// 5 second delay
Wait completed
// Instant
Response
// 5 second delay
Wait completed
// Instant
Response

我已经添加了一个我相信正在发生的事情的图像，这只发生在缓冲模式下，在流模式下主线程不会阻塞。

Answer 1

@下划线

我最近也试图解决同样的问题。尽管我无法确切地确定为什么transfermode.buffered在使用它的线程被释放之前导致WCF通道上的全局锁，但我在等待之后发现了类似的死锁问题。他们建议了一个解决办法，即在等待中添加runcontinuationsasynchronaly()，即await channel.dosomethingasync().runcontinuationsasynchronaly()whereruncontinuationsasynchronaly():

public static class TaskExtensions
{
    public static Task<T> RunContinuationsAsynchronously<T>(this Task<T> task)
    {
        var tcs = new TaskCompletionSource<T>();

        task.ContinueWith((t, o) =>
        {
            if (t.IsFaulted)
            {
                if (t.Exception != null) tcs.SetException(t.Exception.InnerExceptions);
            }
            else if (t.IsCanceled)
            {
                tcs.SetCanceled();
            }
            else
            {
                tcs.SetResult(t.Result);
            }
        }, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);

        return tcs.Task;
    }

    public static Task RunContinuationsAsynchronously(this Task task)
    {
        var tcs = new TaskCompletionSource<object>();

        task.ContinueWith((t, o) =>
        {
            if (t.IsFaulted)
            {
                if (t.Exception != null) tcs.SetException(t.Exception.InnerExceptions);
            }
            else if (t.IsCanceled)
            {
                tcs.SetCanceled();
            }
            else
            {
                tcs.SetResult(null);
            }
        }, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);

        return tcs.Task;
    }
}

它将WCF连续区分开。显然task.yield()也起作用。