UdpClient.ReceiveAsync 正确提前终止

Question

美好的一天。我使用 UdpClient 并对其进行包装。

对于阅读，我有异步方法：

private async Task<byte[]> Receive(UdpClient client, CancellationToken breakToken)
{
    // Выход из async, если произошёл CancellationRequest
    breakToken.ThrowIfCancellationRequested();

    UdpReceiveResult result;
    try
    {
        result = await client.ReceiveAsync().WithCancellation(breakToken);
    }
    catch(OperationCanceledException)
    {
        // Штатная ситуация ручной остановки Task-а
    }

    return result.Buffer;
}

其中 WithCancellation 是我提前终止的扩展方法：

public static async Task<T> WithCancellation<T>(
    this Task<T> task, CancellationToken cancellationToken)
{
    var tcs = new TaskCompletionSource<bool>();

    using (cancellationToken.Register(
        s => ((TaskCompletionSource<bool>)s).TrySetResult(true),
        tcs))
        if (task != await Task.WhenAny(task, tcs.Task))
            throw new OperationCanceledException(cancellationToken);

    return await task;
}

并且在手动读取停止后，当我调用 Dispose 时，出现 System.ObjectDisposedException。 CallStack:

>   System.dll!System.Net.Sockets.UdpClient.EndReceive(System.IAsyncResult asyncResult, ref System.Net.IPEndPoint remoteEP) Unknown
System.dll!System.Net.Sockets.UdpClient.ReceiveAsync.AnonymousMethod__64_1(System.IAsyncResult ar)  Unknown
mscorlib.dll!System.Threading.Tasks.TaskFactory<System.Net.Sockets.UdpReceiveResult>.FromAsyncCoreLogic(System.IAsyncResult iar, System.Func<System.IAsyncResult, System.Net.Sockets.UdpReceiveResult> endFunction, System.Action<System.IAsyncResult> endAction, System.Threading.Tasks.Task<System.Net.Sockets.UdpReceiveResult> promise, bool requiresSynchronization)   Unknown
mscorlib.dll!System.Threading.Tasks.TaskFactory<System.Net.Sockets.UdpReceiveResult>.FromAsyncImpl.AnonymousMethod__0(System.IAsyncResult iar)  Unknown
System.dll!System.Net.LazyAsyncResult.Complete(System.IntPtr userToken) Unknown
System.dll!System.Net.ContextAwareResult.CompleteCallback(object state) Unknown
mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)   Unknown
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)   Unknown
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) Unknown
System.dll!System.Net.ContextAwareResult.Complete(System.IntPtr userToken)  Unknown
System.dll!System.Net.LazyAsyncResult.ProtectedInvokeCallback(object result, System.IntPtr userToken)   Unknown
System.dll!System.Net.Sockets.BaseOverlappedAsyncResult.CompletionPortCallback(uint errorCode, uint numBytes, System.Threading.NativeOverlapped* nativeOverlapped)  Unknown
mscorlib.dll!System.Threading._IOCompletionCallback.PerformIOCompletionCallback(uint errorCode, uint numBytes, System.Threading.NativeOverlapped* pOVERLAP) Unknown

如果我理解正确，错误的根源在 ReceiveAsync 中，确切地说是在我停止它的方法中。但是我不知道怎么解决。

我必须怎么做才能纠正这个错误？

Update after usr comment:

private async Task<byte[]> Receive(UdpClient client, CancellationToken breakToken)
{
    // Выход из async, если произошёл CancellationRequest
    breakToken.ThrowIfCancellationRequested();

    UdpReceiveResult result;
    try
    {
        result = await client.ReceiveAsync().WithCancellation(breakToken);
    }
    catch(OperationCanceledException)
    {
        // Штатная ситуация ручной остановки Task-а
    }
    catch(ObjectDisposedException) { }

    return result.Buffer;
}

和Dispose调用：

public void Dispose()
{
    this.cancelRecieve?.Cancel();
    this.cancelRecieve?.Dispose();

    try
    {
        this.client?.Close();
    }
    catch(ObjectDisposedException) { }
}

但是 catch 对 ObjectDisposedException 没有反应。

Answer 1

取消待定接收的唯一方法是像您一样disconnect/stop/dispose。这是对的。您需要捕获并忽略该异常。

这是 .NET Framework 的一个不幸的设计问题，这是唯一的方法。

请注意，WithCancellation 不会取消 IO。接收仍然是运行。这就是为什么 WithCancellation 之后必须处理套接字以确保没有进一步的未决 IOs.

Answer 2

就这样，折腾了将近一周的时间，找到了原因和解决办法

起初，我看了UdpClient源代码。 ReceiveAsync 方法：

[HostProtection(ExternalThreading = true)]
public Task<UdpReceiveResult> ReceiveAsync()
{
    return Task<UdpReceiveResult>.Factory.FromAsync((callback, state) => BeginReceive(callback, state), (ar)=>
        {
            IPEndPoint remoteEP = null;
            Byte[] buffer = EndReceive(ar, ref remoteEP);
            return new UdpReceiveResult(buffer, remoteEP);

        }, null);
}

第二个，我发现这个post完美的答案：How to abort socket's BeginReceive()?，其中说：

To cancel a pending call to the BeginConnect() method, close the Socket. When the Close() method is called while an asynchronous operation is in progress, the callback provided to the BeginConnect() method is called. A subsequent call to the EndConnect(IAsyncResult) method will throw an ObjectDisposedException to indicate that the operation has been cancelled.

而且，正如我们所见，原始的 ReceiveAsync 方法 return 我们使用了 ObjectDisposedException，因为 IOOperation 在 Close 调用之后还没有完成.

为了克服这个问题我是这样做的：

新ReceiveAsync实现：

/// <summary>
/// Асинхронный запрос на ожидание приёма данных с возможностью досрочного выхода
/// (для выхода из ожидания вызовите метод Disconnect())
/// </summary>
/// <param name="client">Рабочий экземпляр класса UdpClient</param>
/// <param name="breakToken">Признак досрочного завершения</param>
/// <returns>Если breakToken произошёл до вызова данного метода или в режиме ожидания
/// ответа, вернёт пустой UdpReceiveResult; при удачном получении ответа-результат
/// асинхронной операции чтения</returns>
public Task<UdpReceiveResult> ReceiveAsync(UdpClient client, CancellationToken breakToken)
    => breakToken.IsCancellationRequested
        ? Task<UdpReceiveResult>.Run(() => new UdpReceiveResult())
        : Task<UdpReceiveResult>.Factory.FromAsync(
            (callback, state) => client.BeginReceive(callback, state),
            (ar) =>
                {
                    /// Предотвращение <exception cref="ObjectDisposedException"/>
                    if (breakToken.IsCancellationRequested)
                        return new UdpReceiveResult();

                    IPEndPoint remoteEP = null;
                    var buffer = client.EndReceive(ar, ref remoteEP);
                    return new UdpReceiveResult(buffer, remoteEP);
                },
            null);

新Dispose实现：

protected virtual void Dispose(bool disposing)
{
    if (disposing)
    {
        this.cancelReceive?.Cancel();
        this.client?.Close();
        this.cancelReceive?.Dispose();
    }
}

我非常希望，我的决定能够让其他人摆脱我所经历的痛苦。

UdpClient.ReceiveAsync 正确提前终止

UdpClient.ReceiveAsync correct early termination

c#

asynchronous

udpclient

objectdisposedexception