c# - 我如何知道 UdpClient 是否已关闭/处置？

Question

我正在通过通常的异步回调从 UdpClient 接收数据:

private void OnUdpData(IAsyncResult result)
{
    byte[] data = _udpReceive.EndReceive(result, ref _receiveEndPoint);

    //Snip doing stuff with data

    _udpReceive.BeginReceive(OnUdpData, null);
}

当我 Close() 主线程中的 UdpClient 时，回调将如我所料触发，但此时 _udpReceive 已经处理完毕，我得到一个 ObjectDisposedException 当我尝试调用 EndReceive() 时。我原以为只会得到一个空缓冲区。

处理这个问题的正确方法是什么？是否有 UdpClient 的一些成员我可以在尝试使用它之前检查它，或者它是将它全部包装在 try{} 中并捕获 ObjectDisposedException 的唯一方法？对于正常的关闭来说，这似乎很糟糕。

Answer 1

您可以执行此操作以检查其是否已处置。处理 UdpClient 时，Client 设置为 null。

private void OnUdpData(IAsyncResult result)
{
    if (_udpReceive.Client == null)
        return;
    byte[] data = _udpReceive.EndReceive(result, ref _receiveEndPoint);

    //Snip doing stuff with data

    if (_udpReceive.Client == null)
        return;
    _udpReceive.BeginReceive(OnUdpData, null);
}

虽然因为你在一个单独的线程中关闭它，你可能会以竞争条件结束。最好只捕获 ObjectDisposedException 和 SocketException。

private void OnUdpData(IAsyncResult result)
{
    try
    {
        byte[] data = _udpReceive.EndReceive(result, ref _receiveEndPoint);

        //Snip doing stuff with data

        _udpReceive.BeginReceive(OnUdpData, null);
    }
    catch (Exception e)
    {
        //You may also get a SocketException if you close it in a separate thread.
        if (e is ObjectDisposedException || e is SocketException)
        {
            //Log it as a trace here
            return;
        }
        //Wasn't an exception we were looking for so rethrow it.
        throw;
    }
}