如何设置TcpClient的超时？

Question

我有一个TcpClient,我用它来发送数据到远程计算机上的监听器.远程计算机有时会打开,有时会关闭.因此,TcpClient将无法经常连接.我希望TcpClient在一秒钟后超时,因此它无法连接到远程计算机时花费太多时间.目前,我将此代码用于TcpClient:

try
{
    TcpClient client = new TcpClient("remotehost", this.Port);
    client.SendTimeout = 1000;

    Byte[] data = System.Text.Encoding.Unicode.GetBytes(this.Message);
    NetworkStream stream = client.GetStream();
    stream.Write(data, 0, data.Length);
    data = new Byte[512];
    Int32 bytes = stream.Read(data, 0, data.Length);
    this.Response = System.Text.Encoding.Unicode.GetString(data, 0, bytes);

    stream.Close();
    client.Close();    

    FireSentEvent();  //Notifies of success
}
catch (Exception ex)
{
    FireFailedEvent(ex); //Notifies of failure
}

这对于处理任务非常有效.如果可以,它会发送它,如果它无法连接到远程计算机,则捕获异常.但是,当它无法连接时,抛出异常需要十到十五秒.我需要它在大约一秒钟内超时？我怎样才能改变超时时间？

Answer 1

您需要使用异步BeginConnect方法TcpClient而不是尝试同步连接,这是构造函数的作用.像这样的东西:

var client = new TcpClient();
var result = client.BeginConnect("remotehost", this.Port, null, null);

var success = result.AsyncWaitHandle.WaitOne(TimeSpan.FromSeconds(1));

if (!success)
{
    throw new Exception("Failed to connect.");
}

// we have connected
client.EndConnect(result);

Answer 2

从.NET 4.5开始,TcpClient有一个很酷的ConnectAsync方法,我们可以像这样使用,所以它现在非常简单:

var client = new TcpClient();
if (!client.ConnectAsync("remotehost", remotePort).Wait(1000))
{
    // connection failure
}

Answer 3

使用/sf/answers/1797918461/的另一种方法:

var timeOut = TimeSpan.FromSeconds(5);     
var cancellationCompletionSource = new TaskCompletionSource<bool>();
try
{
    using (var cts = new CancellationTokenSource(timeOut))
    {
        using (var client = new TcpClient())
        {
            var task = client.ConnectAsync(hostUri, portNumber);

            using (cts.Token.Register(() => cancellationCompletionSource.TrySetResult(true)))
            {
                if (task != await Task.WhenAny(task, cancellationCompletionSource.Task))
                {
                    throw new OperationCanceledException(cts.Token);
                }
            }

            ...

        }
    }
}
catch(OperationCanceledException)
{
    ...
}

Answer 4

需要注意的一点是,在超时到期之前,BeginConnect调用可能会失败.如果您尝试本地连接,可能会发生这种情况.这是Jon的代码的修改版本......

        var client = new TcpClient();
        var result = client.BeginConnect("remotehost", Port, null, null);

        result.AsyncWaitHandle.WaitOne(TimeSpan.FromSeconds(1));
        if (!client.Connected)
        {
            throw new Exception("Failed to connect.");
        }

        // we have connected
        client.EndConnect(result);

Answer 5

上面的答案不包括如何干净地处理已超时的连接.调用TcpClient.EndConnect,关闭超时后成功的连接,并处理TcpClient.

这可能有点矫枉过正,但这对我有用.

    private class State
    {
        public TcpClient Client { get; set; }
        public bool Success { get; set; }
    }

    public TcpClient Connect(string hostName, int port, int timeout)
    {
        var client = new TcpClient();

        //when the connection completes before the timeout it will cause a race
        //we want EndConnect to always treat the connection as successful if it wins
        var state = new State { Client = client, Success = true };

        IAsyncResult ar = client.BeginConnect(hostName, port, EndConnect, state);
        state.Success = ar.AsyncWaitHandle.WaitOne(timeout, false);

        if (!state.Success || !client.Connected)
            throw new Exception("Failed to connect.");

        return client;
    }

    void EndConnect(IAsyncResult ar)
    {
        var state = (State)ar.AsyncState;
        TcpClient client = state.Client;

        try
        {
            client.EndConnect(ar);
        }
        catch { }

        if (client.Connected && state.Success)
            return;

        client.Close();
    }