Can I set the timeout for UdpClient in C#?

问题:

I am wondering whether I can set a timeout value for UdpClient receive method.

I want to use block mode, but because sometimes udp will lost packet, my program udpClient.receive will hang there forever.

any good ideas how I can manage that?

回答1:

What Filip is referring to is nested within the socket that UdpClient contains (UdpClient.Client.ReceiveTimeout).

You can also use the async methods to do this, but manually block execution:

var timeToWait = TimeSpan.FromSeconds(10);

var udpClient = new UdpClient( portNumber );
var asyncResult = udpClient.BeginReceive( null, null );
asyncResult.AsyncWaitHandle.WaitOne( timeToWait );
if (asyncResult.IsCompleted)
{
    try
    {
        IPEndPoint remoteEP = null;
        byte[] receivedData = udpClient.EndReceive( asyncResult, ref remoteEP );
        // EndReceive worked and we have received data and remote endpoint
    }
    catch (Exception ex)
    {
        // EndReceive failed and we ended up here
    }
} 
else
{
    // The operation wasn't completed before the timeout and we're off the hook
}

回答2:

There is a SendTimeout and a ReceiveTimeout property that you can use in the Socket of the UdpClient.

Here is an example of a 5 second timeout:

var udpClient = new UdpClient();

udpClient.Client.SendTimeout = 5000;
udpClient.Client.ReceiveTimeout = 5000;

...

回答3:

Actually, it appears that UdpClient is broken when it comes to timeouts. I tried to write a server with a thread containing only a Receive which got the data and added it to a queue. I've done this sort of things for years with TCP. The expectation is that the loop blocks at the receive until a message comes in from a requester. However, despite setting the timeout to infinity:

_server.Client.ReceiveTimeout = 0; //block waiting for connections
_server.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 0);

the socket times out after about 3 minutes.

The only workaround I found was to catch the timeout exception and continue the loop. This hides the Microsoft bug but fails to answer the fundamental question of why this is happening.

回答4:

There is a ReceiveTimeout property you can use.

回答5:

you can do like this:

udpClient.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 5000);