How do I fix the error Only one usage of each socket address protocol network address port is normally permitted

Question

I ve done a lot of googling but not had much luck with my issues  I am new to network programming and trying to learn  I ve attempted to set up a simple server  amp  client that communicate  following an online tutorial located here -  http   tech pro tutorial 704 csharp-tutorial-simple-threaded-tcp-server   The issue I m having is that I keep getting the exception  Only one usage of each socket address  protocol network address port  is normally permitted  when trying to start the TcpListener on the server   I ve tried disabling my firewall  changing the port to be used  moving variables around but to no avail  the client works fine  but it obviously can t find the server because I cannot launch it    I ve seen solutions describing the use of Socket Poll   but since I m only using the TcpListener object  I have no idea how to make use of the Poll function   My code    using System  using System Collections Generic  using System Linq  using System Net Sockets  using System Net  using System Threading  using System Text   namespace ServerTutorial   class Server       private readonly Thread m listenThread       public Server             m listenThread   new Thread new ThreadStart ListenForClients            m listenThread Start               public void ListenForClients             var listener   new TcpListener IPAddress Any  3000           listener Start             while  true                  Blocks until a client has connected to the server             TcpClient client   listener AcceptTcpClient                   Send a message to the client             var encoder   new ASCIIEncoding                NetworkStream clientStream   client GetStream                byte   buffer   encoder GetBytes  Hello Client                 clientStream Write buffer  0  buffer Length               clientStream Flush                   Create a thread to handle communication with the connected client             var clientThread   new Thread new ParameterizedThreadStart HandleClient                clientThread Start client                        private void HandleClient object clientObj      Param thread start can only accept object types  hence the cast         var client    TcpClient  clientObj          NetworkStream clientStream   client GetStream             var message   new byte 4096            while  true                int bytesRead   0               try                     Block until a client sends a message                 bytesRead   clientStream Read message  0  4096                 catch                     A socket error has occurred                 System Diagnostics Debug WriteLine  A socket error has occured                    break                             if  bytesRead    0                      The client has disconnected from the server                 System Diagnostics Debug WriteLine  A client has disconnected from the server                    client Close                    break                               Message has been received             var encoder   new ASCIIEncoding                System Diagnostics Debug WriteLine encoder GetString message  0  bytesRead                          In my main method   using System  using System Collections Generic  using System Linq  using System Text   namespace ServerTutorial   class Program       static void Main string   args            var server   new Server            server ListenForClients                Any help is hugely appreciated

User · Answer

You are debugging two or more times  so the application may run more at a time  Then only this issue will occur  You should close all debugging applications using task-manager  Then debug again

User · Answer

ListenForClients is getting invoked twice  on two different threads  - once from the constructor  once from the explicit method call in Main  When two instances of the TcpListener try to listen on the same port  you get that error

User · Answer

I faced similar problem on windows server 2012 STD 64 bit   my problem is resolved after updating windows with all available windows updates

[c#] How do I fix the error "Only one usage of each socket address (protocol/network address/port) is normally permitted"?

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