Talk Nerdy To Me

Applications that open and close a large number of client TCP/IP sockets run the risk of running out of available socket ports.  This can happen in a load and performance testing scenario using a tool like LISA Test from iTKO, or it could happen in a production environment if an active application simply needs to rapidly open and close a large number of outbound connections.

On the .NET platform, the exception raised reads “System.Net.Sockets.SocketException: Only one usage of each socket address (protocol/network address/port) is normally permitted <host>:<port>“. 

In Java, the exception is “java.net.BindException: Address already in use: connect“. 

Both exceptions are misleading because they are generally associated with server socket conflicts – not outbound client socket connections.  However, a better understanding of the TCP state machine sheds some light on this behavior – and a solution.

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Asynchronous operations allow a program to perform time consuming tasks on a background thread while the main application continues to execute.  For example, consider when a program makes a request to a remote system.  In a single-threaded scenario, the call is made and the CPU goes idle as the caller waits on the server’s processing time and the network latency.  If this waiting time can be delegated to a separate thread of execution, the program can complete other tasks until it receives notification the background work is complete.

However, managing multiple threads and cross-thread communication adds complexity to your code.  Fortunately, the .NET Framework has a useful design pattern applied to its I/O classes which easily enables asynchronous calls.  Let’s take a look at an example.

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