TcpListener.BeginAcceptSocket Method (AsyncCallback, Object)


Begins an asynchronous operation to accept an incoming connection attempt.

Namespace:   System.Net.Sockets
Assembly:  System (in System.dll)

<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)>
Public Function BeginAcceptSocket (
	callback As AsyncCallback,
	state As Object
) As IAsyncResult


Type: System.AsyncCallback

An AsyncCallback delegate that references the method to invoke when the operation is complete.

Type: System.Object

A user-defined object containing information about the accept operation. This object is passed to the callback delegate when the operation is complete.

Return Value

Type: System.IAsyncResult

An IAsyncResult that references the asynchronous creation of the Socket.

Exception Condition

An error occurred while attempting to access the socket. See the Remarks section for more information.


The Socket has been closed.

The asynchronous BeginAcceptSocket operation must be completed by calling the EndAcceptSocket method. Typically, the method is invoked by the callback delegate.

This method does not block until the operation completes. To block until the operation completes, use the AcceptSocket method.

For detailed information about using the asynchronous programming model, see Calling Synchronous Methods Asynchronously.


You can call the RemoteEndPoint property of the returned Socket to identify the remote host's network address and port number.


If you receive a SocketException, use the SocketException.ErrorCode property to obtain the specific error code and refer to the Windows Sockets version 2 API error code documentation in the MSDN library at for a detailed description of the error.


This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing in the .NET Framework.

The following code example demonstrates the use of the BeginAcceptSocket method to create and connect a socket. The callback delegate calls the EndAcceptSocket method to end the asynchronous request.

' Thread signal.
Public Shared clientConnected As New ManualResetEvent(False)

' Accept one client connection asynchronously.
Public Shared Sub DoBeginAcceptSocket(listener As TcpListener)
   ' Set the event to nonsignaled state.

   ' Start to listen for connections from a client.
   Console.WriteLine("Waiting for a connection...")

   ' Accept the connection. 
   ' BeginAcceptSocket() creates the accepted socket.
   listener.BeginAcceptSocket(New AsyncCallback(AddressOf DoAcceptSocketCallback), listener)
   ' Wait until a connection is made and processed before 
   ' continuing.
End Sub 'DoBeginAcceptSocket

' Process the client connection.
Public Shared Sub DoAcceptSocketCallback(ar As IAsyncResult)
   ' Get the listener that handles the client request.
   Dim listener As TcpListener = CType(ar.AsyncState, TcpListener)

   ' End the operation and display the received data on the
   Dim clientSocket As Socket = listener.EndAcceptSocket(ar)

   ' Process the connection here. (Add the client to a 
   ' server table, read data, etc.)
   Console.WriteLine("Client connected completed")

   ' Signal the calling thread to continue.
End Sub 'DoAcceptSocketCallback

.NET Framework
Available since 2.0
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