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Socket.BeginAccept Method (AsyncCallback, Object)

Begins an asynchronous operation to accept an incoming connection attempt.

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

public IAsyncResult BeginAccept (
	AsyncCallback callback,
	Object state
)
public IAsyncResult BeginAccept (
	AsyncCallback callback, 
	Object state
)
public function BeginAccept (
	callback : AsyncCallback, 
	state : Object
) : IAsyncResult

Parameters

callback

The AsyncCallback delegate.

state

An object that contains state information for this request.

Return Value

An IAsyncResult that references the asynchronous Socket creation.

Exception typeCondition

ObjectDisposedException

The Socket object has been closed.

NotSupportedException

Windows NT is required for this method.

InvalidOperationException

The accepting socket is not listening for connections. You must call Bind and Listen before calling BeginAccept.

-or-

The accepted socket is bound.

ArgumentOutOfRangeException

receiveSize is less than 0.

SocketException

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

Connection-oriented protocols can use the BeginAccept method to asynchronously process incoming connection attempts. Accepting connections asynchronously gives you the ability to send and receive data within a separate execution thread. Before calling the BeginAccept method, you must call the Listen method to listen for and queue incoming connection requests.

You must create a callback method that implements the AsyncCallback delegate and pass its name to the BeginAccept method. To do this, at the very minimum, you must pass the listening Socket object to BeginAccept through the state parameter. If your callback needs more information, you can create a small class to hold the Socket and the other required information. Pass an instance of this class to the BeginAccept method through the state parameter.

Your callback method should invoke the EndAccept method. When your application calls BeginAccept, the system uses a separate thread to execute the specified callback method and blocks on EndAccept until a pending connection is retrieved. EndAccept will return a new Socket object that you can use to send and receive data with the remote host. You cannot use this returned Socket to accept any additional connections from the connection queue. If you want the original thread to block after you call the BeginAccept method, use WaitHandle.WaitOne. Call the Set method on a ManualResetEvent in the callback method when you want the original thread to continue executing. For additional information on writing callback methods see Callback Sample.

NoteNote

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

NoteNote

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

NoteNote

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

NoteNote

The execution context (the security context, the impersonated user, and the calling context) is cached for the asynchronous Socket methods. After the first use of a particular context (a specific asynchronous Socket method, a specific Socket instance, and a specific callback), subsequent uses of that context will see a performance improvement.

The following code example attempts to receive an incoming connection asynchronously.

IPHostEntry lipa = Dns.Resolve("host.contoso.com");
IPEndPoint lep = new IPEndPoint(lipa.AddressList[0], 11000);

   Socket s = new Socket(lep.Address.AddressFamily,
                                  SocketType.Stream,
                                     ProtocolType.Tcp);
   try{
        s.Bind(lep);
        s.Listen(1000);

        while(true){
             allDone.Reset();

             Console.WriteLine("Waiting for a connection...");
             s.BeginAccept(new AsyncCallback(Async_Send_Receive.Listen_Callback), s);

             allDone.WaitOne();
        }
   }
   catch (Exception e){
        Console.WriteLine(e.ToString());
   }

IPHostEntry lipa = Dns.Resolve("host.contoso.com");
IPEndPoint lep = new IPEndPoint(lipa.get_AddressList()[0], 11000);

Socket s = new Socket(lep.get_Address().get_AddressFamily(),
    SocketType.Stream, ProtocolType.Tcp);
try {
    s.Bind(lep);
    s.Listen(1000);

    while (true) {
        allDone.Reset();
        Console.WriteLine("Waiting for a connection...");
        s.BeginAccept(new AsyncCallback(Async_Send_Receive.
            Listen_Callback), s);
        allDone.WaitOne();
    }
}
catch (System.Exception e) {
    Console.WriteLine(e.ToString());
}

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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