This documentation is archived and is not being maintained.

Socket.BeginSend Method (Generic IList, SocketFlags, SocketError, AsyncCallback, Object)

Note: This method is new in the .NET Framework version 2.0.

Sends data asynchronously to a connected Socket.

This method is not CLS-compliant.  

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

public IAsyncResult BeginSend (
	IList<ArraySegment<byte>> buffers,
	SocketFlags socketFlags,
	out SocketError errorCode,
	AsyncCallback callback,
	Object state
/** @attribute CLSCompliantAttribute(false) */ 
public IAsyncResult BeginSend (
	IList<ArraySegment<byte>> buffers, 
	SocketFlags socketFlags, 
	/** @attribute OutAttribute() */ /** @ref */ SocketError errorCode, 
	AsyncCallback callback, 
	Object state
JScript does not support passing value-type arguments by reference.



An array of type Byte that contains the data to send.


A bitwise combination of the SocketFlags values.


A SocketError object that stores the socket error.


The AsyncCallback delegate.


An object that contains state information for this request.

Return Value

An IAsyncResult that references the asynchronous send.

Exception typeCondition


buffers is a null reference (Nothing in Visual Basic).


buffers is empty.


An error occurred when attempting to access the socket. See remarks section below.


The Socket has been closed.

The BeginSend method starts an asynchronous send operation to the remote host established in the Connect, BeginConnect, Accept, or BeginAccept method. BeginSend will throw an exception if you do not first call Accept, BeginAccept, Connect, or BeginConnect. Calling the BeginSend method gives you the ability to send data within a separate execution thread.

You can create a callback method that implements the AsyncCallback delegate and pass its name to the BeginSend method. To do this, at the very minimum, your state parameter must contain the connected or default Socket being used for communication. If your callback needs more information, you can create a small class or structure to hold the Socket and the other required information. Pass an instance of this class to the BeginSend method through the state parameter.

Your callback method should invoke the EndSend method. When your application calls BeginSend, the system will use a separate thread to execute the specified callback method, and will block on EndSend until the Socket sends the number of bytes requested or throws an exception. If you want the original thread to block after you call the BeginSend method, use the WaitHandle.WaitOne method. Call the Set method on a T:System.Threading.ManualResetEvent in the callback method when you want the original thread to continue executing. For additional information on writing callback methods see Callback Sample.

Although intended for connection-oriented protocols, BeginSend also works for connectionless protocols, provided that you first call the Connect or BeginConnect method to establish a default remote host. If you are using a connectionless protocol and plan to send data to several different hosts, you should use BeginSendTo. It is okay to use BeginSendTo even after you have established a default remote host with Connect. You can also change the default remote host prior to calling BeginSend by making another call to Connect or BeginConnect. With connectionless protocols, you must also be sure that the size of your buffer does not exceed the maximum packet size of the underlying service provider. If it does, the datagram will not be sent and BeginSend will throw a SocketException.

If you specify the DontRoute flag as the socketflags parameter, the data you are sending will not be routed.


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 the MSDN library for a detailed description of the error.


All I/O initiated by a given thread is canceled when that thread exits. A pending asynchronous operation can fail if the thread exits before the operation completes.


state is an instantiation of a user-defined class.


The successful completion of a send does not indicate that the data was successfully delivered. If no buffer space is available within the transport system to hold the data to be transmitted, send will block unless the socket has been placed in nonblocking mode.


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


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.

Windows 98, Windows 2000 SP4, Windows Millennium Edition, 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