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11/18/2011

SocketAsyncEventArgs Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Represents an asynchronous socket operation.

Inheritance Hierarchy

System.Object
System.EventArgs
System.Net.Sockets.SocketAsyncEventArgs

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

Syntax

'Declaration
Public Class SocketAsyncEventArgs _
    Inherits EventArgs _
    Implements IDisposable

public class SocketAsyncEventArgs : EventArgs, 
    IDisposable

The SocketAsyncEventArgs type exposes the following members.

Constructors

	Name	Description
	SocketAsyncEventArgs	Creates an empty SocketAsyncEventArgs instance.

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Properties

	Name	Description
	Buffer	Gets the data buffer to use with an asynchronous socket method.
	BufferList	Gets or sets an array of data buffers to use with an asynchronous socket method.
	BytesTransferred	Gets the number of bytes transferred in the socket operation.
	ConnectByNameError	Gets the exception in the case of a connection failure when a DnsEndPoint was used.
	ConnectSocket	The created and connected Socket object after successful completion of the ConnectAsync method.
	Count	Gets the maximum amount of data, in bytes, to send or receive in an asynchronous operation.
	LastOperation	Gets the type of socket operation most recently performed with this object.
	Offset	Gets the offset, in bytes, into the data buffer referenced by the Buffer property.
	RemoteEndPoint	Gets or sets the remote IP or DNS endpoint for an asynchronous operation.
	SocketClientAccessPolicyProtocol	Gets or sets the method to download the policy file that an instance of the Socket class will use.
	SocketError	Gets or sets the result of the asynchronous socket operation.
	UserToken	Gets or sets a user or application object associated with this asynchronous socket operation.

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Methods

	Name	Description
	Dispose	Releases the unmanaged resources used by the SocketAsyncEventArgs instance and optionally disposes of the managed resources.
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Frees resources used by the SocketAsyncEventArgs class. (Overrides Object.Finalize().)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	OnCompleted	Represents a method that is called when an asynchronous operation completes.
	SetBuffer(Int32, Int32)	Sets the data buffer to use with an asynchronous socket method.
	SetBuffer(array<Byte[], Int32, Int32)	Sets the data buffer to use with an asynchronous socket method.
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Events

	Name	Description
	Completed	An event that indicates an asynchronous operation is completed.

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Remarks

The SocketAsyncEventArgs class provides an asynchronous pattern used by socket applications. The main feature of this pattern is the avoidance of the repeated allocation and synchronization of objects during asynchronous socket I/O.

In the System.Net.Sockets.Socket class, asynchronous socket operations are described by reusable SocketAsyncEventArgs objects allocated and maintained by the application. Socket applications know best the amount of overlapped socket operations that must be sustained. The application can create as many of the SocketAsyncEventArgs objects that it needs. For example, if an application needs to have 15 socket send or receive operations outstanding at all times to support outgoing client connection rates, it can allocate 15 reusable SocketAsyncEventArgs objects for that purpose.

The pattern for performing an asynchronous socket operation with this class consists of the following steps:

Allocate a new SocketAsyncEventArgs object, or get a free one from an application pool.
Set properties on the SocketAsyncEventArgs object required for the operation about to be performed (the completion callback delegate method, the data buffer, the offset into the buffer, and the maximum amount of data to transfer for the ReceiveAsync and SendAsync methods, for example).
Call the appropriate socket method (ConnectAsync, ReceiveAsync, or SendAsync) to initiate the asynchronous operation.
If the asynchronous socket method returns true, the I/O operation is pending. The SocketAsyncEventArgs.Completed event on the System.Net.Sockets.SocketAsyncEventArgs object passed to the socket method will be raised upon completion of the operation. When the event is raised in the event handler, query the SocketAsyncEventArgs properties for the completion status and socket operation result (the amount of received data in the buffer for ReceiveAsync method call, for example).
If the asynchronous socket method returns false, the operation completed synchronously. The SocketAsyncEventArgs properties may be queried for the completion status and socket operation result.
Reuse the SocketAsyncEventArgs object for another operation, put it back in the pool, or discard it.

The lifetime of the new SocketAsyncEventArgs object used in an asynchronous socket operation is determined by references in the application code and asynchronous I/O references. It is not necessary for the application to retain a reference to a SocketAsyncEventArgs object after it is submitted as a parameter to one of the asynchronous socket methods. It will remain referenced until the completion callback returns. However it is advantageous for the application to retain the reference to the SocketAsyncEventArgs object so that it can be reused for a future asynchronous socket operation.

Examples

The following example creates two instances of the SocketAsyncEventArgs class, one for use with the ConnectAsync method and one for use with the ReceiveAsync method. The SocketAsyncEventArgs instance for use on the connect operation still needs the RemoteEndPoint property set to a DnsEndPoint instance for the host before the ConnectAsync method is called.

  public class Example
  {
    static ManualResetEvent clientDone = new ManualResetEvent(false);

    public static void Demo(System.Windows.Controls.TextBlock outputBlock)
    {

        SocketAsyncEventArgs socketEventArg = new SocketAsyncEventArgs();
            DnsEndPoint hostEntry = new DnsEndPoint("https://www.contoso.com", 80);

        // Create a socket and connect to the server
        Socket sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

        socketEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(SocketEventArg_Completed);

        socketEventArg.RemoteEndPoint = hostEntry;
        socketEventArg.UserToken = sock;
        sock.ConnectAsync(socketEventArg);
        clientDone.WaitOne();
    }

    // A single callback is used for all socket operations. 
    // This method forwards execution on to the correct handler 
    // based on the type of completed operation
    static void SocketEventArg_Completed(object sender, SocketAsyncEventArgs e)
    {
        switch (e.LastOperation)
        {
            case SocketAsyncOperation.Connect:
                ProcessConnect(e);
                break;
            case SocketAsyncOperation.Receive:
                ProcessReceive(e);
                break;
            case SocketAsyncOperation.Send:
                ProcessSend(e);
                break;
            default:
                throw new Exception("Invalid operation completed");
        }
    }

    // Called when a ConnectAsync operation completes
    private static void ProcessConnect(SocketAsyncEventArgs e)
    {
        if (e.SocketError == SocketError.Success)
        {
            // Successfully connected to the server

            // Send 'Hello World' to the server
            byte[] buffer = Encoding.UTF8.GetBytes("Hello World");
            e.SetBuffer(buffer, 0, buffer.Length);
            Socket sock = e.UserToken as Socket;
            bool willRaiseEvent = sock.SendAsync(e);
            if (!willRaiseEvent)
            {
                ProcessSend(e);
            }
        }
        else
        {
            throw new SocketException((int)e.SocketError);
        }
    }

        // Called when a ReceiveAsync operation completes
        // </summary>
    private static void ProcessReceive(SocketAsyncEventArgs e)
    {
        if (e.SocketError == SocketError.Success)
        {
            // Received data from server

        // Data has now been sent and received from the server. 
        // Disconnect from the server
            Socket sock = e.UserToken as Socket;
            sock.Shutdown(SocketShutdown.Send);
            sock.Close();
            clientDone.Set();
        }
        else
        {
            throw new SocketException((int)e.SocketError);
        }
    }


    // Called when a SendAsync operation completes
    private static void ProcessSend(SocketAsyncEventArgs e)
    {
        if (e.SocketError == SocketError.Success)
        {
            // Sent "Hello World" to the server successfully

            //Read data sent from the server
            Socket sock = e.UserToken as Socket;
            bool willRaiseEvent = sock.ReceiveAsync(e);
            if (!willRaiseEvent)
            {
                ProcessReceive(e);
            }
        }
        else
        {
            throw new SocketException((int)e.SocketError);
        }
    }
  }

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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