Socket.Poll(Int32, SelectMode) Method

Definition

Determines the status of the Socket.

public:
 bool Poll(int microSeconds, System::Net::Sockets::SelectMode mode);
public bool Poll (int microSeconds, System.Net.Sockets.SelectMode mode);
member this.Poll : int * System.Net.Sockets.SelectMode -> bool
Public Function Poll (microSeconds As Integer, mode As SelectMode) As Boolean

Parameters

microSeconds
Int32

The time to wait for a response, in microseconds.

mode
SelectMode

One of the SelectMode values.

Returns

The status of the Socket based on the polling mode value passed in the mode parameter.

Mode Return Value
SelectReadtrue if Listen(Int32) has been called and a connection is pending; -or- true if data is available for reading; -or- true if the connection has been closed, reset, or terminated; otherwise, returns false.
SelectWritetrue, if processing a Connect(EndPoint), and the connection has succeeded; -or- true if data can be sent; otherwise, returns false.
SelectErrortrue if processing a Connect(EndPoint) that does not block, and the connection has failed; -or- true if OutOfBandInline is not set and out-of-band data is available; otherwise, returns false.

Exceptions

The mode parameter is not one of the SelectMode values.

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

The Socket has been closed.

Examples

The following code example creates a socket, connects to a server, and uses Poll to check the status of the socket.

//Creates the Socket for sending data over TCP.
Socket^ s = gcnew Socket( AddressFamily::InterNetwork, SocketType::Stream,
   ProtocolType::Tcp );

// Connects to host using IPEndPoint.
s->Connect( EPhost );
if ( !s->Connected )
{
   strRetPage = "Unable to connect to host";
}
// Use the SelectWrite enumeration to obtain Socket status.
if ( s->Poll( -1, SelectMode::SelectWrite ) )
{
   Console::WriteLine( "This Socket is writable." );
}
else if ( s->Poll(  -1, SelectMode::SelectRead ) )
{
   Console::WriteLine( "This Socket is readable." );
}
else if ( s->Poll(  -1, SelectMode::SelectError ) )
{
   Console::WriteLine( "This Socket has an error." );
}
   //Creates the Socket for sending data over TCP.
   Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Stream,
      ProtocolType.Tcp );

   // Connects to host using IPEndPoint.
   s.Connect(EPhost);
   if (!s.Connected)
   {
      strRetPage = "Unable to connect to host";
   }
   // Use the SelectWrite enumeration to obtain Socket status.
    if(s.Poll(-1, SelectMode.SelectWrite)){
         Console.WriteLine("This Socket is writable.");
    }
    else if (s.Poll(-1, SelectMode.SelectRead)){
          Console.WriteLine("This Socket is readable." );
    }
    else if (s.Poll(-1, SelectMode.SelectError)){
         Console.WriteLine("This Socket has an error.");
    }

'Creates the Socket for sending data over TCP.
Dim s As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)

' Connects to host using IPEndPoint.
s.Connect(EPhost)
If Not s.Connected Then
   strRetPage = "Unable to connect to host"
End If
' Use the SelectWrite enumeration to obtain Socket status.
If s.Poll(- 1, SelectMode.SelectWrite) Then
   Console.WriteLine("This Socket is writable.")
Else
   If s.Poll(- 1, SelectMode.SelectRead) Then
      Console.WriteLine(("This Socket is readable. "))
   Else
      If s.Poll(- 1, SelectMode.SelectError) Then
         Console.WriteLine("This Socket has an error.")
      End If
   End If 
End If 

Remarks

The Poll method will check the state of the Socket. Specify SelectMode.SelectRead for the selectMode parameter to determine if the Socket is readable. Specify SelectMode.SelectWrite to determine if the Socket is writable. Use SelectMode.SelectError to detect an error condition. Poll will block execution until the specified time period, measured in microseconds, elapses. Set the microSeconds parameter to a negative integer if you would like to wait indefinitely for a response. If you want to check the status of multiple sockets, you might prefer to use the Select method.

Note

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 for a detailed description of the error.

Note

This method cannot detect certain kinds of connection problems, such as a broken network cable, or that the remote host was shut down ungracefully. You must attempt to send or receive data to detect these kinds of errors.

Note

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

Applies to

See also