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Socket.Poll Method

Determines the status of the Socket.

Namespace:  System.Net.Sockets
Assembly:  System (in System.dll)
'Declaration
Public Function Poll ( _
	microSeconds As Integer, _
	mode As SelectMode _
) As Boolean
'Usage
Dim instance As Socket 
Dim microSeconds As Integer 
Dim mode As SelectMode 
Dim returnValue As Boolean 

returnValue = instance.Poll(microSeconds, _
	mode)

Parameters

microSeconds
Type: System.Int32

The time to wait for a response, in microseconds.

mode
Type: System.Net.Sockets.SelectMode

One of the SelectMode values.

Return Value

Type: System.Boolean
The status of the Socket based on the polling mode value passed in the mode parameter.

Mode

Return Value

SelectRead

true if Listen 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.

SelectWrite

true, if processing a Connect, and the connection has succeeded;

-or-

true if data can be sent;

otherwise, returns false.

SelectError

true if processing a Connect 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.

ExceptionCondition
NotSupportedException

The mode parameter is not one of the SelectMode values.

SocketException

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

ObjectDisposedException

The Socket has been closed.

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.

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 the MSDN library for a detailed description of the error.

NoteNote:

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.

NoteNote:

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

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. 
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
//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 = S"Unable to connect to host";
}
// Use the SelectWrite enumeration to obtain Socket status.
if (s->Poll(-1, SelectMode::SelectWrite)) {
    Console::WriteLine(S"This Socket is writable.");
} else if (s->Poll(-1, SelectMode::SelectRead)) {
    Console::WriteLine(S"This Socket is readable.");
} else if (s->Poll(-1, SelectMode::SelectError)) {
    Console::WriteLine(S"This Socket has an error.");
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

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

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0
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