Socket.Poll Method
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)
public boolean Poll ( int microSeconds, SelectMode mode )
public function Poll ( microSeconds : int, mode : SelectMode ) : boolean
Parameters
- microSeconds
The time to wait for a response, in microseconds.
- mode
One of the SelectMode values.
Return Value
| Mode | Return Value |
|---|---|
| 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. | |
| true, if processing a Connect, and the connection has succeeded; -or- true if data can be sent; otherwise, returns false. | |
| 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. |
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 in the MSDN library 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. |
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
//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.get_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 should not print."
+ "Because this is not a listening Socket,"
+ " no incoming connecton requests are expected. ");
}
else {
if (s.Poll(-1, SelectMode.SelectError)) {
Console.WriteLine("This Socket has an error.");
}
}
}
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.
Note