Properties   Methods   Events   Configuration Settings  

The IPDaemon component is used to create TCP/IP servers. The component handles multiple simultaneous connections on the same TCP/IP port (service port). It is designed to balance the load between connections for a fast, powerful server.

NOTE: What follows is a very short description of the component interfaces. For more information, please consult the help files that come with the respective package.

Remarks

IPDaemon is the server complement of IPPort (which is used to create client applications). They share a common design philosophy and interface. We expect you will find IPDaemon as easy to use as IPPort.

By default, each instance of IPDaemon can handle up to 1000 simultaneous incoming connections (this number may be increased up to 100,000, or decreased to a lower value by using the MaxConnections configuration setting).

The connections are identified by a ConnectionId (a number between 1 and MaxConnections). IPDaemon's events also have ConnectionId as a parameter to identify the connection they relate to.

Our main goal in designing IPDaemon was to make it easy to use without sacrificing performance. The component has a minimum of properties, and six events: ConnectionRequest, Connected, DataIn, Disconnected, ReadyToSend, and Error.

IPDaemon can start to listen on a port by setting the Listening property to True. When a remote host asks for a connection, the ConnectionRequest event is fired. At that point, the connection can either be accepted or rejected. If the connection is accepted, a ConnectionId is assigned, and communication can start. From this point on, the operation is very similar to IPPort. Data is sent by assigning the data string to the DataToSend property. The address and port of the incoming connection can be found by querying the RemoteHost and RemotePort properties.

Threading in Server Applications

In .NET, all socket-based components perform all socket IO through asynchronous methods. Each call consumes a thread from the system's thread pool, and thus the number of concurrent calls is limited to the number of worker threads returned by System.Threading.ThreadPool.GetMaxThreads. When using several components that can each create a socket connection or a single component that can create multiple socket connections, the application may enter a state where all of the pool threads are in use for receiving. In a scenario such as this, the remote hosts may be waiting for data from the application before sending, but the application cannot send that data because all the threads are tied up waiting for inbound data. This is particularly important for server applications that use a daemon component.

For example, say a server application 'S' has a max thread pool size of 3, and clients 'A; and 'B' connect to it and each client uploads a large file. After all uploads are complete, S enqueues an asynchronous read request in the thread pool for each client. Since there is no work being done, the thread pool immediately consumes 2 threads which wait for any further data from A and B. While S is still processing the first two files it has received, client 'C' connects and uploads a relatively small file. Similarly, once that upload has completed S enqueues a third read request, and the thread pool immediately consumes the third and final thread to wait for further data from C. Once S completes processing any of the files it will enqueue a send request. However, since all 3 threads are in use and waiting for data from the clients, the send operation cannot be completed. The entire system becomes deadlocked because each of the clients is waiting for data from the server, which cannot send that data since all of its pool threads are in turn waiting for data from the clients.

To avoid a deadlock situation such as this, it is necessary to ensure that the maximum number of socket connections an application can make is always at least one less than the number of available worker threads. One method to achieve this is to call System.Threading.ThreadPool.SetMaxThreads during the application's startup to set the maximum number of threads to a value high enough to support the application for the duration of its execution. Another option is to trap an event such as ConnectionRequest and Disconnected from each component instance with logic to manage the max thread pool size according to the application's current needs.

Property List

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The following is the full list of the properties of the component with short descriptions. Click on the links for further details.

ConnectionBacklog	The maximum number of pending connections maintained by the TCP/IP subsystem.
Connections	A collection of currently connected clients.
DefaultEOL	A default EOL value to be used by incoming connections.
DefaultMaxLineLength	The default maximum line length value for inbound connections.
DefaultSingleLineMode	Tells the component whether or not to treat new connections as line-oriented.
DefaultTimeout	An initial timeout value to be used by incoming connections.
KeepAlive	When True, KEEPALIVE packets are enabled (for long connections).
Linger	When set to True, connections are terminated gracefully.
Listening	If True, the component accepts incoming connections on LocalPort.
LocalHost	The name of the local host or user-assigned IP interface through which connections are initiated or accepted.
LocalPort	The TCP port in the local host where the component listens.

Method List

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The following is the full list of the methods of the component with short descriptions. Click on the links for further details.

Config	Sets or retrieves a configuration setting.
Disconnect	Disconnect from the remote host.
DoEvents	Processes events from the internal message queue.
Interrupt	Send file to the remote host.
Send	Send data to the remote host.
SendFile	Send file to the remote host.
SendLine	Sends a string followed by a newline.
Shutdown	Shutdown the server.

Event List

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The following is the full list of the events fired by the component with short descriptions. Click on the links for further details.

Connected	Fired immediately after a connection completes (or fails).
ConnectionRequest	Fired when a request for connection comes from a remote host.
DataIn	Fired when data (complete lines) comes in.
Disconnected	Fired when a connection is closed.
Error	Information about errors during data delivery.
ReadyToSend	Fired when the component is ready to send data.

Configuration Settings

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The following is a list of configuration settings for the component with short descriptions. Click on the links for further details.

BindExclusively	Whether or not the component considers a local port reserved for exclusive use.
InBufferSize	The size in bytes of the incoming queue of the socket.
MaxConnections	The maximum number of connections available
OutBufferSize	The size in bytes of the outgoing queue of the socket.
TcpNoDelay	Whether or not to delay when sending packets
CodePage	The system code page used for Unicode to Multibyte translations (Windows/COM only).