ProcessModule And Connections

Overview

This document describes how to use the process module with multiple remote connections.

Details

• Every process can have only one instance of vtkProcessModule. ProcessModule is a singleton and this fact is relied upon every where in the ServerManager. Hence it is an error to create more than one instance of a process module in any process.

• vtkProcessModule has support for multiple remote connections (vtkRemoteConnection). Howevever, by default it is set up to behave the ParaView way:
  • In forward connection mode:
    • Server waits for client at start.
    • Client connects to server before GUI starts (in render-client mode, client connects to data server and render server).
    • Once a client connects, the server closes its server sockets so that no more clients can connect to it.
    • When client disconnects, server exits.
  • In reverse connection mode:
    • Client waits for server at start, before GUI starts.
    • Server connects to client at start.
    • When client disconnects, server exits.

• To override this behaviour, vtkProcessModule provides the SupportMultipleConnections flag, which must be set before calling vtkProcessModule::Start().
• When this flag is set:
  • In forward connection mode:
    • Server sets up server sockets and waits for the client at start.
    • If a client connects, the server still keeps the server sockets open and accepts any new client connections comming on the socket.
    • When a client disconnects the server simply closes the connections and processes other connections as well as accepts new incoming connections.
    • Client does not attempt to connect to the server in Start(). Instead vtkProcessModule::ConnectToRemote() must be explicitly called.
    • Client can connect to more that 1 server using ConnectToRemote().
  • In reverse connection mode:
    • The server can connect to only one client, which it attempts to connect at start.
    • The server exits when the client connection is closed.
    • The client does not wait for any server connections at the start. Instead vtkProcessModule::MonitorConnections() must be called to accept any incoming server connection requests.