TechNote (Archived)

Detecting unintentional user disconnections in a Multiuser application

This TechNote is intended for intermediate to advanced developers of applications using the Multiuser Server and Xtra. It assumes a basic understanding of parent/child scripting.

For introductory information on the Multiuser Server and Xtra, please refer to Creating Multiuser Applications with Director.

How can a Multiuser application detect if a client has accidentally disconnected?
Developing an application using the Multiuser Server and Xtra in many cases requires that user connections, user disconnections and user crashes all be broadcast to other connected users. This can be accomplished with a "control movie" which is nothing more than one specialized Director movie with a unique login name. This control movie could reside as a projector on the same machine as the Multiuser Server, a different machine, or as a Shockwave movie in a browser on any machine.

The control movie would keep a list of user objects each with a property called "pConnectionStatus". At a predetermined interval a custom "ping" message would be sent to all users in the object list. Each object's "pConnectionStatus" value would be set to"#pinging".

A callback handler would need to be in place to respond to user messages with the subject "ping".

When a message with the subject "ping" arrives in the Xtra's messaging queue, the sender's object's "pConnectionStatus" property would be updated with the value,"#connected". If, after another interval, a user's "pConnectionStatus" still does not have the value"#connected", the control movie would ping again to verify, or simply delete the user object and send the updated information to all interested clients.

The following is one example of how to create a control movie which manages user connections:

1	In a new Director movie, create scripts which: Instantiate the Multiuser Xtra. Define callback handlers. Connect to the server. Instantiate user objects with the properties "pName" and"pConnectionStatus". These objects could be instantiated when a client sends an "InitPlayer" message to the control movie.
2	Create a callback handler which processes messages with the subject "ping". For example: global gAvatarList, gConnect on playerPingedCallbackHandler newMessage = gConnect.getNetMessage() errCode = newMessage.errorCode if errCode <> 0 then ShowMessageStatus(errCode) sender = newMessage.senderID avatarNum = gAvatarList.count repeat with i = 1 to avatarNum if gAvatarList[i]<> 0 then x = gAvatarList[i] if x <> 0 then if x.pName = sender then x.pConnectionStatus = #connected end if end if end if end repeat end playerPingedCallbackHandler
3	To set an interval in which to ping, use timeOut Scripts. The following could go in a "startMovie" handler: the timeOutScript = "pingUsers" the timeOutLength = 30 * 60 the timeOutKeyDown = FALSE the timeOutMouse = FALSE
4	The actual "ping" handler could look something like the following: global gPingFlag, gAvatarList on pingUsers --flag set so that the following two are alternated if gPingFlag then --go through avatarList and ping all players avatarNum = gAvatarList.count repeat with i = 1 to avatarNum if gAvatarList[i]<> 0 then x = gAvatarList[i] --doubt first x.pConnectionStatus = #pinging --then confirm when they respond to "ping" SendMessage(x.pName, "Ping") end if end repeat gPingFlag = 0 else --go through avatarList and see if --anyone is no longer connected avatarNum = gAvatarList.count repeat with i = 1 to avatarNum if gAvatarList[i]<> 0 then x = gAvatarList[i] if x.pConnectionStatus <> #connected then deleteUser(i) end if end repeat gPingFlag = 1 end if end pingUsers