The History Behind Broadcatch - VOS

Generic Object Communications

(rev. 0.1, 11/22/96)

Communications

Messages & Notifications

Characteristics

• bi-directional
• asynchronous (non-blocking)
• lightweight (ASCII)

Types

• Identification (Machine, AppName, etc...)
• Interest Registration (insert, update, delete)
• setSchemaName( schemaName )
• User Notification
• Application Notification

Message Structure

     #Priority    -- number >= 0
     #TimeStamp   -- creation time of the message
     #Expiration  -- expiration date of the message (0 -> never expires)
     #MessageType -- TBD (from a well-known list)
     #MessageBody -- TBD (open-ended; a propertyList)
     #Recipients  -- optional propertyList; [profile/appName]@machineAddr

Data Transaction

Characteristics

• bi-directional
• synchronous (blocking)
• can be binary

Types

• getAppStyleTemplate
• getReferenceToStationObject
• getData

Station Class

• Msg: Identification (Machine, etc...)
• D/T: createStationObject (all generic data for apps)

Client Application Initialization Process

Base Class Initialization

• put getReferenceToStationObject into pStation
  • put initializeConnection into pConnection
• Msg: setSchema( schemaName )
• Msg: Identification (AppName, etc...)
• D/T: put getAppStyleTemplate(AppName) into pAppStyle
• Msg: Interest Registration (non-app-specific default messages e.g., non-blocking system messages)
• pMessageHandler will point to a generic, possibly ugly, default message handler that clients may override using setMessageHandler

Base Class Methods

• sendMessage(propertyList)

Sub-Class Initialization

• Customize UI according to pAppStyle
• Msg: Interest Registration (app-specific)
• startMovie (perform app-specific initializations)

Sub-Class Destructor

• write userPreferences for any logged-on users

Base Class Destructor

• send terminateApplication(AppName) -- unregisters Interests, kill app-specific message, etc...

Client Application onIdle Loop

• checkForMessagesStart(minPriority) -- returns a message as a propertyList (or void)
• checkForMessagesNext -- returns next message propertyList (or void)
• checkForMessagesEnd -- prematurely terminate the iterator

Message Types

Interest Registration Enumerations (the message body)

     [#onTableChange  : tableName]
     [#onQueryChange  : query] -- under consideration

Connection Class: pConnection

     [#connectionType : string ] -- RAW, FTP, etc...
     [#port : integer ]          --
     [#hostAddress : ipNumber ]  --
     [#socket : sockaddr_in ]    -- the handle used for reading and writing
      ...

Private Methods of pConnection

     bind
     connect
     accept
     close
     put onSend(message) into cookie
     put onRecv(cookie) into message