XPCPlugin

The XPCPlugin module contains the core functions that the X-Plane plugin manager uses to interact with the plugin. These functions handle startup, shutdown, and the the core operation of the plugin.

###Basic Flow When X-Plane is launched, it looks for plugins and runs their XPluginStart function. The plugin manager expects us to copy some basic information into the provided char* parameters. X-Plane Connect also uses the XPluginStart function to perform some basic startup tasks like initializing its log file and setting up the DataManager component.

As X-Plane is running, the plugin can be enabled and disabled by several mechanisms, including directly by the user and by other plugins. Each time the plugin is enabled, the XPluginEnable function is called, and each time the plugin is disabled, the XPluginDisable function is called. X-Plane Connect uses these functions to manage resources that are only needed while the plugin is running. Each time XPluginEnable is called, X-Plane Connect creates a new UDP socket to listen for commands and registers a callback on the flight loop. Each time XPluginDisable is called, the flight loop callback is unregistered and the socket released.

Finally, when X-Plane is shut down normally the XPluginStop function is called. Because XPluginDisable is always called before XPluginStop, there is little for X-Plane Connect to do on shutdown. Currently and event is logged and the log file is closed on shutdown.

###Functions The following functions are declared and implemented in XPCPlugin.cpp.

####XPluginStart Signature: PLUGIN_API int XPluginStart(char* outName, char* outSig, char* outDesc);

XPluginStart performs the following operations:

• Writes the name, signature, and description for the plugin.
• Initializes the log file
• Initializes the DataManager component

####XPluginStop Signature: PLUGIN_API void XPluginStop(void);

XPluginStop performs the following operations:

• Closes the log file

####XPluginEnable Signature: PLUGIN_API int XPluginEnable(void);

XPluginEnable performs the following operations:

• Open a UDP socket
• Register the flight loop callback

####XPluginDisable Signature: PLUGIN_API void XPluginDisable(void);

XPluginDisable performs the following operations:

• Close the UDP socket
• Unregister the flight loop callback

####XPluginReceiveMessage Signature:

PLUGIN_API void XPluginReceiveMessage(XPLMPluginID inFromWho,
                                      int inMessage,
                                      void* inParam);

XPluginReceiveMessage does not currently perform any operations. It is defined only because the X-Plane Plugin manager requires that all plugins implement this function.

####XPCFlightLoopCallback Signature:

static float XPCFlightLoopCallback(float inElapsedSinceLastCall,
                                   float inElapsedTimeSinceLastFlightLoop,
                                   int inCounter,
                                   void* inRefcon);

XPCFlightLoopCallback performs the following operations:

• Try to read a message from the UDP socket.
• If a message is received, pass it to MessageHandlers to be processed.
• Repeat the above two steps up to OPS_PER_CYCLE times