Revel Hooks

Revel Application Start / Stop Hooks

Revel calls a set of functions, that users can register functions for, on startup of Revel and shutdown of Revel. For example the module/db package uses the OnAppStart to open a database connection (and registers a OnAppStop function to close a database connection). On registration you can optionally pass in a priority level as the second argument. The lowest priority gets activated first.

You can register your own actions in the following way

	revel.OnAppStop(func() {
		revel.RevelLog.Info("Opening the database (from module)")
		if err := Db.Close(); err != nil {
			revel.AppLog.Error("Failed to close the database", "error", err)
		}
	})

Revel Module Hooks

Modules have an initialization hook that gets called after the module is loaded in Revel. This callback passes the revel.Module object to the module so that you could perform some additional processing on startup. The revel.Module contains a logger.Multilogger which is specifically initialized for the module. It is recommended to use that when logging in modules.

func init() {
	revel.RegisterModuleInit(func(module *revel.Module) {
		moduleLogger = module.Log
		moduleLogger.Debug("Assigned Logger")
	})
}

Revel Manual Shutdown

You can manually stop your Revel application by calling revel.StopServer(nil). This allows you to gracefully take down a server instance when needed. You can also trigger a shutdown by killing the process using the interrupt level (CTRL+C or syscall.SIGINT). Once triggered the server engine will stop processing requests and run the OnAppStop hooks. This function call will block until the server is halted.

Revel Event Hooks

The startup of Revel is event driven and as a developer you can tie into this process by registration of an event handler object matching by passing a function of revel.EventHandler to revel.AddInitEventHandler like below

	revel.AddInitEventHandler(func(event revel.Event, value interface{}) (returnType revel.EventResponse) {
		if event == revel.REVEL_BEFORE_MODULES_LOADED {
		  // Do something
		}

		return 0
	})

Developers can then perform specific actions based off the core Revel startup process.

Important events are triggered in the same process thread, not on a separate channel, if you block an event Revel will not startup.

Normally the process flow goes as follows

• REVEL_BEFORE_MODULES_LOADED
• REVEL_AFTER_MODULES_LOADED
• ENGINE_BEFORE_INITIALIZED
• TEMPLATE_REFRESH_REQUESTED (May have multiple refreshes depending on file monitoring)
• TEMPLATE_REFRESH_COMPLETED
• (Triggered During OnAppStart)
  • ROUTE_REFRESH_REQUESTED (May have multiple refreshes depending on file monitoring)
  • ROUTE_REFRESH_COMPLETED
• ENGINE_STARTED

Shutdown can be triggered by revel.StopServer() which triggers a ENGINE_SHUTDOWN_REQUEST the server is not shutdown until you receive a ENGINE_SHUTDOWN event

In the case where Revel does not start the following event is triggered

• REVEL_FAILURE