Add global shutdown hook function to modules

modules/start.go

@@ -16,8 +16,9 @@ var (
 	globalPrepFn          func() error
 )
 
-// SetGlobalPrepFn sets a global prep function that is run before all modules. This can be used to pre-initialize modules, such as setting the data root or database path.
 // SetGlobalPrepFn sets a global prep function that is run before all modules.
+// This can be used to pre-initialize modules, such as setting the data root
+// or database path.
 func SetGlobalPrepFn(fn func() error) {
 	if globalPrepFn == nil {
 		globalPrepFn = fn

modules/stop.go

@@ -14,8 +14,17 @@ var (
 	shutdownFlag   = abool.NewBool(false)
 
 	shutdownCompleteSignal = make(chan struct{})
+
+	globalShutdownFn func()
 )
 
+// SetGlobalShutdownFn sets a global shutdown function that is called first when shutting down.
+func SetGlobalShutdownFn(fn func()) {
+	if globalShutdownFn == nil {
+		globalShutdownFn = fn
+	}
+}
+
 // IsShuttingDown returns whether the global shutdown is in progress.
 func IsShuttingDown() bool {
 	return shutdownFlag.IsSet()
@@ -39,6 +48,11 @@ func Shutdown() error {
 		return errors.New("shutdown already initiated")
 	}
 
+	// Execute global shutdown function.
+	if globalShutdownFn != nil {
+		globalShutdownFn()
+	}
+
 	if initialStartCompleted.IsSet() {
 		log.Warning("modules: starting shutdown...")
 	} else {