Improve and fix module startup and shutdown procedures as well as error reporting

modules/modules.go

@@ -13,7 +13,7 @@ import (
 )
 
 var (
-	modulesLock sync.Mutex
+	modulesLock sync.RWMutex
 	modules     = make(map[string]*Module)
 
 	// ErrCleanExit is returned by Start() when the program is interrupted before starting. This can happen for example, when using the "--help" flag.
@@ -46,6 +46,10 @@ type Module struct {
 	microTaskCnt *int32
 	waitGroup    sync.WaitGroup
 
+	// events
+	eventHooks     map[string][]*eventHook
+	eventHooksLock sync.RWMutex
+
 	// dependency mgmt
 	depNames   []string
 	depModules []*Module
@@ -69,9 +73,9 @@ func (m *Module) shutdown() error {
 
 	// start shutdown function
 	m.waitGroup.Add(1)
-	stopFnError := make(chan error)
+	stopFnError := make(chan error, 1)
 	go func() {
-		stopFnError <- m.runModuleCtrlFn("stop module", m.stop)
+		stopFnError <- m.runCtrlFn("stop module", m.stop)
 		m.waitGroup.Done()
 	}()
 
@@ -84,16 +88,8 @@ func (m *Module) shutdown() error {
 
 	// wait for results
 	select {
-	case err := <-stopFnError:
-		return err
 	case <-done:
-		select {
-		case err := <-stopFnError:
-			return err
-		default:
-			return nil
-		}
-	case <-time.After(3 * time.Second):
+	case <-time.After(30 * time.Second):
 		log.Warningf(
 			"%s: timed out while waiting for workers/tasks to finish: workers=%d tasks=%d microtasks=%d, continuing shutdown...",
 			m.Name,
@@ -102,11 +98,18 @@ func (m *Module) shutdown() error {
 			atomic.LoadInt32(m.microTaskCnt),
 		)
 	}
-	return nil
-}
 
-func dummyAction() error {
-	return nil
+	// collect error
+	select {
+	case err := <-stopFnError:
+		return err
+	default:
+		log.Warningf(
+			"%s: timed out while waiting for stop function to finish, continuing shutdown...",
+			m.Name,
+		)
+		return nil
+	}
 }
 
 // Register registers a new module. The control functions `prep`, `start` and `stop` are technically optional. `stop` is called _after_ all added module workers finished.
@@ -141,20 +144,10 @@ func initNewModule(name string, prep, start, stop func() error, dependencies ...
 		prep:         prep,
 		start:        start,
 		stop:         stop,
+		eventHooks:   make(map[string][]*eventHook),
 		depNames:     dependencies,
 	}
 
-	// replace nil arguments with dummy action
-	if newModule.prep == nil {
-		newModule.prep = dummyAction
-	}
-	if newModule.start == nil {
-		newModule.start = dummyAction
-	}
-	if newModule.stop == nil {
-		newModule.stop = dummyAction
-	}
-
 	return newModule
 }