fix(evpn-bridge): fix system behaviour for pending objects

Signed-off-by: Dimitrios Markou <[email protected]>

pkg/infradb/subscriberframework/eventbus/eventbus.go

@@ -6,6 +6,7 @@
 package eventbus
 
 import (
+	"fmt"
 	"log"
 	"sort"
 	"sync"
@@ -89,7 +90,7 @@ func (e *EventBus) Subscribe(moduleName, eventType string, priority int, eventHa
 
 	subscriber := &Subscriber{
 		Name:     moduleName,
-		Ch:       make(chan interface{}, 1),
+		Ch:       make(chan interface{}),
 		Quit:     make(chan bool),
 		Priority: priority,
 	}
@@ -128,10 +129,20 @@ func (e *EventBus) subscriberExist(eventType string, moduleName string) bool {
 }
 
 // Publish api notifies the subscribers with certain eventType
-func (e *EventBus) Publish(objectData *ObjectData, subscriber *Subscriber) {
+func (e *EventBus) Publish(objectData *ObjectData, subscriber *Subscriber) error {
 	e.publishL.RLock()
 	defer e.publishL.RUnlock()
-	subscriber.Ch <- objectData
+	var err error
+	// We need the default case here as if the subscriber is busy then we will not be able to sent to the subscriber channel
+	// and the Publish function will stuck. So the default case serves exctly this purpose.
+	select {
+	case subscriber.Ch <- objectData:
+		log.Printf("Publish(): Notification is sent to subscriber %s\n", subscriber.Name)
+	default:
+		log.Printf("Publish(): Channel for subsriber %s is busy. Notification not sent", subscriber.Name)
+		err = fmt.Errorf("channel is busy")
+	}
+	return err
 }
 
 // Unsubscribe the subscriber, which delete the subscriber(all resources will be washed out)

pkg/infradb/taskmanager/taskmanager.go

@@ -31,8 +31,9 @@ type Task struct {
 	objectType      string
 	resourceVersion string
 	subIndex        int
-	retryTimer      time.Duration
-	subs            []*eventbus.Subscriber
+	// systemTimer is used only when we want to retry a Task due to unavailability of the Subscriber or not receiving a TaskStatus
+	systemTimer time.Duration
+	subs        []*eventbus.Subscriber
 }
 
 // TaskStatus holds info related to the status that has been received
@@ -60,6 +61,7 @@ func newTask(name, objectType, resourceVersion string, subs []*eventbus.Subscrib
 		objectType:      objectType,
 		resourceVersion: resourceVersion,
 		subIndex:        0,
+		systemTimer:     1 * time.Second,
 		subs:            subs,
 	}
 }
@@ -94,13 +96,18 @@ func (t *TaskManager) CreateTask(name, objectType, resourceVersion string, subs
 // StatusUpdated creates a task status and sends it for handling
 func (t *TaskManager) StatusUpdated(name, objectType, resourceVersion, notificationID string, dropTask bool, component *common.Component) {
 	taskStatus := newTaskStatus(name, objectType, resourceVersion, notificationID, dropTask, component)
-
-	// Do we need to make this call happen in a goroutine in order to not make the
-	// StatusUpdated function stuck in case that nobody reads what is written on the channel ?
-	// Is there any case where this can happen
-	// (nobody reads what is written on the channel and the StatusUpdated gets stuck) ?
-	t.taskStatusChan <- taskStatus
-	log.Printf("StatusUpdated(): New Task Status has been created and sent to channel: %+v\n", taskStatus)
+	log.Printf("StatusUpdated(): New Task Status has been created: %+v\n", taskStatus)
+
+	// We need to have a default case here so the call is not stuck if we send to channel but there is nobody reading from the channel.
+	// e.g. a subscriber got stuck and doesn't reply. The task will be requeued after the timer gets expired. In the meanwhile
+	// the subscriber replies and a taskStatus is sent to channel but the call gets stuck there as the previous task has not been requeued yet
+	// as the timer has not expired and the queue is empty (We assume that there is only one task in the queue).
+	select {
+	case t.taskStatusChan <- taskStatus:
+		log.Printf("StatusUpdated(): Task Status has been sent to channel: %+v\n", taskStatus)
+	default:
+		log.Printf("StatusUpdated(): Task Status has not been sent to channel. Channel not available: %+v\n", taskStatus)
+	}
 }
 
 // processTasks processes the task
@@ -123,7 +130,18 @@ func (t *TaskManager) processTasks() {
 				// (e.g. Maybe you have a timeout on the subscribers and you got the notification after the timeout have passed)
 				NotificationID: uuid.NewString(),
 			}
-			eventbus.EBus.Publish(objectData, sub)
+			if err := eventbus.EBus.Publish(objectData, sub); err != nil {
+				log.Printf("processTasks(): Notification not sent to subscriber %+v with data %+v. Subscriber is busy. The Task %+v will be requeued.\n", sub, objectData, task)
+				// We keep this subIndex in order to know from which subscriber to start iterating after the requeue of the Task
+				// so we do start again from the subscriber that returned an error or was unavailable for any reason.
+				task.subIndex += i
+				task.systemTimer *= 2
+				log.Printf("processTasks(): The Task will be requeued after %+v\n", task.systemTimer)
+				time.AfterFunc(task.systemTimer, func() {
+					t.taskQueue.Enqueue(task)
+				})
+				break loopTwo
+			}
 			log.Printf("processTasks(): Notification has been sent to subscriber %+v with data %+v\n", sub, objectData)
 
 		loopThree:
@@ -143,11 +161,17 @@ func (t *TaskManager) processTasks() {
 					log.Printf("processTasks(): received notification id %+v doesn't equal the sent notification id %+v\n", taskStatus.notificationID, objectData.NotificationID)
 
 				// We need a timeout in case that the subscriber doesn't update the status at all for whatever reason.
-				// If that occurs then we just take a note which subscriber need to revisit and we requeue the task without any timer
+				// If that occurs then we just requeue the task with a timer
 				case <-time.After(30 * time.Second):
-					log.Printf("processTasks(): No task status has been received in the channel from subscriber %+v. The task %+v will be requeued immediately Task Status %+v\n", sub, task, taskStatus)
+					log.Printf("processTasks(): No task status has been received in the channel from subscriber %+v. The task %+v will be requeued. Task Status %+v\n", sub, task, taskStatus)
+					// We keep this subIndex in order to know from which subscriber to start iterating after the requeue of the Task
+					// so we do start again from the subscriber that returned an error or was unavailable for any reason.
 					task.subIndex += i
-					go t.taskQueue.Enqueue(task)
+					task.systemTimer *= 2
+					log.Printf("processTasks(): The Task will be requeued after %+v\n", task.systemTimer)
+					time.AfterFunc(task.systemTimer, func() {
+						t.taskQueue.Enqueue(task)
+					})
 					break loopThree
 				}
 			}
@@ -159,19 +183,27 @@ func (t *TaskManager) processTasks() {
 				break loopTwo
 			}
 
+			// We re-initialize the systemTimer every time that we get a taskStatus. That means that the subscriber is available and has responded
+			task.systemTimer = 1 * time.Second
+
 			switch taskStatus.component.CompStatus {
 			case common.ComponentStatusSuccess:
 				log.Printf("processTasks(): Subscriber %+v has processed the task %+v successfully\n", sub, task)
 				continue loopTwo
-			default:
+			case common.ComponentStatusError:
 				log.Printf("processTasks(): Subscriber %+v has not processed the task %+v successfully\n", sub, task)
+				log.Printf("processTasks(): The Task will be requeued after %+v\n", taskStatus.component.Timer)
+				// We keep this subIndex in order to know from which subscriber to start iterating after the requeue of the Task
+				// so we do start again from the subscriber that returned an error or was unavailable for any reason.
 				task.subIndex += i
-				task.retryTimer = taskStatus.component.Timer
-				log.Printf("processTasks(): The Task will be requeued after %+v\n", task.retryTimer)
-				time.AfterFunc(task.retryTimer, func() {
+				time.AfterFunc(taskStatus.component.Timer, func() {
 					t.taskQueue.Enqueue(task)
 				})
 				break loopTwo
+			default:
+				log.Printf("processTasks(): Subscriber %+v has not provided designated status for the task %+v\n", sub, task)
+				log.Printf("processTasks(): The task %+v will be dropped\n", task)
+				break loopTwo
 			}
 		}
 	}