Ensure that Webhook tasks are not double delivered (#21558)

When re-retrieving hook tasks from the DB double check if they have not
been delivered in the meantime. Further ensure that tasks are marked as
delivered when they are being delivered.

In addition:
* Improve the error reporting and make sure that the webhook task
population script runs in a separate goroutine.
* Only get hook task IDs out of the DB instead of the whole task when
repopulating the queue
* When repopulating the queue make the DB request paged

Ref #17940 

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

models/webhook/hooktask.go

@@ -233,14 +233,30 @@ func ReplayHookTask(ctx context.Context, hookID int64, uuid string) (*HookTask,
 	return newTask, db.Insert(ctx, newTask)
 }
 
-// FindUndeliveredHookTasks represents find the undelivered hook tasks
-func FindUndeliveredHookTasks(ctx context.Context) ([]*HookTask, error) {
-	tasks := make([]*HookTask, 0, 10)
+// FindUndeliveredHookTaskIDs will find the next 100 undelivered hook tasks with ID greater than the provided lowerID
+func FindUndeliveredHookTaskIDs(ctx context.Context, lowerID int64) ([]int64, error) {
+	const batchSize = 100
+
+	tasks := make([]int64, 0, batchSize)
 	return tasks, db.GetEngine(ctx).
+		Select("id").
+		Table(new(HookTask)).
 		Where("is_delivered=?", false).
+		And("id > ?", lowerID).
+		Asc("id").
+		Limit(batchSize).
 		Find(&tasks)
 }
 
+func MarkTaskDelivered(ctx context.Context, task *HookTask) (bool, error) {
+	count, err := db.GetEngine(ctx).ID(task.ID).Where("is_delivered = ?", false).Cols("is_delivered").Update(&HookTask{
+		ID:          task.ID,
+		IsDelivered: true,
+	})
+
+	return count != 0, err
+}
+
 // CleanupHookTaskTable deletes rows from hook_task as needed.
 func CleanupHookTaskTable(ctx context.Context, cleanupType HookTaskCleanupType, olderThan time.Duration, numberToKeep int) error {
 	log.Trace("Doing: CleanupHookTaskTable")