feat: implement listener for asynchronous notifications in queue (#146)

- Add `notify` channel to `Queue`
- Notify worker in the `queue` function without blocking the main thread
- Add case to listen for `notify` channel in the `start` function

Signed-off-by: appleboy <appleboy.tw@gmail.com>

Author: appleboy

queue.go

@@ -26,6 +26,7 @@ type (
 		routineGroup  *routineGroup
 		quit          chan struct{}
 		ready         chan struct{}
+		notify        chan struct{}
 		worker        core.Worker
 		stopOnce      sync.Once
 		stopFlag      int32
@@ -44,6 +45,7 @@ func NewQueue(opts ...Option) (*Queue, error) {
 		routineGroup:  newRoutineGroup(),
 		quit:          make(chan struct{}),
 		ready:         make(chan struct{}, 1),
+		notify:        make(chan struct{}, 1),
 		workerCount:   o.workerCount,
 		logger:        o.logger,
 		worker:        o.worker,
@@ -149,6 +151,13 @@ func (q *Queue) queue(m *job.Message) error {
 	}
 
 	q.metric.IncSubmittedTask()
+	// notify worker
+	// if the channel is full, it means that the worker is busy
+	// and we don't want to block the main thread
+	select {
+	case q.notify <- struct{}{}:
+	default:
+	}
 
 	return nil
 }
@@ -325,6 +334,7 @@ func (q *Queue) start() {
 								return
 							}
 						case <-ticker.C:
+						case <-q.notify:
 						}
 					}
 				}