Update Dequeue operation to skip paused queues

internal/rdb/rdb.go

@@ -103,19 +103,14 @@ func (r *RDB) EnqueueUnique(msg *base.TaskMessage, ttl time.Duration) error {
 }
 
 // Dequeue queries given queues in order and pops a task message if there is one and returns it.
+// Dequeue skips a queue if the queue is paused.
 // If all queues are empty, ErrNoProcessableTask error is returned.
 func (r *RDB) Dequeue(qnames ...string) (*base.TaskMessage, error) {
-	var data string
-	var err error
-	if len(qnames) == 1 {
-		data, err = r.dequeueSingle(base.QueueKey(qnames[0]))
-	} else {
 	var keys []string
 	for _, q := range qnames {
 		keys = append(keys, base.QueueKey(q))
 	}
-		data, err = r.dequeue(keys...)
-	}
+	data, err := r.dequeue(keys...)
 	if err == redis.Nil {
 		return nil, ErrNoProcessableTask
 	}
@@ -130,29 +125,30 @@ func (r *RDB) Dequeue(qnames ...string) (*base.TaskMessage, error) {
 	return &msg, nil
 }
 
-func (r *RDB) dequeueSingle(queue string) (data string, err error) {
-	// timeout needed to avoid blocking forever
-	return r.client.BRPopLPush(queue, base.InProgressQueue, time.Second).Result()
-}
-
 // KEYS[1] -> asynq:in_progress
+// KEYS[2] -> asynq:paused
 // ARGV    -> List of queues to query in order
+//
+// dequeueCmd checks whether a queue is paused first, before
+// calling RPOPLPUSH to pop a task from the queue.
 var dequeueCmd = redis.NewScript(`
-local res
 for _, qkey in ipairs(ARGV) do
-	res = redis.call("RPOPLPUSH", qkey, KEYS[1])
+	if redis.call("SISMEMBER", KEYS[2], qkey) == 0 then
+		local res = redis.call("RPOPLPUSH", qkey, KEYS[1])
 		if res then
 			return res
 		end
+	end
 end
-return res`)
+return nil`)
 
 func (r *RDB) dequeue(queues ...string) (data string, err error) {
 	var args []interface{}
 	for _, qkey := range queues {
 		args = append(args, qkey)
 	}
-	res, err := dequeueCmd.Run(r.client, []string{base.InProgressQueue}, args...).Result()
+	res, err := dequeueCmd.Run(r.client,
+		[]string{base.InProgressQueue, base.PausedQueues}, args...).Result()
 	if err != nil {
 		return "", err
 	}

internal/rdb/rdb_test.go

@@ -227,6 +227,97 @@ func TestDequeue(t *testing.T) {
 	}
 }
 
+func TestDequeueIgnoresPausedQueues(t *testing.T) {
+	r := setup(t)
+	t1 := h.NewTaskMessage("send_email", map[string]interface{}{"subject": "hello!"})
+	t2 := h.NewTaskMessage("export_csv", nil)
+
+	tests := []struct {
+		paused         []string // list of paused queues
+		enqueued       map[string][]*base.TaskMessage
+		args           []string // list of queues to query
+		want           *base.TaskMessage
+		err            error
+		wantEnqueued   map[string][]*base.TaskMessage
+		wantInProgress []*base.TaskMessage
+	}{
+		{
+			paused: []string{"default"},
+			enqueued: map[string][]*base.TaskMessage{
+				"default":  {t1},
+				"critical": {t2},
+			},
+			args: []string{"default", "critical"},
+			want: t2,
+			err:  nil,
+			wantEnqueued: map[string][]*base.TaskMessage{
+				"default":  {t1},
+				"critical": {},
+			},
+			wantInProgress: []*base.TaskMessage{t2},
+		},
+		{
+			paused: []string{"default"},
+			enqueued: map[string][]*base.TaskMessage{
+				"default": {t1},
+			},
+			args: []string{"default"},
+			want: nil,
+			err:  ErrNoProcessableTask,
+			wantEnqueued: map[string][]*base.TaskMessage{
+				"default": {t1},
+			},
+			wantInProgress: []*base.TaskMessage{},
+		},
+		{
+			paused: []string{"critical", "default"},
+			enqueued: map[string][]*base.TaskMessage{
+				"default":  {t1},
+				"critical": {t2},
+			},
+			args: []string{"default", "critical"},
+			want: nil,
+			err:  ErrNoProcessableTask,
+			wantEnqueued: map[string][]*base.TaskMessage{
+				"default":  {t1},
+				"critical": {t2},
+			},
+			wantInProgress: []*base.TaskMessage{},
+		},
+	}
+
+	for _, tc := range tests {
+		h.FlushDB(t, r.client) // clean up db before each test case
+		for _, qname := range tc.paused {
+			if err := r.Pause(qname); err != nil {
+				t.Fatal(err)
+			}
+		}
+		for queue, msgs := range tc.enqueued {
+			h.SeedEnqueuedQueue(t, r.client, msgs, queue)
+		}
+
+		got, err := r.Dequeue(tc.args...)
+		if !cmp.Equal(got, tc.want) || err != tc.err {
+			t.Errorf("Dequeue(%v) = %v, %v; want %v, %v",
+				tc.args, got, err, tc.want, tc.err)
+			continue
+		}
+
+		for queue, want := range tc.wantEnqueued {
+			gotEnqueued := h.GetEnqueuedMessages(t, r.client, queue)
+			if diff := cmp.Diff(want, gotEnqueued, h.SortMsgOpt); diff != "" {
+				t.Errorf("mismatch found in %q: (-want,+got):\n%s", base.QueueKey(queue), diff)
+			}
+		}
+
+		gotInProgress := h.GetInProgressMessages(t, r.client)
+		if diff := cmp.Diff(tc.wantInProgress, gotInProgress, h.SortMsgOpt); diff != "" {
+			t.Errorf("mismatch found in %q: (-want,+got):\n%s", base.InProgressQueue, diff)
+		}
+	}
+}
+
 func TestDone(t *testing.T) {
 	r := setup(t)
 	t1 := h.NewTaskMessage("send_email", nil)

processor.go

@@ -166,14 +166,12 @@ func (p *processor) exec() {
 	msg, err := p.broker.Dequeue(qnames...)
 	switch {
 	case err == rdb.ErrNoProcessableTask:
-		// queues are empty, this is a normal behavior.
-		if len(qnames) > 1 {
-			// sleep to avoid slamming redis and let scheduler move tasks into queues.
-			// Note: With multiple queues, we are not using blocking pop operation and
-			// polling queues instead. This adds significant load to redis.
-			time.Sleep(time.Second)
-		}
 		p.logger.Debug("All queues are empty")
+		// Queues are empty, this is a normal behavior.
+		// Sleep to avoid slamming redis and let scheduler move tasks into queues.
+		// Note: We are not using blocking pop operation and polling queues instead.
+		// This adds significant load to redis.
+		time.Sleep(time.Second)
 		return
 	case err != nil:
 		if p.errLogLimiter.Allow() {