Add redis pubsub subscriber for cancelation

subscriber.go

@@ -0,0 +1,58 @@
+// Copyright 2020 Kentaro Hibino. All rights reserved.
+// Use of this source code is governed by a MIT license
+// that can be found in the LICENSE file.
+
+package asynq
+
+import (
+	"github.com/hibiken/asynq/internal/base"
+	"github.com/hibiken/asynq/internal/rdb"
+)
+
+type subscriber struct {
+	rdb *rdb.RDB
+
+	// channel to communicate back to the long running "subscriber" goroutine.
+	done chan struct{}
+
+	// cancelations hold cancel functions for all in-progress tasks.
+	cancelations *base.Cancelations
+}
+
+func newSubscriber(rdb *rdb.RDB, cancelations *base.Cancelations) *subscriber {
+	return &subscriber{
+		rdb:          rdb,
+		done:         make(chan struct{}),
+		cancelations: cancelations,
+	}
+}
+
+func (s *subscriber) terminate() {
+	logger.info("Subscriber shutting down...")
+	// Signal the subscriber goroutine to stop.
+	s.done <- struct{}{}
+}
+
+func (s *subscriber) start() {
+	pubsub, err := s.rdb.CancelationPubSub()
+	cancelCh := pubsub.Channel()
+	if err != nil {
+		logger.error("cannot subscribe to cancelation channel: %v", err)
+		return
+	}
+	go func() {
+		for {
+			select {
+			case <-s.done:
+				pubsub.Close()
+				logger.info("Subscriber done")
+				return
+			case msg := <-cancelCh:
+				cancel := s.cancelations.Get(msg.Payload)
+				if cancel != nil {
+					cancel()
+				}
+			}
+		}
+	}()
+}