Fix: ensure timely shutdown of rebroadcast heads. (#156)

I have observed this routine sometimes just stayed running, potentially
preventing the shutdown of the whole datastore.

Author: hsanjuan

crdt.go

@@ -179,8 +179,6 @@ type Datastore struct {
 	seenHeadsMux sync.RWMutex
 	seenHeads    map[cid.Cid]struct{}
 
-	rebroadcastTicker *time.Ticker
-
 	curDeltaMux sync.Mutex
 	curDelta    *pb.Delta // current, unpublished delta
 
@@ -270,21 +268,20 @@ func New(
 	}
 
 	dstore := &Datastore{
-		ctx:               ctx,
-		cancel:            cancel,
-		opts:              opts,
-		logger:            opts.Logger,
-		store:             store,
-		namespace:         namespace,
-		set:               set,
-		heads:             heads,
-		dagService:        dagSyncer,
-		broadcaster:       bcast,
-		seenHeads:         make(map[cid.Cid]struct{}),
-		rebroadcastTicker: time.NewTicker(opts.RebroadcastInterval),
-		jobQueue:          make(chan *dagJob, opts.NumWorkers),
-		sendJobs:          make(chan *dagJob),
-		queuedChildren:    newCidSafeSet(),
+		ctx:            ctx,
+		cancel:         cancel,
+		opts:           opts,
+		logger:         opts.Logger,
+		store:          store,
+		namespace:      namespace,
+		set:            set,
+		heads:          heads,
+		dagService:     dagSyncer,
+		broadcaster:    bcast,
+		seenHeads:      make(map[cid.Cid]struct{}),
+		jobQueue:       make(chan *dagJob, opts.NumWorkers),
+		sendJobs:       make(chan *dagJob),
+		queuedChildren: newCidSafeSet(),
 	}
 
 	headList, maxHeight, err := dstore.heads.List()
@@ -455,14 +452,27 @@ func (store *Datastore) encodeBroadcast(heads []cid.Cid) ([]byte, error) {
 }
 
 func (store *Datastore) rebroadcast() {
-	ticker := store.rebroadcastTicker
-	defer ticker.Stop()
+	timer := time.NewTimer(store.opts.RebroadcastInterval)
+
 	for {
 		select {
 		case <-store.ctx.Done():
+			if !timer.Stop() {
+				<-timer.C
+			}
 			return
-		case <-ticker.C:
+		default:
+		}
+
+		select {
+		case <-store.ctx.Done():
+			if !timer.Stop() {
+				<-timer.C
+			}
+			return
+		case <-timer.C:
 			store.rebroadcastHeads()
+			timer.Reset(store.opts.RebroadcastInterval)
 		}
 	}
 }