simplify the batcher's timers

nomad/deploymentwatcher/batcher.go

@@ -58,40 +58,28 @@ func (b *EvalBatcher) CreateEval(e *structs.Evaluation) *EvalFuture {
 
 // batcher is the long lived batcher goroutine
 func (b *EvalBatcher) batcher() {
-	timer := time.NewTimer(b.batch)
+	var timerCh <-chan time.Time
 	evals := make(map[string]*structs.Evaluation)
 	for {
 		select {
 		case <-b.ctx.Done():
-			timer.Stop()
 			return
 		case e := <-b.inCh:
-			if len(evals) == 0 {
-				if !timer.Stop() {
-					<-timer.C
-				}
-				timer.Reset(b.batch)
+			if timerCh == nil {
+				timerCh = time.After(b.batch)
 			}
 
 			evals[e.DeploymentID] = e
-		case <-timer.C:
-			if len(evals) == 0 {
-				// Reset the timer
-				timer.Reset(b.batch)
-				continue
-			}
-
+		case <-timerCh:
 			// Capture the future
 			b.l.Lock()
 			f := b.f
 			b.f = nil
 			b.l.Unlock()
 
-			// Shouldn't be possible but protect ourselves
+			// Shouldn't be possible
 			if f == nil {
-				// Reset the timer
-				timer.Reset(b.batch)
-				continue
+				panic("no future")
 			}
 
 			// Capture the evals
@@ -100,14 +88,13 @@ func (b *EvalBatcher) batcher() {
 				all = append(all, e)
 			}
 
-			// Upsert the evals
-			f.Set(b.raft.UpsertEvals(all))
+			// Upsert the evals in a go routine
+			go f.Set(b.raft.UpsertEvals(all))
 
-			// Reset the evals list
+			// Reset the evals list and timer
 			evals = make(map[string]*structs.Evaluation)
+			timerCh = nil
 
-			// Reset the timer
-			timer.Reset(b.batch)
 		}
 	}
 }