Synchronize Close(), fix race conditions.

Close() was not synced through the main dispatcher loop, so it could close
channels that were currently being written to by methods called from said
dispatcher loop. This leads to a crash. Instead, Close() now writes a
closeRequest, which is handled in the dispatcher.

manager/aggregator.go

@@ -110,7 +110,7 @@ type Aggregator struct {
 	getAggregatesRequests   chan *getAggregatesRequest
 	removeAggregateRequests chan EventFingerprint
 	rulesRequests           chan *aggregatorResetRulesRequest
-	closed                  chan bool
+	closeRequests           chan *closeRequest
 }
 
 func NewAggregator() *Aggregator {
@@ -121,18 +121,24 @@ func NewAggregator() *Aggregator {
 		getAggregatesRequests:   make(chan *getAggregatesRequest),
 		removeAggregateRequests: make(chan EventFingerprint),
 		rulesRequests:           make(chan *aggregatorResetRulesRequest),
-		closed:                  make(chan bool),
+		closeRequests:           make(chan *closeRequest),
 	}
 }
 
 func (a *Aggregator) Close() {
+	req := &closeRequest{
+		done: make(chan bool),
+	}
+	a.closeRequests <- req
+	<-req.done
+}
+
+func (a *Aggregator) closeInternal() {
 	close(a.rulesRequests)
 	close(a.aggRequests)
 	close(a.getAggregatesRequests)
 	close(a.removeAggregateRequests)
-
-	<-a.closed
-	close(a.closed)
+	close(a.closeRequests)
 }
 
 type aggregateEventsResponse struct {
@@ -153,6 +159,10 @@ type getAggregatesRequest struct {
 	Response chan getAggregatesResponse
 }
 
+type closeRequest struct {
+	done chan bool
+}
+
 func (a *Aggregator) aggregate(req *aggregateEventsRequest, s SummaryReceiver) {
 	if len(a.Rules) == 0 {
 		req.Response <- &aggregateEventsResponse{
@@ -259,24 +269,14 @@ func (a *Aggregator) Dispatch(s SummaryReceiver) {
 	t := time.NewTicker(time.Second)
 	defer t.Stop()
 
-	closed := 0
-
-	for closed < 2 {
+	for {
 		select {
-		case req, open := <-a.aggRequests:
+		case req := <-a.aggRequests:
 			a.aggregate(req, s)
 
-			if !open {
-				closed++
-			}
-
-		case rules, open := <-a.rulesRequests:
+		case rules := <-a.rulesRequests:
 			a.replaceRules(rules)
 
-			if !open {
-				closed++
-			}
-
 		case req := <-a.getAggregatesRequests:
 			aggs := a.aggregates()
 			req.Response <- getAggregatesResponse{
@@ -288,8 +288,11 @@ func (a *Aggregator) Dispatch(s SummaryReceiver) {
 			log.Println("Deleting expired aggregation instance", a)
 			a.Aggregates[fp].Close()
 			delete(a.Aggregates, fp)
+
+		case req := <-a.closeRequests:
+			a.closeInternal()
+			req.done <- true
+			return
 		}
 	}
-
-	a.closed <- true
 }