Fix hypothetical consumer deadlock, attempt 3

Fixes #475

consumer.go

@@ -130,7 +130,7 @@ func (c *consumer) ConsumePartition(topic string, partition int32, offset int64)
 		errors:    make(chan *ConsumerError, c.conf.ChannelBufferSize),
 		feeder:    make(chan *FetchResponse, 1),
 		trigger:   make(chan none, 1),
-		dying:     make(chan error, 1),
+		dying:     make(chan none),
 		fetchSize: c.conf.Consumer.Fetch.Default,
 	}
 
@@ -269,8 +269,9 @@ type partitionConsumer struct {
 	messages chan *ConsumerMessage
 	errors   chan *ConsumerError
 	feeder   chan *FetchResponse
-	trigger  chan none
-	dying    chan error
+
+	trigger, dying chan none
+	dispatchReason error
 
 	fetchSize           int32
 	offset              int64
@@ -372,7 +373,7 @@ func (child *partitionConsumer) AsyncClose() {
 	// the dispatcher to exit its loop, which removes it from the consumer then closes its 'messages' and
 	// 'errors' channel (alternatively, if the child is already at the dispatcher for some reason, that will
 	// also just close itself)
-	child.dying <- nil
+	close(child.dying)
 }
 
 func (child *partitionConsumer) Close() error {
@@ -412,11 +413,11 @@ func (child *partitionConsumer) responseFeeder() {
 			child.AsyncClose()
 		case ErrUnknownTopicOrPartition, ErrNotLeaderForPartition, ErrLeaderNotAvailable:
 			// these three are not fatal errors, but do require redispatching
-			child.dying <- err
+			child.dispatchReason = err
 		default:
 			// dunno, tell the user and try redispatching
 			child.sendError(err)
-			child.dying <- err
+			child.dispatchReason = err
 		}
 
 		child.broker.acks.Done()
@@ -602,16 +603,18 @@ func (bc *brokerConsumer) updateSubscriptionCache(newSubscriptions []*partitionC
 
 	for child := range bc.subscriptions {
 		select {
-		case err := <-child.dying:
-			if err == nil {
-				Logger.Printf("consumer/broker/%d closed dead subscription to %s/%d\n", bc.broker.ID(), child.topic, child.partition)
-				close(child.trigger)
-			} else {
-				Logger.Printf("consumer/broker/%d abandoned subscription to %s/%d because %s\n", bc.broker.ID(), child.topic, child.partition, err)
-				child.trigger <- none{}
-			}
+		case <-child.dying:
+			Logger.Printf("consumer/broker/%d closed dead subscription to %s/%d\n", bc.broker.ID(), child.topic, child.partition)
+			close(child.trigger)
 			delete(bc.subscriptions, child)
 		default:
+			if child.dispatchReason != nil {
+				Logger.Printf("consumer/broker/%d abandoned subscription to %s/%d because %s\n",
+					bc.broker.ID(), child.topic, child.partition, child.dispatchReason)
+				child.dispatchReason = nil
+				child.trigger <- none{}
+				delete(bc.subscriptions, child)
+			}
 		}
 	}
 }