journald/read: avoid being blocked on send

In case the LogConsumer is gone, the code that sends the message can
stuck forever. Wrap the code in select case, as all other loggers do.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
(cherry picked from commit 79039720c8b7352691350bd56be3cc226d67f205)
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Upstream-commit: 56a8a516127a2630c3a68ab31c416f223b91e9df
Component: engine

components/engine/daemon/logger/journald/read.go

@@ -230,12 +230,17 @@ drain:
 				kv := strings.SplitN(C.GoStringN(data, C.int(length)), "=", 2)
 				attrs = append(attrs, backend.LogAttr{Key: kv[0], Value: kv[1]})
 			}
-			// Send the log message.
-			logWatcher.Msg <- &logger.Message{
+			// Send the log message, unless the consumer is gone
+			select {
+			case <-logWatcher.WatchConsumerGone():
+				done = true // we won't be able to write anything anymore
+				break drain
+			case logWatcher.Msg <- &logger.Message{
 				Line:      line,
 				Source:    source,
 				Timestamp: timestamp.In(time.UTC),
 				Attrs:     attrs,
+			}:
 			}
 		}
 		// If we're at the end of the journal, we're done (for now).