Document what the mutexes are protecting

src/github.com/matrix-org/dendrite/federationsender/queue/destinationqueue.go

@@ -28,10 +28,12 @@ import (
 // ensures that only one request is in flight to a given destination
 // at a time.
 type destinationQueue struct {
+	client      *gomatrixserverlib.FederationClient
+	origin      gomatrixserverlib.ServerName
+	destination gomatrixserverlib.ServerName
+	// The running mutex protects running, sentCounter, lastTransactionIDs and
+	// pendingEvents.
 	runningMutex       sync.Mutex
-	client             *gomatrixserverlib.FederationClient
-	origin             gomatrixserverlib.ServerName
-	destination        gomatrixserverlib.ServerName
 	running            bool
 	sentCounter        int
 	lastTransactionIDs []gomatrixserverlib.TransactionID

src/github.com/matrix-org/dendrite/federationsender/queue/queue.go

@@ -25,8 +25,9 @@ import (
 // OutgoingQueues is a collection of queues for sending transactions to other
 // matrix servers
 type OutgoingQueues struct {
-	origin      gomatrixserverlib.ServerName
-	client      *gomatrixserverlib.FederationClient
+	origin gomatrixserverlib.ServerName
+	client *gomatrixserverlib.FederationClient
+	// The queuesMutex protects queues
 	queuesMutex sync.Mutex
 	queues      map[gomatrixserverlib.ServerName]*destinationQueue
 }