Invalidate lazyLoadCache if we're doing an initial sync (#2623)

* Bypass lazyLoadCache if we're doing an initial sync

* Make the linter happy again?

* Revert "Make the linter happy again?"

This reverts commit 52a5691ba3c17c05698bcc6a13092090f27ace63.

* Try that again

* Invalidate LazyLoadCache on initial syncs

* Remove unneeded check

* Add TODO

* Rename Invalite -> InvalidateLazyLoadedUser

* Thanks IDE

syncapi/streams/stream_pdu.go

@@ -12,9 +12,12 @@ import (
 	roomserverAPI "github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
+
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/tidwall/gjson"
 	"go.uber.org/atomic"
+
+	"github.com/matrix-org/dendrite/syncapi/notifier"
 )
 
 // The max number of per-room goroutines to have running.
@@ -34,6 +37,7 @@ type PDUStreamProvider struct {
 	// userID+deviceID -> lazy loading cache
 	lazyLoadCache caching.LazyLoadCache
 	rsAPI         roomserverAPI.SyncRoomserverAPI
+	notifier      *notifier.Notifier
 }
 
 func (p *PDUStreamProvider) worker() {
@@ -100,6 +104,15 @@ func (p *PDUStreamProvider) CompleteSync(
 		req.Log.WithError(err).Error("unable to update event filter with ignored users")
 	}
 
+	// Invalidate the lazyLoadCache, otherwise we end up with missing displaynames/avatars
+	// TODO: This might be inefficient, when joined to many and/or large rooms.
+	for _, roomID := range joinedRoomIDs {
+		joinedUsers := p.notifier.JoinedUsers(roomID)
+		for _, sharedUser := range joinedUsers {
+			p.lazyLoadCache.InvalidateLazyLoadedUser(req.Device, roomID, sharedUser)
+		}
+	}
+
 	// Build up a /sync response. Add joined rooms.
 	var reqMutex sync.Mutex
 	var reqWaitGroup sync.WaitGroup

syncapi/streams/streams.go

@@ -34,6 +34,7 @@ func NewSyncStreamProviders(
 			StreamProvider: StreamProvider{DB: d},
 			lazyLoadCache:  lazyLoadCache,
 			rsAPI:          rsAPI,
+			notifier:       notifier,
 		},
 		TypingStreamProvider: &TypingStreamProvider{
 			StreamProvider: StreamProvider{DB: d},