From eed5a6f127ec3bb1553ac629457f196d8893665a Mon Sep 17 00:00:00 2001
From: Alexey Rusakov <Kitsune-Ral@users.sf.net>
Date: Mon, 26 Jul 2021 08:19:29 +0200
Subject: Room::usersAtEventId(): switch from QMultiHash to QHash of QSets

While slightly more complex for updating, this allows COW to kick in in
the read accessor; using QSet instead of QList also provides better
consistency guarantees. For QML both are converted to an Array-like
collection since Qt 5.15; Qt 5.12 turns QSet<> in a QVariantList,
according to the documentation, which is quite reasonable too.
---
 lib/room.cpp | 13 ++++++++-----
 lib/room.h   |  2 +-
 2 files changed, 9 insertions(+), 6 deletions(-)

(limited to 'lib')

diff --git a/lib/room.cpp b/lib/room.cpp
index 10e827d7..13589ee9 100644
--- a/lib/room.cpp
+++ b/lib/room.cpp
@@ -121,7 +121,7 @@ public:
     int notificationCount = 0;
     members_map_t membersMap;
     QList<User*> usersTyping;
-    QMultiHash<QString, User*> eventIdReadUsers;
+    QHash<QString, QSet<User*>> eventIdReadUsers;
     QList<User*> usersInvited;
     QList<User*> membersLeft;
     int unreadMessages = 0;
@@ -627,8 +627,11 @@ Room::Changes Room::Private::setLastReadEvent(User* u, QString eventId)
     auto& storedId = lastReadEventIds[u];
     if (storedId == eventId)
         return Change::NoChange;
-    eventIdReadUsers.remove(storedId, u);
-    eventIdReadUsers.insert(eventId, u);
+    auto& oldEventReadUsers = eventIdReadUsers[storedId];
+    oldEventReadUsers.remove(u);
+    if (oldEventReadUsers.isEmpty())
+        eventIdReadUsers.remove(storedId);
+    eventIdReadUsers[eventId].insert(u);
     swap(storedId, eventId);
     emit q->lastReadEventChanged(u);
     emit q->readMarkerForUserMoved(u, eventId, storedId);
@@ -965,9 +968,9 @@ QString Room::readMarkerEventId() const
     return d->lastReadEventIds.value(localUser());
 }
 
-QList<User*> Room::usersAtEventId(const QString& eventId)
+QSet<User*> Room::usersAtEventId(const QString& eventId)
 {
-    return d->eventIdReadUsers.values(eventId);
+    return d->eventIdReadUsers.value(eventId);
 }
 
 int Room::notificationCount() const { return d->notificationCount; }
diff --git a/lib/room.h b/lib/room.h
index cdbfe58f..fa7b6e6d 100644
--- a/lib/room.h
+++ b/lib/room.h
@@ -364,7 +364,7 @@ public:
     rev_iter_t readMarker(const User* user) const;
     rev_iter_t readMarker() const;
     QString readMarkerEventId() const;
-    QList<User*> usersAtEventId(const QString& eventId);
+    QSet<User*> usersAtEventId(const QString& eventId);
     /**
      * \brief Mark the event with uptoEventId as read
      *
-- 
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