From e02a171a47e87048d16faf7167c0fecd46a176b5 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Tue, 17 May 2022 17:01:52 +0200
Subject: [PATCH] Optimize reads from QObjectPrivate::threadData
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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The implicit conversion operator from QAtomicPointer<T> → T* performs
a loadAcquire().

In the cases of this patch, we're only comparing pointer values to
check whether QObject thread affinities are compatible, so relaxed
loads suffice.

Pick-to: 6.3
Change-Id: If19124778b4770d86baeaeb3c91214e47881b288
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
---
 src/corelib/kernel/qcoreapplication.cpp | 6 +++---
 src/corelib/kernel/qobject.cpp          | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
index 9937e018f6..13c792af29 100644
--- a/src/corelib/kernel/qcoreapplication.cpp
+++ b/src/corelib/kernel/qcoreapplication.cpp
@@ -1140,7 +1140,7 @@ bool QCoreApplicationPrivate::sendThroughApplicationEventFilters(QObject *receiv
             QObject *obj = extraData->eventFilters.at(i);
             if (!obj)
                 continue;
-            if (obj->d_func()->threadData != threadData) {
+            if (obj->d_func()->threadData.loadRelaxed() != threadData.loadRelaxed()) {
                 qWarning("QCoreApplication: Application event filter cannot be in a different thread.");
                 continue;
             }
@@ -1158,7 +1158,7 @@ bool QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject *receiver, Q
             QObject *obj = receiver->d_func()->extraData->eventFilters.at(i);
             if (!obj)
                 continue;
-            if (obj->d_func()->threadData != receiver->d_func()->threadData) {
+            if (obj->d_func()->threadData.loadRelaxed() != receiver->d_func()->threadData.loadRelaxed()) {
                 qWarning("QCoreApplication: Object event filter cannot be in a different thread.");
                 continue;
             }
@@ -1678,7 +1678,7 @@ void QCoreApplicationPrivate::sendPostedEvents(QObject *receiver, int event_type
         event_type = 0;
     }
 
-    if (receiver && receiver->d_func()->threadData != data) {
+    if (receiver && receiver->d_func()->threadData.loadRelaxed() != data) {
         qWarning("QCoreApplication::sendPostedEvents: Cannot send "
                  "posted events for objects in another thread");
         return;
diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp
index 3254f2a9fe..e438c11513 100644
--- a/src/corelib/kernel/qobject.cpp
+++ b/src/corelib/kernel/qobject.cpp
@@ -2413,7 +2413,7 @@ void QObjectPrivate::setParent_helper(QObject *o)
     parent = o;
     if (parent) {
         // object hierarchies are constrained to a single thread
-        if (threadData != parent->d_func()->threadData) {
+        if (threadData.loadRelaxed() != parent->d_func()->threadData.loadRelaxed()) {
             qWarning("QObject::setParent: Cannot set parent, new parent is in a different thread");
             parent = nullptr;
             return;
@@ -2475,7 +2475,7 @@ void QObject::installEventFilter(QObject *obj)
     Q_D(QObject);
     if (!obj)
         return;
-    if (d->threadData != obj->d_func()->threadData) {
+    if (d->threadData.loadRelaxed() != obj->d_func()->threadData.loadRelaxed()) {
         qWarning("QObject::installEventFilter(): Cannot filter events for objects in a different thread.");
         return;
     }