From 6b351b8de422be8d7ced3145870270b6a407fac5 Mon Sep 17 00:00:00 2001
From: Paul Olav Tvete <paul.tvete@qt.io>
Date: Tue, 15 Mar 2022 16:53:04 +0100
Subject: [PATCH 25/55] Fix race condition on mWaitingForUpdateDelivery

Change-Id: I0e91bda73722468b9339fc434fe04420b5e7d3da
Reviewed-by: David Edmundson <davidedmundson@kde.org>
---
 src/client/qwaylandwindow.cpp | 7 ++-----
 src/client/qwaylandwindow_p.h | 2 +-
 2 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
index 3d1be31c..014e2d87 100644
--- a/src/client/qwaylandwindow.cpp
+++ b/src/client/qwaylandwindow.cpp
@@ -652,24 +652,21 @@ void QWaylandWindow::handleFrameCallback()
 
     // The rest can wait until we can run it on the correct thread
     auto doHandleExpose = [this]() {
+        mWaitingForUpdateDelivery.storeRelease(false);
         bool wasExposed = isExposed();
         mFrameCallbackTimedOut = false;
         if (!wasExposed && isExposed()) // Did setting mFrameCallbackTimedOut make the window exposed?
             sendExposeEvent(QRect(QPoint(), geometry().size()));
         if (wasExposed && hasPendingUpdateRequest())
             deliverUpdateRequest();
-
-        mWaitingForUpdateDelivery = false;
     };
 
-    if (!mWaitingForUpdateDelivery) {
+    if (mWaitingForUpdateDelivery.testAndSetAcquire(false, true)) {
         // Queued connection, to make sure we don't call handleUpdate() from inside waitForFrameSync()
         // in the single-threaded case.
-        mWaitingForUpdateDelivery = true;
         QMetaObject::invokeMethod(this, doHandleExpose, Qt::QueuedConnection);
     }
 
-
     mFrameSyncWait.notify_all();
 }
 
diff --git a/src/client/qwaylandwindow_p.h b/src/client/qwaylandwindow_p.h
index 54ac67a9..c0a76345 100644
--- a/src/client/qwaylandwindow_p.h
+++ b/src/client/qwaylandwindow_p.h
@@ -228,7 +228,7 @@ protected:
     WId mWindowId;
     bool mWaitingForFrameCallback = false;
     bool mFrameCallbackTimedOut = false; // Whether the frame callback has timed out
-    bool mWaitingForUpdateDelivery = false;
+    QAtomicInt mWaitingForUpdateDelivery = false;
     int mFrameCallbackCheckIntervalTimerId = -1;
     QElapsedTimer mFrameCallbackElapsedTimer;
     struct ::wl_callback *mFrameCallback = nullptr;
-- 
2.52.0

