Fix leaking of callback timers

Use two timers to create timeout trigger for framecallback.
Removes multiple timers approach that is subject to race conditions.

This was mistakenly pushed to 5.12 branch which will not be
automatically merged upstream, so it has to be cherry-picked.

Fixes: QTBUG-82914
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
(cherry picked from commit d18c29931b0bc889fff66bdbde89133544ba0529)
Change-Id: I258c0c08f0ac5803192fc0024e40ba72e72c37a8
Reviewed-by: Janne Koskinen <janne.p.koskinen@qt.io>

2 files changed, 22 insertions, 28 deletions

diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
index 9fa2f15f..884a9793 100644
--- a/src/client/qwaylandwindow.cpp
+++ b/src/client/qwaylandwindow.cpp
@@ -257,10 +257,7 @@ void QWaylandWindow::reset(bool sendDestroyEvent)
         mFrameCallback = nullptr;
     }
 
-    int timerId  = mFrameCallbackTimerId.fetchAndStoreOrdered(-1);
-    if (timerId != -1) {
-        killTimer(timerId);
-    }
+    mFrameCallbackElapsedTimer.invalidate();
     mWaitingForFrameCallback = false;
     mFrameCallbackTimedOut = false;
 
@@ -602,15 +599,11 @@ const wl_callback_listener QWaylandWindow::callbackListener = {
 
 void QWaylandWindow::handleFrameCallback()
 {
-    // Stop the timer and stop waiting immediately
-    int timerId = mFrameCallbackTimerId.fetchAndStoreOrdered(-1);
     mWaitingForFrameCallback = false;
+    mFrameCallbackElapsedTimer.invalidate();
 
     // The rest can wait until we can run it on the correct thread
-    auto doHandleExpose = [this, timerId]() {
-        if (timerId != -1)
-            killTimer(timerId);
-
+    auto doHandleExpose = [this]() {
         bool wasExposed = isExposed();
         mFrameCallbackTimedOut = false;
         if (!wasExposed && isExposed()) // Did setting mFrameCallbackTimedOut make the window exposed?
@@ -645,13 +638,6 @@ bool QWaylandWindow::waitForFrameSync(int timeout)
         sendExposeEvent(QRect());
     }
 
-    // Stop current frame timer if any, can't use killTimer directly, because we might be on a diffent thread
-    // Ordered semantics is needed to avoid stopping the timer twice and not miss it when it's
-    // started by other writes
-    int fcbId = mFrameCallbackTimerId.fetchAndStoreOrdered(-1);
-    if (fcbId != -1)
-        QMetaObject::invokeMethod(this, [this, fcbId] { killTimer(fcbId); }, Qt::QueuedConnection);
-
     return !mWaitingForFrameCallback;
 }
 
@@ -1107,8 +1093,16 @@ QVariant QWaylandWindow::property(const QString &name, const QVariant &defaultVa
 
 void QWaylandWindow::timerEvent(QTimerEvent *event)
 {
-    if (mFrameCallbackTimerId.testAndSetOrdered(event->timerId(), -1)) {
-        killTimer(event->timerId());
+    if (event->timerId() != mFrameCallbackCheckIntervalTimerId)
+        return;
+
+    bool callbackTimerExpired = mFrameCallbackElapsedTimer.hasExpired(100);
+    if (!mFrameCallbackElapsedTimer.isValid() || callbackTimerExpired ) {
+        killTimer(mFrameCallbackCheckIntervalTimerId);
+        mFrameCallbackCheckIntervalTimerId = -1;
+    }
+    if (mFrameCallbackElapsedTimer.isValid() && callbackTimerExpired) {
+        mFrameCallbackElapsedTimer.invalidate();
         qCDebug(lcWaylandBackingstore) << "Didn't receive frame callback in time, window should now be inexposed";
         mFrameCallbackTimedOut = true;
         mWaitingForUpdate = false;
@@ -1162,15 +1156,13 @@ void QWaylandWindow::handleUpdate()
     mWaitingForFrameCallback = true;
     mWaitingForUpdate = false;
 
-    // Stop current frame timer if any, can't use killTimer directly, see comment above.
-    int fcbId = mFrameCallbackTimerId.fetchAndStoreOrdered(-1);
-    if (fcbId != -1)
-        QMetaObject::invokeMethod(this, [this, fcbId] { killTimer(fcbId); }, Qt::QueuedConnection);
-
     // Start a timer for handling the case when the compositor stops sending frame callbacks.
-    QMetaObject::invokeMethod(this, [this] { // Again; can't do it directly
-        if (mWaitingForFrameCallback)
-            mFrameCallbackTimerId = startTimer(100);
+    QMetaObject::invokeMethod(this, [this] {
+        if (mWaitingForFrameCallback) {
+            if (mFrameCallbackCheckIntervalTimerId < 0)
+                mFrameCallbackCheckIntervalTimerId = startTimer(100);
+            mFrameCallbackElapsedTimer.start();
+        }
     }, Qt::QueuedConnection);
 }
 
diff --git a/src/client/qwaylandwindow_p.h b/src/client/qwaylandwindow_p.h
index 352df89d..ef03fd1f 100644
--- a/src/client/qwaylandwindow_p.h
+++ b/src/client/qwaylandwindow_p.h
@@ -58,6 +58,7 @@
 #include <QtGui/QIcon>
 #include <QtCore/QVariant>
 #include <QtCore/QLoggingCategory>
+#include <QtCore/QElapsedTimer>
 
 #include <qpa/qplatformwindow.h>
 
@@ -225,7 +226,8 @@ protected:
     WId mWindowId;
     bool mWaitingForFrameCallback = false;
     bool mFrameCallbackTimedOut = false; // Whether the frame callback has timed out
-    QAtomicInt mFrameCallbackTimerId = -1; // Started on commit, reset on frame callback
+    int mFrameCallbackCheckIntervalTimerId = -1;
+    QElapsedTimer mFrameCallbackElapsedTimer;
     struct ::wl_callback *mFrameCallback = nullptr;
     struct ::wl_event_queue *mFrameQueue = nullptr;
     QWaitCondition mFrameSyncWait;