Delay syncing internal window geometry to end of cycle

Summary:
The syncing of the window geometry to the internal geometry can
unfortunately cause a freeze in very special conditions:
1. create QML component
2. a Plasma::Dialog gets created
3. It creates the DialogShadows
4. This triggers QGlobalStatic creation which locks a non-recursive
mutex
5. The creation of DialogShadows creates a Registry and triggers a
roundtrip on the Wayland server
6. KWin processes all Wayland events
7. This triggers the creation of a ShellClient
8. The ShellClient has a PlasmaShellSurface which requested a position
9. The new geometry does not match the geometry of the Plasma::Dialog
10. ShellClient syncs the geometry to the Plasma::Dialog
11. Plasma::Dialog updates the theme because window geometry changed
12. This accesses the DialogShadows...

which is still in the non recursive mutex and we have a freeze.

By delaying the sync to the end of cycle we jump out of this deadly
sequence.

BUG: 384441

Test Plan:
The freeze doesn't hit any more. It's possible that some test
cases need adjustments.

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D7712

autotests/integration/internal_window.cpp

@@ -538,11 +538,11 @@ void InternalWindowTest::testMove()
     // normal move should be synced
     internalClient->move(5, 10);
     QCOMPARE(internalClient->geometry(), QRect(5, 10, 100, 100));
-    QCOMPARE(win.geometry(), QRect(5, 10, 100, 100));
+    QTRY_COMPARE(win.geometry(), QRect(5, 10, 100, 100));
     // another move should also be synced
     internalClient->move(10, 20);
     QCOMPARE(internalClient->geometry(), QRect(10, 20, 100, 100));
-    QCOMPARE(win.geometry(), QRect(10, 20, 100, 100));
+    QTRY_COMPARE(win.geometry(), QRect(10, 20, 100, 100));
 
     // now move with a Geometry update blocker
     {
@@ -552,7 +552,7 @@ void InternalWindowTest::testMove()
         QCOMPARE(win.geometry(), QRect(10, 20, 100, 100));
     }
     // after destroying the blocker it should be synced
-    QCOMPARE(win.geometry(), QRect(5, 10, 100, 100));
+    QTRY_COMPARE(win.geometry(), QRect(5, 10, 100, 100));
 }
 
 void InternalWindowTest::testSkipCloseAnimation_data()

shell_client.cpp

@@ -543,7 +543,8 @@ void ShellClient::syncGeometryToInternalWindow()
     const QRect windowRect = QRect(geom.topLeft() + QPoint(borderLeft(), borderTop()),
                                     geom.size() - QSize(borderLeft() + borderRight(), borderTop() + borderBottom()));
     if (m_internalWindow->geometry() != windowRect) {
-        m_internalWindow->setGeometry(windowRect);
+        // delay to end of cycle to prevent freeze, see BUG 384441
+        QTimer::singleShot(0, m_internalWindow, std::bind(static_cast<void (QWindow::*)(const QRect&)>(&QWindow::setGeometry), m_internalWindow, windowRect));
     }
 }