Delay releasing the compositor selection

When turning off the compositor do not release the compositor selection
directly but delay it through a timer. The idea is that the internal
change when e.g. restarting the compositor or switching from XRender to
OpenGL should not be visible to the outside world.

This hopefully makes restarting the compositor more robust in Plasma due
to the SelectionWatcher sometimes reporting incorrect results.

When restarting KWin the change does not matter as the selection gets
force claimed by the new instance anyway.

CCBUG: 179042
REVIEW: 106844

composite.cpp

@@ -118,6 +118,11 @@ Compositor::Compositor(QObject* workspace)
     unredirectTimer.setSingleShot(true);
     compositeResetTimer.setSingleShot(true);
     nextPaintReference.invalidate(); // Initialize the timer
+
+    m_releaseSelectionTimer.setSingleShot(true);
+    // 2 sec which should be enough to restart the compositor
+    m_releaseSelectionTimer.setInterval(2000);
+    connect(&m_releaseSelectionTimer, SIGNAL(timeout()), SLOT(releaseCompositorSelection()));
     // delay the call to setup by one event cycle
     // The ctor of this class is invoked from the Workspace ctor, that means before
     // Workspace is completely constructed, so calling Workspace::self() would result
@@ -128,6 +133,7 @@ Compositor::Compositor(QObject* workspace)
 Compositor::~Compositor()
 {
     finish();
+    delete cm_selection;
 }
 
 
@@ -142,6 +148,7 @@ void Compositor::setup()
         kError(1212) << "Compositing is not possible";
         return;
     }
+    m_starting = true;
 
     if (!options->isCompositingInitialized()) {
 #ifndef KWIN_HAVE_OPENGLES
@@ -166,8 +173,10 @@ void Compositor::slotCompositingOptionsInitialized()
 {
     char selection_name[ 100 ];
     sprintf(selection_name, "_NET_WM_CM_S%d", DefaultScreen(display()));
-    cm_selection = new KSelectionOwner(selection_name);
+    if (!cm_selection) {
-    connect(cm_selection, SIGNAL(lostOwnership()), SLOT(finish()));
+        cm_selection = new KSelectionOwner(selection_name);
+        connect(cm_selection, SIGNAL(lostOwnership()), SLOT(finish()));
+    }
     cm_selection->claim(true);   // force claiming
 
     switch(options->compositingMode()) {
@@ -214,7 +223,8 @@ void Compositor::slotCompositingOptionsInitialized()
 #endif
     default:
         kDebug(1212) << "No compositing enabled";
-        delete cm_selection;
+        m_starting = false;
+        cm_selection->release();
         return;
     }
     if (m_scene == NULL || m_scene->initFailed()) {
@@ -222,7 +232,8 @@ void Compositor::slotCompositingOptionsInitialized()
         kError(1212) << "Consult http://techbase.kde.org/Projects/KWin/4.0-release-notes#Setting_up";
         delete m_scene;
         m_scene = NULL;
-        delete cm_selection;
+        m_starting = false;
+        cm_selection->release();
         return;
     }
     m_xrrRefreshRate = KWin::currentRefreshRate();
@@ -247,6 +258,11 @@ void Compositor::slotCompositingOptionsInitialized()
 
     emit compositingToggled(true);
 
+    m_starting = false;
+    if (m_releaseSelectionTimer.isActive()) {
+        m_releaseSelectionTimer.stop();
+    }
+
     // render at least once
     compositeTimer.stop();
     performCompositing();
@@ -263,7 +279,7 @@ void Compositor::finish()
     if (!hasScene())
         return;
     m_finishing = true;
-    delete cm_selection;
+    m_releaseSelectionTimer.start();
     foreach (Client * c, Workspace::self()->clientList())
         m_scene->windowClosed(c, NULL);
     foreach (Client * c, Workspace::self()->desktopList())
@@ -304,6 +320,27 @@ void Compositor::finish()
     emit compositingToggled(false);
 }
 
+void Compositor::releaseCompositorSelection()
+{
+    if (hasScene() && !m_finishing) {
+        // compositor is up and running again, no need to release the selection
+        return;
+    }
+    if (m_starting) {
+        // currently still starting the compositor, it might fail, so restart the timer to test again
+        m_releaseSelectionTimer.start();
+        return;
+    }
+
+    if (m_finishing) {
+        // still shutting down, a restart might follow, so restart the timer to test again
+        m_releaseSelectionTimer.start();
+        return;
+    }
+    kDebug(1212) << "Releasing compositor selection";
+    cm_selection->release();
+}
+
 // OpenGL self-check failed, fallback to XRender
 void Compositor::fallbackToXRenderCompositing()
 {

composite.h

@@ -275,6 +275,7 @@ private Q_SLOTS:
     void performMousePoll();
     void delayedCheckUnredirect();
     void slotConfigChanged();
+    void releaseCompositorSelection();
 
 private:
     Compositor(QObject *workspace);
@@ -298,6 +299,7 @@ private:
     bool m_blocked;
     QBasicTimer compositeTimer;
     KSelectionOwner* cm_selection;
+    QTimer m_releaseSelectionTimer;
     uint vBlankInterval, fpsInterval;
     int m_xrrRefreshRate;
     QElapsedTimer nextPaintReference;
@@ -308,6 +310,7 @@ private:
     bool forceUnredirectCheck;
     QTimer compositeResetTimer; // for compressing composite resets
     bool m_finishing; // finish() sets this variable while shutting down
+    bool m_starting; // start() sets this variable while starting
     int m_timeSinceLastVBlank, m_nextFrameDelay;
     Scene *m_scene;