Fix lockup in creator.

My previous fix to force expose when the render thread is inactive
was not enough. We now lock down access to 'QSGRenderThread::window'
so that it will always be set when the thread is in the "exposed"
state and 0 when the thread is in the "obscured" state.

This introduces another sync point in handleObscurity to protect
the writing of window in the render thread.

Task-number: QTCREATORBUG-10793
Change-Id: I1e1153189b3a3562705892b42625f88ef6329188
Reviewed-by: Ulf Hermann <ulf.hermann@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/src/quick/scenegraph/qsgthreadedrenderloop.cpp b/src/quick/scenegraph/qsgthreadedrenderloop.cpp
index 96dfd1c26f..0c46747e53 100644
--- a/src/quick/scenegraph/qsgthreadedrenderloop.cpp
+++ b/src/quick/scenegraph/qsgthreadedrenderloop.cpp
@@ -381,10 +381,13 @@ bool QSGRenderThread::event(QEvent *e)
 
         Q_ASSERT(!window || window == static_cast<WMWindowEvent *>(e)->window);
 
+        mutex.lock();
         if (window) {
             QSG_RT_DEBUG(" - removed one...");
             window = 0;
         }
+        waitCondition.wakeOne();
+        mutex.unlock();
 
         return true; }
 
@@ -799,7 +802,7 @@ void QSGThreadedRenderLoop::show(QQuickWindow *window)
          *
          * REF: QTCREATORBUG-10699
          */
-        if (window->isExposed() && (!w->thread || !w->thread->isRunning()))
+        if (window->isExposed() && (!w->thread || !w->thread->window))
             handleExposure(w);
         return;
     }
@@ -942,8 +945,12 @@ void QSGThreadedRenderLoop::handleExposure(Window *w)
 void QSGThreadedRenderLoop::handleObscurity(Window *w)
 {
     QSG_GUI_DEBUG(w->window, "handleObscurity");
-    if (w->thread->isRunning())
+    if (w->thread->isRunning()) {
+        w->thread->mutex.lock();
         w->thread->postEvent(new WMWindowEvent(w->window, WM_Obscure));
+        w->thread->waitCondition.wait(&w->thread->mutex);
+        w->thread->mutex.unlock();
+    }
 
     startOrStopAnimationTimer();
 }