Renderer::doRender scene3dBlocking fixes

-Reorder sleep and locks
-Properly protect isFrameQueueComplete lookup
-Reread queueIsEmpty which could have been updated

Change-Id: I2b5a52284bbb3ddb48483c5bf73779e335c8bdda
Task-number: QTBUG-71294
Reviewed-by: Christian Andersen <csandersen3@gmail.com>
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/src/render/renderers/opengl/renderer/renderer.cpp b/src/render/renderers/opengl/renderer/renderer.cpp
index 8039b6412..7aa39aa40 100644
--- a/src/render/renderers/opengl/renderer/renderer.cpp
+++ b/src/render/renderers/opengl/renderer/renderer.cpp
@@ -629,18 +629,21 @@ void Renderer::doRender(bool scene3dBlocking)
     // Lock the mutex to protect access to the renderQueue while we look for its state
     QMutexLocker locker(m_renderQueue->mutex());
     bool queueIsComplete = m_renderQueue->isFrameQueueComplete();
-    const bool queueIsEmpty = m_renderQueue->targetRenderViewCount() == 0;
+    bool queueIsEmpty = m_renderQueue->targetRenderViewCount() == 0;
 
     // Scene3D Blocking Mode
     if (scene3dBlocking && !queueIsComplete && !queueIsEmpty) {
         int i = 0;
         // We wait at most 10ms to avoid a case we could never recover from
-        while (!queueIsComplete && i++ < 10) {
-            QThread::msleep(1);
+        while (!queueIsComplete && !queueIsEmpty && i++ < 10) {
             qCDebug(Backend) << Q_FUNC_INFO << "Waiting for ready queue (try:" << i << "/ 10)";
             locker.unlock();
-            queueIsComplete = m_renderQueue->isFrameQueueComplete();
+            // Give worker threads a chance to complete the queue
+            QThread::msleep(1);
             locker.relock();
+            queueIsComplete = m_renderQueue->isFrameQueueComplete();
+            // This could become true if we've tried to shutdown
+            queueIsEmpty = m_renderQueue->targetRenderViewCount() == 0;
         }
     }