BufferManager: prevent race on buffersToRelease vector

Dirty buffers to release are added in the QAspectThread::syncChanges but we
may be rendering/cleaning up resources at the same time in the render
thread. Now protecting any call that could modify the buffers with a mutex.

Task-number: QTBUG-57655
Change-Id: If98702b901bab0e092c039d4da2f0c3f3cdca7cc
Reviewed-by: Kevin Ottens <kevin.ottens@kdab.com>

3 files changed, 10 insertions, 4 deletions

diff --git a/src/render/backend/renderer.cpp b/src/render/backend/renderer.cpp
index e4ad7d181..59c1c05eb 100644
--- a/src/render/backend/renderer.cpp
+++ b/src/render/backend/renderer.cpp
@@ -1472,7 +1472,7 @@ bool Renderer::requiresVAOAttributeUpdate(Geometry *geometry,
 void Renderer::cleanGraphicsResources()
 {
     // Clean buffers
-    const QVector<Qt3DCore::QNodeId> buffersToRelease = std::move(m_nodesManager->bufferManager()->buffersToRelease());
+    const QVector<Qt3DCore::QNodeId> buffersToRelease = m_nodesManager->bufferManager()->takeBuffersToRelease();
     for (Qt3DCore::QNodeId bufferId : buffersToRelease)
         m_graphicsContext->releaseBuffer(bufferId);
 
diff --git a/src/render/geometry/buffermanager.cpp b/src/render/geometry/buffermanager.cpp
index 09d9cfd50..78c2c0082 100644
--- a/src/render/geometry/buffermanager.cpp
+++ b/src/render/geometry/buffermanager.cpp
@@ -65,14 +65,19 @@ QVector<Qt3DCore::QNodeId> BufferManager::dirtyBuffers()
     return vector;
 }
 
+// Called in QAspectThread::syncChanges
 void BufferManager::addBufferToRelease(Qt3DCore::QNodeId bufferId)
 {
+    QMutexLocker lock(&m_mutex);
     m_buffersToRelease.push_back(bufferId);
 }
 
-QVector<Qt3DCore::QNodeId> &BufferManager::buffersToRelease()
+// Called in Render thread
+QVector<Qt3DCore::QNodeId> BufferManager::takeBuffersToRelease()
 {
-    return m_buffersToRelease;
+    QMutexLocker lock(&m_mutex);
+    // Clears the m_buffersToRelease vector
+    return std::move(m_buffersToRelease);
 }
 
 } // namespace Render
diff --git a/src/render/geometry/buffermanager_p.h b/src/render/geometry/buffermanager_p.h
index 754d65fe6..6862cd973 100644
--- a/src/render/geometry/buffermanager_p.h
+++ b/src/render/geometry/buffermanager_p.h
@@ -78,11 +78,12 @@ public:
     // Aspect Thread
     void addBufferToRelease(Qt3DCore::QNodeId bufferId);
     // Render Thread (no concurrent access)
-    QVector<Qt3DCore::QNodeId> &buffersToRelease();
+    QVector<Qt3DCore::QNodeId> takeBuffersToRelease();
 
 private:
     QVector<Qt3DCore::QNodeId> m_dirtyBuffers;
     QVector<Qt3DCore::QNodeId> m_buffersToRelease;
+    QMutex m_mutex;
 };
 
 } // namespace Render