statistics: refactor QSG memory management

The code was wrong, because it deleted the ChartItems in the
main UI thread, not the render thread. This would delete the
QSG nodes in the UI thread and then crash on mobile.

Therefore refactor this part of the code by adding the
items to be deleted to a list that will be deleted by the
render thread.

As a drop in replacement of std::unique_ptr, implement
a silly ChartItemPtr class, which auto-initializes to null.

This turns the deterministic and easily controlled memory
management into a steaming pile of insanity. Obviously,
this can be made much more elegant, but this has to do for now.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

1 files changed, 20 insertions, 6 deletions

diff --git a/stats/chartitem.h b/stats/chartitem.h
index 44caae9cc..6c8919dec 100644
--- a/stats/chartitem.h
+++ b/stats/chartitem.h
@@ -22,13 +22,14 @@ class ChartItem {
 public:
 	virtual void render() = 0;		// Only call on render thread!
 	bool dirty;				// If true, call render() when rebuilding the scene
-	ChartItem *dirtyPrev, *dirtyNext;	// Double linked list of dirty items
+	ChartItem *prev, *next;			// Double linked list of items
 	const ChartZValue zValue;
+	virtual ~ChartItem();			// Attention: must only be called by render thread.
 protected:
 	ChartItem(StatsView &v, ChartZValue z);
-	virtual ~ChartItem();
 	QSizeF sceneSize() const;
 	StatsView &view;
+	void markDirty();
 };
 
 template <typename Node>
@@ -36,9 +37,11 @@ class HideableChartItem : public ChartItem {
 protected:
 	HideableChartItem(StatsView &v, ChartZValue z);
 	std::unique_ptr<Node> node;
-	bool visible;				// Argh. If visibility is set before node is created, we have to cache it.
+	bool visible;
+	bool visibleChanged;
 	template<class... Args>
 	void createNode(Args&&... args);	// Call to create node with visibility flag.
+	void updateVisible();			// Must be called by child class to update visibility flag!
 public:
 	void setVisible(bool visible);
 };
@@ -186,9 +189,11 @@ private:
 template <typename Node>
 void HideableChartItem<Node>::setVisible(bool visibleIn)
 {
+	if (visible == visibleIn)
+		return;
 	visible = visibleIn;
-	if (node)
-		node->setVisible(visible);
+	visibleChanged = true;
+	markDirty();
 }
 
 template <typename Node>
@@ -196,12 +201,21 @@ template<class... Args>
 void HideableChartItem<Node>::createNode(Args&&... args)
 {
 	node.reset(new Node(visible, std::forward<Args>(args)...));
+	visibleChanged = false;
 }
 
 template <typename Node>
 HideableChartItem<Node>::HideableChartItem(StatsView &v, ChartZValue z) : ChartItem(v, z),
-	visible(true)
+	visible(true), visibleChanged(false)
+{
+}
+
+template <typename Node>
+void HideableChartItem<Node>::updateVisible()
 {
+	if (visibleChanged)
+		node->setVisible(visible);
+	visibleChanged = false;
 }
 
 #endif