SystemMonitor: Register a graph_widget pseudo-property in MemoryStatsW

The property graph_widget on MemoryStatsWidget is a-pseudo property that
specifies the name of the graph widget which should be attached to the
MemoryStatsWidget. When the property is set, the widget looks up the
graph with that name in its parent, therefore automatically linking to
the correct widget given that it's a sibling or descendant of a sibling.

Userland/Applications/SystemMonitor/MemoryStatsWidget.cpp

@@ -10,6 +10,7 @@
 #include <AK/JsonObject.h>
 #include <AK/NumberFormat.h>
 #include <LibCore/File.h>
+#include <LibCore/Object.h>
 #include <LibGUI/BoxLayout.h>
 #include <LibGUI/Label.h>
 #include <LibGUI/Painter.h>
@@ -39,6 +40,8 @@ MemoryStatsWidget::MemoryStatsWidget(GraphWidget* graph)
     VERIFY(!s_the);
     s_the = this;
 
+    REGISTER_STRING_PROPERTY("memory_graph", graph_widget_name, set_graph_widget_via_name);
+
     set_fixed_height(110);
 
     set_layout<GUI::VerticalBoxLayout>();
@@ -73,6 +76,29 @@ void MemoryStatsWidget::set_graph_widget(GraphWidget& graph)
     m_graph = &graph;
 }
 
+void MemoryStatsWidget::set_graph_widget_via_name(String name)
+{
+    m_graph_widget_name = move(name);
+    if (!m_graph_widget_name.is_null()) {
+        // FIXME: We assume here that the graph widget is a sibling or descendant of a sibling. This prevents more complex hierarchies.
+        auto* maybe_graph = parent_widget()->find_descendant_of_type_named<GraphWidget>(m_graph_widget_name);
+        if (maybe_graph) {
+            m_graph = maybe_graph;
+            // Delete the stored graph name to signal that we found the widget
+            m_graph_widget_name = {};
+        } else {
+            dbgln("MemoryStatsWidget: Couldn't find graph of name '{}', retrying later.", m_graph_widget_name);
+        }
+    }
+}
+
+String MemoryStatsWidget::graph_widget_name()
+{
+    if (m_graph)
+        return m_graph->name();
+    return m_graph_widget_name;
+}
+
 static inline u64 page_count_to_bytes(size_t count)
 {
     return count * 4096;
@@ -115,6 +141,11 @@ void MemoryStatsWidget::refresh()
     m_kfree_count_label->set_text(String::formatted("{}", kfree_call_count));
     m_kmalloc_difference_label->set_text(String::formatted("{:+}", kmalloc_call_count - kfree_call_count));
 
+    // Because the initialization order of us and the graph is unknown, we might get a couple of updates where the graph widget lookup fails.
+    // Therefore, we can retry indefinitely. (Should not be too much of a performance hit, as we don't update that often.)
+    if (!m_graph)
+        set_graph_widget_via_name(move(m_graph_widget_name));
+
     if (m_graph) {
         m_graph->set_max(page_count_to_bytes(total_userphysical_and_swappable_pages) + kmalloc_bytes_total);
         m_graph->add_value({ page_count_to_bytes(user_physical_committed), page_count_to_bytes(user_physical_allocated), kmalloc_bytes_total });

Userland/Applications/SystemMonitor/MemoryStatsWidget.h

@@ -22,6 +22,9 @@ public:
 
     void set_graph_widget(GraphWidget& graph);
 
+    void set_graph_widget_via_name(String name);
+    String graph_widget_name();
+
     void refresh();
 
 private:
@@ -29,6 +32,8 @@ private:
     MemoryStatsWidget();
 
     GraphWidget* m_graph;
+    // Is null if we have a valid graph
+    String m_graph_widget_name {};
     RefPtr<GUI::Label> m_user_physical_pages_label;
     RefPtr<GUI::Label> m_user_physical_pages_committed_label;
     RefPtr<GUI::Label> m_supervisor_physical_pages_label;