speed up track creation

For every added Trackview/Mixerstrip, Ardour looks up GUI properties which
results in a total of 13 calls for the initial default items per track:
("height", "visible", "layer-display", "strip-width")

Since the tracks don't yet exist, the properties don't either.
Every lookup result in iterating over all all XMLNotes and for every
"Object". ->property ("id") and ->value () allocates memory.

Adding 64 tracks to an empty session results in 528293 string
allocations and deallocations in XMLNode::property() taking ~30%
of the track creation time.

This commit XMLnode's const method to prevent memory allocation
and caches a pointer to the XMLNode* to skip iterating over object
state.

1 files changed, 19 insertions, 7 deletions

diff --git a/gtk2_ardour/gui_object.h b/gtk2_ardour/gui_object.h
index 39cf579fb5..16b43f31e3 100644
--- a/gtk2_ardour/gui_object.h
+++ b/gtk2_ardour/gui_object.h
@@ -33,12 +33,18 @@ class GUIObjectState
 public:
 	GUIObjectState ();
 
-	XMLNode& get_state () const;
-	int set_state (const XMLNode&);
-
 	static const std::string xml_node_name;
 	void load (const XMLNode&);
 
+	int set_state (const XMLNode&);
+	XMLNode& get_state () const;
+
+	/** Get a string from our state.
+	 *  @param id property of Object node to look for.
+	 *  @param prop_name name of the Object property to return.
+	 *  @param empty if non-0, filled in with true if the property is currently non-existant, otherwise false.
+	 *  @return value of property `prop_name', or empty.
+	 */
 	std::string get_string (const std::string& id, const std::string& prop_name, bool* empty = 0);
 
 	template<typename T> void set_property (const std::string& id, const std::string& prop_name, const T& val) {
@@ -48,17 +54,23 @@ public:
 		child->add_property (prop_name.c_str(), s.str());
 	}
 
+	/** Remove node with provided id.
+	 *  @param id property of Object node to look for.
+	 */
+	void remove_node (const std::string& id);
 	std::list<std::string> all_ids () const;
 
-	static XMLNode* get_node (const XMLNode *, const std::string &);
 	XMLNode* get_or_add_node (const std::string &);
-	static XMLNode* get_or_add_node (XMLNode *, const std::string &);
 
-	void remove_node (const std::string& id);
+	static XMLNode* get_node (const XMLNode *, const std::string &);
+	static XMLNode* get_or_add_node (XMLNode *, const std::string &);
 
   private:
+
 	XMLNode _state;
+	// ideally we'd use a O(1) hash table here,
+	// but O(log(N)) is fine already.
+	std::map <std::string, XMLNode*> object_map;
 };
 
-
 #endif /* __gtk_ardour_gui_object_h__ */