tiny but massively important bug fix that actually deletes commands when they are removed from the unod history

git-svn-id: svn://localhost/ardour2/branches/2.0-ongoing@4240 d708f5d6-7413-0410-9779-e7cbd77b26cf

4 files changed, 47 insertions, 11 deletions

diff --git a/libs/pbd/command.cc b/libs/pbd/command.cc
index f84d99491f..d95c145084 100644
--- a/libs/pbd/command.cc
+++ b/libs/pbd/command.cc
@@ -20,7 +20,6 @@
 #include <pbd/command.h>
 #include <pbd/xml++.h>
 
-
 XMLNode &Command::get_state()
 {
     XMLNode *node = new XMLNode ("Command");
diff --git a/libs/pbd/pbd/command.h b/libs/pbd/pbd/command.h
index 23bcf85b91..96393a0440 100644
--- a/libs/pbd/pbd/command.h
+++ b/libs/pbd/pbd/command.h
@@ -25,7 +25,7 @@
 class Command : public PBD::StatefulDestructible
 {
     public:
-	virtual ~Command() {}
+	virtual ~Command() { /* NOTE: derived classes must call drop_references() */ }
 	virtual void operator() () = 0;
         virtual void undo() = 0;
         virtual void redo() { (*this)(); }
diff --git a/libs/pbd/pbd/undo.h b/libs/pbd/pbd/undo.h
index fa53648b24..c5f60c51af 100644
--- a/libs/pbd/pbd/undo.h
+++ b/libs/pbd/pbd/undo.h
@@ -93,17 +93,24 @@ class UndoHistory : public sigc::trackable
 	void clear_undo ();
 	void clear_redo ();
 
+	/* returns all or part of the history.
+	   If depth==0 it returns just the top
+	   node. If depth<0, it returns everything.
+	   If depth>0, it returns state for that
+	   many elements of the history, or 
+	   the full history, whichever is smaller.
+	*/
+
         XMLNode &get_state(int32_t depth = 0);
         void save_state();
 
-	void set_depth (int32_t);
-	int32_t get_depth() const { return _depth; }
+	void set_depth (uint32_t);
 
 	sigc::signal<void> Changed;
 	
   private:
 	bool _clearing;
-	int32_t _depth;
+	uint32_t _depth;
 	std::list<UndoTransaction*> UndoList;
 	std::list<UndoTransaction*> RedoList;
 
diff --git a/libs/pbd/undo.cc b/libs/pbd/undo.cc
index 8823b2da64..43baad35d2 100644
--- a/libs/pbd/undo.cc
+++ b/libs/pbd/undo.cc
@@ -153,27 +153,57 @@ UndoHistory::UndoHistory ()
 }
 
 void
-UndoHistory::set_depth (int32_t d)
+UndoHistory::set_depth (uint32_t d)
 {
+	UndoTransaction* ut;
+	uint32_t current_depth = UndoList.size();
+
 	_depth = d;
 
-	while (_depth > 0 && UndoList.size() > (uint32_t) _depth) {
-		UndoList.pop_front ();
+	if (d > current_depth) {
+		/* not even transactions to meet request */
+		return;
+	}
+
+	if (_depth > 0) {
+
+		uint32_t cnt = current_depth - d;
+
+		while (cnt--) {
+			ut = UndoList.front();
+			UndoList.pop_front ();
+			delete ut;
+		}
 	}
 }
 
 void
 UndoHistory::add (UndoTransaction* const ut)
 {
+	uint32_t current_depth = UndoList.size();
+
 	ut->GoingAway.connect (bind (mem_fun (*this, &UndoHistory::remove), ut));
 
-	while (_depth > 0 && UndoList.size() > (uint32_t) _depth) {
-		UndoList.pop_front ();
+	/* if the current undo history is larger than or equal to the currently
+	   requested depth, then pop off at least 1 element to make space
+	   at the back for new one.
+	*/
+
+	if ((_depth > 0) && current_depth && (current_depth >= _depth)) {
+
+		uint32_t cnt = 1 + (current_depth - _depth);
+
+		while (cnt--) {
+			UndoTransaction* ut;
+			ut = UndoList.front ();
+			UndoList.pop_front ();
+			delete ut;
+		}
 	}
 
 	UndoList.push_back (ut);
 
-	/* we are now owners of the transaction */
+	/* we are now owners of the transaction and must delete it when finished with it */
 
 	Changed (); /* EMIT SIGNAL */
 }