From 0ed06420c2364a038f9909255bda93d2d134d5cc Mon Sep 17 00:00:00 2001
From: Carl Hetherington <carl@carlh.net>
Date: Wed, 9 Nov 2011 17:43:52 +0000
Subject: [PATCH] Return 0 from the topological sort if it failed due to
 feedback.

git-svn-id: svn://localhost/ardour2/branches/3.0@10509 d708f5d6-7413-0410-9779-e7cbd77b26cf
---
 libs/ardour/route_dag.cc | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libs/ardour/route_dag.cc b/libs/ardour/route_dag.cc
index 6a6e8d2bbd..3b13cf9415 100644
--- a/libs/ardour/route_dag.cc
+++ b/libs/ardour/route_dag.cc
@@ -146,7 +146,9 @@ struct RouteRecEnabledComparator
 	}
 };
 
-		
+/** Perform a topological sort of a list of routes using a directed graph representing connections.
+ *  @return Sorted list of routes, or 0 if the graph contains cycles (feedback loops).
+ */
 boost::shared_ptr<RouteList>
 ARDOUR::topological_sort (
 	boost::shared_ptr<RouteList> routes,
@@ -189,7 +191,8 @@ ARDOUR::topological_sort (
 	}
 
 	if (!edges.empty ()) {
-		cout << "Feedback detected.\n";
+		/* There are cycles in the graph, so we can't do a topological sort */
+		return boost::shared_ptr<RouteList> ();
 	}
 
 	return sorted_routes;