From e9bafde628ef237e6f429a0511112d81e22a8a86 Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Fri, 21 Oct 2022 20:40:15 +0200
Subject: [PATCH] Catch manual removal of subgroup bus (#9022)

---
 libs/ardour/ardour/route_group.h |  1 +
 libs/ardour/route_group.cc       | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/libs/ardour/ardour/route_group.h b/libs/ardour/ardour/route_group.h
index a6998ccdec..f1a95ccf9b 100644
--- a/libs/ardour/ardour/route_group.h
+++ b/libs/ardour/ardour/route_group.h
@@ -189,6 +189,7 @@ private:
 	boost::shared_ptr<ControlGroup> _monitoring_group;
 
 	void remove_when_going_away (boost::weak_ptr<Route>);
+	void unset_subgroup_bus ();
 	int set_state_2X (const XMLNode&, int);
 
 	void post_set (PBD::PropertyChange const &);
diff --git a/libs/ardour/route_group.cc b/libs/ardour/route_group.cc
index a5aa8500ba..29799f0b8a 100644
--- a/libs/ardour/route_group.cc
+++ b/libs/ardour/route_group.cc
@@ -208,6 +208,15 @@ RouteGroup::remove_when_going_away (boost::weak_ptr<Route> wr)
 	}
 }
 
+void
+RouteGroup::unset_subgroup_bus ()
+{
+	if (_session.deletion_in_progress()) {
+		return;
+	}
+	_subgroup_bus.reset ();
+}
+
 int
 RouteGroup::remove (boost::shared_ptr<Route> r)
 {
@@ -316,6 +325,7 @@ RouteGroup::set_state (const XMLNode& node, int version)
 		boost::shared_ptr<Route> r = _session.route_by_id (subgroup_id);
 		if (r) {
 			_subgroup_bus = r;
+			_subgroup_bus->DropReferences.connect_same_thread (*this, boost::bind (&RouteGroup::unset_subgroup_bus, this));
 		}
 	}
 
@@ -565,6 +575,7 @@ RouteGroup::make_subgroup (bool aux, Placement placement)
 
 	_subgroup_bus = rl.front();
 	_subgroup_bus->set_name (_name);
+	_subgroup_bus->DropReferences.connect_same_thread (*this, boost::bind (&RouteGroup::unset_subgroup_bus, this));
 
 	if (aux) {