Turn AutomationCtrl into a SessionHandleRef

This fixes a crash with GUI elements which are only deleted during GUI
Idle and hold a Reference to a Controllable,
The session is already destroyed at that point:

ARDOUR::CoreSelection::remove_control_by_id(PBD::ID const&)
ARDOUR::AutomationControl::~AutomationControl()
ARDOUR::SlavableAutomationControl::~SlavableAutomationControl()
ARDOUR::MonitorControl::~MonitorControl()
boost::detail::sp_counted_base::destroy()
boost::detail::sp_counted_impl_p<AudioGrapher::Interleaver<float>::Input>::dispose()
boost::detail::sp_counted_base::release()
boost::detail::shared_count::~shared_count()
boost::shared_ptr<PBD::Controllable>::~shared_ptr()
boost::shared_ptr<PBD::Connection>::~shared_ptr()
ArdourWidgets::BindingProxy::~BindingProxy()
ArdourWidgets::ArdourButton::~ArdourButton()
VCAMasterStrip::~VCAMasterStrip()
int idle_delete<VCAMasterStrip>(VCAMasterStrip*)

2 files changed, 19 insertions, 6 deletions

diff --git a/libs/ardour/ardour/automation_control.h b/libs/ardour/ardour/automation_control.h
index 6ffcb3b866..e875ea98a6 100644
--- a/libs/ardour/ardour/automation_control.h
+++ b/libs/ardour/ardour/automation_control.h
@@ -36,6 +36,7 @@
 #include "ardour/automation_list.h"
 #include "ardour/control_group_member.h"
 #include "ardour/parameter_descriptor.h"
+#include "ardour/session_handle.h"
 
 #include "ardour/libardour_visibility.h"
 
@@ -52,6 +53,7 @@ class LIBARDOUR_API AutomationControl
 	, public Evoral::Control
 	, public boost::enable_shared_from_this<AutomationControl>
 	, public ControlGroupMember
+	, public SessionHandleRef
 {
 public:
 	AutomationControl(ARDOUR::Session&,
@@ -124,7 +126,6 @@ public:
 	ControlList grouped_controls () const;
 
 protected:
-	ARDOUR::Session& _session;
 	boost::shared_ptr<ControlGroup> _group;
 
 	const ParameterDescriptor _desc;
@@ -147,6 +148,8 @@ protected:
 	/* this will be invoked in turn on behalf of the group or the control by itself */
 	virtual void do_pre_realtime_queue_stuff (double new_value) {}
 
+	void session_going_away ();
+
 private:
 	/* I am unclear on why we have to make ControlGroup a friend in order
 	   to get access to the ::set_group() method when it is already
@@ -155,6 +158,7 @@ private:
 	friend class ControlGroup;
 	void set_group (boost::shared_ptr<ControlGroup>);
 	PBD::ScopedConnection _state_changed_connection;
+	bool _no_session;
 };
 
 
diff --git a/libs/ardour/automation_control.cc b/libs/ardour/automation_control.cc
index 1c4525470b..7deeac4221 100644
--- a/libs/ardour/automation_control.cc
+++ b/libs/ardour/automation_control.cc
@@ -56,8 +56,9 @@ AutomationControl::AutomationControl(ARDOUR::Session&                          s
 
 	: Controllable (name.empty() ? EventTypeMap::instance().to_symbol(parameter) : name, flags)
 	, Evoral::Control(parameter, desc, list)
-	, _session(session)
+	, SessionHandleRef (session)
 	, _desc(desc)
+	, _no_session(false)
 {
 	if (_desc.toggled) {
 		set_flags (Controllable::Toggle);
@@ -70,10 +71,18 @@ AutomationControl::AutomationControl(ARDOUR::Session&                          s
 
 AutomationControl::~AutomationControl ()
 {
-	if (!_session.deletion_in_progress ()) {
+	if (!_no_session && !_session.deletion_in_progress ()) {
 		_session.selection().remove_control_by_id (id());
+		DropReferences (); /* EMIT SIGNAL */
 	}
+}
+
+void
+AutomationControl::session_going_away ()
+{
+	SessionHandleRef::session_going_away ();
 	DropReferences (); /* EMIT SIGNAL */
+	_no_session = true;
 }
 
 bool
@@ -90,7 +99,7 @@ AutomationControl::writable() const
 double
 AutomationControl::get_value() const
 {
-	bool from_list = _list && boost::dynamic_pointer_cast<AutomationList>(_list)->automation_playback();
+	bool from_list = alist() && alist()->automation_playback();
 	return Control::get_double (from_list, _session.transport_frame());
 }
 
@@ -176,7 +185,7 @@ AutomationControl::automation_run (framepos_t start, pframes_t nframes)
 void
 AutomationControl::actually_set_value (double value, PBD::Controllable::GroupControlDisposition gcd)
 {
-	boost::shared_ptr<AutomationList> al = boost::dynamic_pointer_cast<AutomationList> (_list);
+	boost::shared_ptr<AutomationList> al = alist ();
 	const framepos_t pos = _session.transport_frame();
 	bool to_list;
 
@@ -232,7 +241,7 @@ AutomationControl::set_automation_state (AutoState as)
 	if (flags() & NotAutomatable) {
 		return;
 	}
-	if (_list && as != alist()->automation_state()) {
+	if (alist() && as != alist()->automation_state()) {
 
 		const double val = get_value ();