9 files changed, 486 insertions, 221 deletions

diff --git a/libs/ardour/ardour/session.h b/libs/ardour/ardour/session.h
index 337b88a8e8..70b5bc4896 100644
--- a/libs/ardour/ardour/session.h
+++ b/libs/ardour/ardour/session.h
@@ -1447,7 +1447,7 @@ private:
 
 	Butler* _butler;
 
-	boost::shared_ptr<TransportFSM> _transport_fsm;
+	TransportFSM* _transport_fsm;
 
 	static const PostTransportWork ProcessCannotProceedMask =
 		PostTransportWork (
diff --git a/libs/ardour/ardour/transport_fsm.h b/libs/ardour/ardour/transport_fsm.h
index f175f8161a..efc5bb161a 100644
--- a/libs/ardour/ardour/transport_fsm.h
+++ b/libs/ardour/ardour/transport_fsm.h
@@ -1,219 +1,169 @@
 #ifndef _ardour_transport_fsm_h_
 #define _ardour_transport_fsm_h_
 
-#ifdef nil
-#undef nil
-#endif
-
-#ifndef BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS
-#define BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS
-#endif
-
-#include <boost/weak_ptr.hpp>
-#include <boost/msm/back/state_machine.hpp>
-#include <boost/msm/back/tools.hpp>
-#include <boost/msm/front/state_machine_def.hpp>
-#include <boost/msm/front/functor_row.hpp>
+#include <list>
+#include <queue>
 
 #include "pbd/demangle.h"
 #include "pbd/stacktrace.h"
 
 #include "ardour/debug.h"
-
-/* state machine */
-namespace msm = boost::msm;
-namespace mpl = boost::mpl;
+#include "ardour/types.h"
 
 namespace ARDOUR
 {
 
 class TransportAPI;
 
-struct TransportFSM : public msm::front::state_machine_def<TransportFSM>
+struct TransportFSM
 {
+  public:
 	/* events to be delivered to the FSM */
 
-	struct butler_done {};
-	struct butler_required {};
-	struct declick_done {};
-	struct start_transport {};
-
-	struct stop_transport {
-		stop_transport (bool ab = false, bool cl = false)
-			: abort (ab)
-			, clear_state (cl) {}
-
-		bool abort;
-		bool clear_state;
+	enum EventType {
+		ButlerDone,
+		ButlerRequired,
+		DeclickDone,
+		StartTransport,
+		StopTransport,
+		Locate,
+		LocateDone
 	};
 
-	struct locate {
-		locate ()
-			: target (0)
-			, with_roll (false)
-			, with_flush (false)
-			, with_loop (false)
-			, force (false) {}
-
-		locate (samplepos_t target, bool roll, bool flush, bool loop, bool f4c)
-			: target (target)
-			, with_roll (roll)
-			, with_flush (flush)
-			, with_loop (loop)
-			, force (f4c) {}
-
+	struct FSMEvent {
+		EventType type;
+		union {
+			bool abort; /* for stop */
+			bool with_roll; /* for locate */
+		};
+		union {
+			bool clear_state; /* for stop */
+			bool with_flush; /* for locate */
+		};
+		/* for locate */
 		samplepos_t target;
-		bool with_roll;
-		bool with_flush;
 		bool with_loop;
 		bool force;
-	};
-
-	struct locate_done {};
-
-	/* Flags */
-
-	struct DeclickInProgress {};
-	struct LocateInProgress {};
-	struct IsRolling {};
-	struct IsStopped {};
-	struct IsWaitingForButler {};
 
-	typedef msm::active_state_switch_before_transition active_state_switch_policy;
-
-	/* transition actions */
-
-	void start_playback (start_transport const& p);
-	void roll_after_locate (locate_done const& p);
-	void stop_playback (declick_done const& s);
-	void start_locate (locate const& s);
-	void start_saved_locate (declick_done const& s);
-	void interrupt_locate (locate const& s);
-	void schedule_butler_for_transport_work (butler_required const&);
-	void save_locate_and_start_declick (locate const &);
-	void start_declick (stop_transport const &);
+		FSMEvent (EventType t)
+			: type (t)
+			, with_roll (false)
+			, with_flush (false)
+			, target (0)
+			, with_loop (false)
+			, force (false)
+		{}
+		FSMEvent (EventType t, bool ab, bool cl)
+			: type (t)
+			, abort (ab)
+			, clear_state (cl)
+		{
+			assert (t == StopTransport);
+		}
+		FSMEvent (EventType t, samplepos_t pos, bool r, bool fl, bool lp, bool f4c)
+			: type (t)
+			, with_roll (r)
+			, with_flush (fl)
+			, target (pos)
+			, with_loop (lp)
+			, force (f4c)
+		{
+			assert (t == Locate);
+		}
+
+		void* operator new (size_t);
+		void  operator delete (void *ptr, size_t /*size*/);
+
+		static void init_pool ();
+
+          private:
+		static Pool* pool;
 
-	/* guards */
+	};
 
-	bool should_roll_after_locate (locate_done const &);
-	bool should_not_roll_after_locate (locate_done const & e)  { return !should_roll_after_locate (e); }
+	TransportFSM (TransportAPI& tapi);
 
-#define define_state(State) \
-	struct State : public msm::front::state<> \
-	{ \
-		template <class Event,class FSM> void on_entry (Event const&, FSM&) { DEBUG_TRACE (PBD::DEBUG::TFSMState, "entering: " # State "\n"); } \
-		template <class Event,class FSM> void on_exit (Event const&, FSM&) { DEBUG_TRACE (PBD::DEBUG::TFSMState, "leaving: " # State "\n"); } \
+	void start () {
+		init ();
 	}
 
-#define define_state_flag(State,Flag) \
-	struct State : public msm::front::state<> \
-	{ \
-		template <class Event,class FSM> void on_entry (Event const&, FSM&) { DEBUG_TRACE (PBD::DEBUG::TFSMState, "entering: " # State "\n"); } \
-		template <class Event,class FSM> void on_exit (Event const&, FSM&) { DEBUG_TRACE (PBD::DEBUG::TFSMState, "leaving: " # State "\n"); } \
-		typedef mpl::vector1<Flag> flag_list; \
+	void stop () {
+		/* should we do anything here? this method is modelled on the
+		   boost::msm design, but its not clear that we ever need to
+		   do anything like this.
+		*/
 	}
 
-#define define_state_flag2(State,Flag1,Flag2) \
-	struct State : public msm::front::state<> \
-	{ \
-		template <class Event,class FSM> void on_entry (Event const&, FSM&) { DEBUG_TRACE (PBD::DEBUG::TFSMState, "entering: " # State "\n"); } \
-		template <class Event,class FSM> void on_exit (Event const&, FSM&) { DEBUG_TRACE (PBD::DEBUG::TFSMState, "leaving: " # State "\n"); } \
-		typedef mpl::vector2<Flag1,Flag2> flag_list; \
-	}
+	enum MotionState {
+		Stopped,
+		Rolling,
+		DeclickToStop,
+		DeclickToLocate,
+		WaitingForLocate
+	};
 
-	/* FSM states */
+	enum ButlerState {
+		NotWaitingForButler,
+		WaitingForButler
+	};
 
-	define_state_flag (WaitingForButler, IsWaitingForButler);
-	define_state (NotWaitingForButler);
-	define_state_flag (Stopped,IsStopped);
-	define_state_flag (Rolling,IsRolling);
-	define_state_flag (DeclickToLocate,DeclickInProgress);
-	define_state_flag (WaitingForLocate,LocateInProgress);
-	define_state_flag (DeclickToStop,DeclickInProgress);
+	std::string current_state () const;
 
-	// Pick a back-end
-	typedef msm::back::state_machine<TransportFSM> back;
+  private:
+	MotionState _motion_state;
+	ButlerState _butler_state;
 
-	boost::weak_ptr<back> wp;
+	void init();
 
-	bool locating ()                     { return backend()->is_flag_active<LocateInProgress>(); }
-	bool locating (declick_done const &) { return locating(); }
-	bool rolling ()                      { return backend()->is_flag_active<IsRolling>(); }
-	bool stopped ()                      { return backend()->is_flag_active<IsStopped>(); }
-	bool waiting_for_butler()            { return backend()->is_flag_active<IsWaitingForButler>(); }
-	bool declick_in_progress()           { return backend()->is_flag_active<DeclickInProgress>(); }
+	/* transition actions */
 
-	static boost::shared_ptr<back> create(TransportAPI& api) {
+	void schedule_butler_for_transport_work ();
+	void start_playback ();
+	void stop_playback ();
+	void start_saved_locate ();
+	void roll_after_locate ();
+	void start_locate (FSMEvent const *);
+	void interrupt_locate (FSMEvent const *);
+	void save_locate_and_start_declick (FSMEvent const *);
+	void start_declick (FSMEvent const *);
 
-		boost::shared_ptr<back> p (new back ());
+	/* guards */
 
-		p->wp = p;
-		p->api = &api;
-		return p;
+	bool should_roll_after_locate ();
+	bool should_not_roll_after_locate ()  { return !should_roll_after_locate (); }
+
+  public:
+	bool locating ()                     { return _motion_state == WaitingForLocate; }
+	bool rolling ()                      { return _motion_state == Rolling; }
+	bool stopped ()                      { return _motion_state == Stopped; }
+	bool waiting_for_butler()            { return _butler_state == WaitingForButler; }
+	bool declick_in_progress()           { return _motion_state == DeclickToLocate || _motion_state == DeclickToStop; }
+
+	void enqueue (FSMEvent* ev) {
+		queued_events.push (ev);
+		if (!processing) {
+			process_events ();
+		}
 	}
 
-	boost::shared_ptr<back> backend() { return wp.lock(); }
+  private:
 
-	template<typename Event> void enqueue (Event const & e) {
-		backend()->process_event (e);
-	}
+	void transition (MotionState ms);
+	void transition (ButlerState bs);
 
-	/* the initial state */
-	typedef boost::mpl::vector<Stopped,NotWaitingForButler> initial_state;
-
-	/* transition table */
-	typedef TransportFSM T; // makes transition table cleaner
-
-	struct transition_table : mpl::vector<
-		//      Start                Event            Next               Action                Guard
-		//    +----------------------+----------------+------------------+---------------------+----------------------+
-		a_row < Stopped,             start_transport, Rolling,           &T::start_playback                                      >,
-		_row  < Stopped,             stop_transport,  Stopped                                                                    >,
-		a_row < Stopped,             locate,          WaitingForLocate,  &T::start_locate                                        >,
-		g_row < WaitingForLocate,    locate_done,     Stopped,                                  &T::should_not_roll_after_locate >,
-		_row  < Rolling,             butler_done,     Rolling                                                                    >,
-		_row  < Rolling,             start_transport, Rolling                                                                    >,
-		a_row < Rolling,             stop_transport,  DeclickToStop,     &T::start_declick                                       >,
-		a_row < DeclickToStop,       declick_done,    Stopped,           &T::stop_playback                                       >,
-		a_row < Rolling,             locate,          DeclickToLocate,   &T::save_locate_and_start_declick                       >,
-		a_row < DeclickToLocate,     declick_done,    WaitingForLocate,  &T::start_saved_locate                                  >,
-		row   < WaitingForLocate,    locate_done,     Rolling,           &T::roll_after_locate, &T::should_roll_after_locate     >,
-		a_row < NotWaitingForButler, butler_required, WaitingForButler,  &T::schedule_butler_for_transport_work                  >,
-		a_row < WaitingForButler,    butler_required, WaitingForButler,  &T::schedule_butler_for_transport_work                  >,
-		_row  < WaitingForButler,    butler_done,     NotWaitingForButler                                                        >,
-		a_row < WaitingForLocate,    locate,          WaitingForLocate,  &T::interrupt_locate                                    >,
-		a_row < DeclickToLocate,     locate,          DeclickToLocate,   &T::interrupt_locate                                    >,
-
-		// Deferrals
-
-#define defer(start_state,ev) boost::msm::front::Row<start_state, ev, start_state, boost::msm::front::Defer, boost::msm::front::none >
-
-		defer (DeclickToLocate, start_transport),
-		defer (DeclickToLocate, stop_transport),
-		defer (DeclickToStop, start_transport),
-		defer (WaitingForLocate, start_transport),
-		defer (WaitingForLocate, stop_transport)
-
-#undef defer
-		> {};
-
-	typedef int activate_deferred_events;
-
-	locate         _last_locate;
-	stop_transport _last_stop;
+	void process_events ();
+	bool process_event (FSMEvent *);
+
+	FSMEvent _last_locate;
+	FSMEvent _last_stop;
 
 	TransportAPI* api;
+	std::queue<FSMEvent*> queued_events;
+	std::list<FSMEvent*> deferred_events;
+	int processing;
 
-	// Replaces the default no-transition response.
-	template <class FSM,class Event>
-	void no_transition(Event const& e, FSM&,int state)
-	{
-		typedef typename boost::msm::back::recursive_get_transition_table<FSM>::type recursive_stt;
-		typedef typename boost::msm::back::generate_state_set<recursive_stt>::type all_states;
-		std::string stateName;
-		boost::mpl::for_each<all_states,boost::msm::wrap<boost::mpl::placeholders::_1> >(boost::msm::back::get_state_name<recursive_stt>(stateName, state));
-		std::cout << "No transition from state: " << PBD::demangle (stateName) << " on event " << typeid(e).name() << std::endl;
-	}
+	void defer (FSMEvent* ev);
+	void bad_transition (FSMEvent const *);
 };
 
 } /* end namespace ARDOUR */
diff --git a/libs/ardour/enums.cc b/libs/ardour/enums.cc
index 2665a14d94..903861fc02 100644
--- a/libs/ardour/enums.cc
+++ b/libs/ardour/enums.cc
@@ -47,6 +47,7 @@
 #include "ardour/source.h"
 #include "ardour/tempo.h"
 #include "ardour/track.h"
+#include "ardour/transport_fsm.h"
 #include "ardour/transport_master.h"
 #include "ardour/types.h"
 
@@ -151,6 +152,9 @@ setup_enum_writer ()
 	PresentationInfo::Flag _PresentationInfo_Flag;
 	MusicalMode::Type mode;
 	MidiPortFlags _MidiPortFlags;
+	TransportFSM::EventType _TransportFSM_EventType;
+	TransportFSM::MotionState _TransportFSM_MotionState;
+	TransportFSM::ButlerState _TransportFSM_ButlerState;
 
 #define REGISTER(e) enum_writer.register_distinct (typeid(e).name(), i, s); i.clear(); s.clear()
 #define REGISTER_BITS(e) enum_writer.register_bits (typeid(e).name(), i, s); i.clear(); s.clear()
@@ -793,6 +797,27 @@ setup_enum_writer ()
 	REGISTER_CLASS_ENUM (MusicalMode, Persian);
 	REGISTER_CLASS_ENUM (MusicalMode, Algerian);
 	REGISTER (mode);
+
+	REGISTER_CLASS_ENUM (TransportFSM, ButlerDone);
+	REGISTER_CLASS_ENUM (TransportFSM, ButlerRequired);
+	REGISTER_CLASS_ENUM (TransportFSM, DeclickDone);
+	REGISTER_CLASS_ENUM (TransportFSM, StartTransport);
+	REGISTER_CLASS_ENUM (TransportFSM, StopTransport);
+	REGISTER_CLASS_ENUM (TransportFSM, Locate);
+	REGISTER_CLASS_ENUM (TransportFSM, LocateDone);
+	REGISTER (_TransportFSM_EventType);
+
+	REGISTER_CLASS_ENUM (TransportFSM, Stopped);
+	REGISTER_CLASS_ENUM (TransportFSM, Rolling);
+	REGISTER_CLASS_ENUM (TransportFSM, DeclickToStop);
+	REGISTER_CLASS_ENUM (TransportFSM, DeclickToLocate);
+	REGISTER_CLASS_ENUM (TransportFSM, WaitingForLocate);
+	REGISTER (_TransportFSM_MotionState);
+
+
+	REGISTER_CLASS_ENUM (TransportFSM, NotWaitingForButler);
+	REGISTER_CLASS_ENUM (TransportFSM, WaitingForButler);
+	REGISTER (_TransportFSM_ButlerState);
 }
 
 } /* namespace ARDOUR */
diff --git a/libs/ardour/globals.cc b/libs/ardour/globals.cc
index cbb7e4da0e..2a47fd9dea 100644
--- a/libs/ardour/globals.cc
+++ b/libs/ardour/globals.cc
@@ -125,6 +125,7 @@
 #include "ardour/runtime_functions.h"
 #include "ardour/session_event.h"
 #include "ardour/source_factory.h"
+#include "ardour/transport_fsm.h"
 #include "ardour/transport_master_manager.h"
 #ifdef LV2_SUPPORT
 #include "ardour/uri_map.h"
@@ -467,6 +468,7 @@ ARDOUR::init (bool use_windows_vst, bool try_optimization, const char* localedir
 #endif
 
 	SessionEvent::init_event_pool ();
+	TransportFSM::FSMEvent::init_pool ();
 
 	Operations::make_operations_quarks ();
 	SessionObject::make_property_quarks ();
diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index f96f59e516..a042dbf4f3 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -251,7 +251,7 @@ Session::Session (AudioEngine &eng,
 	, lua (lua_newstate (&PBD::ReallocPool::lalloc, &_mempool))
 	, _n_lua_scripts (0)
 	, _butler (new Butler (*this))
-	, _transport_fsm (TransportFSM::create (*this))
+	, _transport_fsm (new TransportFSM (*this))
 	, _post_transport_work (0)
 	, _locations (new Locations (*this))
 	, _ignore_skips_updates (false)
@@ -609,7 +609,7 @@ Session::immediately_post_engine ()
 
 	/* Restart transport FSM */
 
-	_transport_fsm->backend()->start ();
+	_transport_fsm->start ();
 
 	/* every time we reconnect, do stuff ... */
 
@@ -884,8 +884,7 @@ Session::destroy ()
 	delete _selection;
 	_selection = 0;
 
-	_transport_fsm->backend()->stop ();
-	_transport_fsm.reset ();
+	_transport_fsm->stop ();
 
 	DEBUG_TRACE (DEBUG::Destruction, "Session::destroy() done\n");
 
diff --git a/libs/ardour/session_process.cc b/libs/ardour/session_process.cc
index 7661115463..fbcf4c648e 100644
--- a/libs/ardour/session_process.cc
+++ b/libs/ardour/session_process.cc
@@ -59,7 +59,10 @@ using namespace ARDOUR;
 using namespace PBD;
 using namespace std;
 
-#define TFSM_EVENT(ev) { DEBUG_TRACE (DEBUG::TFSMEvents, string_compose ("TFSM(%1)\n", typeid(ev).name())); _transport_fsm->enqueue (ev); }
+#define TFSM_EVENT(evtype) { _transport_fsm->enqueue (new TransportFSM::FSMEvent (evtype)); }
+#define TFSM_STOP(abort,clear) { _transport_fsm->enqueue (new TransportFSM::FSMEvent (TransportFSM::StopTransport,abort,clear)); }
+#define TFSM_LOCATE(target,roll,flush,loop,force) { _transport_fsm->enqueue (new TransportFSM::FSMEvent (TransportFSM::Locate,target,roll,flush,loop,force)); }
+
 
 /** Called by the audio engine when there is work to be done with JACK.
  * @param nframes Number of samples to process.
@@ -127,7 +130,7 @@ Session::process (pframes_t nframes)
 
 	if (!one_or_more_routes_declicking && declick_in_progress()) {
 		/* end of the declick has been reached by all routes */
-		TFSM_EVENT (TransportFSM::declick_done());
+		TFSM_EVENT (TransportFSM::DeclickDone);
 	}
 
 	_engine.main_thread()->drop_buffers ();
@@ -241,7 +244,7 @@ Session::process_routes (pframes_t nframes, bool& need_butler)
 			bool b = false;
 
 			if ((ret = (*i)->roll (nframes, start_sample, end_sample, b)) < 0) {
-				TFSM_EVENT (TransportFSM::stop_transport (false, false));
+				TFSM_STOP (false, false);
 				return -1;
 			}
 
@@ -851,7 +854,7 @@ Session::process_event (SessionEvent* ev)
 			/* roll after locate, do not flush, set "with loop"
 			   true only if we are seamless looping
 			*/
-			TFSM_EVENT (TransportFSM::locate (ev->target_sample, true, false, Config->get_seamless_loop(), false));
+			TFSM_LOCATE (ev->target_sample, true, false, Config->get_seamless_loop(), false);
 		}
 		remove = false;
 		del = false;
@@ -859,19 +862,19 @@ Session::process_event (SessionEvent* ev)
 
 	case SessionEvent::Locate:
 		/* args: do not roll after locate, do flush, not with loop, force */
-		TFSM_EVENT (TransportFSM::locate (ev->target_sample, false, true, false, ev->yes_or_no));
+		TFSM_LOCATE (ev->target_sample, false, true, false, ev->yes_or_no);
 		_send_timecode_update = true;
 		break;
 
 	case SessionEvent::LocateRoll:
 		/* args: roll after locate, do flush, not with loop, force */
-		TFSM_EVENT (TransportFSM::locate (ev->target_sample, true, true, false, ev->yes_or_no));
+		TFSM_LOCATE (ev->target_sample, true, true, false, ev->yes_or_no);
 		_send_timecode_update = true;
 		break;
 
 	case SessionEvent::Skip:
 		if (Config->get_skip_playback()) {
-			TFSM_EVENT (TransportFSM::locate (ev->target_sample, true, true, false, false));
+			TFSM_LOCATE (ev->target_sample, true, true, false, false);
 			_send_timecode_update = true;
 		}
 		remove = false;
@@ -912,14 +915,14 @@ Session::process_event (SessionEvent* ev)
 		break;
 
 	case SessionEvent::RangeStop:
-		TFSM_EVENT (TransportFSM::stop_transport (ev->yes_or_no, false));
+		TFSM_STOP (ev->yes_or_no, false);
 		remove = false;
 		del = false;
 		break;
 
 	case SessionEvent::RangeLocate:
 		/* args: roll after locate, do flush, not with loop */
-		TFSM_EVENT (TransportFSM::locate (ev->target_sample, true, true, false, false));
+		TFSM_LOCATE (ev->target_sample, true, true, false, false);
 		remove = false;
 		del = false;
 		break;
@@ -1109,7 +1112,7 @@ Session::follow_transport_master (pframes_t nframes)
 		DiskReader::inc_no_disk_output ();
 		if (!_transport_fsm->locating()) {
 			DEBUG_TRACE (DEBUG::Slave, string_compose ("request locate to master position %1\n", slave_transport_sample));
-			TFSM_EVENT (TransportFSM::locate (slave_transport_sample, true, true, false, false));
+			TFSM_LOCATE (slave_transport_sample, true, true, false, false);
 		}
 		return true;
 	}
@@ -1117,12 +1120,12 @@ Session::follow_transport_master (pframes_t nframes)
 	if (slave_speed != 0.0) {
 		if (_transport_speed == 0.0f) {
 			DEBUG_TRACE (DEBUG::Slave, string_compose ("slave starts transport: %1 sample %2 tf %3\n", slave_speed, slave_transport_sample, _transport_sample));
-			TFSM_EVENT (TransportFSM::start_transport ());
+			TFSM_EVENT (TransportFSM::StartTransport);
 		}
 	} else {
 		if (_transport_speed != 0.0f) {
 			DEBUG_TRACE (DEBUG::Slave, string_compose ("slave stops transport: %1 sample %2 tf %3\n", slave_speed, slave_transport_sample, _transport_sample));
-			TFSM_EVENT (TransportFSM::stop_transport (false, false));
+			TFSM_STOP (false, false);
 		}
 	}
 
diff --git a/libs/ardour/session_time.cc b/libs/ardour/session_time.cc
index 674ea7b67b..185a86bf4c 100644
--- a/libs/ardour/session_time.cc
+++ b/libs/ardour/session_time.cc
@@ -43,7 +43,7 @@ using namespace std;
 using namespace ARDOUR;
 using namespace PBD;
 
-#define TFSM_EVENT(ev) { DEBUG_TRACE (DEBUG::TFSMEvents, string_compose ("TFSM(%1)\n", typeid(ev).name())); _transport_fsm->enqueue (ev); }
+#define TFSM_EVENT(evtype) { _transport_fsm->enqueue (new TransportFSM::FSMEvent (evtype)); }
 
 /* BBT TIME*/
 
@@ -217,7 +217,7 @@ Session::backend_sync_callback (TransportState state, samplepos_t pos)
 	case TransportRolling:
 		// cerr << "SYNC: rolling slave = " << slave << endl;
 		if (slave) {
-			TFSM_EVENT (TransportFSM::start_transport());
+			TFSM_EVENT (TransportFSM::StartTransport);
 		}
 		break;
 
diff --git a/libs/ardour/session_transport.cc b/libs/ardour/session_transport.cc
index 2f5325b82e..e9f6ed6bbe 100644
--- a/libs/ardour/session_transport.cc
+++ b/libs/ardour/session_transport.cc
@@ -82,7 +82,9 @@ using namespace PBD;
 #endif
 
 
-#define TFSM_EVENT(ev) { DEBUG_TRACE (DEBUG::TFSMEvents, string_compose ("TFSM(%1)\n", typeid(ev).name())); _transport_fsm->enqueue (ev); }
+#define TFSM_EVENT(evtype) { _transport_fsm->enqueue (new TransportFSM::FSMEvent (evtype)); }
+#define TFSM_STOP(abort,clear) { _transport_fsm->enqueue (new TransportFSM::FSMEvent (TransportFSM::StopTransport,abort,clear)); }
+#define TFSM_LOCATE(target,roll,flush,loop,force) { _transport_fsm->enqueue (new TransportFSM::FSMEvent (TransportFSM::Locate,target,roll,flush,loop,force)); }
 
 /* *****************************************************************************
  * REALTIME ACTIONS (to be called on state transitions)
@@ -159,7 +161,7 @@ Session::realtime_stop (bool abort, bool clear_state)
 	}
 
 	if (todo) {
-		TFSM_EVENT (TransportFSM::butler_required());
+		TFSM_EVENT (TransportFSM::ButlerRequired);
 	}
 }
 
@@ -239,7 +241,7 @@ Session::do_locate (samplepos_t target_sample, bool with_roll, bool with_flush,
 			set_transport_speed (1.0, 0, false);
 		}
 		loop_changing = false;
-		TFSM_EVENT (TransportFSM::locate_done());
+		TFSM_EVENT (TransportFSM::LocateDone);
 		Located (); /* EMIT SIGNAL */
 		return;
 	}
@@ -382,9 +384,9 @@ Session::do_locate (samplepos_t target_sample, bool with_roll, bool with_flush,
 	}
 
 	if (need_butler) {
-		TFSM_EVENT (TransportFSM::butler_required());
+		TFSM_EVENT (TransportFSM::ButlerRequired);
 	} else {
-		TFSM_EVENT (TransportFSM::locate_done());
+		TFSM_EVENT (TransportFSM::LocateDone);
 	}
 
 	loop_changing = false;
@@ -484,7 +486,7 @@ Session::set_transport_speed (double speed, samplepos_t destination_sample, bool
 				_requested_return_sample = destination_sample;
 			}
 
-			TFSM_EVENT (TransportFSM::stop_transport (abort, false));
+			TFSM_STOP (abort, false);
 		}
 
 	} else if (transport_stopped() && speed == 1.0) {
@@ -521,7 +523,7 @@ Session::set_transport_speed (double speed, samplepos_t destination_sample, bool
 			_engine.transport_start ();
 			_count_in_once = false;
 		} else {
-			TFSM_EVENT (TransportFSM::start_transport());
+			TFSM_EVENT (TransportFSM::StartTransport);
 		}
 
 	} else {
@@ -576,7 +578,7 @@ Session::set_transport_speed (double speed, samplepos_t destination_sample, bool
 
 		if (todo) {
 			add_post_transport_work (todo);
-			TFSM_EVENT (TransportFSM::butler_required());
+			TFSM_EVENT (TransportFSM::ButlerRequired);
 		}
 
 		DEBUG_TRACE (DEBUG::Transport, string_compose ("send TSC3 with speed = %1\n", _transport_speed));
@@ -748,7 +750,7 @@ Session::butler_completed_transport_work ()
 
 	if (ptw & PostTransportLocate) {
 		post_locate ();
-		TFSM_EVENT (TransportFSM::locate_done());
+		TFSM_EVENT (TransportFSM::LocateDone);
 	}
 
 	if (ptw & PostTransportAdjustPlaybackBuffering) {
@@ -763,7 +765,7 @@ Session::butler_completed_transport_work ()
 	set_post_transport_work (PostTransportWork (0));
 
 	if (_transport_fsm->waiting_for_butler()) {
-		TFSM_EVENT (TransportFSM::butler_done());
+		TFSM_EVENT (TransportFSM::ButlerDone);
 	}
 
 	DiskReader::dec_no_disk_output ();
@@ -785,7 +787,7 @@ Session::maybe_stop (samplepos_t limit)
 		if (synced_to_engine () && config.get_jack_time_master ()) {
 			_engine.transport_stop ();
 		} else if (!synced_to_engine ()) {
-			TFSM_EVENT (TransportFSM::stop_transport ());
+			TFSM_EVENT (TransportFSM::StopTransport);
 		}
 		return true;
 	}
@@ -894,11 +896,11 @@ Session::set_play_loop (bool yn, double speed)
 				   rolling, do not locate to loop start.
 				*/
 				if (!transport_rolling() && (speed != 0.0)) {
-					TFSM_EVENT (TransportFSM::locate (loc->start(), true, true, false, true));
+					TFSM_LOCATE (loc->start(), true, true, false, true);
 				}
 			} else {
 				if (speed != 0.0) {
-					TFSM_EVENT (TransportFSM::locate (loc->start(), true, true, false, true));
+					TFSM_LOCATE (loc->start(), true, true, false, true);
 				}
 			}
 		}
@@ -1779,7 +1781,7 @@ Session::unset_play_loop ()
 		if (Config->get_seamless_loop()) {
 			/* likely need to flush track buffers: this will locate us to wherever we are */
 			add_post_transport_work (PostTransportLocate);
-			TFSM_EVENT (TransportFSM::butler_required());
+			TFSM_EVENT (TransportFSM::ButlerRequired);
 		}
 		TransportStateChange (); /* EMIT SIGNAL */
 	}
@@ -1936,7 +1938,7 @@ Session::engine_halted ()
 	 * ::engine_running() (if we ever get there)
 	 */
 
-	_transport_fsm->backend()->stop ();
+	_transport_fsm->stop ();
 
 	/* Synchronously do the realtime part of a transport stop.
 	 *
@@ -1952,7 +1954,7 @@ void
 Session::engine_running ()
 {
 	initialize_latencies ();
-	_transport_fsm->backend()->start ();
+	_transport_fsm->start ();
 }
 
 void
diff --git a/libs/ardour/transport_fsm.cc b/libs/ardour/transport_fsm.cc
index ea2be0eb3f..0528f95304 100644
--- a/libs/ardour/transport_fsm.cc
+++ b/libs/ardour/transport_fsm.cc
@@ -1,5 +1,6 @@
 /*
  * Copyright (C) 2019 Robin Gareus <robin@gareus.org>
+ * Copyright (C) 2019 Paul Davis <paul@linuxaudiosystems.com>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -16,6 +17,11 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  */
 
+#include <sstream>
+
+#include "pbd/error.h"
+#include "pbd/i18n.h"
+
 #include "ardour/debug.h"
 #include "ardour/session.h"
 #include "ardour/transport_fsm.h"
@@ -23,69 +29,327 @@
 using namespace ARDOUR;
 using namespace PBD;
 
+Pool* TransportFSM::FSMEvent::pool = 0;
+
+void
+TransportFSM::FSMEvent::init_pool ()
+{
+	pool = new Pool (X_("FSMEvents"), sizeof (FSMEvent), 128);
+}
+
+void*
+TransportFSM::FSMEvent::operator new (size_t)
+{
+	return pool->alloc();
+}
+
+void
+TransportFSM::FSMEvent::operator delete (void *ptr, size_t /*size*/)
+{
+	return pool->release (ptr);
+}
+
+TransportFSM::TransportFSM (TransportAPI& tapi)
+	: _last_locate (Locate)
+	, _last_stop (StopTransport)
+	, api (&tapi)
+	, processing (0)
+{
+	init ();
+}
+
+void
+TransportFSM::init ()
+{
+	_motion_state = Stopped;
+	_butler_state = NotWaitingForButler;
+}
+
+void
+TransportFSM::process_events ()
+{
+	processing++;
+
+	while (!queued_events.empty()) {
+		FSMEvent* ev = queued_events.front();
+		queued_events.pop ();
+
+		MotionState oms = _motion_state;
+		ButlerState obs = _butler_state;
+
+		if (process_event (ev)) { /* event processed successfully */
+
+			if (oms != _motion_state || obs != _butler_state) {
+
+				/* state changed, so now check deferred events
+				 * to see if they can be processed now
+				 */
+
+				if (!deferred_events.empty() ){
+					DEBUG_TRACE (DEBUG::TFSMEvents, string_compose ("processing %1 deferred events\n", deferred_events.size()));
+
+					for (std::list<FSMEvent*>::iterator e = deferred_events.begin(); e != deferred_events.end(); ) {
+						FSMEvent* deferred_ev = *e;
+						if (process_event (deferred_ev)) { /* event processed, remove from deferred */
+							e = deferred_events.erase (e);
+							delete deferred_ev;
+						} else {
+							++e;
+						}
+					}
+				}
+			}
+		}
+
+		delete ev;
+	}
+
+	processing--;
+}
+
+/* This is the transition table from the original boost::msm
+ * implementation of this FSM. It is more easily readable and
+ * consultable. Please keep it updated as the FSM changes.
+ */
+
+/*
+        Start                Event            Next               Action                Guard
+      +----------------------+----------------+------------------+---------------------+---------------------------------+
+a_row < Stopped,             start_transport, Rolling,           &T::start_playback                                      >,
+_row  < Stopped,             stop_transport,  Stopped                                                                    >,
+a_row < Stopped,             locate,          WaitingForLocate,  &T::start_locate                                        >,
+g_row < WaitingForLocate,    locate_done,     Stopped,                                  &T::should_not_roll_after_locate >,
+_row  < Rolling,             butler_done,     Rolling                                                                    >,
+_row  < Rolling,             start_transport, Rolling                                                                    >,
+a_row < Rolling,             stop_transport,  DeclickToStop,     &T::start_declick                                       >,
+a_row < DeclickToStop,       declick_done,    Stopped,           &T::stop_playback                                       >,
+a_row < Rolling,             locate,          DeclickToLocate,   &T::save_locate_and_start_declick                       >,
+a_row < DeclickToLocate,     declick_done,    WaitingForLocate,  &T::start_saved_locate                                  >,
+row   < WaitingForLocate,    locate_done,     Rolling,           &T::roll_after_locate, &T::should_roll_after_locate     >,
+a_row < NotWaitingForButler, butler_required, WaitingForButler,  &T::schedule_butler_for_transport_work                  >,
+a_row < WaitingForButler,    butler_required, WaitingForButler,  &T::schedule_butler_for_transport_work                  >,
+_row  < WaitingForButler,    butler_done,     NotWaitingForButler                                                        >,
+a_row < WaitingForLocate,    locate,          WaitingForLocate,  &T::interrupt_locate                                    >,
+a_row < DeclickToLocate,     locate,          DeclickToLocate,   &T::interrupt_locate                                    >,
+
+// Deferrals
+
+#define defer(start_state,ev) boost::msm::front::Row<start_state, ev, start_state, boost::msm::front::Defer, boost::msm::front::none >
+
+defer (DeclickToLocate, start_transport),
+defer (DeclickToLocate, stop_transport),
+defer (DeclickToStop, start_transport),
+defer (WaitingForLocate, start_transport),
+defer (WaitingForLocate, stop_transport)
+
+#undef defer
+*/
+
+std::string
+TransportFSM::current_state () const
+{
+	std::stringstream s;
+	s << enum_2_string (_motion_state) << '/' << enum_2_string (_butler_state);
+	return s.str();
+}
+
+void
+TransportFSM::bad_transition (FSMEvent const * ev)
+{
+	error << "bad transition, current state = " << current_state() << " event = " << enum_2_string (ev->type) << endmsg;
+	std::cerr << "bad transition, current state = " << current_state() << " event = " << enum_2_string (ev->type) << std::endl;
+}
+
+bool
+TransportFSM::process_event (FSMEvent* ev)
+{
+	DEBUG_TRACE (DEBUG::TFSMEvents, string_compose ("process %1\n", enum_2_string (ev->type)));
+
+	switch (ev->type) {
+
+	case StartTransport:
+		switch (_motion_state) {
+		case Stopped:
+			transition (Rolling);
+			start_playback ();
+			break;
+		case Rolling:
+			break;
+		case DeclickToLocate:
+		case WaitingForLocate:
+			defer (ev);
+			break;
+		case DeclickToStop:
+			defer (ev);
+			break;
+		default:
+			bad_transition (ev); return false;
+			break;
+		}
+		break;
+
+	case StopTransport:
+		switch (_motion_state) {
+		case Rolling:
+			transition (DeclickToStop);
+			start_declick (ev);
+			break;
+		case Stopped:
+			break;
+		case DeclickToLocate:
+		case WaitingForLocate:
+			defer (ev);
+			break;
+		default:
+			bad_transition (ev); return false;
+			break;
+		}
+		break;
+
+	case Locate:
+		switch (_motion_state) {
+		case Stopped:
+			transition (WaitingForLocate);
+			start_locate (ev);
+			break;
+		case Rolling:
+			transition (DeclickToLocate);
+			save_locate_and_start_declick (ev);
+			break;
+		case WaitingForLocate:
+		case DeclickToLocate:
+			interrupt_locate (ev);
+			break;
+		default:
+			bad_transition (ev); return false;
+		}
+		break;
+
+	case LocateDone:
+		switch (_motion_state) {
+		case WaitingForLocate:
+			if (should_not_roll_after_locate()) {
+				transition (Stopped);
+			} else {
+				transition (Rolling);
+				roll_after_locate ();
+			}
+			break;
+		default:
+			bad_transition (ev); return false;
+		}
+		break;
+
+	case DeclickDone:
+		switch (_motion_state) {
+		case DeclickToLocate:
+			transition (WaitingForLocate);
+			start_saved_locate ();
+			break;
+		case DeclickToStop:
+			transition (Stopped);
+			stop_playback ();
+			break;
+		default:
+			bad_transition (ev); return false;
+		}
+		break;
+
+	case ButlerRequired:
+		switch (_butler_state) {
+		case NotWaitingForButler:
+			transition (WaitingForButler);
+			schedule_butler_for_transport_work ();
+			break;
+		case WaitingForButler:
+			schedule_butler_for_transport_work ();
+			break;
+		default:
+			bad_transition (ev); return false;
+		}
+		break;
+
+	case ButlerDone:
+		switch (_butler_state) {
+		case WaitingForButler:
+			transition (NotWaitingForButler);
+			break;
+		default:
+			bad_transition (ev); return false;
+		}
+		break;
+	}
+
+	return true;
+}
+
 /* transition actions */
 
 void
-TransportFSM::start_playback (TransportFSM::start_transport const& p)
+TransportFSM::start_playback ()
 {
 	DEBUG_TRACE (DEBUG::TFSMEvents, "tfsm::start_playback\n");
 	api->start_transport();
 }
 
 void
-TransportFSM::start_declick (TransportFSM::stop_transport const &s)
+TransportFSM::start_declick (FSMEvent const * s)
 {
+	assert (s->type == StopTransport);
 	DEBUG_TRACE (DEBUG::TFSMEvents, "tfsm::start_declick\n");
-	_last_stop = s;
+	_last_stop = *s;
 }
 
 void
-TransportFSM::stop_playback (TransportFSM::declick_done const& /*ignored*/)
+TransportFSM::stop_playback ()
 {
 	DEBUG_TRACE (DEBUG::TFSMEvents, "tfsm::stop_playback\n");
 	api->stop_transport (_last_stop.abort, _last_stop.clear_state);
 }
 
 void
-TransportFSM::save_locate_and_start_declick (TransportFSM::locate const & l)
+TransportFSM::save_locate_and_start_declick (FSMEvent const * l)
 {
+	assert (l->type == Locate);
 	DEBUG_TRACE (DEBUG::TFSMEvents, "tfsm::save_locate_and_stop\n");
-	_last_locate = l;
-	start_declick (stop_transport (false, false));
+	_last_locate = *l;
+	_last_stop = FSMEvent (StopTransport, false, false);
 }
 
 void
-TransportFSM::start_locate (TransportFSM::locate const& l)
+TransportFSM::start_locate (FSMEvent const * l)
 {
+	assert (l->type == Locate);
 	DEBUG_TRACE (DEBUG::TFSMEvents, "tfsm::start_locate\n");
-	api->locate (l.target, l.with_roll, l.with_flush, l.with_loop, l.force);
+	api->locate (l->target, l->with_roll, l->with_flush, l->with_loop, l->force);
 }
 
 void
-TransportFSM::start_saved_locate (TransportFSM::declick_done const&)
+TransportFSM::start_saved_locate ()
 {
 	DEBUG_TRACE (DEBUG::TFSMEvents, "tfsm::start_save\n");
 	api->locate (_last_locate.target, _last_locate.with_roll, _last_locate.with_flush, _last_locate.with_loop, _last_locate.force);
 }
 
 void
-TransportFSM::interrupt_locate (TransportFSM::locate const& l)
+TransportFSM::interrupt_locate (FSMEvent const * l)
 {
+	assert (l->type == Locate);
 	DEBUG_TRACE (DEBUG::TFSMEvents, "tfsm::interrupt\n");
 	/* maintain original "with-roll" choice of initial locate, even though
 	 * we are interrupting the locate to start a new one.
 	 */
-	api->locate (l.target, _last_locate.with_roll, l.with_flush, l.with_loop, l.force);
+	api->locate (l->target, _last_locate.with_roll, l->with_flush, l->with_loop, l->force);
 }
 
 void
-TransportFSM::schedule_butler_for_transport_work (TransportFSM::butler_required const&)
+TransportFSM::schedule_butler_for_transport_work ()
 {
 	api->schedule_butler_for_transport_work ();
 }
 
 bool
-TransportFSM::should_roll_after_locate (TransportFSM::locate_done const &)
+TransportFSM::should_roll_after_locate ()
 {
 	bool ret = api->should_roll_after_locate ();
 	DEBUG_TRACE (DEBUG::TFSMEvents, string_compose ("tfsm::should_roll_after_locate() ? %1\n", ret));
@@ -93,9 +357,29 @@ TransportFSM::should_roll_after_locate (TransportFSM::locate_done const &)
 }
 
 void
-TransportFSM::roll_after_locate (TransportFSM::locate_done const &)
+TransportFSM::roll_after_locate ()
 {
 	DEBUG_TRACE (DEBUG::TFSMEvents, "rolling after locate\n");
 	api->start_transport ();
 }
 
+void
+TransportFSM::defer (FSMEvent* ev)
+{
+	DEBUG_TRACE (DEBUG::TFSMEvents, string_compose ("Defer %1 during %2\n", enum_2_string (ev->type), current_state()));
+	deferred_events.push_back (ev);
+}
+
+void
+TransportFSM::transition (MotionState ms)
+{
+	DEBUG_TRACE (DEBUG::TFSMState, string_compose ("Leave %1, enter %2\n", enum_2_string (_motion_state), enum_2_string (ms)));
+	_motion_state = ms;
+}
+
+void
+TransportFSM::transition (ButlerState bs)
+{
+	DEBUG_TRACE (DEBUG::TFSMState, string_compose ("Leave %1, enter %2\n", enum_2_string (_butler_state), enum_2_string (bs)));
+	_butler_state = bs;
+}