Cache MIDI generator port latency

This reduces excessive, expensive calls to get_connected_latency_range()

libs/ardour/ardour/session.h

@@ -1726,6 +1726,7 @@ private:
 	bool              ltc_timecode_negative_offset;
 
 	LatencyRange      ltc_out_latency;
+	LatencyRange      mtc_out_latency;
 
 	void ltc_tx_initialize();
 	void ltc_tx_cleanup();
@@ -1789,6 +1790,7 @@ private:
 	 * cycle
 	 */
 
+	void mtc_tx_resync_latency (bool);
 	int  send_full_time_code (samplepos_t, pframes_t nframes);
 	void send_song_position_pointer (samplepos_t);
 

libs/ardour/ardour/ticker.h

@@ -49,6 +49,7 @@ private:
 	boost::shared_ptr<MidiPort> _midi_port;
 
 	void   reset ();
+	void   resync_latency (bool);
 	double one_ppqn_in_samples (samplepos_t transport_position) const;
 
 	void send_midi_clock_event (pframes_t offset, pframes_t nframes);
@@ -64,7 +65,9 @@ private:
 	samplepos_t _transport_pos;
 
 	ARDOUR::Session* _session;
-	LatencyRange     _mclk_out_latency;
+
+	LatencyRange          _mclk_out_latency;
+	PBD::ScopedConnection _latency_connection;
 };
 
 } // namespace ARDOUR

libs/ardour/session_midi.cc

@@ -376,6 +376,19 @@ Session::mmc_record_enable (MIDI::MachineControl &mmc, size_t trk, bool enabled)
 	}
 }
 
+void
+Session::mtc_tx_resync_latency (bool playback)
+{
+	if (deletion_in_progress() || !playback) {
+		return;
+	}
+	boost::shared_ptr<Port> mtxport = _midi_ports->mtc_output_port ();
+	if (mtxport) {
+		mtxport->get_connected_latency_range(mtc_out_latency, true);
+		DEBUG_TRACE (DEBUG::MTC, string_compose ("resync latency: %1\n", mtc_out_latency.max));
+	}
+}
+
 /** Send MTC Full Frame message (complete Timecode time) for the start of this cycle.
  * This resets the MTC code, the next quarter frame message that is sent will be
  * the first one with the beginning of this cycle as the new start point.
@@ -409,8 +422,6 @@ Session::send_full_time_code (samplepos_t const t, MIDI::pframes_t nframes)
 	outbound_mtc_timecode_frame = mtc_tc;
 	transmitting_timecode_time = timecode;
 
-	LatencyRange mtc_out_latency;
-	_midi_ports->mtc_output_port ()->get_connected_latency_range (ltc_out_latency, true);
 	sampleoffset_t mtc_offset = mtc_out_latency.max;
 
 	// only if rolling.. ?

libs/ardour/session_state.cc

@@ -242,6 +242,10 @@ Session::post_engine_init ()
 
 	setup_midi_machine_control ();
 
+	/* setup MTC generator */
+	mtc_tx_resync_latency (true);
+	LatencyUpdated.connect_same_thread (*this, boost::bind (&Session::mtc_tx_resync_latency, this, _1));
+
 	if (_butler->start_thread()) {
 		error << _("Butler did not start") << endmsg;
 		return -1;

libs/ardour/ticker.cc

@@ -45,6 +45,7 @@ MidiClockTicker::MidiClockTicker (Session* s)
 	_session   = s;
 	_midi_port = s->midi_clock_output_port ();
 	reset ();
+	s->LatencyUpdated.connect_same_thread (_latency_connection, boost::bind (&MidiClockTicker::resync_latency, this, _1));
 }
 
 MidiClockTicker::~MidiClockTicker ()
@@ -59,6 +60,19 @@ MidiClockTicker::reset ()
 	_beat_pos      = 0;
 	_clock_cnt     = 0;
 	_transport_pos = -1;
+
+	resync_latency (true);
+}
+
+void
+MidiClockTicker::resync_latency (bool playback)
+{
+	if (_session->deletion_in_progress() || !playback) {
+		return;
+	}
+	assert (_midi_port);
+	_midi_port->get_connected_latency_range(_mclk_out_latency, true);
+	DEBUG_TRACE (DEBUG::MidiClock, string_compose ("resync latency: %1\n", _mclk_out_latency.max));
 }
 
 void
@@ -77,9 +91,6 @@ MidiClockTicker::tick (samplepos_t start_sample, samplepos_t end_sample, pframes
 		goto out;
 	}
 
-	// TODO: cache
-	_midi_port->get_connected_latency_range (_mclk_out_latency, true);
-
 	if (speed == 0 && start_sample == 0 && end_sample == 0) {
 		/* test if pre-roll is active, special-case
 		 * "start at zero"