livetrax/libs/backends/jack/jack_audiobackend.cc

/*
 * Copyright (C) 2013-2015 Tim Mayberry <mojofunk@gmail.com>
 * Copyright (C) 2013-2017 Paul Davis <paul@linuxaudiosystems.com>
 * Copyright (C) 2014-2018 Robin Gareus <robin@gareus.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <string>
#include <list>
#include <math.h>

#include <glibmm/timer.h>
#include <glibmm/spawn.h>

#include "pbd/error.h"

#include "ardour/audioengine.h"
#include "ardour/debug.h"
#include "ardour/session.h"
#include "ardour/types.h"

#include "jack_audiobackend.h"
#include "jack_connection.h"
#include "jack_utils.h"
#include "jack_session.h"

#include "pbd/i18n.h"

using namespace ARDOUR;
using namespace PBD;
using std::string;
using std::vector;


#define GET_PRIVATE_JACK_POINTER(localvar)  jack_client_t* localvar = _jack_connection->jack(); if (!(localvar)) { return; }
#define GET_PRIVATE_JACK_POINTER_RET(localvar,r) jack_client_t* localvar = _jack_connection->jack(); if (!(localvar)) { return r; }
// #define JACK_SERVER_CALL(expr) { std::cerr << "JACK SERVER CALL: " << DEBUG_THREAD_SELF << '/' << pthread_name() << ' ' << #expr << std::endl; Glib::Threads::Mutex::Lock lm (server_call_mutex); expr; }
#define JACK_SERVER_CALL(expr) { Glib::Threads::Mutex::Lock lm (server_call_mutex); expr; }

JACKAudioBackend::JACKAudioBackend (AudioEngine& e, AudioBackendInfo& info, std::shared_ptr<JackConnection> jc)
	: AudioBackend (e, info)
	, _jack_connection (jc)
	, _running (false)
	, _freewheeling (false)
	, _target_sample_rate (48000)
	, _target_buffer_size (1024)
	, _target_num_periods (2)
	, _target_interleaved (false)
	, _target_input_channels (0)
	, _target_output_channels (0)
	, _target_systemic_input_latency (0)
	, _target_systemic_output_latency (0)
	, _current_sample_rate (0)
	, _current_buffer_size (0)
	, _jack_ports (new JackPorts)
	, _session (0)
{
	_jack_connection->Connected.connect_same_thread (jack_connection_connection, std::bind (&JACKAudioBackend::when_connected_to_jack, this));
	_jack_connection->Disconnected.connect_same_thread (disconnect_connection, std::bind (&JACKAudioBackend::disconnected, this, _1));
}

JACKAudioBackend::~JACKAudioBackend()
{
	{
		RCUWriter<JackPorts> writer (_jack_ports);
		std::shared_ptr<JackPorts> jp = writer.get_copy ();
		jp->clear ();
	}

	_jack_ports.flush ();
}

string
JACKAudioBackend::name() const
{
#if ! (defined(__APPLE__) || defined(PLATFORM_WINDOWS))
	return X_("JACK/Pipewire");
#else
	return X_("JACK");
#endif
}

void*
JACKAudioBackend::private_handle() const
{
	return _jack_connection->jack();
}

bool
JACKAudioBackend::available() const
{
	return (private_handle() != 0);
}

bool
JACKAudioBackend::is_realtime () const
{
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack,false);
	return jack_is_realtime (_priv_jack);
}

bool
JACKAudioBackend::requires_driver_selection() const
{
	return true;
}

vector<string>
JACKAudioBackend::enumerate_drivers () const
{
	vector<string> currently_available;
	get_jack_audio_driver_names (currently_available);
	return currently_available;
}

int
JACKAudioBackend::set_driver (const std::string& name)
{
	_target_driver = name;
	return 0;
}

vector<AudioBackend::DeviceStatus>
JACKAudioBackend::enumerate_devices () const
{
	vector<string> currently_available = get_jack_device_names_for_audio_driver (_target_driver);
	vector<DeviceStatus> statuses;

	if (all_devices.find (_target_driver) == all_devices.end()) {
		all_devices.insert (make_pair (_target_driver, std::set<string>()));
	}

	/* store every device we've found, by driver name.
	 *
	 * This is so we do not confuse ALSA, FFADO, netjack etc. devices
	 * with each other.
	 */

	DeviceList& all (all_devices[_target_driver]);

	for (vector<string>::const_iterator d = currently_available.begin(); d != currently_available.end(); ++d) {
		all.insert (*d);
	}

	for (DeviceList::const_iterator d = all.begin(); d != all.end(); ++d) {
		if (find (currently_available.begin(), currently_available.end(), *d) == currently_available.end()) {
			statuses.push_back (DeviceStatus (*d, false));
		} else {
			statuses.push_back (DeviceStatus (*d, false));
		}
	}

	return statuses;
}

vector<float>
JACKAudioBackend::available_sample_rates (const string& device) const
{
	vector<float> f;

	if (device == _target_device && available()) {
		f.push_back (sample_rate());
		return f;
	}

	/* if JACK is not already running, just list a bunch of reasonable
	   values and let the future sort it all out.
	*/

	f.push_back (8000.0);
	f.push_back (16000.0);
	f.push_back (24000.0);
	f.push_back (32000.0);
	f.push_back (44100.0);
	f.push_back (48000.0);
	f.push_back (88200.0);
	f.push_back (96000.0);
	f.push_back (192000.0);
	f.push_back (384000.0);

	return f;
}

vector<uint32_t>
JACKAudioBackend::available_buffer_sizes (const string& device) const
{
	vector<uint32_t> s;

	if (device == _target_device && available()) {
		s.push_back (buffer_size());
		return s;
	}

	s.push_back (8);
	s.push_back (16);
	s.push_back (32);
	s.push_back (64);
	s.push_back (128);
	s.push_back (256);
	s.push_back (512);
	s.push_back (1024);
	s.push_back (2048);
	s.push_back (4096);
	s.push_back (8192);

	return s;
}

std::vector<uint32_t>
JACKAudioBackend::available_period_sizes (const std::string& driver, const std::string&) const
{
	vector<uint32_t> s;
	if (ARDOUR::get_jack_audio_driver_supports_setting_period_count (driver)) {
		s.push_back (2);
		s.push_back (3);
	}
	return s;
}

/* -- parameter setting -- */

int
JACKAudioBackend::set_device_name (const string& dev)
{
	if (available()) {
		/* need to stop and restart JACK for this to work, at present */
		return -1;
	}

	_target_device = dev;
	return 0;
}

int
JACKAudioBackend::set_sample_rate (float sr)
{
	if (!available()) {
		_target_sample_rate = sr;
		return 0;
	}

	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, -1);

	if (sr == jack_get_sample_rate (_priv_jack)) {
                return 0;
	}

	return -1;
}

int
JACKAudioBackend::set_peridod_size (uint32_t nperiods)
{
	if (!available()) {
		_target_num_periods = nperiods;
		return 0;
	}
	return -1;
}

int
JACKAudioBackend::set_buffer_size (uint32_t nframes)
{
	if (!available()) {
		_target_buffer_size = nframes;
		return 0;
	}

	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, -1);

	if (nframes == jack_get_buffer_size (_priv_jack)) {
                return 0;
	}

	return jack_set_buffer_size (_priv_jack, nframes);
}

int
JACKAudioBackend::set_interleaved (bool yn)
{
	/* as far as JACK clients are concerned, the hardware is always
	 * non-interleaved
	 */
	if (!yn) {
		return 0;
	}
	return -1;
}

int
JACKAudioBackend::set_systemic_input_latency (uint32_t l)
{
	if (available()) {
		/* can't do this while JACK runs */
		return -1;
	}

	_target_systemic_input_latency = l;

	return 0;
}

int
JACKAudioBackend::set_systemic_output_latency (uint32_t l)
{
	if (available()) {
		/* can't do this while JACK runs */
		return -1;
	}

	_target_systemic_output_latency = l;

	return 0;
}

/* --- Parameter retrieval --- */

std::string
JACKAudioBackend::device_name () const
{
	if (!_jack_connection->in_control()) {
		return "???"; // JACK has no way (as of fall 2013) to return
			      // the device name
	}

	return _target_device;
}

std::string
JACKAudioBackend::driver_name() const
{
	if (!_jack_connection->in_control()) {
		return "???"; // JACK has no way (as of fall 2013) to return
			      // the driver name
	}

	return _target_driver;
}

float
JACKAudioBackend::sample_rate () const
{
	if (!_jack_connection->in_control()) {
		if (available()) {
			return _current_sample_rate;
		} else {
			return _jack_connection->probed_sample_rate ();
		}
	}
	return _target_sample_rate;
}

uint32_t
JACKAudioBackend::buffer_size () const
{
	if (!_jack_connection->in_control()) {
		if (available()) {
			return _current_buffer_size;
		} else {
			return _jack_connection->probed_buffer_size ();
		}
	}
	return _target_buffer_size;
}

uint32_t
JACKAudioBackend::period_size () const
{
	return _target_num_periods;
}

bool
JACKAudioBackend::interleaved () const
{
	return false;
}

string
JACKAudioBackend::midi_option () const
{
	return _target_midi_option;
}

uint32_t
JACKAudioBackend::systemic_input_latency () const
{
	return _target_systemic_output_latency;
}

uint32_t
JACKAudioBackend::systemic_output_latency () const
{
	return _target_systemic_output_latency;
}

size_t
JACKAudioBackend::raw_buffer_size(DataType t)
{
	std::map<DataType,size_t>::const_iterator s = _raw_buffer_sizes.find(t);
	return (s != _raw_buffer_sizes.end()) ? s->second : 0;
}

void
JACKAudioBackend::setup_jack_startup_command (bool for_latency_measurement)
{
	/* first we map the parameters that have been set onto a
	 * JackCommandLineOptions object.
	 */

	JackCommandLineOptions options;

	get_jack_default_server_path (options.server_path);
	options.driver = _target_driver;
	options.samplerate = _target_sample_rate;
	options.period_size = _target_buffer_size;
	options.num_periods = _target_num_periods;
	options.input_device = _target_device;
	options.output_device = _target_device;
	if (for_latency_measurement) {
		options.input_latency = 0;
		options.output_latency = 0;
	} else {
		options.input_latency = _target_systemic_input_latency;
		options.output_latency = _target_systemic_output_latency;
	}
	options.input_channels = _target_input_channels;
	options.output_channels = _target_output_channels;
	if (_target_sample_format == FormatInt16) {
		options.force16_bit = _target_sample_format;
	}
	options.realtime = true;
	options.ports_max = 2048;

	ARDOUR::set_midi_option (options, _target_midi_option);

	/* this must always be true for any server instance we start ourselves
	 */

	options.temporary = true;

	string cmdline;

	if (!get_jack_command_line_string (options, cmdline)) {
		/* error, somehow - we will still try to start JACK
		 * automatically but it will be without our preferred options
		 */
		std::cerr << "get_jack_command_line_string () failed: using default settings." << std::endl;
		return;
	}

	std::cerr << "JACK command line will be: " << cmdline << std::endl;

	write_jack_config_file (get_jack_server_user_config_file_path(), cmdline);
}

/* ---- BASIC STATE CONTROL API: start/stop/pause/freewheel --- */

int
JACKAudioBackend::_start (bool for_latency_measurement)
{
	if (!available()) {

		if (_jack_connection->in_control()) {
			/* we will be starting JACK, so set up the
			   command that JACK will use when it (auto-)starts
			*/
			setup_jack_startup_command (for_latency_measurement);
		}

		if (_jack_connection->open ()) {
			return -1;
		}
	}

	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, -1);

	/* get the buffer size and sample rates established */

	jack_sample_rate_callback (jack_get_sample_rate (_priv_jack));
	jack_bufsize_callback (jack_get_buffer_size (_priv_jack));

	/* Now that we have buffer size and sample rate established, the engine
	   can go ahead and do its stuff
	*/

	if (engine.reestablish_ports ()) {
		error << _("Could not re-establish ports after connecting to JACK") << endmsg;
		return -1;
	}

	if (!jack_port_type_get_buffer_size) {
		warning << _("This version of JACK is old - you should upgrade to a newer version that supports jack_port_type_get_buffer_size()") << endmsg;
	}

	set_jack_callbacks ();

	if (jack_activate (_priv_jack) == 0) {
		_running = true;
	} else {
		// error << _("cannot activate JACK client") << endmsg;
	}

	engine.reconnect_ports ();

	return 0;
}

int
JACKAudioBackend::stop ()
{
	_running = false; // no 'engine halted message'.
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, -1);

	_jack_connection->close ();

	_current_buffer_size = 0;
	_current_sample_rate = 0;

	_raw_buffer_sizes.clear();

	return 0;
}

int
JACKAudioBackend::freewheel (bool onoff)
{
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, -1);

	if (onoff == _freewheeling) {
		/* already doing what has been asked for */

		return 0;
	}

	int ret;

	JACK_SERVER_CALL (ret = jack_set_freewheel (_priv_jack, onoff));

	if (ret == 0) {
		_freewheeling = onoff;
		return 0;
	}

	return -1;
}

/* --- TRANSPORT STATE MANAGEMENT --- */

void
JACKAudioBackend::transport_stop ()
{
	GET_PRIVATE_JACK_POINTER (_priv_jack);
	jack_transport_stop (_priv_jack);
}

void
JACKAudioBackend::transport_start ()
{
	GET_PRIVATE_JACK_POINTER (_priv_jack);
	jack_transport_start (_priv_jack);
}

void
JACKAudioBackend::transport_locate (samplepos_t where)
{
	GET_PRIVATE_JACK_POINTER (_priv_jack);
	jack_transport_locate (_priv_jack, where);
}

samplepos_t
JACKAudioBackend::transport_sample () const
{
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, 0);
	return jack_get_current_transport_frame (_priv_jack);
}

TransportState
JACKAudioBackend::transport_state () const
{
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, ((TransportState) JackTransportStopped));
	jack_position_t pos;
	return (TransportState) jack_transport_query (_priv_jack, &pos);
}

int
JACKAudioBackend::set_time_master (bool yn)
{
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, -1);
	if (yn) {
		JACK_SERVER_CALL (return jack_set_timebase_callback (_priv_jack, 0, _jack_timebase_callback, this));
	} else {
		JACK_SERVER_CALL (return jack_release_timebase (_priv_jack));
	}
}

/* process-time */

bool
JACKAudioBackend::get_sync_offset (pframes_t& offset) const
{

#ifdef HAVE_JACK_VIDEO_SUPPORT

	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, false);

	jack_position_t pos;

	if (_priv_jack) {
		(void) jack_transport_query (_priv_jack, &pos);

		if (pos.valid & JackVideoFrameOffset) {
			offset = pos.video_offset;
			return true;
		}
	}
#else
	/* keep gcc happy */
	offset = 0;
#endif

	return false;
}

samplepos_t
JACKAudioBackend::sample_time ()
{
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, 0);
	return jack_frame_time (_priv_jack);
}

samplepos_t
JACKAudioBackend::sample_time_at_cycle_start ()
{
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, 0);
	return jack_last_frame_time (_priv_jack);
}

pframes_t
JACKAudioBackend::samples_since_cycle_start ()
{
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, 0);
	return jack_frames_since_cycle_start (_priv_jack);
}

/* JACK Callbacks */

static void
ardour_jack_error (const char* msg)
{
	error << "JACK: " << msg << endmsg;
}

void
JACKAudioBackend::set_jack_callbacks ()
{
	GET_PRIVATE_JACK_POINTER (_priv_jack);

	/* no need to set the thread_init_callback because we use the
	 * non-callback API, and run the thread init callback in our own code.
	 */

	JACK_SERVER_CALL (jack_set_process_thread (_priv_jack, _process_thread, this));
	JACK_SERVER_CALL (jack_set_sample_rate_callback (_priv_jack, _sample_rate_callback, this));
	JACK_SERVER_CALL (jack_set_buffer_size_callback (_priv_jack, _bufsize_callback, this));
	JACK_SERVER_CALL (jack_set_xrun_callback (_priv_jack, _xrun_callback, this));
	JACK_SERVER_CALL (jack_set_sync_callback (_priv_jack, _jack_sync_callback, this));
	JACK_SERVER_CALL (jack_set_freewheel_callback (_priv_jack, _freewheel_callback, this));

#ifdef HAVE_JACK_SESSION
	if (jack_set_session_callback) {
		JACK_SERVER_CALL (jack_set_session_callback (_priv_jack, _session_callback, this));
	}
#endif

        if (jack_set_latency_callback) {
	        JACK_SERVER_CALL (jack_set_latency_callback (_priv_jack, _latency_callback, this));
        }

        jack_set_error_function (ardour_jack_error);
}

void
JACKAudioBackend::_jack_timebase_callback (jack_transport_state_t state, pframes_t nframes,
				      jack_position_t* pos, int new_position, void *arg)
{
	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose ("%1/%2 jack timebase callback\n", DEBUG_THREAD_SELF, pthread_name()));
	static_cast<JACKAudioBackend*> (arg)->jack_timebase_callback (state, nframes, pos, new_position);
}

void
JACKAudioBackend::jack_timebase_callback (jack_transport_state_t state, pframes_t nframes,
					  jack_position_t* pos, int new_position)
{
	ARDOUR::Session* session = engine.session();

	if (session) {
		JACKSession jsession (session);
		jsession.timebase_callback (state, nframes, pos, new_position);
	}
}

int
JACKAudioBackend::_jack_sync_callback (jack_transport_state_t state, jack_position_t* pos, void* arg)
{
	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose ("%1/%2 jack sync callback\n", DEBUG_THREAD_SELF, pthread_name()));
	return static_cast<JACKAudioBackend*> (arg)->jack_sync_callback (state, pos);
}

int
JACKAudioBackend::jack_sync_callback (jack_transport_state_t state, jack_position_t* pos)
{
	TransportState tstate;
	bool tstate_valid = true;

	switch (state) {
	case JackTransportRolling:
		tstate = TransportRolling;
		break;
	case JackTransportLooping:
		tstate = TransportLooping;
		break;
	case JackTransportStarting:
		tstate = TransportStarting;
		break;
	case JackTransportStopped:
		tstate = TransportStopped;
		break;
	default:
		// ignore "unofficial" states like JackTransportNetStarting (jackd2)
		tstate_valid = false;
		break;
	}

	if (tstate_valid) {
		return engine.sync_callback (tstate, pos->frame);
	}

	return true;
}

int
JACKAudioBackend::_xrun_callback (void *arg)
{
	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose ("%1/%2 jack sync callback\n", DEBUG_THREAD_SELF, pthread_name()));

	JACKAudioBackend* jab = static_cast<JACKAudioBackend*> (arg);
	if (jab->available()) {
		jab->engine.Xrun (); /* EMIT SIGNAL */
	}
	return 0;
}

void
JACKAudioBackend::_session_callback (jack_session_event_t *event, void *arg)
{
	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose ("%1/%2 jack session callback\n", DEBUG_THREAD_SELF, pthread_name()));

	JACKAudioBackend* jab = static_cast<JACKAudioBackend*> (arg);
	ARDOUR::Session* session = jab->engine.session();

	if (session) {
		JACKSession jsession (session);
		jsession.session_event (event);
	}
}

void
JACKAudioBackend::_freewheel_callback (int onoff, void *arg)
{
	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose ("%1/%2 jack freewheel callback\n", DEBUG_THREAD_SELF, pthread_name()));
	static_cast<JACKAudioBackend*>(arg)->freewheel_callback (onoff);
}

void
JACKAudioBackend::freewheel_callback (int onoff)
{
	_freewheeling = onoff;
	engine.freewheel_callback (onoff);
}

void
JACKAudioBackend::_latency_callback (jack_latency_callback_mode_t mode, void* arg)
{
	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose ("%1/%2 jack latency callback\n", DEBUG_THREAD_SELF, pthread_name()));
	return static_cast<JACKAudioBackend*> (arg)->jack_latency_callback (mode);
}

int
JACKAudioBackend::create_process_thread (std::function<void()> f)
{
        GET_PRIVATE_JACK_POINTER_RET (_priv_jack, -1);

	jack_native_thread_t thread_id;
        ThreadData* td = new ThreadData (this, f, thread_stack_size());

        if (jack_client_create_thread (_priv_jack, &thread_id, jack_client_real_time_priority (_priv_jack),
                                       jack_is_realtime (_priv_jack), _start_process_thread, td)) {
                return -1;
        }

	_jack_threads.push_back(thread_id);
	return 0;
}

int
JACKAudioBackend::join_process_threads ()
{
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, -1);

	int ret = 0;

	for (auto & thread : _jack_threads) {

#if defined(USING_JACK2_EXPANSION_OF_JACK_API) || defined __jack_systemdeps_h__
		// jack_client is not used by JACK2's implementation
		// also jack_client_close() leaves threads active
		if (jack_client_stop_thread (_priv_jack, thread) != 0)
#else
		void* status;
		if (pthread_join (thread, &status) != 0)
#endif
		{
			error << "AudioEngine: cannot stop process thread" << endmsg;
			ret += -1;
		}
	}

	_jack_threads.clear();

	return ret;
}

bool
JACKAudioBackend::in_process_thread ()
{
#if defined COMPILER_MINGW && (!defined PTW32_VERSION || defined __jack_systemdeps_h__)
	if (_main_thread == GetCurrentThread()) {
		return true;
	}
#else // pthreads
	if (pthread_equal (_main_thread, pthread_self()) != 0) {
		return true;
	}
#endif

	for (auto & thread : _jack_threads) {

#if defined COMPILER_MINGW && (!defined PTW32_VERSION || defined __jack_systemdeps_h__)
		if (thread == GetCurrentThread()) {
			return true;
		}
#else // pthreads
		if (pthread_equal (thread, pthread_self()) != 0) {
			return true;
		}
#endif
	}

	return false;
}

uint32_t
JACKAudioBackend::process_thread_count ()
{
	return _jack_threads.size();
}

int
JACKAudioBackend::client_real_time_priority ()
{
	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, 0);
	return jack_client_real_time_priority (_priv_jack);
}

void*
JACKAudioBackend::_start_process_thread (void* arg)
{
        ThreadData* td = reinterpret_cast<ThreadData*> (arg);
        std::function<void()> f = td->f;
        delete td;

        f ();

        return 0;
}

void*
JACKAudioBackend::_process_thread (void *arg)
{
	return static_cast<JACKAudioBackend*> (arg)->process_thread ();
}

void*
JACKAudioBackend::process_thread ()
{
        /* JACK doesn't do this for us when we use the wait API
         */

#if defined COMPILER_MINGW && (!defined PTW32_VERSION || defined __jack_systemdeps_h__)
	_main_thread = GetCurrentThread();
#else
	_main_thread = pthread_self ();
#endif


        AudioEngine::thread_init_callback (this);

        while (1) {
                GET_PRIVATE_JACK_POINTER_RET(_priv_jack,0);
                dsp_stats[AudioBackend::DeviceWait].start ();
                pframes_t nframes = jack_cycle_wait (_priv_jack);
                dsp_stats[AudioBackend::DeviceWait].update ();
                dsp_stats[RunLoop].start();

                if (engine.process_callback (nframes)) {
                        return 0;
                }

		jack_cycle_signal (_priv_jack, 0);
                dsp_stats[AudioBackend::RunLoop].update ();
        }

        return 0;
}

int
JACKAudioBackend::_sample_rate_callback (pframes_t nframes, void *arg)
{
	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose ("%1/%2 jack sample rate callback\n", DEBUG_THREAD_SELF, pthread_name()));
	return static_cast<JACKAudioBackend*> (arg)->jack_sample_rate_callback (nframes);
}

int
JACKAudioBackend::jack_sample_rate_callback (pframes_t nframes)
{
	_current_sample_rate = nframes;
	return engine.sample_rate_change (nframes);
}

void
JACKAudioBackend::jack_latency_callback (jack_latency_callback_mode_t mode)
{
	engine.latency_callback (mode == JackPlaybackLatency);
}

int
JACKAudioBackend::_bufsize_callback (pframes_t nframes, void *arg)
{
	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose ("%1/%2 jack buffer size callback\n", DEBUG_THREAD_SELF, pthread_name()));
	return static_cast<JACKAudioBackend*> (arg)->jack_bufsize_callback (nframes);
}

int
JACKAudioBackend::jack_bufsize_callback (pframes_t nframes)
{
        /* if the size has not changed, this should be a no-op */

        if (nframes == _current_buffer_size) {
                return 0;
        }

	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, 1);

	_current_buffer_size = nframes;

        if (jack_port_type_get_buffer_size) {
                _raw_buffer_sizes[DataType::AUDIO] = jack_port_type_get_buffer_size (_priv_jack, JACK_DEFAULT_AUDIO_TYPE);
                _raw_buffer_sizes[DataType::MIDI] = jack_port_type_get_buffer_size (_priv_jack, JACK_DEFAULT_MIDI_TYPE);
        } else {

                /* Old version of JACK.

                   These crude guesses, see below where we try to get the right answers.

                   Note that our guess for MIDI deliberatey tries to overestimate
                   by a little. It would be nicer if we could get the actual
                   size from a port, but we have to use this estimate in the
                   event that there are no MIDI ports currently. If there are
                   the value will be adjusted below.
                */

                _raw_buffer_sizes[DataType::AUDIO] = nframes * sizeof (Sample);
                _raw_buffer_sizes[DataType::MIDI] = nframes * 4 - (nframes/2);
        }

	engine.buffer_size_change (nframes);

	return 0;
}

void
JACKAudioBackend::disconnected (const char* why)
{
	bool was_running = _running;

        _running = false;
        _current_buffer_size = 0;
        _current_sample_rate = 0;

        if (was_running) {
		engine.halted_callback (why); /* EMIT SIGNAL */
        }
}

float
JACKAudioBackend::dsp_load() const
{
	GET_PRIVATE_JACK_POINTER_RET(_priv_jack,0);
	return jack_cpu_load (_priv_jack);
}

void
JACKAudioBackend::update_latencies ()
{
	GET_PRIVATE_JACK_POINTER (_priv_jack);
	JACK_SERVER_CALL (jack_recompute_total_latencies (_priv_jack));
}

ChanCount
JACKAudioBackend::n_physical (unsigned long flags) const
{
	ChanCount c;

	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, c);

	const char ** ports = jack_get_ports (_priv_jack, NULL, NULL, JackPortIsPhysical | flags);

	if (ports) {
		for (uint32_t i = 0; ports[i]; ++i) {
			if (!strstr (ports[i], "Midi-Through")) {
				std::shared_ptr<JackPort> jp (new JackPort (jack_port_by_name (_priv_jack, ports[i])));
				DataType t = port_data_type (jp);
				if (t != DataType::NIL) {
					c.set (t, c.get (t) + 1);
				}
			}
		}

		jack_free (ports);
	}

	return c;
}

bool
JACKAudioBackend::can_change_sample_rate_when_running () const
{
	return false;
}

bool
JACKAudioBackend::can_change_buffer_size_when_running () const
{
	return true;
}

string
JACKAudioBackend::control_app_name () const
{
	/* Since JACK/ALSA really don't provide particularly integrated support
	   for the idea of a control app to be used to control a device,
	   allow the user to take some control themselves if necessary.
	*/

	const char* env_value  = g_getenv ("ARDOUR_DEVICE_CONTROL_APP");
	string appname;

	if (!env_value) {
		if (_target_driver.empty() || _target_device.empty()) {
			return appname;
		}

		if (_target_driver == "ALSA") {

			if (_target_device == "Hammerfall DSP") {
				appname = "hdspconf";
			} else if (_target_device == "M Audio Delta 1010") {
				appname = "mudita24";
			} else if (_target_device == "M2496") {
				appname = "mudita24";
			}
		}
	} else {
		appname = env_value;
	}

	return appname;
}

void
JACKAudioBackend::launch_control_app ()
{
	string appname = control_app_name();

	if (appname.empty()) {
		error << string_compose (_("There is no control application for the device \"%1\""), _target_device) << endmsg;
		return;
	}

	std::list<string> args;
	args.push_back (appname);
	Glib::spawn_async ("", args, Glib::SPAWN_SEARCH_PATH);
}

vector<string>
JACKAudioBackend::enumerate_midi_options () const
{
	return ARDOUR::enumerate_midi_options ();
}

int
JACKAudioBackend::set_midi_option (const string& opt)
{
	_target_midi_option = opt;
	return 0;
}

bool
JACKAudioBackend::speed_and_position (double& speed, samplepos_t& position)
{
	jack_position_t pos;
	jack_transport_state_t state;
	bool starting;

	/* this won't be called if the port engine in use is not JACK, so we do
	   not have to worry about the type of PortEngine::private_handle()
	*/

	speed = 0;
	position = 0;

	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, true);

	state = jack_transport_query (_priv_jack, &pos);

	switch (state) {
	case JackTransportStopped:
		speed = 0;
		starting = false;
		break;
	case JackTransportRolling:
		speed = 1.0;
		starting = false;
		break;
	case JackTransportLooping:
		speed = 1.0;
		starting = false;
		break;
	case JackTransportStarting:
		starting = true;
		// don't adjust speed here, just leave it as it was
		break;
	default:
		starting = true; // jack2: JackTransportNetStarting
		std::cerr << "WARNING: Unknown JACK transport state: " << state << std::endl;
	}

	position = pos.frame;

	DEBUG_TRACE (DEBUG::Slave, string_compose ("JACK transport: speed %1 position %2 starting %3\n", speed, position, starting));

	return starting;
}

int
JACKAudioBackend::reset_device ()
{
        /* XXX need to figure out what this means for JACK
         */
        return 0;
}