xref: /dports/audio/ardour6/Ardour-6.8.0/libs/ardour/disk_reader.cc

/*
 * Copyright (C) 2017-2018 Paul Davis <paul@linuxaudiosystems.com>
 * Copyright (C) 2017-2019 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 <boost/smart_ptr/scoped_array.hpp>

#include "pbd/enumwriter.h"
#include "pbd/memento_command.h"
#include "pbd/playback_buffer.h"

#include "evoral/Range.h"

#include "ardour/amp.h"
#include "ardour/audio_buffer.h"
#include "ardour/audioengine.h"
#include "ardour/audioplaylist.h"
#include "ardour/butler.h"
#include "ardour/debug.h"
#include "ardour/disk_reader.h"
#include "ardour/midi_playlist.h"
#include "ardour/midi_ring_buffer.h"
#include "ardour/midi_track.h"
#include "ardour/pannable.h"
#include "ardour/playlist.h"
#include "ardour/playlist_factory.h"
#include "ardour/session.h"
#include "ardour/session_playlists.h"

#include "pbd/i18n.h"

using namespace ARDOUR;
using namespace PBD;
using namespace std;

ARDOUR::samplecnt_t   DiskReader::_chunk_samples = default_chunk_samples ();
PBD::Signal0<void>    DiskReader::Underrun;
Sample*               DiskReader::_sum_buffer     = 0;
Sample*               DiskReader::_mixdown_buffer = 0;
gain_t*               DiskReader::_gain_buffer    = 0;
GATOMIC_QUAL gint     DiskReader::_no_disk_output (0);
DiskReader::Declicker DiskReader::loop_declick_in;
DiskReader::Declicker DiskReader::loop_declick_out;
samplecnt_t           DiskReader::loop_fade_length (0);

DiskReader::DiskReader (Session& s, Track& t, string const& str, DiskIOProcessor::Flag f)
	: DiskIOProcessor (s, t, X_("player:") + str, f)
	, overwrite_sample (0)
	, run_must_resolve (false)
	, _declick_amp (s.nominal_sample_rate ())
	, _declick_offs (0)
	, _declick_enabled (false)
	, last_refill_loop_start (0)
{
	file_sample[DataType::AUDIO] = 0;
	file_sample[DataType::MIDI]  = 0;
	g_atomic_int_set (&_pending_overwrite, 0);
}

DiskReader::~DiskReader ()
{
	DEBUG_TRACE (DEBUG::Destruction, string_compose ("DiskReader %1 @ %2 deleted\n", _name, this));
}

std::string
DiskReader::display_name () const
{
	return std::string (_("Player"));
}

void
DiskReader::ReaderChannelInfo::resize (samplecnt_t bufsize)
{
	delete rbuf;
	rbuf = 0;

	rbuf = new PlaybackBuffer<Sample> (bufsize);
	/* touch memory to lock it */
	memset (rbuf->buffer (), 0, sizeof (Sample) * rbuf->bufsize ());
	initialized = false;
}

void
DiskReader::ReaderChannelInfo::resize_preloop (samplecnt_t bufsize)
{
	if (bufsize == 0) {
		return;
	}

	if (bufsize > pre_loop_buffer_size) {
		delete[] pre_loop_buffer;
		pre_loop_buffer      = new Sample[bufsize];
		pre_loop_buffer_size = bufsize;
	}
}

int
DiskReader::add_channel_to (boost::shared_ptr<ChannelList> c, uint32_t how_many)
{
	while (how_many--) {
		c->push_back (new ReaderChannelInfo (_session.butler ()->audio_playback_buffer_size (), loop_fade_length));
		DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1: new reader channel, write space = %2 read = %3\n",
		                                            name (),
		                                            c->back ()->rbuf->write_space (),
		                                            c->back ()->rbuf->read_space ()));
	}

	return 0;
}

void
DiskReader::allocate_working_buffers ()
{
	/* with varifill buffer refilling, we compute the read size in bytes (to optimize
	   for disk i/o bandwidth) and then convert back into samples. These buffers
	   need to reflect the maximum size we could use, which is 4MB reads, or 2M samples
	   using 16 bit samples.
	*/
	_sum_buffer     = new Sample[2 * 1048576];
	_mixdown_buffer = new Sample[2 * 1048576];
	_gain_buffer    = new gain_t[2 * 1048576];
}

void
DiskReader::free_working_buffers ()
{
	delete[] _sum_buffer;
	delete[] _mixdown_buffer;
	delete[] _gain_buffer;
	_sum_buffer     = 0;
	_mixdown_buffer = 0;
	_gain_buffer    = 0;
}

samplecnt_t
DiskReader::default_chunk_samples ()
{
	return 65536;
}

bool
DiskReader::set_name (string const& str)
{
	string my_name = X_("player:");
	my_name += str;

	if (_name != my_name) {
		SessionObject::set_name (my_name);
	}

	return true;
}

XMLNode&
DiskReader::state ()
{
	XMLNode& node (DiskIOProcessor::state ());
	node.set_property (X_("type"), X_("diskreader"));
	return node;
}

int
DiskReader::set_state (const XMLNode& node, int version)
{
	if (DiskIOProcessor::set_state (node, version)) {
		return -1;
	}

	return 0;
}

void
DiskReader::realtime_handle_transport_stopped ()
{
	/* can't do the resolve here because we don't have a place to put the
	 * note resolving data. Defer to
	 * MidiTrack::realtime_handle_transport_stopped() which will call
	 * ::resolve_tracker() and put the output in its _immediate_events store.
	 */
}

void
DiskReader::realtime_locate (bool for_loop_end)
{
	if (!for_loop_end) {
		MidiTrack* mt = dynamic_cast<MidiTrack*> (&_track);
		_tracker.resolve_notes (mt->immediate_events (), 0);
	}
}

float
DiskReader::buffer_load () const
{
	/* Note: for MIDI it's not trivial to differentiate the following two cases:
	 *
	 * 1.  The playback buffer is empty because the system has run out of time to fill it.
	 * 2.  The playback buffer is empty because there is no more data on the playlist.
	 *
	 * If we use a simple buffer load computation, we will report that the MIDI diskstream
	 * cannot keep up when #2 happens, when in fact it can.  Since MIDI data rates
	 * are so low compared to audio, just use the audio value here.
	 */

	boost::shared_ptr<ChannelList> c = channels.reader ();

	if (c->empty ()) {
		/* no channels, so no buffers, so completely full and ready to playback, sir! */
		return 1.0;
	}

	PBD::PlaybackBuffer<Sample>* b = c->front ()->rbuf;
	return (float)((double)b->read_space () / (double)b->bufsize ());
}

void
DiskReader::adjust_buffering ()
{
	boost::shared_ptr<ChannelList> c = channels.reader ();

	for (ChannelList::iterator chan = c->begin (); chan != c->end (); ++chan) {
		(*chan)->resize (_session.butler ()->audio_playback_buffer_size ());
	}
}

void
DiskReader::playlist_modified ()
{
	_session.request_overwrite_buffer (_track.shared_ptr (), PlaylistModified);
}

int
DiskReader::use_playlist (DataType dt, boost::shared_ptr<Playlist> playlist)
{
	bool prior_playlist = false;

	if (_playlists[dt]) {
		prior_playlist = true;
	}

	if (DiskIOProcessor::use_playlist (dt, playlist)) {
		return -1;
	}

	/* don't do this if we've already asked for it *or* if we are setting up
	 * the diskstream for the very first time - the input changed handling will
	 * take care of the buffer refill. */

	if (!(g_atomic_int_get (&_pending_overwrite) & PlaylistChanged) || prior_playlist) {
		_session.request_overwrite_buffer (_track.shared_ptr (), PlaylistChanged);
	}

	return 0;
}

void
DiskReader::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_sample, double speed, pframes_t nframes, bool result_required)
{
	uint32_t                       n;
	boost::shared_ptr<ChannelList> c = channels.reader ();
	ChannelList::iterator          chan;
	sampleoffset_t                 disk_samples_to_consume;
	MonitorState                   ms = _track.monitoring_state ();
	const bool                     midi_only = (c->empty() || !_playlists[DataType::AUDIO]);
	bool                           no_disk_output = g_atomic_int_get (&_no_disk_output) != 0;

	if (_active) {
		if (!_pending_active) {
			_active = false;
			return;
		}
	} else {
		if (_pending_active) {
			_active = true;
		} else {
			return;
		}
	}

	const gain_t target_gain = ((speed == 0.0) || ((ms & MonitoringDisk) == 0)) ? 0.0 : 1.0;
	bool         declick_out = (_declick_amp.gain () != target_gain) && target_gain == 0.0;

	if (declick_out && _declick_amp.gain () == GAIN_COEFF_UNITY) {
		/* beginning a de-click, set de-click reason */
		if (speed == 0) {
			_declick_enabled = _session.cfg ()->get_use_transport_fades ();
		} else {
			_declick_enabled = _session.cfg ()->get_use_monitor_fades ();
		}
	} else if (_declick_amp.gain () == GAIN_COEFF_ZERO && speed == 0) {
		/* fade in */
		_declick_enabled = _session.cfg ()->get_use_transport_fades ();
	}

	if (!_declick_enabled || (_session.exporting () && !_session.realtime_export ())) {
		/* no transport fades or exporting - no declick out logic */

		if (!midi_only) {
			_declick_amp.set_gain (target_gain);
			declick_out = false;
		}

	} else {
		/* using transport fades and not exporting - declick login in effect */

		if (ms == MonitoringDisk) {
			/* Only monitoring from disk, so if we've finished a
			 * declick (for stop/locate), do not accidentally pass
			 * any data from disk to our outputs.
			 */

			if ((target_gain == 0.0) && (_declick_amp.gain () == target_gain)) {
				/* we were heading for zero (declick out for
				 * stop), and we've reached there. Done. */
				return;
			}
		}
	}

	BufferSet& scratch_bufs (_session.get_scratch_buffers (bufs.count ()));
	const bool still_locating = _session.global_locate_pending ();

	assert (speed == -1 || speed == 0 || speed == 1);

	if (speed == 0) {
		disk_samples_to_consume = 0;
	} else {
		disk_samples_to_consume = nframes;
	}

	if (midi_only) {
		/* do nothing with audio */
		goto midi;
	}

	if (declick_out) {
		/* fade-out */

		// printf ("DR fade-out speed=%.1f gain=%.3f off=%ld start=%ld playpos=%ld (%s)\n", speed, _declick_amp.gain (), _declick_offs, start_sample, playback_sample, owner()->name().c_str());

		ms = MonitorState (ms | MonitoringDisk);
		assert (result_required);
		result_required = true;
		disk_samples_to_consume = 0; // non-committing read
	} else {
		_declick_offs = 0;
	}

	if (!result_required || ((ms & MonitoringDisk) == 0) || still_locating || no_disk_output) {
		/* no need for actual disk data, just advance read pointer */

		if (!still_locating || no_disk_output) {
			for (ChannelList::iterator chan = c->begin (); chan != c->end (); ++chan) {
				assert ((*chan)->rbuf);
				(*chan)->rbuf->increment_read_ptr (disk_samples_to_consume);
			}
		}

		/* if monitoring disk but locating put silence in the buffers */

		if ((no_disk_output || still_locating) && (ms == MonitoringDisk)) {
			bufs.silence (nframes, 0);
		}

	} else {
		/* we need audio data from disk */

		size_t n_buffers = bufs.count ().n_audio ();
		size_t n_chans   = c->size ();
		gain_t scaling;

		if (n_chans > n_buffers) {
			scaling = ((float)n_buffers) / n_chans;
		} else {
			scaling = 1.0;
		}

		const float          initial_declick_gain = _declick_amp.gain ();
		const sampleoffset_t declick_offs         = _declick_offs;

		for (n = 0, chan = c->begin (); chan != c->end (); ++chan, ++n) {
			ReaderChannelInfo* chaninfo = dynamic_cast<ReaderChannelInfo*> (*chan);
			AudioBuffer& output (bufs.get_audio (n % n_buffers));

			AudioBuffer& disk_buf ((ms & MonitoringInput) ? scratch_bufs.get_audio (n) : output);

			if (start_sample != playback_sample && target_gain != 0) {
				samplepos_t ss  = start_sample;
				Location*   loc = _loop_location;
				if (loc) {
					Evoral::Range<samplepos_t> loop_range (loc->start (), loc->end () - 1);
					ss = loop_range.squish (playback_sample);
				}
				if (ss != playback_sample) {
					if (can_internal_playback_seek (ss - playback_sample)) {
						internal_playback_seek (ss - playback_sample);
					} else {
						disk_samples_to_consume = 0; /* will force an underrun below */
					}
				}
			}

			/* reset _declick_amp to the correct gain before processing this channel. */
			_declick_amp.set_gain (initial_declick_gain);

			if (!declick_out) {
				const samplecnt_t available = chaninfo->rbuf->read (disk_buf.data (), disk_samples_to_consume);

				if (available == 0 && !chaninfo->initialized) {
					disk_buf.silence (disk_samples_to_consume);
				} else if (disk_samples_to_consume > available) {
					cerr << "underrun for " << _name << " Available samples: " << available << " required: " << disk_samples_to_consume << endl;
					DEBUG_TRACE (DEBUG::Butler, string_compose ("%1 underrun in %2, total space = %3 vs %4\n", DEBUG_THREAD_SELF, name (), available, disk_samples_to_consume));
					Underrun ();
					return;
				}

			} else if (_declick_amp.gain () != target_gain) {
				assert (target_gain == 0);

				/* note that this is a non-committing read: it
				 * retrieves data from the ringbuffer but does not
				 * advance the read pointer. As a result,
				 * subsequent calls (as we declick) need to
				 * pass in an offset describing where to read
				 * from. We maintain _declick_offs across calls
				 * to ::run()
				 */

				const samplecnt_t total = chaninfo->rbuf->read (disk_buf.data (), nframes, false, declick_offs);

				if (n == 0) {
					_declick_offs += total;
				}
			}

			_declick_amp.apply_gain (disk_buf, nframes, target_gain);

			/* _declick_amp is now left with the correct gain after processing nframes */

			Amp::apply_simple_gain (disk_buf, nframes, scaling);

			if (ms & MonitoringInput) {
				/* mix the disk signal into the input signal (already in bufs) */
				mix_buffers_no_gain (output.data (), disk_buf.data (), nframes);
			}
		}
	}

midi:

	/* MIDI data handling */

	const bool no_playlist_modification_pending = !(pending_overwrite () & PlaylistModified);

	if (bufs.count ().n_midi ()) {
		MidiBuffer& dst (bufs.get_midi (0));

		if (run_must_resolve) {
			resolve_tracker (dst, 0);
			run_must_resolve = false;
		}

		if (!no_disk_output && !declick_in_progress () && (ms & MonitoringDisk) && !still_locating && no_playlist_modification_pending && speed) {
			get_midi_playback (dst, start_sample, end_sample, ms, scratch_bufs, speed, disk_samples_to_consume);
		}
	}

	/* decide if we need the butler */

	if (!still_locating && no_playlist_modification_pending) {
		bool butler_required = false;

		if (speed < 0.0) {
			playback_sample -= disk_samples_to_consume;
		} else {
			playback_sample += disk_samples_to_consume;
		}

		Location* loc = _loop_location;
		if (loc) {
			Evoral::Range<samplepos_t> loop_range (loc->start (), loc->end () - 1);
			playback_sample = loop_range.squish (playback_sample);
		}

		if (_playlists[DataType::AUDIO]) {
			if (!c->empty ()) {
				if (_slaved) {
					if (c->front ()->rbuf->write_space () >= c->front ()->rbuf->bufsize () / 2) {
						DEBUG_TRACE (DEBUG::Butler, string_compose ("%1: slaved, write space = %2 of %3\n", name (), c->front ()->rbuf->write_space (), c->front ()->rbuf->bufsize ()));
						butler_required = true;
					}
				} else {
					if ((samplecnt_t)c->front ()->rbuf->write_space () >= _chunk_samples) {
						DEBUG_TRACE (DEBUG::Butler, string_compose ("%1: write space = %2 of %3\n", name (), c->front ()->rbuf->write_space (),
						                                            _chunk_samples));
						butler_required = true;
					}
				}
			}
		}

		/* All of MIDI is in RAM, no need to call the butler unless we
		 * have to overwrite buffers because of a playlist change.
		 */

		_need_butler = butler_required;
	}

	if (_need_butler) {
		DEBUG_TRACE (DEBUG::Butler, string_compose ("%1 reader run, needs butler = %2\n", name (), _need_butler));
	}
}

bool
DiskReader::declick_in_progress () const
{
	if (!_declick_enabled || (_session.exporting () && !_session.realtime_export ())) {
		return false;
	}
	return _declick_amp.gain () != 0; // declick-out
}

void
DiskReader::configuration_changed ()
{
	boost::shared_ptr<ChannelList> c = channels.reader ();
	if (!c->empty ()) {
		ReaderChannelInfo* chaninfo = dynamic_cast<ReaderChannelInfo*> (c->front ());
		if (!chaninfo->initialized) {
			seek (_session.transport_sample(), true);
			return;
		}
	}
	_session.request_overwrite_buffer (_track.shared_ptr (), LoopDisabled);
}

bool
DiskReader::pending_overwrite () const
{
	return g_atomic_int_get (&_pending_overwrite) != 0;
}

void
DiskReader::set_pending_overwrite (OverwriteReason why)
{
	boost::shared_ptr<ChannelList> c = channels.reader ();

	/* called from audio thread, so we can use the read ptr and playback sample as we wish */

	if (!c->empty ()) {

		if (c->size () > 1) {
			/* Align newly added buffers.
			 *
			 * overwrite_sample and file_sample[] are are maintained
			 * per DiskReader, not per channel.
			 * ::refill_audio() and ::overwrite_existing_audio() expect
			 * that read-pointers and fill_level of all buffers are in sync.
			 */
			ChannelList::iterator chan = c->begin ();
			for (++chan; chan != c->end (); ++chan) {
				ReaderChannelInfo* chaninfo = dynamic_cast<ReaderChannelInfo*> (*chan);
				if (!chaninfo->initialized) {
					(*chan)->rbuf->align_to (*(c->front ()->rbuf));
				}
			}
		}

		const samplecnt_t reserved_size = c->front ()->rbuf->reserved_size ();
		const samplecnt_t bufsize       = c->front ()->rbuf->bufsize ();

		overwrite_offset = c->front ()->rbuf->read_ptr ();
		overwrite_sample = playback_sample - reserved_size;

		if (overwrite_offset > reserved_size) {
			/*
			 * |----------------------------------------------------------------------|
			 *                         ^               ^
			 *                         RRRRRRRRRRRRRRRRoverwrite_offset  (old read_ptr)
			 * |<- second ->|<------------------ first chunk ------------------------>|
			 *
			 * Fill the the end of the buffer ("first chunk"), above
			 */

			overwrite_offset -= reserved_size;

		} else {
			/*
			 * |----------------------------------------------------------------------|
			 * RRRRRRRRE^                                                     RRRRRRRRR
			 *          overwrite_offset  (old read_ptr)
			 * |<                second chunk                                >|<first>|
			 *
			 * Fill the end of the buffer ("R1R1R1" aka "first" above)
			 */

			overwrite_offset = bufsize - (reserved_size - overwrite_offset);
		}
	}

	if (why & (LoopChanged | PlaylistModified | PlaylistChanged)) {
		run_must_resolve = true;
	}

	while (true) {
		OverwriteReason current = OverwriteReason (g_atomic_int_get (&_pending_overwrite));
		OverwriteReason next    = OverwriteReason (current | why);
		if (g_atomic_int_compare_and_exchange (&_pending_overwrite, current, next)) {
			break;
		}
	}
}

bool
DiskReader::overwrite_existing_audio ()
{
	/* This is a tricky and/or clever little method. Let's try to describe
	 * precisely what it does.
	 *
	 * Our goal is to completely overwrite the playback buffers for each
	 * audio channel with new data. The wrinkle is that we want to preserve
	 * the EXACT mapping between a given timeline position and buffer
	 * offset that existed when we requested an overwrite. That is, if the
	 * Nth position in the buffer contained the sample corresponding to
	 * timeline position T, then once this is complete that condition
	 * should still hold. The actual value of the sample (and even whether it
	 * corresponds to any actual material on disk - it may just be silence)
	 * may change, but this buffer_offset<->timeline_position mapping must
	 * remain constant.
	 *
	 * Why do this? There are many reasons. A trivial example is that the
	 * region gain level for one region has been changed, and the user
	 * should be able to hear the result.
	 *
	 * In ::set_pending_overwrite() (above) we stored a sample and a buffer
	 * offset. These corresponded to the next sample to be played and the
	 * buffer position holding that sample. We were able to determine this
	 * pair atomically because ::set_pending_overwrite() is called from
	 * within process context, and thus neither playback_sample nor the
	 * buffer read ptr can change while it runs. We computed the earliest
	 * sample/timeline position in the buffer (at the start of the reserved
	 * zone, if any) and its corresponding buffer offset.
	 *
	 * Here, we will refill the buffer, starting with the sample and buffer
	 * offset computed by ::set_pending_overwrite(). Typically this will
	 * take two reads from the playlist, because our read will be "split"
	 * by the end of the buffer (i.e. we fill from some mid-buffer point to
	 * the end, then fill from the start to the mid-buffer point, as is
	 * common with ring buffers).
	 *
	 * Note that the process thread may indeed access the buffer while we
	 * are doing this. There is a strong likelihood of colliding read/write
	 * between this thread (the butler) and a process thread. But we don't
	 * care: we know that the samples being read/written will correspond to
	 * the same timeline position, and that the user has just done
	 * something forcing us to update the value(s). Given that a Sample is
	 * currently (and likely forever) a floating point value, and that on
	 * many/most architectures, a store for a floating point value is
	 * non-atomic, there is some chance of the process read reading a
	 * sample value while it is being written. This could theoretically
	 * cause a brief glitch, but no more or less than any other
	 * "discontinuity" in the sample's value will.
	 *
	 * It goes without saying that this relies on being serialized within
	 * the butler thread with respect any other buffer write operation
	 * (e.g. via ::refill()). It should also be noted that it has no effect
	 * at all on the write-related members of the playback buffer - we
	 * simply replace the contents of the buffer.
	 */

	boost::shared_ptr<ChannelList> c = channels.reader ();

	if (c->empty ()) {
		return true;
	}

	const bool reversed = !_session.transport_will_roll_forwards ();

	sampleoffset_t chunk1_offset;
	samplecnt_t    chunk1_cnt;
	samplecnt_t    chunk2_cnt;

	const samplecnt_t to_overwrite = c->front()->rbuf->overwritable_at (overwrite_offset);

	chunk1_offset = overwrite_offset;
	chunk1_cnt    = min (c->front()->rbuf->bufsize() - overwrite_offset, to_overwrite);

	/* note: because we are overwriting buffer contents but not moving the
	 * write/read pointers, we actually want to fill all the way to the
	 * write pointer (the value returned by PlaybackBuffer::overwritable_at().
	 *
	 * This differs from what happens during ::refill_audio() where we are
	 * careful not to allow the read pointer to catch the write pointer
	 * (that indicates an empty buffer)
	 */

	if (chunk1_cnt == to_overwrite) {
		chunk2_cnt = 0;
	} else {
		chunk2_cnt = to_overwrite - chunk1_cnt;
	}

	boost::scoped_array<Sample> mixdown_buffer (new Sample[to_overwrite]);
	boost::scoped_array<float>  gain_buffer (new float[to_overwrite]);
	uint32_t                    n   = 0;
	bool                        ret = true;
	samplepos_t                 start;

	for (ChannelList::iterator chan = c->begin (); chan != c->end (); ++chan, ++n) {

		Sample*            buf = (*chan)->rbuf->buffer ();
		ReaderChannelInfo* rci = dynamic_cast<ReaderChannelInfo*> (*chan);

		/* Note that @param start is passed by reference and will be
		 * updated by the ::audio_read() call
		 */

		start = overwrite_sample;

		if (chunk1_cnt) {
			if (audio_read (buf + chunk1_offset, mixdown_buffer.get (), gain_buffer.get (), start, chunk1_cnt, rci, n, reversed) != chunk1_cnt) {
				error << string_compose (_("DiskReader %1: when overwriting(1), cannot read %2 from playlist at sample %3"), id (), chunk1_cnt, overwrite_sample) << endmsg;
				ret = false;
				continue;
			}

		}

		if (chunk2_cnt) {
			if (audio_read (buf, mixdown_buffer.get (), gain_buffer.get (), start, chunk2_cnt, rci, n, reversed) != chunk2_cnt) {
				error << string_compose (_("DiskReader %1: when overwriting(2), cannot read %2 from playlist at sample %3"), id (), chunk2_cnt, overwrite_sample) << endmsg;
				ret = false;
			}
		}

		if (!rci->initialized) {
			DEBUG_TRACE (DEBUG::DiskIO, string_compose ("Init ReaderChannel '%1' overwriting at: %2, avail: %3\n", name (), overwrite_sample, (*chan)->rbuf->read_space ()));
			if ((*chan)->rbuf->read_space () > 0) {
				rci->initialized = true;
			}
		}
	}

	file_sample[DataType::AUDIO] = start;

	return ret;
}

bool
DiskReader::overwrite_existing_midi ()
{
	RTMidiBuffer* mbuf = rt_midibuffer ();

	if (mbuf) {
		MidiTrack* mt = dynamic_cast<MidiTrack*> (&_track);
		MidiChannelFilter* filter = mt ? &mt->playback_filter () : 0;

		PBD::Timing minsert;
		minsert.start ();

		midi_playlist ()->render (filter);

		minsert.update ();
		assert (midi_playlist ()->rendered ());
		cerr << "Reading " << name () << " took " << minsert.elapsed () << " microseconds, final size = " << midi_playlist ()->rendered ()->size () << endl;
	}

	return true;
}

bool
DiskReader::overwrite_existing_buffers ()
{
	/* called from butler thread */

	DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1 overwriting existing buffers at %2 (because %3%4%5\n", owner ()->name (), overwrite_sample, std::hex, g_atomic_int_get (&_pending_overwrite), std::dec));

	bool ret = true;

	if (g_atomic_int_get (&_pending_overwrite) & (PlaylistModified | LoopDisabled | LoopChanged | PlaylistChanged)) {
		if (_playlists[DataType::AUDIO] && !overwrite_existing_audio ()) {
			ret = false;
		}
	}

	if (g_atomic_int_get (&_pending_overwrite) & (PlaylistModified | PlaylistChanged)) {
		if (_playlists[DataType::MIDI] && !overwrite_existing_midi ()) {
			ret = false;
		}
	}

	g_atomic_int_set (&_pending_overwrite, 0);

	return ret;
}

int
DiskReader::seek (samplepos_t sample, bool complete_refill)
{
	/* called via non_realtime_locate() from butler thread */

	int ret = -1;

	const bool read_reversed = !_session.transport_will_roll_forwards ();
	const bool read_loop     = (bool)_loop_location;

	boost::shared_ptr<ChannelList> c = channels.reader ();

	if (c->empty ()) {
		return 0;
	}

	/* There are two possible shortcuts we can take that will completely
	 * skip reading from disk. However, they are invalid if we need to read
	 * data in the opposite direction than we did last time, or if our need
	 * for looped data has chaned since the last read. Both of these change
	 * the semantics of a read from disk, even if the position we are
	 * reading from is the same.
	 */

	if ((_last_read_reversed.value_or (read_reversed) == read_reversed) && (_last_read_loop.value_or (read_loop) == read_loop)) {
		if (sample == playback_sample && !complete_refill) {
			return 0;
		}

		if (abs (sample - playback_sample) < (c->front ()->rbuf->reserved_size () / 6)) {
			/* we're close enough. Note: this is a heuristic */
			return 0;
		}
	}

	g_atomic_int_set (&_pending_overwrite, 0);

	DEBUG_TRACE (DEBUG::DiskIO, string_compose ("DiskReader::seek %1 %2 -> %3 refill=%4\n", owner ()->name ().c_str (), playback_sample, sample, complete_refill));

	const samplecnt_t distance = sample - playback_sample;
	if (!complete_refill && can_internal_playback_seek (distance)) {
		internal_playback_seek (distance);
		return 0;
	}

	for (ChannelList::iterator chan = c->begin (); chan != c->end (); ++chan) {
		(*chan)->rbuf->reset ();
		assert ((*chan)->rbuf->reserved_size () == 0);
	}

	/* move the intended read target, so that after the refill is done,
	 * the intended read target is "reservation" from the start of the
	 * playback buffer. Then increment the read ptr, so that we can
	 * potentially do an internal seek backwards of up "reservation"
	 * samples.
	 */

	samplecnt_t shift = sample > c->front ()->rbuf->reservation_size () ? c->front ()->rbuf->reservation_size () : sample;

	if (read_reversed) {
		/* reading in reverse, so start at a later sample, and read
		 * "backwards" from there. */
		shift = -shift;
	}

	/* start the read at an earlier position (or later if reversed) */

	sample -= shift;

	playback_sample              = sample;
	file_sample[DataType::AUDIO] = sample;
	file_sample[DataType::MIDI]  = sample;

	if (complete_refill) {
		/* call _do_refill() to refill the entire buffer, using
		 * the largest reads possible. */
		while ((ret = do_refill_with_alloc (false, read_reversed)) > 0)
			;
	} else {
		/* call _do_refill() to refill just one chunk, and then return. */
		ret = do_refill_with_alloc (true, read_reversed);
	}

	if (shift) {
		/* now tell everyone where we really are, leaving the
		 * "reserved" data represented by "shift" available in the
		 * buffer for backwards-internal-seek
		 */

		playback_sample += shift;

		/* we always move the read-ptr forwards, since even when in
		 * reverse, the data is placed in the buffer in normal read
		 * (increment) order.
		 */

		shift = abs (shift);

		for (ChannelList::iterator chan = c->begin (); chan != c->end (); ++chan) {
			(*chan)->rbuf->increment_read_ptr (shift);
		}
	}

	return ret;
}

bool
DiskReader::can_internal_playback_seek (sampleoffset_t distance)
{
	/* 1. Audio */

	ChannelList::iterator          chan;
	boost::shared_ptr<ChannelList> c = channels.reader ();

	for (chan = c->begin (); chan != c->end (); ++chan) {
		if (!(*chan)->rbuf->can_seek (distance)) {
			return false;
		}
	}

	/* 2. MIDI can always seek any distance */

	return true;
}

void
DiskReader::internal_playback_seek (sampleoffset_t distance)
{
	if (distance == 0) {
		return;
	}

	sampleoffset_t off = distance;

	ChannelList::iterator          chan;
	boost::shared_ptr<ChannelList> c = channels.reader ();
	for (chan = c->begin (); chan != c->end (); ++chan) {
		if (distance < 0) {
			off = 0 - (sampleoffset_t) (*chan)->rbuf->decrement_read_ptr (::llabs (distance));
		} else {
			off = (*chan)->rbuf->increment_read_ptr (distance);
		}
	}

	playback_sample += off;
}

static void
swap_by_ptr (Sample* first, Sample* last)
{
	while (first < last) {
		Sample tmp = *first;
		*first++   = *last;
		*last--    = tmp;
	}
}

/** Read some data for 1 channel from our playlist into a buffer.
 *
 *  @param sum_buf sample-containing buffer to write to. Must be contiguous.
 *  @param mixdown_buffer sample-containing buffer that will be used to mix layers
 *  @param gain_buffer ptr to a buffer used to hold any necessary gain (automation) data
 *  @param start Session sample to start reading from; updated to where we end up
 *         after the read. Global timeline position.
 *  @param cnt Count of samples to read.
 *  @param rci ptr to ReaderChannelInfo for the channel we're reading
 *  @param channel the number of the channel we're reading (0..N)
 *  @param reversed true if we are running backwards, otherwise false.
 */

samplecnt_t
DiskReader::audio_read (Sample*            sum_buffer,
                        Sample*            mixdown_buffer,
                        float*             gain_buffer,
                        samplepos_t&       start,
                        samplecnt_t        cnt,
                        ReaderChannelInfo* rci,
                        int                channel,
                        bool               reversed)
{
	samplecnt_t       this_read  = 0;
	bool              reloop     = false;
	samplepos_t       loop_end   = 0;
	samplepos_t       loop_start = 0;
	Location*         loc        = 0;
	const samplecnt_t rcnt       = cnt;

	/* XXX we don't currently play loops in reverse. not sure why */

	if (!reversed) {

		/* Make the use of a Location atomic for this read operation.

		   Note: Locations don't get deleted, so all we care about
		   when I say "atomic" is that we are always pointing to
		   the same one and using a start/length values obtained
		   just once.
		*/

		if ((loc = _loop_location) != 0) {
			loop_start  = loc->start ();
			loop_end    = loc->end ();

			/* Evoral::Range has inclusive range semantics. Ugh. Hence the -1 */
			const Evoral::Range<samplepos_t> loop_range (loop_start, loop_end - 1);
			start = loop_range.squish (start);
		}

	} else {

		start -= cnt;
		start = max (samplepos_t (0), start);
	}

	/* We need this while loop in case we hit a loop boundary, in which case our read from
	 * the playlist must be split into more than one section. */

	while (cnt) {
		/* take any loop into account. we can't read past the end of the loop. */

		if (loc && (loop_end - start < cnt)) {
			this_read = loop_end - start;
			reloop    = true;
		} else {
			reloop    = false;
			this_read = cnt;
		}

		if (this_read == 0) {
			break;
		}

		this_read = min (cnt, this_read);

		/* note that the mixdown and gain buffers are purely for the
		 * internal use of the playlist, and cannot be considered
		 * useful after the return from AudioPlayback::read()
		 */

		if (audio_playlist ()->read (sum_buffer, mixdown_buffer, gain_buffer, start, this_read, channel) != this_read) {
			error << string_compose (_("DiskReader %1: cannot read %2 from playlist at sample %3"), id (), this_read, start) << endmsg;
			return 0;
		}

		if (loc) {
			/* Looping: do something (maybe) about the loop boundaries */

			switch (Config->get_loop_fade_choice ()) {
				case NoLoopFade:
					break;
				case BothLoopFade:
					loop_declick_in.run (sum_buffer, start, start + this_read);
					loop_declick_out.run (sum_buffer, start, start + this_read);
					break;
				case EndLoopFade:
					loop_declick_out.run (sum_buffer, start, start + this_read);
					break;
				case XFadeLoop:
					if (last_refill_loop_start != loc->start() || rci->pre_loop_buffer == 0) {
						setup_preloop_buffer ();
						last_refill_loop_start = loc->start();
					}
					maybe_xfade_loop (sum_buffer, start, start + this_read, rci);
					break;
			}
		}

		if (reversed) {
			swap_by_ptr (sum_buffer, sum_buffer + this_read - 1);

		} else {
			/* if we read to the end of the loop, go back to the beginning */

			if (reloop) {
				start = loop_start;
			} else {
				start += this_read;
			}
		}

		cnt -= this_read;
		sum_buffer += this_read;
	}

	_last_read_reversed = reversed;
	_last_read_loop     = (bool)loc;

	return rcnt;
}

int
DiskReader::do_refill ()
{
	const bool reversed = !_session.transport_will_roll_forwards ();
	return refill (_sum_buffer, _mixdown_buffer, _gain_buffer, 0, reversed);
}

int
DiskReader::do_refill_with_alloc (bool partial_fill, bool reversed)
{
	/* We limit disk reads to at most 4MB chunks, which with floating point
	 * samples would be 1M samples. But we might use 16 or 14 bit samples,
	 * in which case 4MB is more samples than that. Therefore size this for
	 * the smallest sample value .. 4MB = 2M samples (16 bit).
	 */

	boost::scoped_array<Sample> sum_buf (new Sample[2 * 1048576]);
	boost::scoped_array<Sample> mix_buf (new Sample[2 * 1048576]);
	boost::scoped_array<float>  gain_buf (new float[2 * 1048576]);

	return refill_audio (sum_buf.get (), mix_buf.get (), gain_buf.get (), (partial_fill ? _chunk_samples : 0), reversed);
}

int
DiskReader::refill (Sample* sum_buffer, Sample* mixdown_buffer, float* gain_buffer, samplecnt_t fill_level, bool reversed)
{
	/* NOTE: Audio refill MUST come first so that in contexts where ONLY it
	 * is called, _last_read_reversed is set correctly.
	 */

	if (refill_audio (sum_buffer, mixdown_buffer, gain_buffer, fill_level, reversed)) {
		return -1;
	}

	if (rt_midibuffer () && (reversed != rt_midibuffer ()->reversed ())) {
		rt_midibuffer ()->reverse ();
	}

	return 0;
}

/** Get some more data from disk and put it in our channels' bufs,
 *  if there is suitable space in them.
 *
 * If fill_level is non-zero, then we will refill the buffer so that there is
 * still at least fill_level samples of space left to be filled. This is used
 * after locates so that we do not need to wait to fill the entire buffer.
 *
 */

int
DiskReader::refill_audio (Sample* sum_buffer, Sample* mixdown_buffer, float* gain_buffer, samplecnt_t fill_level, bool reversed)
{
	/* do not read from disk while session is marked as Loading, to avoid
	   useless redundant I/O.
	*/

	if (_session.loading ()) {
		return 0;
	}

	int32_t                        ret = 0;
	samplecnt_t                    zero_fill;
	uint32_t                       chan_n;
	ChannelList::iterator          i;
	boost::shared_ptr<ChannelList> c = channels.reader ();

	_last_read_reversed = reversed;

	if (c->empty ()) {
		return 0;
	}

	assert (mixdown_buffer);
	assert (gain_buffer);

	samplecnt_t total_space = c->front ()->rbuf->write_space ();

	if (total_space == 0) {
		DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1: no space to refill\n", name ()));
		/* nowhere to write to */
		return 0;
	}

	if (fill_level) {
		if (fill_level < total_space) {
			total_space -= fill_level;
		} else {
			/* we can't do anything with it */
			fill_level = 0;
		}
	}

	/* if we're running close to normal speed and there isn't enough
	 * space to do disk_read_chunk_samples of I/O, then don't bother.
	 *
	 * at higher speeds, just do it because the sync between butler
	 * and audio thread may not be good enough.
	 *
	 * Note: it is a design assumption that disk_read_chunk_samples is smaller
	 * than the playback buffer size, so this check should never trip when
	 * the playback buffer is empty.
	 */

	DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1: space to refill %2 vs. chunk %3 (speed = %4)\n", name (), total_space, _chunk_samples, _session.transport_speed ()));
	if ((total_space < _chunk_samples) && fabs (_session.transport_speed ()) < 2.0f) {
		return 0;
	}

	/* when slaved, don't try to get too close to the read pointer. this
	 * leaves space for the buffer reversal to have something useful to
	 * work with.
	 */

	if (_slaved && total_space < (samplecnt_t) (c->front ()->rbuf->bufsize () / 2)) {
		DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1: not enough to refill while slaved\n", this));
		return 0;
	}

	samplepos_t fsa = file_sample[DataType::AUDIO];

	if (reversed) {
		if (fsa == 0) {
			/* at start: nothing to do but fill with silence */
			for (chan_n = 0, i = c->begin (); i != c->end (); ++i, ++chan_n) {
				ChannelInfo* chan (*i);
				chan->rbuf->write_zero (chan->rbuf->write_space ());
			}
			return 0;
		}

		if (fsa < total_space) {
			/* too close to the start: read what we can, and then zero fill the rest */
			zero_fill   = total_space - fsa;
			total_space = fsa;
		} else {
			zero_fill = 0;
		}

	} else {
		if (fsa == max_samplepos) {
			/* at end: nothing to do but fill with silence */
			for (chan_n = 0, i = c->begin (); i != c->end (); ++i, ++chan_n) {
				ChannelInfo* chan (*i);
				chan->rbuf->write_zero (chan->rbuf->write_space ());
			}
			return 0;
		}

		if (fsa > max_samplepos - total_space) {
			/* to close to the end: read what we can, and zero fill the rest */
			zero_fill   = total_space - (max_samplepos - fsa);
			total_space = max_samplepos - fsa;

		} else {
			zero_fill = 0;
		}
	}

	/* total_space is in samples. We want to optimize read sizes in various sizes using bytes */
	const size_t bits_per_sample = format_data_width (_session.config.get_native_file_data_format ());
	size_t       total_bytes     = total_space * bits_per_sample / 8;

	/* chunk size range is 256kB to 4MB. Bigger is faster in terms of MB/sec, but bigger chunk size always takes longer */
	size_t byte_size_for_read = max ((size_t) (256 * 1024), min ((size_t) (4 * 1048576), total_bytes));

	/* find nearest (lower) multiple of 16384 */

	byte_size_for_read = (byte_size_for_read / 16384) * 16384;

	/* now back to samples */
	samplecnt_t samples_to_read = byte_size_for_read / (bits_per_sample / 8);

	DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1: will refill %2 channels with %3 samples\n", name (), c->size (), total_space));

	samplepos_t file_sample_tmp = fsa;

#if 0
	int64_t before = g_get_monotonic_time ();
	int64_t elapsed;
#endif

	for (chan_n = 0, i = c->begin (); i != c->end (); ++i, ++chan_n) {
		ChannelInfo* chan (*i);

		/* we want all channels to read from the same position, but
		 * audio_read() will increment its position argument. So
		 * reinitialize this for every channel.
		 */

		file_sample_tmp = fsa;
		samplecnt_t ts  = total_space;

		samplecnt_t to_read = min (ts, (samplecnt_t)chan->rbuf->write_space ());
		to_read             = min (to_read, samples_to_read);
		assert (to_read >= 0);

		// cerr << owner()->name() << " to-read: " << to_read << endl;

		if (to_read) {
			ReaderChannelInfo* rci = dynamic_cast<ReaderChannelInfo*> (chan);

			if (!_playlists[DataType::AUDIO]) {
				chan->rbuf->write_zero (to_read);

			} else {
				samplecnt_t nread;
				if ((nread = audio_read (sum_buffer, mixdown_buffer, gain_buffer, file_sample_tmp, to_read, rci, chan_n, reversed)) != to_read) {
					error << string_compose (_("DiskReader %1: when refilling, cannot read %2 from playlist at sample %3"), name (), to_read, fsa) << endmsg;
					ret = -1;
					goto out;
				}

				if (chan->rbuf->write (sum_buffer, nread) != nread) {
					error << string_compose (_("DiskReader %1: when refilling, cannot write %2 into buffer"), name (), nread) << endmsg;
					ret = -1;
				}
			}
			if (!rci->initialized) {
				DEBUG_TRACE (DEBUG::DiskIO, string_compose (" -- Init ReaderChannel '%1' read: %2 samples, at: %4, avail: %5\n", name (), to_read, file_sample_tmp , rci->rbuf->read_space ()));
				rci->initialized = true;
			}
		}

		if (zero_fill) {
			/* not sure if action is needed,
			 * we'll later hit the "to close to the end" case
			 */
			//chan->rbuf->write_zero (zero_fill);
		}
	}

#if 0
	elapsed = g_get_monotonic_time () - before;
	cerr << '\t' << name() << ": bandwidth = " << (byte_size_for_read / 1048576.0) / (elapsed/1000000.0) << "MB/sec\n";
#endif

	file_sample[DataType::AUDIO] = file_sample_tmp;
	assert (file_sample[DataType::AUDIO] >= 0);

	ret = ((total_space - samples_to_read) > _chunk_samples);

out:
	return ret;
}

void
DiskReader::playlist_ranges_moved (list<Evoral::RangeMove<samplepos_t> > const& movements_samples, bool from_undo_or_shift)
{
	/* If we're coming from an undo, it will have handled
	 * automation undo (it must, since automation-follows-regions
	 * can lose automation data).  Hence we can do nothing here.
	 *
	 * Likewise when shifting regions (insert/remove time)
	 * automation is taken care of separately (busses with
	 * automation have no disk-reader).
	 */

	if (from_undo_or_shift) {
		return;
	}

	if (Config->get_automation_follows_regions () == false) {
		return;
	}

	list<Evoral::RangeMove<double> > movements;

	for (list<Evoral::RangeMove<samplepos_t> >::const_iterator i = movements_samples.begin ();
	     i != movements_samples.end ();
	     ++i) {
		movements.push_back (Evoral::RangeMove<double> (i->from, i->length, i->to));
	}

	/* move panner automation */
	boost::shared_ptr<Pannable>   pannable = _track.pannable ();
	Evoral::ControlSet::Controls& c (pannable->controls ());

	for (Evoral::ControlSet::Controls::iterator ci = c.begin (); ci != c.end (); ++ci) {
		boost::shared_ptr<AutomationControl> ac = boost::dynamic_pointer_cast<AutomationControl> (ci->second);
		if (!ac) {
			continue;
		}
		boost::shared_ptr<AutomationList> alist = ac->alist ();
		if (!alist->size ()) {
			continue;
		}
		XMLNode&   before       = alist->get_state ();
		bool const things_moved = alist->move_ranges (movements);
		if (things_moved) {
			_session.add_command (new MementoCommand<AutomationList> (
			    *alist.get (), &before, &alist->get_state ()));
		}
	}
	/* move processor automation */
	_track.foreach_processor (boost::bind (&DiskReader::move_processor_automation, this, _1, movements_samples));
}

void
DiskReader::move_processor_automation (boost::weak_ptr<Processor> p, list<Evoral::RangeMove<samplepos_t> > const& movements_samples)
{
	boost::shared_ptr<Processor> processor (p.lock ());
	if (!processor) {
		return;
	}

	list<Evoral::RangeMove<double> > movements;
	for (list<Evoral::RangeMove<samplepos_t> >::const_iterator i = movements_samples.begin (); i != movements_samples.end (); ++i) {
		movements.push_back (Evoral::RangeMove<double> (i->from, i->length, i->to));
	}

	set<Evoral::Parameter> const a = processor->what_can_be_automated ();

	for (set<Evoral::Parameter>::const_iterator i = a.begin (); i != a.end (); ++i) {
		boost::shared_ptr<AutomationList> al = processor->automation_control (*i)->alist ();
		if (!al->size ()) {
			continue;
		}
		XMLNode&   before       = al->get_state ();
		bool const things_moved = al->move_ranges (movements);
		if (things_moved) {
			_session.add_command (
			    new MementoCommand<AutomationList> (
			        *al.get (), &before, &al->get_state ()));
		}
	}
}

void
DiskReader::reset_tracker ()
{
	_tracker.reset ();
}

void
DiskReader::resolve_tracker (Evoral::EventSink<samplepos_t>& buffer, samplepos_t time)
{
	_tracker.resolve_notes (buffer, time);
}

/** Writes playback events from playback_sample for nframes to dst, translating time stamps
 *  so that an event at playback_sample has time = 0
 */
void
DiskReader::get_midi_playback (MidiBuffer& dst, samplepos_t start_sample, samplepos_t end_sample, MonitorState ms, BufferSet& scratch_bufs, double speed, samplecnt_t disk_samples_to_consume)
{
	RTMidiBuffer* rtmb = rt_midibuffer ();

	if (!rtmb || (rtmb->size () == 0)) {
		/* no data to read, so do nothing */
		return;
	}

	MidiBuffer* target;

	if (ms & MonitoringInput) {
		/* data from disk needs to be *merged* not written into the
		 * dst, because it may contain input data that we want to
		 * monitor. Since RTMidiBuffer currently (Oct 2019) has no
		 * suitable method, put the disk data into a scratch buffer and
		 * then merge later.
		 */

		target = &scratch_bufs.get_midi (0);
	} else {
		/* No need to preserve the contents of the input buffer. But
		 * Route::process_output_buffers() clears the buffer as-needed
		 * so know we do not need to clear it.
		 */
		target = &dst;
	}

	if (!g_atomic_int_get (&_no_disk_output)) {
		const samplecnt_t nframes = abs (end_sample - start_sample);

		if (ms & MonitoringDisk) {
			/* disk data needed */

			Location* loc = _loop_location;

			if (loc) {
				/* Evoral::Range has inclusive range semantics. Ugh. Hence the -1 */
				const Evoral::Range<samplepos_t> loop_range (loc->start (), loc->end () - 1);
				samplepos_t                      effective_start = start_sample;
				samplecnt_t                      cnt             = nframes;
				sampleoffset_t                   offset          = 0;

				DEBUG_TRACE (DEBUG::MidiDiskIO, string_compose ("LOOP read, loop is %1..%2 range is %3..%4 nf %5\n", loc->start (), loc->end (), start_sample, end_sample, nframes));

				do {
					samplepos_t effective_end;

					effective_start = loop_range.squish (effective_start);
					effective_end   = min (effective_start + cnt, loc->end ());
					assert (effective_end > effective_start);

					const samplecnt_t this_read = effective_end - effective_start;

					DEBUG_TRACE (DEBUG::MidiDiskIO, string_compose ("playback buffer LOOP read, from %1 to %2 (%3)\n", effective_start, effective_end, this_read));

					size_t events_read = rtmb->read (*target, effective_start, effective_end, _tracker, offset);
					cnt -= this_read;
					effective_start += this_read;
					offset += this_read;

					DEBUG_TRACE (DEBUG::MidiDiskIO, string_compose ("%1 MDS events LOOP read %2 cnt now %3\n", _name, events_read, cnt));

					if (cnt) {
						/* We re going to have to read across the loop end. Resolve any notes the extend across the loop end.
						 * Time is relative to start_sample.
						 */
						DEBUG_TRACE (DEBUG::MidiDiskIO, string_compose ("read crosses loop end, resolve @ %1\n", effective_end - start_sample));
						_tracker.resolve_notes (*target, effective_end - start_sample);
					}

				} while (cnt);

			} else {
				DEBUG_TRACE (DEBUG::MidiDiskIO, string_compose ("playback buffer read, from %1 to %2 (%3)\n", start_sample, end_sample, nframes));
				size_t events_read = rtmb->read (*target, start_sample, end_sample, _tracker);
				DEBUG_TRACE (DEBUG::MidiDiskIO, string_compose ("%1 MDS events read %2 range %3 .. %4\n", _name, events_read, playback_sample, playback_sample + nframes));
			}
		}

		if (ms & MonitoringInput) {
			/* merges data from disk (in "target", which is a scratch
			 * buffer in this case) into the actual destination buffer
			 * (which holds existing input data).
			 */
			dst.merge_from (*target, nframes);
		}
	}

#if 0
	if (!target->empty ()) {
		cerr << "======== MIDI OUT ========\n";
		for (MidiBuffer::iterator i = target->begin(); i != target->end(); ++i) {
			const Evoral::Event<MidiBuffer::TimeType> ev (*i, false);
			cerr << "MIDI EVENT (from disk) @ " << ev.time();
			for (size_t xx = 0; xx < ev.size(); ++xx) {
				cerr << ' ' << hex << (int) ev.buffer()[xx];
			}
			cerr << dec << endl;
		}
		cerr << "----------------\n";
	}
#endif
}
void
DiskReader::inc_no_disk_output ()
{
	g_atomic_int_inc (&_no_disk_output);
}

void
DiskReader::dec_no_disk_output ()
{
	/* this is called unconditionally when things happen that ought to end
	 * a period of "no disk output". It's OK for that to happen when there
	 * was no corresponding call to ::inc_no_disk_output(), but we must
	 * stop the value from becoming negative.
	 */

	do {
		gint v = g_atomic_int_get (&_no_disk_output);
		if (v > 0) {
			if (g_atomic_int_compare_and_exchange (&_no_disk_output, v, v - 1)) {
				break;
			}
		} else {
			break;
		}
	} while (true);
}

/* min gain difference for de-click and loop-fadess
 * (-60dB difference to target)
 */
#define GAIN_COEFF_DELTA (1e-5)

DiskReader::DeclickAmp::DeclickAmp (samplecnt_t sample_rate)
{
	_a = 800.f / (gain_t)sample_rate; // ~ 1/50Hz to fade by 40dB
	_l = -log1p (_a);
	_g = 0;
}

void
DiskReader::DeclickAmp::apply_gain (AudioBuffer& buf, samplecnt_t n_samples, const float target, sampleoffset_t buffer_offset)
{
	if (n_samples == 0) {
		return;
	}
	float g = _g;

	if (g == target) {
		assert (buffer_offset == 0);
		Amp::apply_simple_gain (buf, n_samples, target, 0);
		return;
	}

	const float   a      = _a;
	Sample* const buffer = buf.data ();

	const int max_nproc = 4;
	uint32_t  remain    = n_samples;
	uint32_t  offset    = buffer_offset;

	while (remain > 0) {
		uint32_t n_proc = remain > max_nproc ? max_nproc : remain;
		for (uint32_t i = 0; i < n_proc; ++i) {
			buffer[offset + i] *= g;
		}
#if 1
		g += a * (target - g);
#else /* accurate exponential fade */
		if (n_proc == max_nproc) {
			g += a * (target - g);
		} else {
			g = target - (target - g) * expf (_l * n_proc / max_nproc);
		}
#endif
		remain -= n_proc;
		offset += n_proc;
	}

	if (fabsf (g - target) < GAIN_COEFF_DELTA) {
		_g = target;
	} else {
		_g = g;
	}
}

DiskReader::Declicker::Declicker ()
    : fade_start (0)
    , fade_end (0)
    , fade_length (0)
    , vec (0)
{
}

DiskReader::Declicker::~Declicker ()
{
	delete[] vec;
}

void
DiskReader::Declicker::alloc (samplecnt_t sr, bool fadein, bool linear)
{
	delete[] vec;
	vec = new Sample[loop_fade_length];

	if (linear) {
		if (fadein) {
			for (samplecnt_t n = 0; n < loop_fade_length; ++n) {
				vec[n] = n / (float) loop_fade_length;
			}
		} else {
			for (samplecnt_t n = 0; n < loop_fade_length; ++n) {
				vec[n] = 1.f - n / (float) loop_fade_length;
			}
		}
		fade_length = loop_fade_length - 1;
		return;
	}

	/* Exponential fade */

	const float a = 390.f / sr; // ~ 1/100Hz for 40dB

	/* build a psuedo-exponential (linear-volume) shape for the fade */

	samplecnt_t n;

	if (fadein) {
		gain_t g = 0.0;
		for (n = 0; (n < loop_fade_length) && ((1.f - g) > GAIN_COEFF_DELTA); ++n) {
			vec[n] = g;
			g += a * (1.0 - g);
		}
	} else {
		gain_t g = 1.0;
		for (n = 0; (n < loop_fade_length) && (g > GAIN_COEFF_DELTA); ++n) {
			vec[n] = g;
			g += a * -g;
		}
	}

	assert (n > 0 && n <= loop_fade_length);

	fade_length = n - 1;

	/* Fill remaining fader-buffer with the target value.
	 *
	 * This is needed for loop x-fade. Due to float precision near 1.0, fade-in length
	 * is can be one or two samples shorter than fade-out length (depending on sample-rate).
	 * Summing the fade-in and fade-out curve over the complete fade-range (fade-out,
	 * as done by DiskReader::maybe_xfade_loop) must yield 1.0 +/- GAIN_COEFF_DELTA.
	 */
	for (; n < loop_fade_length; ++n) {
		vec[n] = fadein ? 1.f : 0.f;
	}
}

void
DiskReader::Declicker::reset (samplepos_t loop_start, samplepos_t loop_end, bool fadein, samplecnt_t sr)
{
	if (loop_start == loop_end) {
		fade_start = 0;
		fade_end   = 0;
		return;
	}

	/* adjust the position of the fade (this is absolute (global) timeline units) */

	if (fadein) {
		fade_start = loop_start;
		fade_end   = loop_start + fade_length;
	} else {
		fade_start = loop_end - fade_length;
		fade_end   = loop_end;
	}
}

void
DiskReader::Declicker::run (Sample* buf, samplepos_t read_start, samplepos_t read_end)
{
	samplecnt_t    n;  /* how many samples to process */
	sampleoffset_t bo; /* offset into buffer */
	sampleoffset_t vo; /* offset into gain vector */

	if (fade_start == fade_end) {
		return;
	}

	/* Determine how the read range overlaps with the fade range, so we can determine
	 * which part of the fade gain vector to apply to which part of the buffer.
	 *
	 * see also DiskReader::maybe_xfade_loop()
	 */

	switch (Evoral::coverage (fade_start, fade_end, read_start, read_end)) {
		case Evoral::OverlapInternal:
			/* note: start and end points cannot coincide (see evoral/Range.h)
			 *
			 * read range is entirely within fade range
			 */
			bo = 0;
			vo = read_start - fade_start;
			n  = read_end - read_start;
			break;

		case Evoral::OverlapExternal:
			/* read range extends on either side of fade range
			 *
			 * External allows coincidental start & end points, so check for that
			 */
			if (fade_start == read_start && fade_end == read_end) {
				/* fade entire read ... this is SO unlikely ! */
				bo = 0;
				vo = 0;
				n  = fade_end - fade_start;
			} else {
				bo = fade_start - read_start;
				vo = 0;
				n  = fade_end - fade_start;
			}
			break;

		case Evoral::OverlapStart:
			/* read range starts before and ends within fade or at same end as fade */
			n  = fade_end - read_start;
			vo = 0;
			bo = fade_start - read_start;
			break;

		case Evoral::OverlapEnd:
			/* read range starts within fade range, but possibly at it's end, so check */
			if (read_start == fade_end) {
				/* nothing to do */
				return;
			}
			bo = 0;
			vo = read_start - fade_start;
			n  = fade_end - read_start;
			break;

		case Evoral::OverlapNone:
			/* no overlap ... nothing to do */
			return;
	}

	Sample* b = &buf[bo];
	gain_t* g = &vec[vo];

	for (sampleoffset_t i = 0; i < n; ++i) {
		b[i] *= g[i];
	}
}

void
DiskReader::maybe_xfade_loop (Sample* buf, samplepos_t read_start, samplepos_t read_end, ReaderChannelInfo* chan)
{
	samplecnt_t    n;  /* how many samples to process */
	sampleoffset_t bo; /* offset into buffer */
	sampleoffset_t vo; /* offset into gain vector */

	const samplepos_t fade_start = loop_declick_out.fade_start;
	const samplepos_t fade_end   = loop_declick_out.fade_end;

	if (fade_start == fade_end) {
		return;
	}

	/* Determine how the read range overlaps with the fade range, so we can determine
	 * which part of the fade gain vector to apply to which part of the buffer.
	 *
	 * see also DiskReader::Declicker::run()
	 */

	switch (Evoral::coverage (fade_start, fade_end, read_start, read_end)) {
		case Evoral::OverlapInternal:
			/* note: start and end points cannot coincide (see evoral/Range.h)
			 *
			 * read range is entirely within fade range
			 */
			bo = 0;
			vo = read_start - fade_start;
			n  = read_end - read_start;
			break;

		case Evoral::OverlapExternal:
			/* read range extends on either side of fade range
			 *
			 * External allows coincidental start & end points, so check for that
			 */
			if (fade_start == read_start && fade_end == read_end) {
				/* fade entire read ... this is SO unlikely ! */
				bo = 0;
				vo = 0;
				n  = fade_end - fade_start;
			} else {
				bo = fade_start - read_start;
				vo = 0;
				n  = fade_end - fade_start;
			}
			break;

		case Evoral::OverlapStart:
			/* read range starts before and ends within fade or at same end as fade */
			n  = read_end - fade_start;
			vo = 0;
			bo = fade_start - read_start;
			break;

		case Evoral::OverlapEnd:
			/* read range starts within fade range, but possibly at it's end, so check */
			if (read_start == fade_end) {
				/* nothing to do */
				return;
			}
			bo = 0;
			vo = read_start - fade_start;
			n  = fade_end - read_start;
			break;

		case Evoral::OverlapNone:
			/* no overlap ... nothing to do */
			return;
	}

	Sample* b    = &buf[bo];                   /* data to be faded out */
	Sample* sbuf = &chan->pre_loop_buffer[vo]; /* pre-loop (maybe silence) to be faded in */
	gain_t* og   = &loop_declick_out.vec[vo];  /* fade out gain vector */
	gain_t* ig   = &loop_declick_in.vec[vo];   /* fade in gain vector */

	for (sampleoffset_t i = 0; i < n; ++i) {
		b[i] = (b[i] * og[i]) + (sbuf[i] * ig[i]);
	}
}

RTMidiBuffer*
DiskReader::rt_midibuffer ()
{
	boost::shared_ptr<Playlist> pl = _playlists[DataType::MIDI];

	if (!pl) {
		return 0;
	}

	boost::shared_ptr<MidiPlaylist> mpl = boost::dynamic_pointer_cast<MidiPlaylist> (pl);

	if (!mpl) {
		/* error, but whatever ... */
		return 0;
	}

	return mpl->rendered ();
}

void
DiskReader::alloc_loop_declick (samplecnt_t sr)
{
	loop_fade_length = lrintf (ceil (-log (GAIN_COEFF_DELTA / 2.) / (390. / sr)));
	loop_declick_in.alloc (sr, true, Config->get_loop_fade_choice () == XFadeLoop);
	loop_declick_out.alloc (sr, false, Config->get_loop_fade_choice () == XFadeLoop);
}

#undef GAIN_COEFF_DELTA

void
DiskReader::reset_loop_declick (Location* loc, samplecnt_t sr)
{
	if (loc) {
		loop_declick_in.reset (loc->start (), loc->end (), true, sr);
		loop_declick_out.reset (loc->start (), loc->end (), false, sr);
	} else {
		loop_declick_in.reset (0, 0, true, sr);
		loop_declick_out.reset (0, 0, false, sr);
	}
}

void
DiskReader::set_loop (Location* loc)
{
	Processor::set_loop (loc);

	if (!loc) {
		return;
	}
}

void
DiskReader::setup_preloop_buffer ()
{
	if (!_loop_location) {
		return;
	}

	boost::shared_ptr<ChannelList> c = channels.reader ();

	if (c->empty () || !_playlists[DataType::AUDIO]) {
		return;
	}

	Location*                   loc = _loop_location;
	boost::scoped_array<Sample> mix_buf (new Sample[loop_fade_length]);
	boost::scoped_array<Sample> gain_buf (new Sample[loop_fade_length]);

	uint32_t channel = 0;

	for (ChannelList::iterator chan = c->begin (); chan != c->end (); ++chan, ++channel) {
		ReaderChannelInfo* rci = dynamic_cast<ReaderChannelInfo*> (*chan);

		rci->resize_preloop (loop_fade_length);

		if (loc->start () > loop_fade_length) {
			audio_playlist ()->read (rci->pre_loop_buffer, mix_buf.get (), gain_buf.get (), loc->start () - loop_declick_out.fade_length, loop_declick_out.fade_length, channel);
		} else {
			memset (rci->pre_loop_buffer, 0, sizeof (Sample) * loop_fade_length);
		}
	}
}