Debugging underruns, needs cleanup

examples/loopback.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# -*- mode: python; indent-tabs-mode: t; c-basic-offset: 4; tab-width: 4 -*-
+# -*- mode: python; indent-tabs-mode: t; c-basic-offset: 4; tab-width: 4; python-indent: 4 -*-
 
 import sys
 import select
@@ -7,12 +7,21 @@ import logging
 import re
 import struct
 import subprocess
+import errno
+from enum import Enum, auto
 from datetime import datetime, timedelta
 from alsaaudio import (PCM, pcms, PCM_PLAYBACK, PCM_CAPTURE, PCM_NONBLOCK, Mixer,
 	PCM_STATE_OPEN, PCM_STATE_SETUP, PCM_STATE_PREPARED, PCM_STATE_RUNNING, PCM_STATE_XRUN, PCM_STATE_DRAINING,
 	PCM_STATE_PAUSED, PCM_STATE_SUSPENDED, ALSAAudioError)
 from argparse import ArgumentParser
 
+# wake up at least after *idle_timer_period* seconds
+idle_timer_period = 0.25
+# grace period for opening the device in seconds
+open_grace_period = 0.5
+# close the device after *idle_close_timeout* seconds silence
+idle_close_timeout = 2.0
+
 poll_names = {
 	select.POLLIN: 'POLLIN',
 	select.POLLPRI: 'POLLPRI',
@@ -34,6 +43,10 @@ state_names = {
 	PCM_STATE_SUSPENDED: 'PCM_STATE_SUSPENDED'
 }
 
+type NamedProcess = tuple[str, subprocess.Popen]
+
+cmd_process : NamedProcess = None
+
 def poll_desc(mask):
 	return '|'.join([poll_names[bit] for bit, name in poll_names.items() if mask & bit])
 
@@ -57,14 +70,19 @@ class PollDescriptor(object):
 
 		return cls(name, fd, mask)
 
+class LoopbackState(Enum):
+	LISTENING = auto()
+	PLAYING = auto()
+	DEVICE_BUSY = auto()
+
 class Loopback(object):
 	'''Loopback state and event handling'''
 
 	def __init__(self, capture, playback_args, volume_handler, run_after_stop=None, run_before_start=None):
 		self.playback_args = playback_args
 		self.playback = None
+
 		self.volume_handler = volume_handler
-		self.capture_started = None
 		self.last_capture_event = None
 
 		self.capture = capture
@@ -77,13 +95,10 @@ class Loopback(object):
 		self.run_before_start = None
 		if run_before_start:
 			self.run_before_start = run_before_start.split(' ')
-		self.run_after_stop_did_run = False
 
-		self.waitBeforeOpen = False
+		self.state = None
-		self.queue = []
+		self.last_state_change = None
-
+		self.silence_start = None
-		self.period_size = 0
-		self.silent_periods = 0
 
 	@staticmethod
 	def compute_energy(data):
@@ -97,43 +112,84 @@ class Loopback(object):
 	@staticmethod
 	def run_command(cmd):
 		if cmd:
-			rc = subprocess.run(cmd)
+			global cmd_process
+			cmd_process = (cmd, subprocess.Popen(cmd))
+
+	@staticmethod
+	def check_command_idle_handler():
+		# an idle handler to watch the process created above
+		if cmd_process:
+			rc = cmd_process[1].poll()
+			if rc:
 				if rc.returncode:
-				logging.warning(f'run {cmd}, return code {rc.returncode}')
+					logging.warning(f'run {cmd_process[0]}, return code {rc.returncode}')
 				else:
-				logging.info(f'run {cmd}, return code {rc.returncode}')
+					logging.info(f'run {cmd_process[0]}, return code {rc.returncode}')
+				cmd_process = None
 
 	def register(self, reactor):
-		reactor.register_timeout_handler(self.timeout_handler)
+		reactor.register_idle_handler(self.check_command_idle_handler)
+		reactor.register_idle_handler(self.idle_handler)
 		reactor.register(self.capture_pd, self)
 
 	def start(self):
+		assert self.state == None, "start must only be called once"
 		# start reading data
-		size, data = self.capture.read()
+		size, _ = self.capture.read()
 		if size:
-			self.queue.append(data)
+			logging.warning(f'initial data discarded ({size} bytes)')
 
-	def timeout_handler(self):
+		self.state = LoopbackState.LISTENING
-		if self.playback and self.capture_started:
+
-			if self.last_capture_event:
+	def set_state(self, new_state: LoopbackState) -> LoopbackState:
-				if datetime.now() - self.last_capture_event > timedelta(seconds=2):
+		'''Implement the Loopback state as a state machine'''
-					logging.info('timeout - closing playback device')
+
+		if self.state == new_state:
+			return self.state
+
+		logging.info(f'{self.state} -> {new_state}')
+		self.last_state_change = datetime.now()
+
+		if new_state == LoopbackState.LISTENING:
+			if self.state == LoopbackState.PLAYING:
 				self.playback.close()
 				self.playback = None
-					self.capture_started = None
+				self.last_capture_event = None
 				if self.volume_handler:
 					self.volume_handler.stop()
 				self.run_command(self.run_after_stop)
+			elif self.state == LoopbackState.DEVICE_BUSY:
+				pass
+		elif new_state == LoopbackState.PLAYING:
+			if self.state == LoopbackState.LISTENING:
+				try:
+					self.run_command(self.run_before_start)
+					self.playback = PCM(**self.playback_args)
+					period_size = self.playback.info()['period_size']
+					logging.info(f'opened playback device with period_size {period_size}')
+					if self.volume_handler:
+						self.volume_handler.start()
+				except ALSAAudioError as e:
+					logging.warning('opening PCM playback device failed: %s', e)
+					self.state = LoopbackState.DEVICE_BUSY
+					return self.state
+			elif self.state == LoopbackState.DEVICE_BUSY:
+				# Only try to reopen the device after the grace period
+				if datetime.now() - self.last_state_change > timedelta(seconds=open_grace_period):
+					return self.set_state(LoopbackState.PLAYING)
+		elif new_state == LoopbackState.DEVICE_BUSY:
+			logging.error(f'{new_state} is internal and cannot be set directly')
+
+		self.state = new_state
+		return self.state
+
+	def idle_handler(self):
+		if self.state == LoopbackState.PLAYING:
+			if datetime.now() - self.last_capture_event > timedelta(seconds=idle_close_timeout):
+				logging.info('timeout - closing playback device')
+				self.set_state(LoopbackState.LISTENING)
 			return
 
-		self.waitBeforeOpen = False
-
-		if not self.run_after_stop_did_run and not self.playback:
-			if self.volume_handler:
-				self.volume_handler.stop()
-			self.run_command(self.run_after_stop)
-			self.run_after_stop_did_run = True
-
 	def pop(self):
 		if len(self.queue):
 			return self.queue.pop()
@@ -141,6 +197,15 @@ class Loopback(object):
 			return None
 
 	def handle_capture_event(self, eventmask, name):
+
+		if eventmask & select.POLLERR == select.POLLERR:
+			# This is typically an underrun caused by the external command being run synchronously
+   			# (on the same thread)
+			state = self.capture.state()
+			if state == PCM_STATE_XRUN:
+				self.capture.drop()
+				logging.warning(f'POLLERR for capture device: {state_names[state]}')
+
 		'''called when data is available for reading'''
 		self.last_capture_event = datetime.now()
 		size, data = self.capture.read()
@@ -148,65 +213,37 @@ class Loopback(object):
 			logging.warning(f'capture event but no data')
 			return False
 
-		energy = self.compute_energy(data)
-		logging.debug(f'energy: {energy}')
-
 		# the usecase is a USB capture device where we get perfect silence when it's idle
+		# compute the energy and go back to LISTENING if nothing is captured
+		energy = self.compute_energy(data)
 		if energy == 0:
-			self.silent_periods = self.silent_periods + 1
+			if self.silence_start is None:
+				self.silence_start = datetime.now()
 
-			# turn off playback after two seconds of silence
+			# turn off playback after idle_close_timeout when there was only silence
-			# 2 channels * 2 seconds * 2 bytes per sample
+			if datetime.now() - self.silence_start > timedelta(seconds=idle_close_timeout):
-			fps = self.playback_args['rate']  * 8 // (self.playback_args['periodsize'] * self.playback_args['periods'])
+				logging.debug('silence')
-
+				self.set_state(LoopbackState.LISTENING)
-			logging.debug(f'{self.silent_periods} of {fps} silent periods: {self.playback}')
+				return False
-
-			if self.silent_periods > fps and self.playback:
-				logging.info(f'closing playback due to silence')
-				self.playback.close()
-				self.playback = None
-				if self.volume_handler:
-					self.volume_handler.stop()
-				self.run_command(self.run_after_stop)
-				self.run_after_stop_did_run = True
-
-			if not self.playback:
-				return
 		else:
-			self.silent_periods = 0
+			self.silence_start = None
 
-		if not self.playback:
+		loop_state = self.set_state(LoopbackState.PLAYING)
-			if self.waitBeforeOpen:
+		if loop_state != LoopbackState.PLAYING:
-				return False
+			logging.warning(f'setting state PLAYING failed: {str(loop_state)}')
-			try:
-				if self.volume_handler:
-					self.volume_handler.start()
-				self.run_command(self.run_before_start)
-				self.playback = PCM(**self.playback_args)
-				self.period_size = self.playback.info()['period_size']
-				logging.info(f'opened playback device with period_size {self.period_size}')
-			except ALSAAudioError as e:
-				logging.info('opening PCM playback device failed: %s', e)
-				self.waitBeforeOpen = True
 			return False
 
-			self.capture_started = datetime.now()
-			logging.info(f'{self.playback} capture started: {self.capture_started}')
-
-		self.queue.append(data)
-
-		if len(self.queue) <= 2:
-			logging.info(f'buffering: {len(self.queue)}')
-			return False
-
-		try:
-			data = self.pop()
 		if data:
 			space = self.playback.avail()
+			if space > 0:
 				written = self.playback.write(data)
-				logging.debug(f'wrote {written} bytes while space was {space}')
+				if written == -errno.EPIPE:
-		except ALSAAudioError:
+					logging.warning('playback underrun')
-			logging.error('underrun', exc_info=1)
+					self.playback.write(data)
+				silence = ''
+				if energy == 0:
+					silence = '(silence)'
+				logging.debug(f'wrote {written} bytes while space was {space} {silence}')
 
 		return True
 
@@ -239,11 +276,13 @@ class VolumeForwarder(object):
 	def start(self):
 		self.active = True
 		if self.volume:
+			logging.info(f'start volume is {self.volume}')
 			self.volume = playback_control.setvolume(self.volume)
 
 	def stop(self):
 		self.active = False
 		self.volume = self.playback_control.getvolume(pcmtype=PCM_CAPTURE)[0]
+		logging.info(f'stop volume is {self.volume}')
 
 	def __call__(self, fd, eventmask, name):
 		if not self.active:
@@ -263,7 +302,7 @@ class Reactor(object):
 	def __init__(self):
 		self.poll = select.poll()
 		self.descriptors = {}
-		self.timeout_handlers = set()
+		self.idle_handlers = set()
 
 	def register(self, polldescriptor, callable):
 		logging.debug(f'registered {polldescriptor.name}: {poll_desc(polldescriptor.mask)}')
@@ -274,17 +313,17 @@ class Reactor(object):
 		self.poll.unregister(polldescriptor.fd)
 		del self.descriptors[polldescriptor.fd]
 
-	def register_timeout_handler(self, callable):
+	def register_idle_handler(self, callable):
-		self.timeout_handlers.add(callable)
+		self.idle_handlers.add(callable)
 
-	def unregister_timeout_handler(self, callable):
+	def unregister_idle_handler(self, callable):
-		self.timeout_handlers.remove(callable)
+		self.idle_handlers.remove(callable)
 
 	def run(self):
 		last_timeout_ev = datetime.now()
 		while True:
 			# poll for a bit, then send a timeout to registered handlers
-			events = self.poll.poll(0.25)
+			events = self.poll.poll(idle_timer_period)
 			for fd, ev in events:
 				polldescriptor, handler = self.descriptors[fd]
 
@@ -293,8 +332,8 @@ class Reactor(object):
 
 				handler(fd, ev, polldescriptor.name)
 
-			if datetime.now() - last_timeout_ev > timedelta(seconds=0.25):
+			if datetime.now() - last_timeout_ev > timedelta(seconds=idle_timer_period):
-				for t in self.timeout_handlers:
+				for t in self.idle_handlers:
 					t()
 				last_timeout_ev = datetime.now()
 
@@ -344,6 +383,16 @@ if __name__ == '__main__':
 		'periods': args.periods
 	}
 
+	capture_args = {
+		'type': PCM_CAPTURE,
+		'mode': PCM_NONBLOCK,
+		'device': args.input,
+		'rate': args.rate,
+		'channels': args.channels,
+		'periodsize': args.periodsize,
+		'periods': args.periods
+	}
+
 	reactor = Reactor()
 
 	# If args.input_mixer and args.output_mixer are set, forward the capture volume to the playback volume.
@@ -378,8 +427,7 @@ if __name__ == '__main__':
 			sys.exit(1)
 
 		if input_mixer_card is None:
-			capture = PCM(type=PCM_CAPTURE, mode=PCM_NONBLOCK, device=args.input, rate=args.rate,
+			capture = PCM(**capture_args)
-				channels=args.channels, periodsize=args.periodsize, periods=args.periods)
 			input_mixer_card = capture.info()['card_no']
 
 		if output_mixer_card is None:

src/alsaaudio.c

@@ -106,6 +106,9 @@ typedef struct {
 
 	snd_pcm_t *handle;
 
+	// Debug logging
+	int state;
+
 	// Configurable parameters
 	unsigned int channels;
 	unsigned int rate;
@@ -360,6 +363,40 @@ alsapcm_list(PyObject *self, PyObject *args, PyObject *kwds)
 	return result;
 }
 
+const char* state_name(int state) {
+	switch (state) {
+		case SND_PCM_STATE_OPEN:
+			return "SND_PCM_STATE_OPEN";
+		case SND_PCM_STATE_SETUP:
+			return "SND_PCM_STATE_SETUP";
+		case SND_PCM_STATE_PREPARED:
+			return "SND_PCM_STATE_PREPARED";
+		case SND_PCM_STATE_RUNNING:
+			return "SND_PCM_STATE_RUNNING";
+		case SND_PCM_STATE_XRUN:
+			return "SND_PCM_STATE_XRUN";
+		case SND_PCM_STATE_DISCONNECTED:
+			return "SND_PCM_STATE_DISCONNECTED";
+		case SND_PCM_STATE_DRAINING:
+			return "SND_PCM_STATE_DRAINING";
+		case SND_PCM_STATE_PAUSED:
+			return "SND_PCM_STATE_PAUSED";
+		case SND_PCM_STATE_SUSPENDED:
+			return "SND_PCM_STATE_SUSPENDED";
+		default:
+			return "invalid PCM state";
+	}
+}
+
+void print_state(alsapcm_t *self)
+{
+	int state = snd_pcm_state(self->handle);
+	if (state != self->state) {
+		printf("[%s %s] %s->%s\n", self->cardname, self->pcmtype == SND_PCM_STREAM_CAPTURE ? "capture" : "playback", state_name(self->state), state_name(state));
+		self->state = state;
+	}
+}
+
 static int alsapcm_setup(alsapcm_t *self)
 {
 	int res,dir;
@@ -405,6 +442,8 @@ static int alsapcm_setup(alsapcm_t *self)
 
 	self->framesize = self->channels * snd_pcm_format_physical_width(self->format)/8;
 
+	self->state = snd_pcm_state(self->handle);
+
 	return res;
 }
 
@@ -1347,7 +1386,6 @@ static PyObject *
 alsapcm_read(alsapcm_t *self, PyObject *args)
 {
 	snd_pcm_state_t state;
-	int res;
 	int size = self->framesize * self->periodsize;
 	int sizeout = 0;
 	PyObject *buffer_obj, *tuple_obj, *res_obj;
@@ -1380,11 +1418,19 @@ alsapcm_read(alsapcm_t *self, PyObject *args)
 	buffer = PyBytes_AS_STRING(buffer_obj);
 #endif
 
+	int res = 0;
+
+	print_state(self);
+
 	// After drop() and drain(), we need to prepare the stream again.
 	// Note that fresh streams are already prepared by snd_pcm_hw_params().
 	state = snd_pcm_state(self->handle);
-	if ((state != SND_PCM_STATE_SETUP) ||
+	if (state == SND_PCM_STATE_SETUP) {
-		!(res = snd_pcm_prepare(self->handle))) {
+		res = snd_pcm_prepare(self->handle);
+		printf("[%s] called snd_pcm_prepare: %d\n", self->cardname, res);
+	}
+
+	if (res == 0) {
 
 		Py_BEGIN_ALLOW_THREADS
 		res = snd_pcm_readi(self->handle, buffer, self->periodsize);
@@ -1488,6 +1534,8 @@ static PyObject *alsapcm_write(alsapcm_t *self, PyObject *args)
 		return NULL;
 	}
 
+	print_state(self);
+
 	int res;
 	// After drop() and drain(), we need to prepare the stream again.
 	// Note that fresh streams are already prepared by snd_pcm_hw_params().
@@ -1577,6 +1625,9 @@ static PyObject *alsapcm_pause(alsapcm_t *self, PyObject *args)
 
 		return NULL;
 	}
+
+	print_state(self);
+
 	return PyLong_FromLong(res);
 }
 
@@ -1599,6 +1650,8 @@ static PyObject *alsapcm_drop(alsapcm_t *self)
 		return NULL;
 	}
 
+	print_state(self);
+
 	return PyLong_FromLong(res);
 }
 
@@ -1623,6 +1676,8 @@ static PyObject *alsapcm_drain(alsapcm_t *self)
 		return NULL;
 	}
 
+	print_state(self);
+
 	return PyLong_FromLong(res);
 }