From c2a6b6e58307034ad8febd3f7d296c9bd8727ca6 Mon Sep 17 00:00:00 2001
From: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Date: Fri, 5 Aug 2022 20:37:13 +0200
Subject: [PATCH] reshuffle XRUN recovery somewhat

perform it prior to invoking read()/write() if necessary, not right
after a failure event. this makes things more uniform and predictable.

we don't use snd_pcm_recover() any more, as we used it only for the
EPIPE case anyway, which boils down to snd_pcm_prepare() exactly.
handling ESTRPIPE as well might be desirable, but that's a separate
consideration.
---
 alsaaudio.c | 39 ++++++++++++++-------------------------
 1 file changed, 14 insertions(+), 25 deletions(-)

diff --git a/alsaaudio.c b/alsaaudio.c
index f4089b9..d4d9747 100644
--- a/alsaaudio.c
+++ b/alsaaudio.c
@@ -1311,6 +1311,7 @@ alsapcm_setperiodsize(alsapcm_t *self, PyObject *args)
 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;
@@ -1344,14 +1345,13 @@ alsapcm_read(alsapcm_t *self, PyObject *args)
 	buffer = PyBytes_AS_STRING(buffer_obj);
 #endif
 
-	Py_BEGIN_ALLOW_THREADS
-	res = snd_pcm_readi(self->handle, buffer, self->periodsize);
-	if (res == -EPIPE)
-	{
-		/* EPIPE means overrun */
-		snd_pcm_prepare(self->handle);
+	state = snd_pcm_state(self->handle);
+	if ((state != SND_PCM_STATE_XRUN && state != SND_PCM_STATE_SETUP) ||
+		(res = snd_pcm_prepare(self->handle)) >= 0) {
+		Py_BEGIN_ALLOW_THREADS
+		res = snd_pcm_readi(self->handle, buffer, self->periodsize);
+		Py_END_ALLOW_THREADS
 	}
-	Py_END_ALLOW_THREADS
 
 	if (res != -EPIPE)
 	{
@@ -1404,6 +1404,7 @@ alsapcm_read(alsapcm_t *self, PyObject *args)
 
 static PyObject *alsapcm_write(alsapcm_t *self, PyObject *args)
 {
+	snd_pcm_state_t state;
 	int res;
 	int datalen;
 	char *data;
@@ -1435,16 +1436,13 @@ static PyObject *alsapcm_write(alsapcm_t *self, PyObject *args)
 		return NULL;
 	}
 
-	Py_BEGIN_ALLOW_THREADS
-	res = snd_pcm_writei(self->handle, data, datalen/self->framesize);
-	if (res == -EPIPE)
-	{
-		/* EPIPE means underrun */
-		res = snd_pcm_recover(self->handle, res, 1);
-		if (res >= 0)
-			res = snd_pcm_writei(self->handle, data, datalen/self->framesize);
+	state = snd_pcm_state(self->handle);
+	if ((state != SND_PCM_STATE_XRUN && state != SND_PCM_STATE_SETUP) ||
+		(res = snd_pcm_prepare(self->handle)) >= 0) {
+		Py_BEGIN_ALLOW_THREADS
+		res = snd_pcm_writei(self->handle, data, datalen/self->framesize);
+		Py_END_ALLOW_THREADS
 	}
-	Py_END_ALLOW_THREADS
 
 	if (res == -EAGAIN) {
 		rc = PyLong_FromLong(0);
@@ -1507,15 +1505,6 @@ static PyObject *alsapcm_drop(alsapcm_t *self)
 		return NULL;
 	}
 
-	res = snd_pcm_prepare(self->handle);
-	if (res < 0)
-	{
-		PyErr_Format(ALSAAudioError, "%s [%s]", snd_strerror(res),
-					 self->cardname);
-
-		return NULL;
-	}
-
 	return PyLong_FromLong(res);
 }