From cbdd29c403137e2517441c1f66c8547e337aee39 Mon Sep 17 00:00:00 2001
From: Alexandre Ratchov <alex@caoua.org>
Date: Mon, 1 Jul 2019 17:12:00 +0200
Subject: [PATCH] alsa: use (blksz - round) as start threshold.

The threshold making poll() return POLLOUT is one block (according to
alsa library sources). If a poll-based program writes blksz - 1
samples, playback never starts but poll won't return POLLOUT either.
In turn the program deadlocks. The problem could be observed in the
sio_alsa_xrun() routine.
---
 libsndio/sio_alsa.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libsndio/sio_alsa.c b/libsndio/sio_alsa.c
index 615cbed..d8df57f 100644
--- a/libsndio/sio_alsa.c
+++ b/libsndio/sio_alsa.c
@@ -875,7 +875,7 @@ sio_alsa_setpar(struct sio_hdl *sh, struct sio_par *par)
 			return 0;
 		}
 		err = snd_pcm_sw_params_set_start_threshold(hdl->opcm,
-		    oswp, hdl->par.bufsz);
+		    oswp, hdl->par.bufsz - hdl->par.round);
 		if (err < 0) {
 			DALSA("couldn't set play start threshold", err);
 			hdl->sio.eof = 1;