From: Andre Noll <maan@systemlinux.org>
Date: Thu, 18 Aug 2011 13:19:41 +0000 (+0200)
Subject: Merge branch 't/alsa_poll_fd'
X-Git-Tag: v0.4.8~5
X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=commitdiff_plain;h=9fe520149ef6bbc6bed4ee538bd2310af9d6a2cd;hp=c6991cf20bdfe7426e536f7020a0ff741df84dee

Merge branch 't/alsa_poll_fd'
---

diff --git a/NEWS b/NEWS
index 40c30bf9..05c866b4 100644
--- a/NEWS
+++ b/NEWS
@@ -20,6 +20,7 @@ are the highlights of this release.
 	  tarballs. This reduces the size of the tarballs but requires
 	  gengetopt to build the tarball.
 	- Compiles cleanly also with llvm/clang.
+	- The alsa writer used poll fds instead of computing timeouts.
 	- Corrupt mp3 files are handled more gracefully.
 	- sched: Optimized zero timeouts.
 	- vss timeout cleanups.
diff --git a/alsa_write.c b/alsa_write.c
index 5965159e..047e88f2 100644
--- a/alsa_write.c
+++ b/alsa_write.c
@@ -52,6 +52,8 @@ struct private_alsa_write_data {
 	 */
 	unsigned channels;
 	struct timeval drain_barrier;
+	/* File descriptor for select(). */
+	int poll_fd;
 };
 
 static snd_pcm_format_t get_alsa_pcm_format(enum sample_format sf)
@@ -143,11 +145,13 @@ static int alsa_init(struct private_alsa_write_data *pad,
 
 static void alsa_write_pre_select(struct sched *s, struct task *t)
 {
+	struct pollfd pfd;
 	struct writer_node *wn = container_of(t, struct writer_node, task);
 	struct private_alsa_write_data *pad = wn->private_data;
-	snd_pcm_sframes_t avail, underrun;
 	int ret = btr_node_status(wn->btrn, wn->min_iqs, BTR_NT_LEAF);
 
+	if (pad)
+		pad->poll_fd = -1;
 	if (ret == 0)
 		return;
 	if (!pad) {
@@ -158,25 +162,14 @@ static void alsa_write_pre_select(struct sched *s, struct task *t)
 		sched_request_barrier_or_min_delay(&pad->drain_barrier, s);
 		return;
 	}
-	/*
-	 * Data is available to be written to the alsa handle.  Compute number
-	 * of milliseconds until next buffer underrun would occur.
-	 *
-	 * snd_pcm_avail_update() updates the current available count of
-	 * samples for writing.  It is a light method to obtain current stream
-	 * position, because it does not require the user <-> kernel context
-	 * switch, but the value is less accurate, because ring buffer pointers
-	 * are updated in kernel drivers only when an interrupt occurs.
-	 */
-	avail = snd_pcm_avail_update(pad->handle);
-	if (avail < 0)
-		avail = 0;
-	underrun = (pad->buffer_frames - avail) * pad->buffer_time
-		/ pad->buffer_frames / 1000;
-	if (underrun < 50)
-		underrun = 50;
-	underrun -= 50;
-	sched_request_timeout_ms(underrun, s);
+	ret = snd_pcm_poll_descriptors(pad->handle, &pfd, 1);
+	if (ret < 0) {
+		PARA_ERROR_LOG("%s\n", snd_strerror(-ret));
+		t->error = -E_ALSA_POLL_FDS;
+		return;
+	}
+	pad->poll_fd = pfd.fd;
+	para_fd_set(pfd.fd, &s->rfds, &s->max_fileno);
 }
 
 static void alsa_close(struct writer_node *wn)
@@ -255,6 +248,8 @@ again:
 		wn->min_iqs = pad->bytes_per_frame;
 		goto again;
 	}
+	if (pad->poll_fd >= 0 && !FD_ISSET(pad->poll_fd, &s->rfds))
+		return;
 	frames = bytes / pad->bytes_per_frame;
 	frames = snd_pcm_writei(pad->handle, data, frames);
 	if (frames == 0 || frames == -EAGAIN)
diff --git a/error.h b/error.h
index b8078770..da0efc47 100644
--- a/error.h
+++ b/error.h
@@ -441,6 +441,7 @@ extern const char **para_errlist[];
 	PARA_ERROR(SET_RATE, "snd_pcm_hw_params_set_rate_near failed"), \
 	PARA_ERROR(START_THRESHOLD, "snd_pcm_sw_params_set_start_threshold() failed"), \
 	PARA_ERROR(STOP_THRESHOLD, "snd_pcm_sw_params_set_stop_threshold() failed"), \
+	PARA_ERROR(ALSA_POLL_FDS, "could not get alsa poll fd"), \
 
 
 #define WRITE_COMMON_ERRORS \