From 26ec62714c06f061269d42a742bff2713e789068 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@duempel.org>
Date: Thu, 5 Jan 2012 00:48:54 +0100
Subject: [PATCH] mixer/alsa: listen for external volume changes
Use libasound's polling functions, implement a bridge to GSource /
GPollFD and send idle events to clients when an external program
changes the ALSA mixer volume.
---
NEWS | 2 +
src/mixer/alsa_mixer_plugin.c | 181 +++++++++++++++++++++++++++++++++-
2 files changed, 182 insertions(+), 1 deletion(-)
diff --git a/NEWS b/NEWS
index f5b8fb203..2d3f8f1a4 100644
--- a/NEWS
+++ b/NEWS
@@ -22,6 +22,8 @@ ver 0.17 (2011/??/??)
- shout: add possibility to set url
- roar: new output plugin for RoarAudio
- winmm: fail if wrong device specified instead of using default device
+* mixer:
+ - alsa: listen for external volume changes
* playlist:
- allow references to songs outside the music directory
* state_file: add option "restore_paused"
diff --git a/src/mixer/alsa_mixer_plugin.c b/src/mixer/alsa_mixer_plugin.c
index a6e6f364e..22e4e22bd 100644
--- a/src/mixer/alsa_mixer_plugin.c
+++ b/src/mixer/alsa_mixer_plugin.c
@@ -20,6 +20,7 @@
#include "config.h"
#include "mixer_api.h"
#include "output_api.h"
+#include "event_pipe.h"
#include <glib.h>
#include <alsa/asoundlib.h>
@@ -28,6 +29,15 @@
#define VOLUME_MIXER_ALSA_CONTROL_DEFAULT "PCM"
#define VOLUME_MIXER_ALSA_INDEX_DEFAULT 0
+struct alsa_mixer_source {
+ GSource source;
+
+ snd_mixer_t *mixer;
+
+ /** a linked list of all registered GPollFD objects */
+ GSList *fds;
+};
+
struct alsa_mixer {
/** the base mixer class */
struct mixer base;
@@ -41,6 +51,8 @@ struct alsa_mixer {
long volume_min;
long volume_max;
int volume_set;
+
+ struct alsa_mixer_source *source;
};
/**
@@ -52,6 +64,161 @@ alsa_mixer_quark(void)
return g_quark_from_static_string("alsa_mixer");
}
+/*
+ * GSource helper functions
+ *
+ */
+
+static GSList **
+find_fd(GSList **list_r, int fd)
+{
+ while (true) {
+ GSList *list = *list_r;
+ if (list == NULL)
+ return NULL;
+
+ GPollFD *p = list->data;
+ if (p->fd == fd)
+ return list_r;
+
+ list_r = &list->next;
+ }
+}
+
+static void
+alsa_mixer_update_fd(struct alsa_mixer_source *source, const struct pollfd *p,
+ GSList **old_r)
+{
+ GSList **found_r = find_fd(old_r, p->fd);
+ if (found_r == NULL) {
+ /* new fd */
+ GPollFD *q = g_new(GPollFD, 1);
+ q->fd = p->fd;
+ q->events = p->events;
+ g_source_add_poll(&source->source, q);
+ source->fds = g_slist_prepend(source->fds, q);
+ return;
+ }
+
+ GSList *found = *found_r;
+ *found_r = found->next;
+
+ GPollFD *q = found->data;
+ if (q->events != p->events) {
+ /* refresh events */
+ g_source_remove_poll(&source->source, q);
+ q->events = p->events;
+ g_source_add_poll(&source->source, q);
+ }
+
+ found->next = source->fds;
+ source->fds = found;
+}
+
+static void
+alsa_mixer_update_fds(struct alsa_mixer_source *source)
+{
+ int count = snd_mixer_poll_descriptors_count(source->mixer);
+ if (count < 0)
+ count = 0;
+
+ struct pollfd *pfds = g_new(struct pollfd, count);
+ count = snd_mixer_poll_descriptors(source->mixer, pfds, count);
+ if (count < 0)
+ count = 0;
+
+ GSList *old = source->fds;
+ source->fds = NULL;
+
+ for (int i = 0; i < count; ++i)
+ alsa_mixer_update_fd(source, &pfds[i], &old);
+ g_free(pfds);
+
+ for (; old != NULL; old = old->next) {
+ GPollFD *q = old->data;
+ g_source_remove_poll(&source->source, q);
+ g_free(q);
+ }
+
+ g_slist_free(old);
+}
+
+/*
+ * GSource methods
+ *
+ */
+
+static gboolean
+alsa_mixer_source_prepare(GSource *_source, G_GNUC_UNUSED gint *timeout_r)
+{
+ struct alsa_mixer_source *source = (struct alsa_mixer_source *)_source;
+ alsa_mixer_update_fds(source);
+
+ return false;
+}
+
+static gboolean
+alsa_mixer_source_check(GSource *_source)
+{
+ struct alsa_mixer_source *source = (struct alsa_mixer_source *)_source;
+
+ for (const GSList *i = source->fds; i != NULL; i = i->next) {
+ const GPollFD *poll_fd = i->data;
+ if (poll_fd->revents != 0)
+ return true;
+ }
+
+ return false;
+}
+
+static gboolean
+alsa_mixer_source_dispatch(GSource *_source,
+ G_GNUC_UNUSED GSourceFunc callback,
+ G_GNUC_UNUSED gpointer user_data)
+{
+ struct alsa_mixer_source *source = (struct alsa_mixer_source *)_source;
+
+ snd_mixer_handle_events(source->mixer);
+ return true;
+}
+
+static void
+alsa_mixer_source_finalize(GSource *_source)
+{
+ struct alsa_mixer_source *source = (struct alsa_mixer_source *)_source;
+
+ for (GSList *i = source->fds; i != NULL; i = i->next)
+ g_free(i->data);
+
+ g_slist_free(source->fds);
+}
+
+static GSourceFuncs alsa_mixer_source_funcs = {
+ .prepare = alsa_mixer_source_prepare,
+ .check = alsa_mixer_source_check,
+ .dispatch = alsa_mixer_source_dispatch,
+ .finalize = alsa_mixer_source_finalize,
+};
+
+/*
+ * libasound callbacks
+ *
+ */
+
+static int
+alsa_mixer_elem_callback(G_GNUC_UNUSED snd_mixer_elem_t *elem, unsigned mask)
+{
+ if (mask & SND_CTL_EVENT_MASK_VALUE)
+ event_pipe_emit(PIPE_EVENT_MIXER);
+
+ return 0;
+}
+
+/*
+ * mixer_plugin methods
+ *
+ */
+
static struct mixer *
alsa_mixer_init(G_GNUC_UNUSED void *ao, const struct config_param *param,
G_GNUC_UNUSED GError **error_r)
@@ -95,7 +262,6 @@ alsa_mixer_lookup_elem(snd_mixer_t *handle, const char *name, unsigned idx)
}
return NULL;
-
}
static bool
@@ -135,6 +301,15 @@ alsa_mixer_setup(struct alsa_mixer *am, GError **error_r)
snd_mixer_selem_get_playback_volume_range(am->elem,
&am->volume_min,
&am->volume_max);
+
+ snd_mixer_elem_set_callback(am->elem, alsa_mixer_elem_callback);
+
+ am->source = (struct alsa_mixer_source *)
+ g_source_new(&alsa_mixer_source_funcs, sizeof(*am->source));
+ am->source->mixer = am->handle;
+ am->source->fds = NULL;
+ g_source_attach(&am->source->source, g_main_context_default());
+
return true;
}
@@ -168,6 +343,10 @@ alsa_mixer_close(struct mixer *data)
assert(am->handle != NULL);
+ g_source_destroy(&am->source->source);
+ g_source_unref(&am->source->source);
+
+ snd_mixer_elem_set_callback(am->elem, NULL);
snd_mixer_close(am->handle);
}