audio/out: make ao_request_reload() idempotent

This is what you would expect. Before this commit, each
ao_request_reload() call would just queue a reload command, and then
recreate the AO for the number of times the function was called.

Instead of sending a command, introduce some sort of event retrieval
mechanism. At least for the reload case, use atomics, because we're too
lazy to setup an extra mutex.

audio/out/ao.c

@@ -397,6 +397,22 @@ bool ao_eof_reached(struct ao *ao)
     return ao->api->get_eof ? ao->api->get_eof(ao) : true;
 }
 
+// Query the AO_EVENT_*s as requested by the events parameter, and return them.
+int ao_query_and_reset_events(struct ao *ao, int events)
+{
+    int actual_events = 0;
+    if (atomic_load(&ao->request_reload)) // don't need to reset it
+        actual_events |= AO_EVENT_RELOAD;
+    return actual_events & events;
+}
+
+// Request that the player core destroys and recreates the AO.
+void ao_request_reload(struct ao *ao)
+{
+    atomic_store(&ao->request_reload, true);
+    mp_input_wakeup(ao->input_ctx);
+}
+
 bool ao_chmap_sel_adjust(struct ao *ao, const struct mp_chmap_sel *s,
                          struct mp_chmap *map)
 {
@@ -409,13 +425,6 @@ bool ao_chmap_sel_get_def(struct ao *ao, const struct mp_chmap_sel *s,
     return mp_chmap_sel_get_def(s, map, num);
 }
 
-// Request that the player core destroys and recreates the AO.
-void ao_request_reload(struct ao *ao)
-{
-    const char *cmd[] = {"ao_reload", NULL};
-    mp_input_run_cmd(ao->input_ctx, cmd);
-}
-
 // --- The following functions just return immutable information.
 
 void ao_get_format(struct ao *ao, struct mp_audio *format)

audio/out/ao.h

@@ -46,6 +46,10 @@ enum aocontrol {
 // data might be written again, instead of closing the AO.
 #define AOPLAY_FINAL_CHUNK 1
 
+enum {
+    AO_EVENT_RELOAD = 1,
+};
+
 typedef struct ao_control_vol {
     float left;
     float right;
@@ -85,6 +89,8 @@ void ao_pause(struct ao *ao);
 void ao_resume(struct ao *ao);
 void ao_drain(struct ao *ao);
 bool ao_eof_reached(struct ao *ao);
+int ao_query_and_reset_events(struct ao *ao, int events);
+void ao_request_reload(struct ao *ao);
 
 struct ao_device_list *ao_get_device_list(struct mpv_global *global);
 void ao_print_devices(struct mpv_global *global, struct mp_log *log);

audio/out/internal.h

@@ -22,6 +22,7 @@
 #include <stdbool.h>
 #include <pthread.h>
 
+#include "osdep/atomics.h"
 #include "audio/out/ao.h"
 
 /* global data used by ao.c and ao drivers */
@@ -55,6 +56,8 @@ struct ao {
     // Used during init: if init fails, redirect to this ao
     char *redirect;
 
+    atomic_bool request_reload;
+
     int buffer;
     double def_buffer;
     void *api_priv;
@@ -186,8 +189,6 @@ bool ao_chmap_sel_adjust(struct ao *ao, const struct mp_chmap_sel *s,
 bool ao_chmap_sel_get_def(struct ao *ao, const struct mp_chmap_sel *s,
                           struct mp_chmap *map, int num);
 
-void ao_request_reload(struct ao *ao);
-
 // Add a deep copy of e to the list.
 // Call from ao_driver->list_devs callback only.
 void ao_device_list_add(struct ao_device_list *list, struct ao *ao,

player/audio.c

@@ -434,6 +434,11 @@ static void do_fill_audio_out_buffers(struct MPContext *mpctx, double endpts)
     struct MPOpts *opts = mpctx->opts;
     struct dec_audio *d_audio = mpctx->d_audio;
 
+    if (mpctx->ao && ao_query_and_reset_events(mpctx->ao, AO_EVENT_RELOAD)) {
+        ao_reset(mpctx->ao);
+        uninit_audio_out(mpctx);
+    }
+
     if (!d_audio)
         return;
 

player/command.c

@@ -1462,12 +1462,7 @@ static void reload_audio_output(struct MPContext *mpctx)
 {
     if (!mpctx->ao)
         return;
-    ao_reset(mpctx->ao);
+    ao_request_reload(mpctx->ao);
-    uninit_audio_out(mpctx);
-    // This normally recreates the AO, although there are situations when AO
-    // creation is delayed; for example if there are no audio packets around,
-    // and the audio format is yet unknown.
-    reinit_audio_chain(mpctx);
 }
 
 static int mp_property_audio_device(void *ctx, struct m_property *prop,