audio: introduce ao_read_data_nonblocking()

This behaves similar to ao_read_data() but does not block and may return
partial data.

2 files changed, 38 insertions, 10 deletions

diff --git a/audio/out/buffer.c b/audio/out/buffer.c
index 4ab3e405bc..a5520f3a21 100644
--- a/audio/out/buffer.c
+++ b/audio/out/buffer.c
@@ -170,6 +170,27 @@ static int read_buffer(struct ao *ao, void **data, int samples, bool *eof)
     return pos;
 }
 
+static int ao_read_data_unlocked(struct ao *ao, void **data, int samples,
+                                 int64_t out_time_ns)
+{
+    struct buffer_state *p = ao->buffer_state;
+    assert(!ao->driver->write);
+
+    int pos = read_buffer(ao, data, samples, &(bool){0});
+
+    if (pos > 0)
+        p->end_time_ns = out_time_ns;
+
+    if (pos < samples && p->playing && !p->paused) {
+        p->playing = false;
+        ao->wakeup_cb(ao->wakeup_ctx);
+        // For ao_drain().
+        mp_cond_broadcast(&p->wakeup);
+    }
+
+    return pos;
+}
+
 // Read the given amount of samples in the user-provided data buffer. Returns
 // the number of samples copied. If there is not enough data (buffer underrun
 // or EOF), return the number of samples that could be copied, and fill the
@@ -181,21 +202,26 @@ static int read_buffer(struct ao *ao, void **data, int samples, bool *eof)
 int ao_read_data(struct ao *ao, void **data, int samples, int64_t out_time_ns)
 {
     struct buffer_state *p = ao->buffer_state;
-    assert(!ao->driver->write);
 
     mp_mutex_lock(&p->lock);
 
-    int pos = read_buffer(ao, data, samples, &(bool){0});
+    int pos = ao_read_data_unlocked(ao, data, samples, out_time_ns);
 
-    if (pos > 0)
-        p->end_time_ns = out_time_ns;
+    mp_mutex_unlock(&p->lock);
 
-    if (pos < samples && p->playing && !p->paused) {
-        p->playing = false;
-        ao->wakeup_cb(ao->wakeup_ctx);
-        // For ao_drain().
-        mp_cond_broadcast(&p->wakeup);
-    }
+    return pos;
+}
+
+// Like ao_read_data() but does not block and also may return partial data.
+// Callers have to check the return value.
+int ao_read_data_nonblocking(struct ao *ao, void **data, int samples, int64_t out_time_ns)
+{
+    struct buffer_state *p = ao->buffer_state;
+
+    if (mp_mutex_trylock(&p->lock))
+            return 0;
+
+    int pos = ao_read_data_unlocked(ao, data, samples, out_time_ns);
 
     mp_mutex_unlock(&p->lock);
 
diff --git a/audio/out/internal.h b/audio/out/internal.h
index 1ae92a8b92..7951b3861e 100644
--- a/audio/out/internal.h
+++ b/audio/out/internal.h
@@ -200,6 +200,8 @@ struct ao_driver {
 // These functions can be called by AOs.
 
 int ao_read_data(struct ao *ao, void **data, int samples, int64_t out_time_ns);
+MP_WARN_UNUSED_RESULT
+int ao_read_data_nonblocking(struct ao *ao, void **data, int samples, int64_t out_time_ns);
 
 bool ao_chmap_sel_adjust(struct ao *ao, const struct mp_chmap_sel *s,
                          struct mp_chmap *map);