ao_alsa: reduce spurious wakeups

Apparently this can happen. So actually only return from waiting if ALSA
excplicitly signals that new output is available, or if we are woken up
externally.

1 files changed, 14 insertions, 8 deletions

diff --git a/audio/out/ao_alsa.c b/audio/out/ao_alsa.c
index 6b755a6d5c..081f9efebf 100644
--- a/audio/out/ao_alsa.c
+++ b/audio/out/ao_alsa.c
@@ -712,14 +712,20 @@ static int audio_wait(struct ao *ao, pthread_mutex_t *lock)
     err = snd_pcm_poll_descriptors(p->alsa, fds, num_fds);
     CHECK_ALSA_ERROR("cannot get pollfds");
 
-    int r = ao_wait_poll(ao, fds, num_fds, lock);
-    if (r < 0)
-        return r;
-
-    unsigned short revents;
-    snd_pcm_poll_descriptors_revents(p->alsa, fds, num_fds, &revents);
-    CHECK_ALSA_ERROR("cannot read poll events");
-
+    while (1) {
+        int r = ao_wait_poll(ao, fds, num_fds, lock);
+        if (r)
+            return r;
+
+        unsigned short revents;
+        snd_pcm_poll_descriptors_revents(p->alsa, fds, num_fds, &revents);
+        CHECK_ALSA_ERROR("cannot read poll events");
+
+        if (revents & POLLERR)
+            return -1;
+        if (revents & POLLOUT)
+            return 0;
+    }
     return 0;
 
 alsa_error: