From c5b93022b4fdd15a56f238ad3b9928f2302f4d40 Mon Sep 17 00:00:00 2001
From: awakening <lucidsunlight@yandex.ru>
Date: Sun, 20 Jan 2019 22:20:27 +0700
Subject: [PATCH] Implement audio timing

---
 android/audio/audio_hw.cpp            |  8 ++++++++
 src/anbox/platform/sdl/audio_sink.cpp | 17 ++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/android/audio/audio_hw.cpp b/android/audio/audio_hw.cpp
index f44e73826..39b845669 100644
--- a/android/audio/audio_hw.cpp
+++ b/android/audio/audio_hw.cpp
@@ -180,6 +180,14 @@ static ssize_t out_write(struct audio_stream_out *stream, const void *buffer,
   pthread_mutex_lock(&adev->lock);
   if (out->fd >= 0)
     bytes = write(out->fd, buffer, bytes);
+
+  // wait until session writes the data we sent,
+  // this will block if sink queue is full,
+  // acting as synchronization to time audio
+  int64_t arrived_us;
+  read(out->fd, &arrived_us, sizeof(arrived_us));
+  (void) arrived_us;
+
   pthread_mutex_unlock(&adev->lock);
   return bytes;
 }
diff --git a/src/anbox/platform/sdl/audio_sink.cpp b/src/anbox/platform/sdl/audio_sink.cpp
index 118093de7..480fe1844 100644
--- a/src/anbox/platform/sdl/audio_sink.cpp
+++ b/src/anbox/platform/sdl/audio_sink.cpp
@@ -19,11 +19,12 @@
 #include "anbox/logger.h"
 
 #include <stdexcept>
+#include <time.h>
 
 #include <boost/throw_exception.hpp>
 
 namespace {
-const constexpr size_t max_queue_size{16};
+const constexpr size_t max_queue_size{1};
 }
 
 namespace anbox {
@@ -114,6 +115,20 @@ void AudioSink::write_data(const std::vector<std::uint8_t> &data) {
   }
   graphics::Buffer buffer{data.data(), data.data() + data.size()};
   queue_.push_locked(std::move(buffer), l);
+
+  // Android side is waiting for "confirmation" that data arrived,
+  // if sink queue is full, Android audio thread will be blocked 
+  // untill there's space available in the queue
+  // 
+  // this acts as sychronization to time audio
+  //
+  // at the time of implementation, 
+  // the data we send to Android is not actually used
+  timespec t;
+  clock_gettime(CLOCK_MONOTONIC, &t);
+  int64_t now_us = (t.tv_sec * 1000000000LL + t.tv_nsec) / 1000;
+
+  messenger_->send(reinterpret_cast<char*>(&now_us), sizeof(now_us));
 }
 } // namespace sdl
 } // namespace platform