audio: Wait for samples on the emulated DSP side to avoid desyncs

Waiting on the host side is inaccurate and leads to desyncs in the event of the sink missing a deadline that require stalls to fix. By waiting for the sink to have space before even starting rendering such desyncs can be avoided.

src/audio_core/sink/sink_stream.cpp

@@ -205,6 +205,10 @@ void SinkStream::ProcessAudioOutAndRender(std::span<s16> output_buffer, std::siz
     // If we're paused or going to shut down, we don't want to consume buffers as coretiming is
     // paused and we'll desync, so just play silence.
     if (system.IsPaused() || system.IsShuttingDown()) {
+        if (system.IsShuttingDown()) {
+            release_cv.notify_one();
+        }
+
         static constexpr std::array<s16, 6> silence{};
         for (size_t i = frames_written; i < num_frames; i++) {
             std::memcpy(&output_buffer[i * frame_size], &silence[0], frame_size_bytes);
@@ -240,6 +244,12 @@ void SinkStream::ProcessAudioOutAndRender(std::span<s16> output_buffer, std::siz
             }
             // Successfully dequeued a new buffer.
             queued_buffers--;
+
+            {
+                std::unique_lock lk{release_mutex};
+            }
+
+            release_cv.notify_one();
         }
 
         // Get the minimum frames available between the currently playing buffer, and the
@@ -303,4 +313,9 @@ u64 SinkStream::GetExpectedPlayedSampleCount() {
     return std::min<u64>(exp_played_sample_count, max_played_sample_count);
 }
 
+void SinkStream::WaitFreeSpace() {
+    std::unique_lock lk{release_mutex};
+    release_cv.wait(lk, [this]() { return queued_buffers < max_queue_size || system.IsShuttingDown(); });
+}
+
 } // namespace AudioCore::Sink

src/audio_core/sink/sink_stream.h

@@ -16,6 +16,7 @@
 #include "common/reader_writer_queue.h"
 #include "common/ring_buffer.h"
 #include "common/thread.h"
+#include "common/polyfill_thread.h"
 
 namespace Core {
 class System;
@@ -219,6 +220,11 @@ public:
      */
     u64 GetExpectedPlayedSampleCount();
 
+    /**
+     * Waits for free space in the sample ring buffer
+     */
+    void WaitFreeSpace();
+
 protected:
     /// Core system
     Core::System& system;
@@ -258,6 +264,9 @@ private:
     f32 system_volume{1.0f};
     /// Set via IAudioDevice service calls
     f32 device_volume{1.0f};
+    /// Signalled when ring buffer entries are consumed
+    std::condition_variable release_cv;
+    std::mutex release_mutex;
     std::mutex stall_guard;
     std::unique_lock<std::mutex> stalled_lock;
 };