System: Reset throttler when audio buffers underflow

Should hopefully reduce the chances of the audio source ending up out of
phase from the emulation when vsync is disabled.

src/common/audio_stream.cpp

@@ -170,12 +170,14 @@ void AudioStream::ReadFrames(SampleType* samples, u32 num_frames, bool apply_vol
       }
 
       Log_DevPrintf("Audio buffer underflow, resampled %u frames to %u", samples_copied / m_channels, num_frames);
+      m_underflow_flag.store(true);
     }
     else
     {
       // read nothing, so zero-fill
       std::memset(samples, 0, sizeof(SampleType) * total_samples);
       Log_DevPrintf("Audio buffer underflow with no samples, added %u frames silence", num_frames);
+      m_underflow_flag.store(true);
     }
   }
 
@@ -218,4 +220,5 @@ void AudioStream::EmptyBuffers()
 {
   std::unique_lock<std::mutex> lock(m_buffer_mutex);
   m_buffer.Clear();
+  m_underflow_flag.store(false);
 }

src/common/audio_stream.h

@@ -1,6 +1,7 @@
 #pragma once
 #include "fifo_queue.h"
 #include "types.h"
+#include <atomic>
 #include <condition_variable>
 #include <memory>
 #include <mutex>
@@ -45,6 +46,12 @@ public:
   void WriteFrames(const SampleType* frames, u32 num_frames);
   void EndWrite(u32 num_frames);
 
+  bool DidUnderflow()
+  {
+    bool expected = true;
+    return m_underflow_flag.compare_exchange_strong(expected, false);
+  }
+
   static std::unique_ptr<AudioStream> CreateNullAudioStream();
 
   // Latency computation - returns values in seconds
@@ -84,6 +91,7 @@ private:
   mutable std::mutex m_buffer_mutex;
   std::condition_variable m_buffer_draining_cv;
   std::vector<SampleType> m_resample_buffer;
+  std::atomic_bool m_underflow_flag{false};
   u32 m_max_samples = 0;
 
   bool m_output_paused = true;