Split AudioIO into two classes

AudioIO.cpp has nearly 6000 lines and needs to be broken up into separate aspects.
The main point of the new split is to better separate the time critical callback code (that runs in the portaudio thread) from the code that interacts with the disk (that runs in the Audio Thread).

src/AudioIO.cpp

@@ -17,6 +17,15 @@
 
 ********************************************************************//**
 
+\class AudioIoCallback
+\brief AudioIoCallback is a class that implements the callback required 
+by PortAudio.  The callback needs to be responsive, has no GUI, and 
+copies data into and out of the sound card buffers.  It also sends data
+to the meters.
+
+
+*//*****************************************************************//**
+
 \class AudioIO
 \brief AudioIO uses the PortAudio library to play and record sound.
 
@@ -487,14 +496,14 @@ wxDEFINE_EVENT(EVT_AUDIOIO_CAPTURE, wxCommandEvent);
 wxDEFINE_EVENT(EVT_AUDIOIO_MONITOR, wxCommandEvent);
 
 // static
-int AudioIO::mNextStreamToken = 0;
-int AudioIO::mCachedPlaybackIndex = -1;
-std::vector<long> AudioIO::mCachedPlaybackRates;
-int AudioIO::mCachedCaptureIndex = -1;
-std::vector<long> AudioIO::mCachedCaptureRates;
-std::vector<long> AudioIO::mCachedSampleRates;
-double AudioIO::mCachedBestRateIn = 0.0;
-double AudioIO::mCachedBestRateOut;
+int AudioIoCallback::mNextStreamToken = 0;
+int AudioIoCallback::mCachedPlaybackIndex = -1;
+std::vector<long> AudioIoCallback::mCachedPlaybackRates;
+int AudioIoCallback::mCachedCaptureIndex = -1;
+std::vector<long> AudioIoCallback::mCachedCaptureRates;
+std::vector<long> AudioIoCallback::mCachedSampleRates;
+double AudioIoCallback::mCachedBestRateIn = 0.0;
+double AudioIoCallback::mCachedBestRateOut;
 
 enum {
    // This is the least positive latency we can
@@ -522,7 +531,7 @@ constexpr size_t TimeQueueGrainSize = 2000;
 #endif
 
 
-struct AudioIO::ScrubState
+struct AudioIoCallback::ScrubState
 {
    ScrubState(double t0,
               double rate,
@@ -2712,7 +2721,7 @@ void AudioIO::SetPaused(bool state)
    mPaused = state;
 }
 
-bool AudioIO::IsPaused() const
+bool AudioIoCallback::IsPaused() const
 {
    return mPaused;
 }
@@ -3253,7 +3262,7 @@ size_t AudioIO::GetCommonlyFreePlayback()
    return commonlyAvail - std::min(size_t(10), commonlyAvail);
 }
 
-size_t AudioIO::GetCommonlyReadyPlayback()
+size_t AudioIoCallback::GetCommonlyReadyPlayback()
 {
    if (mPlaybackTracks.empty())
       return 0;
@@ -4709,7 +4718,7 @@ int audacityAudioCallback(const void *inputBuffer, void *outputBuffer,
 }
 
 
-void AudioIO::ComputeMidiTimings(
+void AudioIoCallback::ComputeMidiTimings(
    const PaStreamCallbackTimeInfo *timeInfo,
    unsigned long framesPerBuffer
    )
@@ -4792,9 +4801,6 @@ void AudioIO::ComputeMidiTimings(
 #endif
 }
 
-void AudioIO::ComputeAudibilities(){
-}
-
 // Stop recording if 'silence' is detected
 // Start recording if sound detected.
 //
@@ -4802,7 +4808,7 @@ void AudioIO::ComputeAudibilities(){
 //   to run in the main GUI thread after the next event loop iteration.
 //   That's important, because Pause() updates GUI, such as status bar,
 //   and that should NOT happen in this audio non-gui thread.
-void AudioIO::CheckSoundActivatedRecordingLevel( )
+void AudioIoCallback::CheckSoundActivatedRecordingLevel( )
 {
    if(mPauseRec && mInputMeter) {
       bool bShouldBePaused = mInputMeter->GetMaxPeak() < mSilenceLevel;
@@ -4818,7 +4824,7 @@ void AudioIO::CheckSoundActivatedRecordingLevel( )
 //
 // Mix and copy to PortAudio's output buffer
 //
-bool AudioIO::FillOutputBuffers(
+bool AudioIoCallback::FillOutputBuffers(
    const void *inputBuffer, 
    void *outputBuffer,
    unsigned long framesPerBuffer,
@@ -5065,7 +5071,7 @@ bool AudioIO::FillOutputBuffers(
 //
 // Copy from PortAudio to our input buffers.
 //
-bool AudioIO::FillInputBuffers(
+bool AudioIoCallback::FillInputBuffers(
    const void *inputBuffer, 
    unsigned long framesPerBuffer,
    const PaStreamCallbackFlags statusFlags,
@@ -5213,7 +5219,7 @@ bool AudioIO::FillInputBuffers(
 // return true, IFF we have fully handled the callback.
 // No tracks to play, but we should clear the output, and
 // possibly do software playthrough...
-bool AudioIO::OnlyDoPlaythrough(
+bool AudioIoCallback::OnlyDoPlaythrough(
       const void *inputBuffer, 
       void *outputBuffer,
       unsigned long framesPerBuffer,
@@ -5247,7 +5253,7 @@ bool AudioIO::OnlyDoPlaythrough(
 }
 
 // Also computes rms
-void AudioIO::SendVuInputMeterData(
+void AudioIoCallback::SendVuInputMeterData(
    float *tempFloats,
    const void *inputBuffer,
    unsigned long framesPerBuffer   
@@ -5288,7 +5294,7 @@ void AudioIO::SendVuInputMeterData(
    }  // end recording VU meter update
 }
 
-void AudioIO::SendVuOutputMeterData(
+void AudioIoCallback::SendVuOutputMeterData(
    float *outputMeterFloats,
    unsigned long framesPerBuffer)
 {
@@ -5331,7 +5337,7 @@ void AudioIO::SendVuOutputMeterData(
 
 }
 
-unsigned AudioIO::CountSoloingTracks(){
+unsigned AudioIoCallback::CountSoloingTracks(){
    const auto numPlaybackTracks = mPlaybackTracks.size();
 
    // MOVE_TO: CountSoloedTracks() function
@@ -5354,7 +5360,7 @@ unsigned AudioIO::CountSoloingTracks(){
 // true IFF the track should be silent. 
 // The track may not yet be silent, since it may still be
 // fading out.
-bool AudioIO::TrackShouldBeSilent( const WaveTrack &wt )
+bool AudioIoCallback::TrackShouldBeSilent( const WaveTrack &wt )
 {
    return mPaused || (!wt.GetSolo() && (
       // Cut if somebody else is soloing
@@ -5365,7 +5371,7 @@ bool AudioIO::TrackShouldBeSilent( const WaveTrack &wt )
 }
 
 // This is about micro-fades.
-bool AudioIO::TrackHasBeenFadedOut( const WaveTrack &wt )
+bool AudioIoCallback::TrackHasBeenFadedOut( const WaveTrack &wt )
 {
    const auto channel = wt.GetChannelIgnoringPan();
    if ((channel == Track::LeftChannel  || channel == Track::MonoChannel) &&
@@ -5377,7 +5383,7 @@ bool AudioIO::TrackHasBeenFadedOut( const WaveTrack &wt )
    return true;
 }
 
-bool AudioIO::AllTracksAlreadySilent()
+bool AudioIoCallback::AllTracksAlreadySilent()
 {
    const bool dropAllQuickly = std::all_of(
       mPlaybackTracks.begin(), mPlaybackTracks.end(),
@@ -5399,7 +5405,7 @@ bool AudioIO::AllTracksAlreadySilent()
 // this callback, and so the next time round 'AllTracksAlreadySilent' will be true.
 // All this logic will be easier when we shift over to working with gains that
 // go to zero, and not flags.
-bool AudioIO::QuickSilentPlayback(const void *inputBuffer, void *outputBuffer,
+bool AudioIoCallback::QuickSilentPlayback(const void *inputBuffer, void *outputBuffer,
                           unsigned long framesPerBuffer)
 {
    const auto numPlaybackTracks = mPlaybackTracks.size();
@@ -5424,9 +5430,17 @@ bool AudioIO::QuickSilentPlayback(const void *inputBuffer, void *outputBuffer,
    return false;
 }
 
+AudioIoCallback::AudioIoCallback()
+{
+}
 
 
-int AudioIO::AudioCallback(const void *inputBuffer, void *outputBuffer,
+AudioIoCallback::~AudioIoCallback()
+{
+}
+
+
+int AudioIoCallback::AudioCallback(const void *inputBuffer, void *outputBuffer,
                           unsigned long framesPerBuffer,
                           const PaStreamCallbackTimeInfo *timeInfo,
                           const PaStreamCallbackFlags statusFlags, void * WXUNUSED(userData) )
@@ -5519,7 +5533,7 @@ int AudioIO::AudioCallback(const void *inputBuffer, void *outputBuffer,
    return mCallbackReturn;
 }
 
-PaStreamCallbackResult AudioIO::CallbackDoSeek()
+PaStreamCallbackResult AudioIoCallback::CallbackDoSeek()
 {
    const int token = mStreamToken;
    wxMutexLocker locker(mSuspendAudioThread);
@@ -5570,7 +5584,7 @@ PaStreamCallbackResult AudioIO::CallbackDoSeek()
    return paContinue;
 }
 
-void AudioIO::CallbackCheckCompletion(
+void AudioIoCallback::CallbackCheckCompletion(
    int &callbackReturn, unsigned long len)
 {
    if (mPaused)