Play head is green during pre-roll, then turns red for real recording

src/AudioIO.cpp

@@ -1934,6 +1934,7 @@ int AudioIO::StartStream(const TransportTracks &tracks,
    mT0      = t0 - preRoll;
    mT1      = t1;
    mRecordingSchedule = {};
+   mRecordingPosition.store(0.0, std::memory_order_relaxed);
    mRecordingSchedule.mPreRoll = preRoll;
    mRecordingSchedule.mLatencyCorrection =
       (gPrefs->ReadDouble(wxT("/AudioIO/LatencyCorrection"),
@@ -2564,6 +2565,7 @@ void AudioIO::StopStream()
    auto cleanup = finally ( [this] {
       ClearRecordingException();
       mRecordingSchedule = {}; // free arrays
+      mRecordingPosition.store(0.0, std::memory_order_relaxed);
    } );
 
    if( mPortStreamV19 == NULL
@@ -3989,8 +3991,9 @@ void AudioIO::FillBuffers()
       GuardedCall( [&] {
          // start record buffering
          const auto avail = GetCommonlyAvailCapture(); // samples
+         const auto position = mRecordingPosition.load(std::memory_order_relaxed);
          const auto remainingTime =
-            std::max(0.0, mRecordingSchedule.ToConsume());
+            std::max(0.0, mRecordingSchedule.ToConsume(position));
          // This may be a very big double number:
          const auto remainingSamples = remainingTime * mRate;
          bool latencyCorrected = true;
@@ -4028,7 +4031,7 @@ void AudioIO::FillBuffers()
                      // Leftward shift
                      // discard some samples from the ring buffers.
                      size_t size = floor(
-                        mRecordingSchedule.ToDiscard() * mRate );
+                        mRecordingSchedule.ToDiscard(position) * mRate );
 
                      // The ring buffer might have grown concurrently -- don't discard more
                      // than the "avail" value noted above.
@@ -4051,7 +4054,8 @@ void AudioIO::FillBuffers()
                   totalCrossfadeLength = data.size();
                   if (totalCrossfadeLength) {
                      crossfadeStart =
-                        floor(mRecordingSchedule.Consumed() * mCaptureTracks[i]->GetRate());
+                        floor(mRecordingSchedule.Consumed(position) *
+                              mCaptureTracks[i]->GetRate());
                      if (crossfadeStart < totalCrossfadeLength)
                         pCrossfadeSrc = data.data() + crossfadeStart;
                   }
@@ -4139,8 +4143,13 @@ void AudioIO::FillBuffers()
                }
             } // end loop over capture channels
 
-            // Now update the recording shedule position
-            mRecordingSchedule.mPosition += avail / mRate;
+            // Now update the recording schedule position
+            // Main thread may need to read it for drawing, so update atomically
+            // Relaxed order here, with the frequent memory fencing done by
+            // the ring buffers, should give frequent enough update in the
+            // main thread.
+            mRecordingPosition.store(
+               position + avail / mRate, std::memory_order_relaxed);
             mRecordingSchedule.mLatencyCorrected = latencyCorrected;
 
             if (mListener && !blockFileLog.IsEmpty())
@@ -5463,17 +5472,29 @@ int audacityAudioCallback(const void *inputBuffer, void *outputBuffer,
    return callbackReturn;
 }
 
-double AudioIO::RecordingSchedule::ToConsume() const
+double AudioIO::RecordingSchedule::ToConsume(double position) const
 {
-   return mDuration - Consumed();
+   return mDuration - Consumed(position);
 }
 
-double AudioIO::RecordingSchedule::Consumed() const
+double AudioIO::RecordingSchedule::Consumed(double position) const
 {
-   return std::max( 0.0, mPosition + TotalCorrection() );
+   return std::max( 0.0, position + TotalCorrection() );
 }
 
-double AudioIO::RecordingSchedule::ToDiscard() const
+double AudioIO::RecordingSchedule::ToDiscard(double position) const
 {
-   return std::max(0.0, -( mPosition + TotalCorrection() ) );
+   return std::max(0.0, -( position + TotalCorrection() ) );
+}
+
+bool AudioIO::IsCapturing() const
+{
+   // This is for purposes of choosing the color of the play indicator
+   // Returns false during a pre-roll but true when time before actual recording
+   // is less than latency
+   return
+   GetNumCaptureChannels() > 0 &&
+   mRecordingSchedule.ToDiscard(
+      mRecordingPosition.load(std::memory_order_relaxed)) <=
+         -std::min(0.0, mRecordingSchedule.mLatencyCorrection);
 }

src/AudioIO.h

@@ -18,6 +18,7 @@
 #include "Experimental.h"
 
 #include "MemoryX.h"
+#include <atomic>
 #include <utility>
 #include <vector>
 #include <wx/atomic.h>
@@ -398,6 +399,9 @@ class AUDACITY_DLL_API AudioIO final {
    unsigned GetNumPlaybackChannels() const { return mNumPlaybackChannels; }
    unsigned GetNumCaptureChannels() const { return mNumCaptureChannels; }
 
+   // Meaning really capturing, not just pre-rolling
+   bool IsCapturing() const;
+
    /** \brief Array of common audio sample rates
     *
     * These are the rates we will always support, regardless of hardware support
@@ -846,16 +850,20 @@ private:
       double mDuration{};
       PRCrossfadeData mCrossfadeData;
 
-      // These are initialized by the main thread, then updated
+      // This is initialized by the main thread, then updated
       // only by the thread calling FillBuffers:
-      double mPosition{};
       bool mLatencyCorrected{};
 
       double TotalCorrection() const { return mLatencyCorrection - mPreRoll; }
-      double ToConsume() const;
-      double Consumed() const;
-      double ToDiscard() const;
+      double ToConsume(double position) const;
+      double Consumed(double position) const;
+      double ToDiscard(double position) const;
    } mRecordingSchedule{};
+
+   // This is initialized by the main thread, then updated
+   // only by the thread calling FillBuffers, but may need to be read by the
+   // main thread to draw display correctly.
+   std::atomic<double> mRecordingPosition{};
 };
 
 #endif

src/tracks/ui/PlayIndicatorOverlay.cpp

@@ -60,7 +60,7 @@ std::pair<wxRect, bool> PlayIndicatorOverlayBase::DoGetRectangle(wxSize size)
 void PlayIndicatorOverlayBase::Draw(OverlayPanel &panel, wxDC &dc)
 {
    // Set play/record color
-   bool rec = (gAudioIO->GetNumCaptureChannels() > 0);
+   bool rec = gAudioIO->IsCapturing();
    AColor::IndicatorColor(&dc, !rec);
    mLastIndicatorX = mNewIndicatorX;
    if (!between_incexc(0, mLastIndicatorX, dc.GetSize().GetWidth()))