From 6dca4f785904fd870d6829dd51aa0c56803012dc Mon Sep 17 00:00:00 2001
From: Paul Licameli <paul.licameli@audacityteam.org>
Date: Sat, 17 Mar 2018 23:41:27 -0400
Subject: [PATCH] Possibly correct some cases of clicky playback or corrupt
 recording...

... By reusing portaudio's ring buffer class, which has more safe
inter-thread synchronization with memory fences
---
 src/Experimental.h |  6 +++++
 src/RingBuffer.cpp | 63 ++++++++++++++++++++++++++++++++++++++++++++--
 src/RingBuffer.h   |  6 ++++-
 3 files changed, 72 insertions(+), 3 deletions(-)

diff --git a/src/Experimental.h b/src/Experimental.h
index 2fc7b1557..899168e5f 100644
--- a/src/Experimental.h
+++ b/src/Experimental.h
@@ -245,4 +245,10 @@
 // Easy change of keystroke bindings for menu items
 #define EXPERIMENTAL_EASY_CHANGE_KEY_BINDINGS
 
+// PRL 17 Mar 2018
+// Hoping to commit to use of this branch before 2.3.0 is out.
+// Don't use our own RingBuffer class, but reuse PortAudio's which includes
+// proper memory fences.
+#undef EXPERIMENTAL_REWRITE_RING_BUFFER
+
 #endif
diff --git a/src/RingBuffer.cpp b/src/RingBuffer.cpp
index de3eb08a5..b9272be5a 100644
--- a/src/RingBuffer.cpp
+++ b/src/RingBuffer.cpp
@@ -23,12 +23,45 @@
 
 
 #include "RingBuffer.h"
+#include "Experimental.h"
+
+#undef REWRITE_RING_BUFFER
+
+// For now enabling the rewrite only for Mac
+
+#ifdef EXPERIMENTAL_REWRITE_RING_BUFFER
+#define REWRITE_RING_BUFFER
+#elif defined (__APPLE__)
+#define REWRITE_RING_BUFFER
+#endif
+
+namespace {
+   size_t roundUp(size_t n)
+   {
+#ifdef REWRITE_RING_BUFFER
+      // PaUtilRingBuffer requires a power of 2
+      if (n == 0)
+         return 1;
+
+      size_t prev = n;
+      for (size_t temp = n; temp != 0; prev = temp, temp = ((temp - 1) & temp))
+         ;
+      return prev == n ? prev : prev << 1;
+#else
+      return n;
+#endif
+   }
+}
 
 RingBuffer::RingBuffer(sampleFormat format, size_t size)
    : mFormat{ format }
-   , mBufferSize{ std::max<size_t>(size, 64) }
+   , mBufferSize{ roundUp( std::max<size_t>(size, 64) ) }
    , mBuffer{ mBufferSize, mFormat }
 {
+#ifdef REWRITE_RING_BUFFER
+   PaUtil_InitializeRingBuffer(
+      &mRingBuffer, SAMPLE_SIZE(format), mBufferSize, mBuffer.ptr() );
+#endif
 }
 
 RingBuffer::~RingBuffer()
@@ -37,7 +70,11 @@ RingBuffer::~RingBuffer()
 
 size_t RingBuffer::Len()
 {
+#ifdef REWRITE_RING_BUFFER
    return (mEnd + mBufferSize - mStart) % mBufferSize;
+#else
+   assert(false);
+#endif
 }
 
 //
@@ -46,12 +83,19 @@ size_t RingBuffer::Len()
 
 size_t RingBuffer::AvailForPut()
 {
+#ifdef REWRITE_RING_BUFFER
+   return PaUtil_GetRingBufferWriteAvailable(&mRingBuffer);
+#else
    return std::max<size_t>(mBufferSize - Len(), 4) - 4;
+#endif
 }
 
 size_t RingBuffer::Put(samplePtr buffer, sampleFormat format,
                     size_t samplesToCopy)
 {
+#ifdef REWRITE_RING_BUFFER
+   return PaUtil_WriteRingBuffer(&mRingBuffer, buffer, samplesToCopy);
+#else
    samplesToCopy = std::min( samplesToCopy, AvailForPut() );
    auto src = buffer;
    size_t copied = 0;
@@ -73,8 +117,11 @@ size_t RingBuffer::Put(samplePtr buffer, sampleFormat format,
    mEnd = pos;
 
    return copied;
+#endif
 }
 
+#if 0
+// not used
 size_t RingBuffer::Clear(sampleFormat format, size_t samplesToClear)
 {
    samplesToClear = std::min( samplesToClear, AvailForPut() );
@@ -95,6 +142,7 @@ size_t RingBuffer::Clear(sampleFormat format, size_t samplesToClear)
 
    return cleared;
 }
+#endif
 
 //
 // For the reader only:
@@ -102,12 +150,19 @@ size_t RingBuffer::Clear(sampleFormat format, size_t samplesToClear)
 
 size_t RingBuffer::AvailForGet()
 {
+#ifdef REWRITE_RING_BUFFER
+   return PaUtil_GetRingBufferReadAvailable(&mRingBuffer);
+#else
    return Len();
+#endif
 }
 
 size_t RingBuffer::Get(samplePtr buffer, sampleFormat format,
                        size_t samplesToCopy)
 {
+#ifdef REWRITE_RING_BUFFER
+   return PaUtil_ReadRingBuffer(&mRingBuffer, buffer, samplesToCopy);
+#else
    samplesToCopy = std::min( samplesToCopy, Len() );
    auto dest = buffer;
    size_t copied = 0;
@@ -126,13 +181,17 @@ size_t RingBuffer::Get(samplePtr buffer, sampleFormat format,
    }
 
    return copied;
+#endif
 }
 
 size_t RingBuffer::Discard(size_t samplesToDiscard)
 {
+#ifdef REWRITE_RING_BUFFER
+   PaUtil_AdvanceRingBufferReadIndex(&mRingBuffer, samplesToDiscard);
+#else
    samplesToDiscard = std::min( samplesToDiscard, Len() );
 
    mStart = (mStart + samplesToDiscard) % mBufferSize;
-
+#endif
    return samplesToDiscard;
 }
diff --git a/src/RingBuffer.h b/src/RingBuffer.h
index 6fc19bd42..4d72fde00 100644
--- a/src/RingBuffer.h
+++ b/src/RingBuffer.h
@@ -13,6 +13,8 @@
 
 #include "SampleFormat.h"
 
+#include "../lib-src/portaudio-v19/src/common/pa_ringbuffer.h"
+
 class RingBuffer {
  public:
    RingBuffer(sampleFormat format, size_t size);
@@ -24,7 +26,7 @@ class RingBuffer {
 
    size_t AvailForPut();
    size_t Put(samplePtr buffer, sampleFormat format, size_t samples);
-   size_t Clear(sampleFormat format, size_t samples);
+//   size_t Clear(sampleFormat format, size_t samples);
 
    //
    // For the reader only:
@@ -42,6 +44,8 @@ class RingBuffer {
    size_t        mEnd { 0 };
    size_t        mBufferSize;
    SampleBuffer  mBuffer;
+
+   PaUtilRingBuffer mRingBuffer;
 };
 
 #endif /*  __AUDACITY_RING_BUFFER__ */