From 7d9ca913ec73c005ae9cd193426709dafb94e850 Mon Sep 17 00:00:00 2001
From: f4exb <f4exb06@gmail.com>
Date: Mon, 19 Nov 2018 18:49:12 +0100
Subject: [PATCH] Attempt to fix race condition in glScope traces processing

---
 sdrgui/dsp/scopevis.cpp | 17 +++++++++++++----
 sdrgui/gui/glscope.cpp  | 25 +++++++++++++++++++++++--
 sdrgui/gui/glscope.h    |  5 +++++
 3 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/sdrgui/dsp/scopevis.cpp b/sdrgui/dsp/scopevis.cpp
index 872d34f05..30c817191 100644
--- a/sdrgui/dsp/scopevis.cpp
+++ b/sdrgui/dsp/scopevis.cpp
@@ -607,15 +607,24 @@ int ScopeVis::processTraces(const SampleVector::const_iterator& cbegin, const Sa
     float traceTime = ((float) m_traceSize) / m_sampleRate;
 
     if (traceTime >= 1.0f) { // display continuously if trace time is 1 second or more
-        m_glScope->newTraces(&m_traces.m_traces[m_traces.currentBufferIndex()]);
+        m_glScope->newTraces(m_traces.m_traces, m_traces.currentBufferIndex());
     }
 
     if (m_nbSamples == 0) // finished
     {
-        if (traceTime < 1.0f) { // display only at trace end if trace time is less than 1 second
-            m_glScope->newTraces(&m_traces.m_traces[m_traces.currentBufferIndex()]);
+        // display only at trace end if trace time is less than 1 second
+        if (traceTime < 1.0f)
+        {
+            if (m_glScope->getProcessingTraceIndex().load() < 0) {
+                m_glScope->newTraces(m_traces.m_traces, m_traces.currentBufferIndex());
+            }
         }
-        m_traces.switchBuffer();
+
+        // switch to next buffer only if it is not being processed by the scope
+        if (m_glScope->getProcessingTraceIndex().load() != ((m_traces.currentBufferIndex() + 1) % 2)) {
+            m_traces.switchBuffer();
+        }
+
         return end - begin; // return remainder count
     }
     else
diff --git a/sdrgui/gui/glscope.cpp b/sdrgui/gui/glscope.cpp
index 76418b698..bdba1e1eb 100644
--- a/sdrgui/gui/glscope.cpp
+++ b/sdrgui/gui/glscope.cpp
@@ -30,6 +30,7 @@ GLScope::GLScope(QWidget* parent) :
     QGLWidget(parent),
     m_tracesData(0),
     m_traces(0),
+    m_processingTraceIndex(-1),
     m_bufferIndex(0),
     m_displayMode(DisplayX),
     m_dataChanged(false),
@@ -112,6 +113,21 @@ void GLScope::newTraces(std::vector<float *>* traces)
     }
 }
 
+void GLScope::newTraces(std::vector<float *>* traces, int traceIndex)
+{
+    if (traces->size() > 0)
+    {
+        if(!m_mutex.tryLock(2))
+            return;
+
+        m_processingTraceIndex.store(traceIndex);
+        m_traces = &traces[traceIndex];
+        m_dataChanged = true;
+
+        m_mutex.unlock();
+    }
+}
+
 void GLScope::initializeGL()
 {
     QOpenGLContext *glCurrentContext =  QOpenGLContext::currentContext();
@@ -176,11 +192,15 @@ void GLScope::resizeGL(int width, int height)
 
 void GLScope::paintGL()
 {
-    if(!m_mutex.tryLock(2))
+    if (!m_mutex.tryLock(2))
+    {
+        m_processingTraceIndex.store(-1);
         return;
+    }
 
-    if(m_configChanged)
+    if (m_configChanged) {
         applyConfig();
+    }
 
 //    qDebug("GLScope::paintGL: m_traceCounter: %d", m_traceCounter);
 //    m_traceCounter = 0;
@@ -920,6 +940,7 @@ void GLScope::paintGL()
         } // trace length > 0
     } // XY mixed + polar display
 
+    m_processingTraceIndex.store(-1);
     m_mutex.unlock();
 }
 
diff --git a/sdrgui/gui/glscope.h b/sdrgui/gui/glscope.h
index c33e91cc0..6120a2217 100644
--- a/sdrgui/gui/glscope.h
+++ b/sdrgui/gui/glscope.h
@@ -24,6 +24,8 @@
 #include <QMutex>
 #include <QFont>
 #include <QMatrix4x4>
+#include <QAtomicInt>
+
 #include "dsp/dsptypes.h"
 #include "dsp/scopevis.h"
 #include "gui/scaleengine.h"
@@ -54,6 +56,7 @@ public:
 
     void setTraces(std::vector<ScopeVis::TraceData>* tracesData, std::vector<float *>* traces);
     void newTraces(std::vector<float *>* traces);
+    void newTraces(std::vector<float *>* traces, int traceIndex);
 
     int getSampleRate() const { return m_sampleRate; }
     int getTraceSize() const { return m_traceSize; }
@@ -75,6 +78,7 @@ public:
     bool getDataChanged() const { return m_dataChanged; }
     DisplayMode getDisplayMode() const { return m_displayMode; }
     void setDisplayXYPoints(bool value) { m_displayXYPoints = value; }
+    const QAtomicInt& getProcessingTraceIndex() const { return m_processingTraceIndex; }
 
 signals:
     void sampleRateChanged(int);
@@ -84,6 +88,7 @@ signals:
 private:
     std::vector<ScopeVis::TraceData> *m_tracesData;
     std::vector<float *> *m_traces;
+    QAtomicInt m_processingTraceIndex;
     ScopeVis::TriggerData m_focusedTriggerData;
     //int m_traceCounter;
     uint32_t m_bufferIndex;