Playback engine atomic variables cleanup

* use acquire-release memory order instead of default mem-seq.
  The strict sequeintial order is not needed if not having
  special sync requirements; the order might be a bottle-neck
  if widely used in many threads.
  In the future, it might be investigated and optimized
  with relaxed operations in some cases.
* use QAtomic instead of std::atomic, since QAtomic has
  explicit convenient methods and std::atomic sets
  the mem-seq order by default.

Change-Id: Iabd9c1bc072db491e0eba7eacaf8f4ea8343cee4
Reviewed-by: Jøger Hansegård <joger.hansegard@qt.io>
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
(cherry picked from commit d64c490eb977258fd30e7a78cfed1ad6d86d3f3f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

6 files changed, 24 insertions, 25 deletions

diff --git a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegdemuxer.cpp b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegdemuxer.cpp
index 696460c00..3c5ea8e6b 100644
--- a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegdemuxer.cpp
+++ b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegdemuxer.cpp
@@ -26,15 +26,14 @@ static qint64 streamTimeToUs(const AVStream *stream, qint64 time)
 
 Demuxer::Demuxer(AVFormatContext *context, const PositionWithOffset &posWithOffset,
                  const StreamIndexes &streamIndexes, int loops)
-    : m_context(context), m_posWithOffset(posWithOffset)
+    : m_context(context), m_posWithOffset(posWithOffset), m_loops(loops)
 {
     qCDebug(qLcDemuxer) << "Create demuxer."
                         << "pos:" << posWithOffset.pos << "loop offset:" << posWithOffset.offset.pos
                         << "loop index:" << posWithOffset.offset.index << "loops:" << loops;
-    m_loops = loops;
 
     Q_ASSERT(m_context);
-    Q_ASSERT(m_loops < 0 || m_posWithOffset.offset.index < m_loops);
+    Q_ASSERT(loops < 0 || m_posWithOffset.offset.index < loops);
 
     for (auto i = 0; i < QPlatformMediaPlayer::NTrackTypes; ++i) {
         if (streamIndexes[i] >= 0) {
@@ -53,7 +52,8 @@ void Demuxer::doNextStep()
     if (av_read_frame(m_context, packet.avPacket()) < 0) {
         ++m_posWithOffset.offset.index;
 
-        if (m_loops >= 0 && m_posWithOffset.offset.index >= m_loops) {
+        const auto loops = m_loops.loadAcquire();
+        if (loops >= 0 && m_posWithOffset.offset.index >= loops) {
             qCDebug(qLcDemuxer) << "finish demuxing";
             setAtEnd(true);
         } else {
@@ -163,7 +163,7 @@ Demuxer::RequestingSignal Demuxer::signalByTrackType(QPlatformMediaPlayer::Track
 void Demuxer::setLoops(int loopsCount)
 {
     qCDebug(qLcDemuxer) << "setLoops to demuxer" << loopsCount;
-    m_loops = loopsCount;
+    m_loops.storeRelease(loopsCount);
 }
 
 } // namespace QFFmpeg
diff --git a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegdemuxer_p.h b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegdemuxer_p.h
index 290626af2..9ab293c55 100644
--- a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegdemuxer_p.h
+++ b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegdemuxer_p.h
@@ -65,7 +65,7 @@ private:
     std::unordered_map<int, StreamData> m_streams;
     PositionWithOffset m_posWithOffset;
     qint64 m_endPts = 0;
-    std::atomic<int> m_loops = QMediaPlayer::Once;
+    QAtomicInt m_loops = QMediaPlayer::Once;
 };
 
 } // namespace QFFmpeg
diff --git a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegplaybackengineobject.cpp b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegplaybackengineobject.cpp
index f22799c70..2d23802de 100644
--- a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegplaybackengineobject.cpp
+++ b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegplaybackengineobject.cpp
@@ -10,9 +10,9 @@ QT_BEGIN_NAMESPACE
 
 namespace QFFmpeg {
 
-static std::atomic<PlaybackEngineObject::Id> PersistentId = 0;
+static QAtomicInteger<PlaybackEngineObject::Id> PersistentId = 0;
 
-PlaybackEngineObject::PlaybackEngineObject() : m_id(++PersistentId) { }
+PlaybackEngineObject::PlaybackEngineObject() : m_id(PersistentId.fetchAndAddRelaxed(1)) { }
 
 PlaybackEngineObject::~PlaybackEngineObject()
 {
@@ -27,7 +27,7 @@ bool PlaybackEngineObject::isPaused() const
 
 void PlaybackEngineObject::setAtEnd(bool isAtEnd)
 {
-    if (m_atEnd.exchange(isAtEnd) != isAtEnd)
+    if (m_atEnd.testAndSetRelease(!isAtEnd, isAtEnd) && isAtEnd)
         emit atEnd();
 }
 
@@ -43,13 +43,13 @@ PlaybackEngineObject::Id PlaybackEngineObject::id() const
 
 void PlaybackEngineObject::setPaused(bool isPaused)
 {
-    if (m_paused.exchange(isPaused) != isPaused)
+    if (m_paused.testAndSetRelease(!isPaused, isPaused))
         QMetaObject::invokeMethod(this, &PlaybackEngineObject::onPauseChanged);
 }
 
 void PlaybackEngineObject::kill()
 {
-    m_deleting = true;
+    m_deleting.storeRelease(true);
 
     disconnect();
     deleteLater();
diff --git a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegplaybackengineobject_p.h b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegplaybackengineobject_p.h
index 409d18c43..02943a55b 100644
--- a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegplaybackengineobject_p.h
+++ b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegplaybackengineobject_p.h
@@ -16,8 +16,7 @@
 
 #include "playbackengine/qffmpegplaybackenginedefs_p.h"
 #include "qthread.h"
-
-#include <atomic>
+#include "qatomic.h"
 
 QT_BEGIN_NAMESPACE
 
@@ -73,9 +72,9 @@ private slots:
 private:
     std::unique_ptr<QTimer> m_timer;
 
-    std::atomic_bool m_paused = true;
-    std::atomic_bool m_atEnd = false;
-    std::atomic_bool m_deleting = false;
+    QAtomicInteger<bool> m_paused = true;
+    QAtomicInteger<bool> m_atEnd = false;
+    QAtomicInteger<bool> m_deleting = false;
     const Id m_id;
 };
 } // namespace QFFmpeg
diff --git a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegrenderer.cpp b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegrenderer.cpp
index 56bfd9092..8ef298105 100644
--- a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegrenderer.cpp
+++ b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegrenderer.cpp
@@ -46,7 +46,7 @@ void Renderer::setPlaybackRate(float rate)
 
 void Renderer::doForceStep()
 {
-    if (!m_isStepForced.exchange(true))
+    if (m_isStepForced.testAndSetOrdered(false, true))
         QMetaObject::invokeMethod(this, [this]() {
             // maybe set m_forceStepMaxPos
 
@@ -72,11 +72,11 @@ void Renderer::onFinalFrameReceived()
 
 void Renderer::render(Frame frame)
 {
-    const auto isFrameOutdated = frame.isValid() && frame.absoluteEnd() < m_seekPos;
+    const auto isFrameOutdated = frame.isValid() && frame.absoluteEnd() < seekPosition();
 
     if (isFrameOutdated) {
         qCDebug(qLcRenderer) << "frame outdated! absEnd:" << frame.absoluteEnd() << "absPts"
-                             << frame.absolutePts() << "seekPos:" << m_seekPos;
+                             << frame.absolutePts() << "seekPos:" << seekPosition();
         emit frameProcessed(frame);
         return;
     }
@@ -122,7 +122,7 @@ int Renderer::timerInterval() const
 
 bool Renderer::setForceStepDone()
 {
-    if (!m_isStepForced.exchange(false))
+    if (!m_isStepForced.testAndSetOrdered(true, false))
         return false;
 
     m_explicitNextFrameTime.reset();
@@ -148,8 +148,8 @@ void Renderer::doNextStep()
         m_frames.dequeue();
 
         if (frame.isValid()) {
-            m_lastPosition = std::max(frame.absolutePts(), m_lastPosition.load());
-            m_seekPos = frame.absoluteEnd();
+            m_lastPosition.storeRelease(std::max(frame.absolutePts(), lastPosition()));
+            m_seekPos.storeRelaxed(frame.absoluteEnd());
 
             const auto loopIndex = frame.loopOffset().index;
             if (m_loopIndex < loopIndex) {
diff --git a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegrenderer_p.h b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegrenderer_p.h
index e14076624..9b5139ad9 100644
--- a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegrenderer_p.h
+++ b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegrenderer_p.h
@@ -102,12 +102,12 @@ private:
 
 private:
     TimeController m_timeController;
-    std::atomic<qint64> m_lastPosition = 0;
-    std::atomic<qint64> m_seekPos = 0;
+    QAtomicInteger<qint64> m_lastPosition = 0;
+    QAtomicInteger<qint64> m_seekPos = 0;
     int m_loopIndex = 0;
     QQueue<Frame> m_frames;
 
-    std::atomic_bool m_isStepForced = false;
+    QAtomicInteger<bool> m_isStepForced = false;
     std::optional<TimePoint> m_explicitNextFrameTime;
 };