GStreamer: use glib to resolve/reference `QGstPipelinePrivate`

We attach `QGstPipelinePrivate` to the the `QGstPipeline`, which means
that we cannot cast from base classes to the pipeline.
So we rework this code a bit to use glib's `g_object_set_data` to attach
the private data to pipelines constructed by us.

Pick-to: 6.5
Change-Id: I09e60af4ef566d87483f318ac6b9b573325ed155
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
(cherry picked from commit 63d629446ecd2a2c8e0ee86c4c363455d454f6f9)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 147c77a3c01514e96305c076db8068da927895ae)

5 files changed, 98 insertions, 48 deletions

diff --git a/src/plugins/multimedia/gstreamer/audio/qgstreameraudiodecoder.cpp b/src/plugins/multimedia/gstreamer/audio/qgstreameraudiodecoder.cpp
index 9c7f52e28..d286ceb3a 100644
--- a/src/plugins/multimedia/gstreamer/audio/qgstreameraudiodecoder.cpp
+++ b/src/plugins/multimedia/gstreamer/audio/qgstreameraudiodecoder.cpp
@@ -44,7 +44,8 @@ QMaybe<QPlatformAudioDecoder *> QGstreamerAudioDecoder::create(QAudioDecoder *pa
         return errorMessageCannotFindElement("audioconvert");
 
     QGstPipeline playbin(
-            GST_PIPELINE_CAST(QGstElement::createFromFactory("playbin", "playbin").element()));
+            GST_PIPELINE_CAST(QGstElement::createFromFactory("playbin", "playbin").element()),
+            QGstPipeline::NeedsRef);
     if (!playbin)
         return errorMessageCannotFindElement("playbin");
 
diff --git a/src/plugins/multimedia/gstreamer/common/qgst.cpp b/src/plugins/multimedia/gstreamer/common/qgst.cpp
index bd951d11a..0aafd6499 100644
--- a/src/plugins/multimedia/gstreamer/common/qgst.cpp
+++ b/src/plugins/multimedia/gstreamer/common/qgst.cpp
@@ -3,6 +3,7 @@
 
 #include <common/qgst_p.h>
 #include <common/qgst_debug_p.h>
+#include <common/qgstpipeline_p.h>
 #include <common/qgstreamermessage_p.h>
 
 #include <QtCore/qdebug.h>
@@ -852,6 +853,31 @@ GstElement *QGstElement::element() const
     return GST_ELEMENT_CAST(get());
 }
 
+QGstElement QGstElement::getParent() const
+{
+    return QGstElement{
+        qGstCheckedCast<GstElement>(gst_element_get_parent(object())),
+        QGstElement::HasRef,
+    };
+}
+
+QGstPipeline QGstElement::getPipeline() const
+{
+    QGstElement ancestor = *this;
+    for (;;) {
+        QGstElement greatAncestor = ancestor.getParent();
+        if (greatAncestor) {
+            ancestor = std::move(greatAncestor);
+            continue;
+        }
+
+        return QGstPipeline{
+            qGstSafeCast<GstPipeline>(ancestor.element()),
+            QGstPipeline::NeedsRef,
+        };
+    }
+}
+
 // QGstBin
 
 QGstBin QGstBin::create(const char *name)
diff --git a/src/plugins/multimedia/gstreamer/common/qgst_p.h b/src/plugins/multimedia/gstreamer/common/qgst_p.h
index 3123af7b2..5db195c17 100644
--- a/src/plugins/multimedia/gstreamer/common/qgst_p.h
+++ b/src/plugins/multimedia/gstreamer/common/qgst_p.h
@@ -80,6 +80,27 @@ QGST_DEFINE_CAST_TRAITS(GstElement, ELEMENT);
 QGST_DEFINE_CAST_TRAITS(GstBin, BIN);
 QGST_DEFINE_CAST_TRAITS(GstPad, PAD);
 
+template <>
+struct GstObjectTraits<GObject>
+{
+    using Type = GObject;
+    template <typename U>
+    static bool isObjectOfType(U *arg)
+    {
+        return G_IS_OBJECT(arg);
+    }
+    template <typename U>
+    static Type *cast(U *arg)
+    {
+        return G_OBJECT(arg);
+    }
+    template <typename U>
+    static Type *checked_cast(U *arg)
+    {
+        return G_OBJECT(arg);
+    }
+};
+
 #undef QGST_DEFINE_CAST_TRAITS
 
 } // namespace QGstImpl
@@ -315,8 +336,6 @@ public:
     QGstObject(const QGstObject &) = default;
     QGstObject(QGstObject &&) noexcept = default;
 
-    virtual ~QGstObject() = default;
-
     QGstObject &operator=(const QGstObject &) = default;
     QGstObject &operator=(QGstObject &&) noexcept = default;
 
@@ -435,6 +454,8 @@ public:
     GstClockTime time() const;
 };
 
+class QGstPipeline;
+
 class QGstElement : public QGstObject
 {
 public:
@@ -503,6 +524,9 @@ public:
     void setBaseTime(GstClockTime time) const;
 
     GstElement *element() const;
+
+    QGstElement getParent() const;
+    QGstPipeline getPipeline() const;
 };
 
 template <typename... Ts>
diff --git a/src/plugins/multimedia/gstreamer/common/qgstpipeline.cpp b/src/plugins/multimedia/gstreamer/common/qgstpipeline.cpp
index e81bb0d1a..7ac6debd6 100644
--- a/src/plugins/multimedia/gstreamer/common/qgstpipeline.cpp
+++ b/src/plugins/multimedia/gstreamer/common/qgstpipeline.cpp
@@ -166,90 +166,74 @@ void QGstPipelinePrivate::removeMessageFilter(QGstreamerBusMessageFilter *filter
         busFilters.removeAll(filter);
 }
 
-QGstPipeline::QGstPipeline(const QGstPipeline &o)
-    : QGstBin(o.bin(), NeedsRef),
-    d(o.d)
+QGstPipeline QGstPipeline::create(const char *name)
 {
-    if (d)
-        d->ref();
-}
+    GstPipeline *pipeline = qGstCheckedCast<GstPipeline>(gst_pipeline_new(name));
 
-QGstPipeline &QGstPipeline::operator=(const QGstPipeline &o)
-{
-    if (this == &o)
-        return *this;
-    if (o.d)
-        o.d->ref();
-    if (d)
-        d->deref();
-    QGstBin::operator=(o);
-    d = o.d;
-    return *this;
-}
+    QGstPipelinePrivate *d = new QGstPipelinePrivate(gst_pipeline_get_bus(pipeline));
+    g_object_set_data_full(qGstCheckedCast<GObject>(pipeline), "pipeline-private", d,
+                           [](gpointer ptr) {
+                               delete reinterpret_cast<QGstPipelinePrivate *>(ptr);
+                               return;
+                           });
 
-QGstPipeline QGstPipeline::create(const char *name)
-{
     return QGstPipeline{
-        GST_PIPELINE(gst_pipeline_new(name)),
+        pipeline,
+        QGstPipeline::NeedsRef,
     };
 }
 
-QGstPipeline::QGstPipeline(GstPipeline *p)
-    : QGstBin(&p->bin, NeedsRef)
+QGstPipeline::QGstPipeline(GstPipeline *p, RefMode mode) : QGstBin(qGstCheckedCast<GstBin>(p), mode)
 {
-    d = new QGstPipelinePrivate(gst_pipeline_get_bus(pipeline()));
-    d->ref();
 }
 
-QGstPipeline::~QGstPipeline()
-{
-    if (d)
-        d->deref();
-}
+QGstPipeline::~QGstPipeline() = default;
 
 bool QGstPipeline::inStoppedState() const
 {
-    Q_ASSERT(d);
+    QGstPipelinePrivate *d = getPrivate();
     return d->inStoppedState;
 }
 
 void QGstPipeline::setInStoppedState(bool stopped)
 {
-    Q_ASSERT(d);
+    QGstPipelinePrivate *d = getPrivate();
     d->inStoppedState = stopped;
 }
 
 void QGstPipeline::setFlushOnConfigChanges(bool flush)
 {
+    QGstPipelinePrivate *d = getPrivate();
     d->m_flushOnConfigChanges = flush;
 }
 
 void QGstPipeline::installMessageFilter(QGstreamerSyncMessageFilter *filter)
 {
-    Q_ASSERT(d);
+    QGstPipelinePrivate *d = getPrivate();
     d->installMessageFilter(filter);
 }
 
 void QGstPipeline::removeMessageFilter(QGstreamerSyncMessageFilter *filter)
 {
-    Q_ASSERT(d);
+    QGstPipelinePrivate *d = getPrivate();
     d->removeMessageFilter(filter);
 }
 
 void QGstPipeline::installMessageFilter(QGstreamerBusMessageFilter *filter)
 {
-    Q_ASSERT(d);
+    QGstPipelinePrivate *d = getPrivate();
     d->installMessageFilter(filter);
 }
 
 void QGstPipeline::removeMessageFilter(QGstreamerBusMessageFilter *filter)
 {
-    Q_ASSERT(d);
+    QGstPipelinePrivate *d = getPrivate();
     d->removeMessageFilter(filter);
 }
 
 GstStateChangeReturn QGstPipeline::setState(GstState state)
 {
+    QGstPipelinePrivate *d = getPrivate();
     auto retval = gst_element_set_state(element(), state);
     if (d->m_pendingFlush) {
         d->m_pendingFlush = false;
@@ -268,8 +252,7 @@ void QGstPipeline::dumpGraph(const char *fileName)
 
 void QGstPipeline::beginConfig()
 {
-    if (!d)
-        return;
+    QGstPipelinePrivate *d = getPrivate();
     Q_ASSERT(!isNull());
 
     ++d->m_configCounter;
@@ -283,8 +266,7 @@ void QGstPipeline::beginConfig()
 
 void QGstPipeline::endConfig()
 {
-    if (!d)
-        return;
+    QGstPipelinePrivate *d = getPrivate();
     Q_ASSERT(!isNull());
 
     --d->m_configCounter;
@@ -300,11 +282,13 @@ void QGstPipeline::endConfig()
 
 void QGstPipeline::flush()
 {
+    QGstPipelinePrivate *d = getPrivate();
     seek(position(), d->m_rate);
 }
 
 bool QGstPipeline::seek(qint64 pos, double rate)
 {
+    QGstPipelinePrivate *d = getPrivate();
     // always adjust the rate, so it can be  set before playback starts
     // setting position needs a loaded media file that's seekable
     d->m_rate = rate;
@@ -323,6 +307,7 @@ bool QGstPipeline::seek(qint64 pos, double rate)
 
 bool QGstPipeline::setPlaybackRate(double rate)
 {
+    QGstPipelinePrivate *d = getPrivate();
     if (rate == d->m_rate)
         return false;
 
@@ -343,17 +328,20 @@ bool QGstPipeline::setPlaybackRate(double rate)
 
 double QGstPipeline::playbackRate() const
 {
+    QGstPipelinePrivate *d = getPrivate();
     return d->m_rate;
 }
 
 bool QGstPipeline::setPosition(qint64 pos)
 {
+    QGstPipelinePrivate *d = getPrivate();
     return seek(pos, d->m_rate);
 }
 
 qint64 QGstPipeline::position() const
 {
     gint64 pos;
+    QGstPipelinePrivate *d = getPrivate();
     if (gst_element_query_position(element(), GST_FORMAT_TIME, &pos))
         d->m_position = pos;
     return d->m_position;
@@ -367,6 +355,14 @@ qint64 QGstPipeline::duration() const
     return d;
 }
 
+QGstPipelinePrivate *QGstPipeline::getPrivate() const
+{
+    gpointer p = g_object_get_data(qGstCheckedCast<GObject>(object()), "pipeline-private");
+    auto *d = reinterpret_cast<QGstPipelinePrivate *>(p);
+    Q_ASSERT(d);
+    return d;
+}
+
 QT_END_NAMESPACE
 
 #include "qgstpipeline.moc"
diff --git a/src/plugins/multimedia/gstreamer/common/qgstpipeline_p.h b/src/plugins/multimedia/gstreamer/common/qgstpipeline_p.h
index d73467b06..c13196d12 100644
--- a/src/plugins/multimedia/gstreamer/common/qgstpipeline_p.h
+++ b/src/plugins/multimedia/gstreamer/common/qgstpipeline_p.h
@@ -41,13 +41,14 @@ class QGstPipelinePrivate;
 
 class QGstPipeline : public QGstBin
 {
-    QGstPipelinePrivate *d = nullptr;
 public:
     constexpr QGstPipeline() = default;
-    QGstPipeline(const QGstPipeline &o);
-    QGstPipeline &operator=(const QGstPipeline &o);
-    explicit QGstPipeline(GstPipeline *p);
-    ~QGstPipeline() override;
+    QGstPipeline(const QGstPipeline &) = default;
+    QGstPipeline(QGstPipeline &&) = default;
+    QGstPipeline &operator=(const QGstPipeline &) = default;
+    QGstPipeline &operator=(QGstPipeline &&) noexcept = default;
+    QGstPipeline(GstPipeline *, RefMode mode);
+    ~QGstPipeline();
 
     static QGstPipeline create(const char *name);
 
@@ -92,6 +93,8 @@ public:
     qint64 duration() const;
 
 private:
+    QGstPipelinePrivate *getPrivate() const;
+
     void beginConfig();
     void endConfig();
 };