Fix crash at exit when tracing

The crash is caused by the cleanup sending trace messages when the
plugin has already been destroyed. Add shutdown callback to the plugin
to indicate this has happened. We can't use signals since that also
generetes trace event.

Change-Id: I2e490fc51c2aaa97c240c1496a528a6ff6077bd0
Reviewed-by: Hatem ElKharashy <hatem.elkharashy@qt.io>
Reviewed-by: Janne Koskinen <janne.p.koskinen@qt.io>
(cherry picked from commit bb8aada627e23a7f7e23dfdb97d443f1b847086a)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/tracing/qctf.cpp

@@ -15,6 +15,7 @@ QT_BEGIN_NAMESPACE
 static bool s_initialized = false;
 static bool s_triedLoading = false;
 static bool s_prevent_recursion = false;
+static bool s_shutdown = false;
 static QCtfLib* s_plugin = nullptr;
 
 #if defined(Q_OS_ANDROID)
@@ -59,18 +60,13 @@ static bool loadPlugin(bool &retry)
     s_plugin = qobject_cast<QCtfLib *>(loader.instance());
     if (!s_plugin)
         return false;
-    QObject *obj = loader.instance();
-    if (obj) {
-        QObject::connect(obj, &QObject::destroyed, []() {
-            s_plugin = nullptr;
-        });
-    }
+    s_plugin->shutdown(&s_shutdown);
     return true;
 }
 
 static bool initialize()
 {
-    if (s_prevent_recursion)
+    if (s_shutdown || s_prevent_recursion)
         return false;
     if (s_initialized || s_triedLoading)
         return s_initialized;

src/corelib/tracing/qctf_p.h

@@ -232,6 +232,7 @@ public:
     virtual void doTracepoint(const QCtfTracePointEvent &point, const QByteArray &arr) = 0;
     virtual bool sessionEnabled() = 0;
     virtual QCtfTracePointPrivate *initializeTracepoint(const QCtfTracePointEvent &point) = 0;
+    virtual void shutdown(bool *shutdown) = 0;
 };
 
 QT_END_NAMESPACE

src/plugins/tracing/qctflib.cpp

@@ -50,6 +50,7 @@ void QCtfLibImpl::cleanup()
 {
     if (s_instance)
         delete s_instance;
+    s_instance = nullptr;
 }
 
 QCtfLibImpl::QCtfLibImpl()

src/plugins/tracing/qctflib_p.h

@@ -78,6 +78,10 @@ public:
     QCtfTracePointPrivate *initializeTracepoint(const QCtfTracePointEvent &point) override;
     void registerMetadata(const QCtfTraceMetadata &metadata);
     int eventId();
+    void shutdown(bool *) override
+    {
+
+    }
 
     static QCtfLib *instance();
     static void cleanup();

src/plugins/tracing/qctfplugin.cpp

@@ -22,9 +22,13 @@ public:
     ~QCtfTracePlugin()
     {
         m_cleanup = true;
+        *m_shutdown = true;
         QCtfLibImpl::cleanup();
     }
-
+    void shutdown(bool *shutdown) override
+    {
+        m_shutdown = shutdown;
+    }
     bool tracepointEnabled(const QCtfTracePointEvent &point) override
     {
         if (m_cleanup)
@@ -51,6 +55,7 @@ public:
     }
 private:
     bool m_cleanup = false;
+    bool *m_shutdown = nullptr;
 };
 
 #include "qctfplugin.moc"