[Development] [QML] Singletons are deleted before the other objects

[BogDan]

On Monday 22. September 2014 01.19.17 BogDan wrote:
> Hi Simon,
> 
> I took a look and I'm pretty sure I'm right ;-). BTW I'm using 5.4
> branch (sha1 f9ee33f96), is a little  bit old, but I bet nobody
> fixed it. The same problem is in previous releases.
> 
> So, the singletons are deleted in QQmlEngine::~QQmlEngine():910
> The other active objects are deleted in  MemoryManager::sweep(*true*)
> which is called by MemoryManager::~MemoryManager()
> which is called by ExecutionEngine::~ExecutionEngine()
> which is called by QV8Engine::~QV8Engine()
> which is called by QJSEngine::~QJSEngine()
> which is called *after* QQmlEngine::~QQmlEngine()
> 
> Check the call-stack:
> 0   MyObject::~MyObject myobject.cpp    44  0x7fffd141eb4b
> 1   MyObject::~MyObject myobject.cpp    46  0x7fffd141ec8a
> 2   (anonymous namespace)::QObjectDeleter::~QObjectDeleter 
> qv4qobjectwrapper.cpp   1018    0x7ffff5f79ee1  f9ee33f96f9ee33f96 3  
> (anonymous namespace)::QObjectDeleter::~QObjectDeleter 
> qv4qobjectwrapper.cpp   1021    0x7ffff5f79f2e 4  
> QV4::MemoryManager::sweep   qv4mm.cpp   377 0x7ffff5efd080
> 5   QV4::MemoryManager::~MemoryManager  qv4mm.cpp   515 0x7ffff5efda18
> 6   QV4::ExecutionEngine::~ExecutionEngine  qv4engine.cpp   421
> 0x7ffff5ee4f54 7   QV8Engine::~QV8Engine   qv8engine.cpp   116
> 0x7ffff606b7f2
> 8   QV8Engine::~QV8Engine   qv8engine.cpp   117 0x7ffff606b87e
> 9   QJSEngine::~QJSEngine   qjsengine.cpp   203 0x7ffff5e64b1e
> 10  QQmlEngine::~QQmlEngine qqmlengine.cpp  893 0x7ffff5fb0b5d
> 11  QQmlEngine::~QQmlEngine qqmlengine.cpp  916 0x7ffff5fb0b8c
> 12  QObjectPrivate::deleteChildren  qobject.cpp 1943    0x7ffff599efd0
> 13  QObject::~QObject   qobject.cpp 1034    0x7ffff599d760
> 14  QWindow::~QWindow   qwindow.cpp 210 0x7ffff63f5bdc
> 15  QQuickWindow::~QQuickWindow qquickwindow.cpp    1099    0x7ffff6bc0353
> 16  QQuickView::~QQuickView qquickview.cpp  220 0x7ffff6c9fe35
> 17  main    main.cpp    12  0x4021fb
> 
> IMHO the sequence from QQmlEngine::~QQmlEngine():910 should be moved
> after/in MemoryManager::~MemoryManager ...

Ahh, so what you're talking about are the _JavaScript_ wrappers for the 
singletons, not the singleton objects themselves. That explains the confusion.

Yes, due to the inheritance the final garbage collection runs as the very last 
step - and it has to, conceptually. I'm wondering: What code do you have 
running at that point that gets still called? Is it code in C++ destructors?






Yes, the code from their destructors needs the singletons objects which are
not available anymore.

Cheers,
BogDan.