[Interest] Debugging a double dealloc
Ben Haller
bhaller at mac.com
Wed Sep 23 14:08:37 CEST 2020
Thanks for the suggestion. However, this problem is only on macOS, and Valgrind doesn’t appear to run on any macOS later than 10.12 (“preliminary” support for 10.13, according to their website; I’m not sure what that means). I’m on macOS 10.15.6, and I’m using Qt 5.14.2 which has a minimum macOS version of 10.13, so Valgrind seems to be a no-go for at least one reason, perhaps two reasons (depending on “preliminary”).
Are there other approaches?
Cheers,
-B.
Benjamin C. Haller
Messer Lab
Cornell University
> On Sep 23, 2020, at 7:55 AM, Crocker, William <William.Crocker at analog.com> wrote:
>
> Valgrind.
>
>> -----Original Message-----
>> From: Interest <interest-bounces at qt-project.org> On Behalf Of Ben Haller via
>> Interest
>> Sent: Wednesday, September 23, 2020 7:50 AM
>> To: qt qt <interest at qt-project.org>
>> Subject: [Interest] Debugging a double dealloc
>>
>> [External]
>>
>> Hi all. I’m trying to figure out what appears to be a double dealloc problem of some
>> sort. I’m sure the actual bug is in my code (I’m trying to get a window with complex
>> subsidiary windows, etc., to disassemble and free the things it owns, without freeing
>> itself), but the backtrace at the point that the crash happens doesn’t have any of my
>> code in it at all. I’ve appended the full backtrace below my signature, in case it is
>> informative; maybe somebody has seen this pattern before and knows what I’m
>> likely to be doing wrong. My code does not use QFontCache or QScopedPointer at
>> all, so it’s hard to guess where my bug might be.
>>
>> My question, though, is bigger: how would folks here recommend debugging a
>> double dealloc in a Qt-based app, running under Qt Creator? I’m coming from the
>> Cocoa/Xcode world, and in that world there’s a very nice tool called NSZombie: you
>> set a flag, and then whenever an object would be deallocated, it instead turns into an
>> NSZombie object that produces nice console logs if anybody ever tries to use that
>> memory as an object again. But that’s for NSObject. Is there something similar in
>> the Qt world, such that I could get a console log or a break in the debugger at the
>> point where a C++/Qt object that has been dealloced gets touched again? Or if not,
>> how would you recommend approaching this? Thanks for any help.
>>
>> Cheers,
>> -B.
>>
>> Benjamin C. Haller
>> Messer Lab
>> Cornell University
>>
>>
>> 1 QScopedPointer<QObjectData,
>> QScopedPointerDeleter<QObjectData>>::operator->() const
>> qscopedpointer.h 118 0x10201b594
>> 2 decltype(fp.operator->()) qGetPtrHelper<QScopedPointer<QObjectData,
>> QScopedPointerDeleter<QObjectData>> const>(QScopedPointer<QObjectData,
>> QScopedPointerDeleter<QObjectData>> const&)
>> qglobal.h 1133 0x10201b594
>> 3 QObject::d_func() const
>> qobject.h 132 0x10201b594
>> 4 QObject::thread() const
>> qobject.cpp 1512 0x10201b594
>> 5 QOpenGLVertexArrayObjectPrivate::destroy()
>> qopenglvertexarrayobject.cpp 212 0x101b21481
>> 6 QOpenGLVertexArrayObject::destroy()
>> qopenglvertexarrayobject.cpp 424 0x101b217cc
>> 7 QOpenGLVertexArrayObject::~QOpenGLVertexArrayObject()
>> qopenglvertexarrayobject.cpp 392 0x101b217c3
>> 8 QOpenGLVertexArrayObject::~QOpenGLVertexArrayObject()
>> qopenglvertexarrayobject.cpp 391 0x101b217b9
>> 9 QOpenGLTextureGlyphCache::~QOpenGLTextureGlyphCache()
>> qopengltextureglyphcache.cpp 93 0x101b1cacd
>> 10 QOpenGLTextureGlyphCache::~QOpenGLTextureGlyphCache()
>> qopengltextureglyphcache.cpp 88 0x101b1cbce
>> 11 QOpenGLTextureGlyphCache::~QOpenGLTextureGlyphCache()
>> qopengltextureglyphcache.cpp 88 0x101b1cbc9
>> 12
>> QExplicitlySharedDataPointer<QFontEngineGlyphCache>::~QExplicitlySharedData
>> Pointer()
>> qshareddata.h 184 0x101883c92
>> 13
>> QExplicitlySharedDataPointer<QFontEngineGlyphCache>::~QExplicitlySharedData
>> Pointer()
>> qshareddata.h 184 0x101883c74
>> 14 QFontEngine::GlyphCacheEntry::~GlyphCacheEntry()
>> qfontengine.cpp 1570 0x101883c74
>> 15 QFontEngine::GlyphCacheEntry::~GlyphCacheEntry()
>> qfontengine.cpp 1569 0x101883c74
>> 16 void
>> std::allocator_traits<std::allocator<std::__list_node<QFontEngine::GlyphCacheEntry
>> , void
>> *>>>::__destroy<QFontEngine::GlyphCacheEntry>(std::integral_constant<bool,
>> false>, std::allocator<std::__list_node<QFontEngine::GlyphCacheEntry, void *>>&,
>> QFontEngine::GlyphCacheEntry *) memory 1732 0x101883c74
>> 17 void
>> std::allocator_traits<std::allocator<std::__list_node<QFontEngine::GlyphCacheEntry
>> , void
>> *>>>::destroy<QFontEngine::GlyphCacheEntry>(std::allocator<std::__list_node<QF
>> ontEngine::GlyphCacheEntry, void *>>&, QFontEngine::GlyphCacheEntry *)
>> memory 1595 0x101883c74
>> 18 std::__list_imp<QFontEngine::GlyphCacheEntry,
>> std::allocator<QFontEngine::GlyphCacheEntry>>::clear()
>> list 733 0x101883c74
>> 19 std::__list_imp<QFontEngine::GlyphCacheEntry,
>> std::allocator<QFontEngine::GlyphCacheEntry>>::~__list_imp()
>> list 712 0x101883c24
>> 20 std::list<QFontEngine::GlyphCacheEntry>::~list()
>> list 805 0x101883c24
>> 21 std::list<QFontEngine::GlyphCacheEntry>::~list()
>> list 805 0x101883c24
>> 22 QHashNode<void const *,
>> std::list<QFontEngine::GlyphCacheEntry>>::~QHashNode()
>> qhash.h 147 0x101883c24
>> 23 QHashNode<void const *,
>> std::list<QFontEngine::GlyphCacheEntry>>::~QHashNode()
>> qhash.h 147 0x101883c24
>> 24 QHash<void const *,
>> std::list<QFontEngine::GlyphCacheEntry>>::deleteNode2(QHashData::Node *)
>> qhash.h 563 0x101883c24
>> 25 QHashData::free_helper(void ( *)(QHashData::Node *))
>> qhash.cpp 572 0x101e5db39
>> 26 QHash<void const *,
>> std::list<QFontEngine::GlyphCacheEntry>>::freeData(QHashData *)
>> qhash.h 603 0x10187a47b
>> 27 QHash<void const *, std::list<QFontEngine::GlyphCacheEntry>>::~QHash()
>> qhash.h 250 0x10187a46f
>> 28 QHash<void const *, std::list<QFontEngine::GlyphCacheEntry>>::~QHash()
>> qhash.h 250 0x10187a44f
>> 29 QFontEngine::~QFontEngine()
>> qfontengine.cpp 277 0x10187a44f
>> 30 QCoreTextFontEngine::~QCoreTextFontEngine()
>> qfontengine_coretext.mm 215 0x105b7cf8e
>> 31 QCoreTextFontEngine::~QCoreTextFontEngine()
>> qfontengine_coretext.mm 215 0x105b7cf89
>> 32 QFontEngineMulti::~QFontEngineMulti()
>> qfontengine.cpp 1782 0x101880039
>> 33 QFontEngineMulti::~QFontEngineMulti()
>> qfontengine.cpp 1778 0x10188012e
>> 34 QFontEngineMulti::~QFontEngineMulti()
>> qfontengine.cpp 1778 0x101880129
>> 35 QFontCache::clear()
>> qfont.cpp 2861 0x1018762eb
>> 36 QFontCache::~QFontCache()
>> qfont.cpp 2817 0x10187603c
>> 37 QFontCache::~QFontCache()
>> qfont.cpp 2816 0x1018763ee
>> 38 QFontCache::~QFontCache()
>> qfont.cpp 2816 0x1018763e9
>> 39 QThreadStorageData::set(void *)
>> qthreadstorage.cpp 162 0x101e25777
>> 40 QGuiApplicationPrivate::~QGuiApplicationPrivate()
>> qguiapplication.cpp 1694 0x1017ca490
>> 41 QApplicationPrivate::~QApplicationPrivate()
>> qapplication.cpp 184 0x10116f81e
>> 42 QApplicationPrivate::~QApplicationPrivate()
>> qapplication.cpp 184 0x10116f819
>> 43 QScopedPointerDeleter<QObjectData>::cleanup(QObjectData *)
>> qscopedpointer.h 60 0x10201c06c
>> 44 QScopedPointer<QObjectData,
>> QScopedPointerDeleter<QObjectData>>::~QScopedPointer()
>> qscopedpointer.h 107 0x10201c061
>> 45 QScopedPointer<QObjectData,
>> QScopedPointerDeleter<QObjectData>>::~QScopedPointer()
>> qscopedpointer.h 105 0x10201c05d
>> 46 QObject::~QObject()
>> qobject.cpp 1119 0x10201c05d
>> 47 QApplication::~QApplication()
>> qapplication.cpp 837 0x101171b3d
>> 48 main
>> main.cpp 246 0x100012256
>> 49 start
>> (x86_64) /usr/lib/system/libdyld.dylib 0x7fff6b461cc9
>>
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