Shotcut crashes after timeline undo operations with MLT 7.20.0

[BSDKaffee]

MLT version 7.20.0; FreeBSD 15-CURRENT; all versions of Shotcut seem to be affected, even Qt5-based versions like 22.06.23. Kdenlive does not seem to be affected.

After b4943c5, Shotcut consistently crashes after opening a project, selecting a clip from the timeline, hitting Ctrl+X, then Ctrl+Z, similar to the issue noted in that commit by @ddennedy. Subsequent commits attempting to resolve the issue 8a821cc and 5eefee5 have had no effect. Applying 20b9bc7 from #951 on top of HEAD resolves the issue for me.

Crash log from Shotcut 23.09.29 built against MLT 7.20.0:

#0  check_and_init_mutex (mutex=0x5a5a5a5a5a5a5da2, m=<optimized out>) at /usr/src/lib/libthr/thread/thr_mutex.c:595
595             *m = *mutex;
[Current thread is 1 (LWP 772468)]
(gdb) bt
#0  check_and_init_mutex (mutex=0x5a5a5a5a5a5a5da2, m=<optimized out>) at /usr/src/lib/libthr/thread/thr_mutex.c:595
#1  __Tthr_mutex_lock (mutex=0x5a5a5a5a5a5a5da2) at /usr/src/lib/libthr/thread/thr_mutex.c:751
#2  0x0000000828b8956b in mlt_properties_lock (self=0x4cd9cc64180)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_properties.c:2187
#3  0x0000000828b89a8c in mlt_properties_find (self=0x4cd9cc64180, name=0x828b60b48 "_events")
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_properties.c:542
#4  0x0000000828b8a841 in mlt_properties_get_data (self=0x4cd9cc64180, name=0x828b60b48 "_events", length=0x0)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_properties.c:1226
#5  0x0000000828b751e3 in mlt_events_fetch (self=0x4cd9cc64180)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_events.c:450
#6  0x0000000828b75b59 in mlt_events_disconnect (self=0x4cd9cc64180, listener_data=0x4cdd9f61400)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_events.c:347
#7  0x0000000873948e51 in producer_avformat_close (self=0x4cdd9f61400)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/modules/avformat/producer_avformat.c:3855
#8  0x0000000828b6e0d3 in cache_object_close (cache=0x4cd59d34a00, object=0x4cd9cc64180, data=0x4cdd9f61400)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_cache.c:145
#9  0x0000000828b6dfc6 in mlt_cache_item_close (item=0x4cdda197e70)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_cache.c:189
#10 0x0000000828b8e36f in clear_property (self=0x4cdf118cb60)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_property.c:113
#11 0x0000000828b8f8e5 in mlt_property_close (self=0x4cdf118cb60)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_property.c:884
#12 0x0000000828b8b744 in mlt_properties_close (self=0x4cdd881bdc0)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_properties.c:1508
#13 0x0000000828b7934a in mlt_frame_close (self=0x4cdd881bdc0)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_frame.c:827
#14 0x0000000828b8e36f in clear_property (self=0x4cdd89f53c0)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_property.c:113
#15 0x0000000828b8f8e5 in mlt_property_close (self=0x4cdd89f53c0)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_property.c:884
#16 0x0000000828b8b744 in mlt_properties_close (self=0x4cdd881bd20)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_properties.c:1508
#17 0x0000000828b7934a in mlt_frame_close (self=0x4cdd881bd20)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/framework/mlt_frame.c:827
#18 0x0000000826720f1b in Mlt::Frame::~Frame() (this=0x4cdd8809158)
    at /usr/home/jhale/src/freebsd/ports/multimedia/mlt7/work/mlt-7.20.0/src/mlt++/MltFrame.cpp:53
#19 0x0000000000777e0a in FrameData::~FrameData() (this=0x4cdd8809150)
    at /usr/home/jhale/src/freebsd/ports/multimedia/shotcut/work/src/shotcut/src/sharedframe.cpp:32
#20 0x0000000000777e9f in QExplicitlySharedDataPointer<FrameData>::reset(FrameData*) (this=0x4cd9ca37210, ptr=0x4cdd8809180)
    at /usr/local/include/qt6/QtCore/qshareddata.h:178
#21 0x0000000000777d34 in QExplicitlySharedDataPointer<FrameData>::operator=(QExplicitlySharedDataPointer<FrameData> const&)
    (this=0x4cd9ca37210, o=...) at /usr/local/include/qt6/QtCore/qshareddata.h:184
#22 0x0000000000776ee1 in SharedFrame::operator=(SharedFrame const&) (this=0x4cd9ca37210, other=...)
    at /usr/home/jhale/src/freebsd/ports/multimedia/shotcut/work/src/shotcut/src/sharedframe.cpp:61
--Type <RET> for more, q to quit, c to continue without paging--
#23 0x0000000000834a27 in AudioWaveformScopeWidget::refreshScope(QSize const&, bool) (this=0x4cd9ca37100, size=..., full=false)
    at /usr/home/jhale/src/freebsd/ports/multimedia/shotcut/work/src/shotcut/src/widgets/scopes/audiowaveformscopewidget.cpp:80
#24 0x0000000000836d2e in ScopeWidget::refreshInThread() (this=0x4cd9ca37100)
    at /usr/home/jhale/src/freebsd/ports/multimedia/shotcut/work/src/shotcut/src/widgets/scopes/scopewidget.cpp:68
#25 0x00000000008376c9 in std::__1::__invoke[abi:v160006]<void (ScopeWidget::*&)(), ScopeWidget*&, , void>(void (ScopeWidget::*&)(), ScopeWidget*&) (__f=@0x90e7d7d38: &virtual ScopeWidget::refreshInThread(), __a0=@0x90e7d7d30: 0x4cd9ca37100) at /usr/include/c++/v1/__functional/invoke.h:359
#26 0x000000000083764d in std::__1::invoke[abi:v160006]<void (ScopeWidget::*&)(), ScopeWidget*&>(void (ScopeWidget::*&)(), ScopeWidget*&)
    (__f=@0x90e7d7d38: &virtual ScopeWidget::refreshInThread(), __args=@0x90e7d7d30: 0x4cd9ca37100)
    at /usr/include/c++/v1/__functional/invoke.h:539
#27 0x0000000000837603 in QtConcurrent::StoredFunctionCall<void (ScopeWidget::*)(), ScopeWidget*>::runFunctor()::{lambda(void (ScopeWidget::*)(), ScopeWidget*)#1}::operator()(void (ScopeWidget::*)(), ScopeWidget*) const
    (this=0x90e7d7e20, function=&virtual ScopeWidget::refreshInThread(), args=0x4cd9ca37100)
    at /usr/local/include/qt6/QtConcurrent/qtconcurrentstoredfunctioncall.h:116
#28 0x000000000083756f in std::__1::__invoke[abi:v160006]<QtConcurrent::StoredFunctionCall<void (ScopeWidget::*)(), ScopeWidget*>::runFunctor()::{lambda(void (ScopeWidget::* const&)(), ScopeWidget*)#1}, void (ScopeWidget::*)(), ScopeWidget*>(QtConcurrent::StoredFunctionCall<void (ScopeWidget::*)(), ScopeWidget*>::runFunctor()::{lambda(void (ScopeWidget::* const&)(), ScopeWidget*)#1}, void (ScopeWidget::*&&)(), ScopeWidget*&&)
    (__f=..., __args=@0x4cdecd53d20: &virtual ScopeWidget::refreshInThread(), __args=@0x4cdecd53d30: 0x4cd9ca37100)
    at /usr/include/c++/v1/__functional/invoke.h:394
#29 0x000000000083751e in std::__1::__apply_tuple_impl[abi:v160006]<QtConcurrent::StoredFunctionCall<void (ScopeWidget::*)(), ScopeWidget*>::runFunctor()::{lambda(void (ScopeWidget::* const&)(), ScopeWidget*)#1}, std::__1::tuple<void (ScopeWidget::*)(), ScopeWidget*>, 0ul, 1ul>(QtConcurrent::StoredFunctionCall<void (ScopeWidget::*)(), ScopeWidget*>::runFunctor()::{lambda(void (ScopeWidget::* const&)(), ScopeWidget*)#1}, std::__1::tuple<void (ScopeWidget::*)(), ScopeWidget*>&&, std::__1::__tuple_indices<0ul, 1ul>) (__f=..., __t=...) at /usr/include/c++/v1/tuple:1816
#30 0x00000000008374cd in std::__1::apply[abi:v160006]<QtConcurrent::StoredFunctionCall<void (ScopeWidget::*)(), ScopeWidget*>::runFunctor()::{lambda(void (ScopeWidget::* const&)(), ScopeWidget*)#1}, std::__1::tuple<void (ScopeWidget::*)(), ScopeWidget*> >(QtConcurrent::StoredFunctionCall<void (ScopeWidget::*)(), ScopeWidget*>::runFunctor()::{lambda(void (ScopeWidget::* const&)(), ScopeWidget*)#1}, std::__1::tuple<void (ScopeWidget::*)(), ScopeWidget*>&&) (__f=..., __t=...) at /usr/include/c++/v1/tuple:1825
#31 0x0000000000837484 in QtConcurrent::StoredFunctionCall<void (ScopeWidget::*)(), ScopeWidget*>::runFunctor() (this=0x4cdecd53d00)
    at /usr/local/include/qt6/QtConcurrent/qtconcurrentstoredfunctioncall.h:120
#32 0x00000000004ccfa7 in QtConcurrent::RunFunctionTaskBase<void>::run() (this=0x4cdecd53d00)
    at /usr/local/include/qt6/QtConcurrent/qtconcurrentrunbase.h:83
#33 0x0000000832c9e672 in  () at /usr/local/lib/qt6/libQt6Core.so.6
#34 0x0000000832c9a5b0 in  () at /usr/local/lib/qt6/libQt6Core.so.6
#35 0x00000008348f1a75 in thread_start (curthread=0x4cddaaa5e00) at /usr/src/lib/libthr/thread/thr_create.c:290
#36 0x0000000000000000 in  ()

[ddennedy]

I have not been able to reproduce it or my steps in the comment on b4943c5

[BSDKaffee]

Strange. Even after creating a new project, opening a file, adding the source to the playlist, dragging it to the timeline, then hitting CTRL+Z, it crashes. After applying 20b9bc7 or before b4943c5 this does not happen.