Return a local copy of m_cuePoints to avaoid a race condition

[daschuer]

The QList copy constructor seems to be not thread-safe in case it is not already shared.
https://github.com/qt/qtbase/blob/d8efc8d718e3b3a0464f321e740541f5b221a5d6/src/corelib/tools/qlist.h#L809

This may be fix
#10956
#10689
With two backtraces, where a crash originates to the same function.

[uklotzde]

Please note that there are more occurrences were this illegal assumption about implicit sharing was used, e.g. ControlDoublePrivate::getControlAliases().

[uklotzde]

Probably also the access to QFileInfo in Track requires a mutex guard.

[daschuer]

QFileInfo is implemented by QSharedDataPointer which is thread-safe, see: https://doc.qt.io/qt-5/qshareddatapointer.html#details

[uklotzde]

QFileInfo is implemented by QSharedDataPointer which is thread-safe, see: https://doc.qt.io/qt-5/qshareddatapointer.html#details

Thanks for investigating. The Qt documentation is lacking.

[uklotzde]

Nitpick: Explicitly assigning to a temporary, local variable is both redundant and uncommon when using a scoped lock primitive. This is legacy C-style and only causes noise.

[uklotzde]

I recommend to leave comments about the thread-unsafe copy constructors of QList and QHash.

[daschuer]

Done

[uklotzde]

This PR should be merged and released asap.

[Holzhaus]

LGTM, thank you.