QTextToSpeech crashes app on exit (only on Linux)

Any applications initializing QTextToSpeech crash upon application exit. This happens on Linux only, Mac-OS and Windows are not affected.

 Note: This can be reproduced by executing the Hello Speech example, no changes are needed to reproduce.

The crash happens in a secondary thread while the main application is shutting down QTextToSpeech. It looks like the crashing thread is accessing a deleted synchronization object.

The bug looks similar to https://bugreports.qt.io/browse/QTBUG-55890 but this bug was reported as closed in 5.8.

This is the thread crashing:

{{1 _GI__libc_read read.c 26 0x7ffff613f17c }}

{{2 _GI__libc_read read.c 24 0x7ffff613f17c }}

{{3 _IO_new_file_underflow libioP.h 948 0x7ffff60c1d1f }}

{{4 _IO_getdelim iogetdelim.c 73 0x7ffff60b4898 }}

{{5 ?? 0x7fffe9aa3b39 }}

{{6 ?? 0x7fffe9aa3d48 }}

{{7 start_thread pthread_create.c 477 0x7ffff6014609 }}

8 clone clone.S 95 0x7ffff6150293

This is what the main thread does at the same time:

{{1 __pthread_clockjoin_ex pthread_join_common.c 145 0x7ffff6015cd7 }}

{{2 spd_close 0x7fffe9aa4281 }}

{{3 QTextToSpeechEngineSpeechd::~QTextToSpeechEngineSpeechd qtexttospeech_speechd.cpp 78 0x7fffe9ac451d }}

{{4 QTextToSpeechEngineSpeechd::~QTextToSpeechEngineSpeechd qtexttospeech_speechd.cpp 81 0x7fffe9ac4ea9 }}

{{5 QTextToSpeechPrivate::~QTextToSpeechPrivate qtexttospeech.cpp 88 0x7ffff6c2ef16 }}

{{6 QTextToSpeechPrivate::~QTextToSpeechPrivate qtexttospeech.cpp 89 0x7ffff6c2ef69 }}

{{7 QScopedPointerDeleter<QObjectData>::cleanup qscopedpointer.h 60 0x7ffff6707ee6 }}

{{8 QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData>>::~QScopedPointer qscopedpointer.h 107 0x7ffff6707ee6 }}

{{9 QObject::~QObject qobject.cpp 972 0x7ffff6707ee6 }}

{{10 QTextToSpeech::~QTextToSpeech qtexttospeech.h 54 0x7ffff6c322b7 }}

{{11 QTextToSpeech::~QTextToSpeech qtexttospeech.h 54 0x7ffff6c322b7 }}

{{12 QObjectPrivate::deleteChildren qobject.cpp 2104 0x7ffff66fd7c3 }}

{{13 QWidget::~QWidget qwidget.cpp 1522 0x7ffff7904297 }}

{{14 MainWindow::~MainWindow mainwindow.h 62 0x55555555a240 }}

15 main main.cpp 59 0x55555555a001