1. machine_info.h: zero-initialise Screen struct members
Max_width, Max_height, count, width[] and height[] were bare
int32_t with no initialiser. The comparisons in
init_get_Screen_info() read them before any write, producing
undefined behaviour flagged by Valgrind as 'Conditional jump
or move depends on uninitialised value(s)'.
2. main.cpp: pre-initialise MachineInfo on the main thread
MachineInfo::instance() was first called inside QtConcurrent::run(),
causing its constructor (which calls qApp->screens()) to run on a
background thread. QScreen methods are not thread-safe in Qt5.
Calling instance() once on the main thread before the worker
launches guarantees the singleton is fully built first; subsequent
calls from the worker just return the cached pointer.
3. qetdiagrameditor.h: move m_first_show before the QActionGroup members
C++ initialises members in declaration order. m_first_show was
declared after the QActionGroup members (line 256 vs 168). During
construction of m_row_column_actions_group(this), Qt dispatches a
QObject parent-change event that reaches QETDiagramEditor::event(),
which reads m_first_show before it has been initialised.
Moving the declaration to the top of the first private: block
ensures it is initialised before any member that can trigger events.
All three found via Valgrind --tool=memcheck on Ubuntu 22.04 / Qt 5.15.3.
Relates-to: PR #514 (same QtConcurrent thread-safety pattern).
Because on windows MachineInfo take a little time to init, we make it to
a singleton.
MachineInfo is build the first time in main.cpp.
Now all other places where we use MachineInfo (aboutqetdialog and
configdialog) gui don't hang anymore in waiting to MachineInfo finish to
build.
Instead of build machine_info class which take time, only to get the max
width and height of screens, call of methods
Machine_info::i_max_screen_width() and
Machine_info::i_max_screen_height() are now static and compute only
this.
The project properties dialog is now faster because don't wait the end
build of machine_info.
Shane Ringrose