[Development] Automatic signal-slot statistics

[Olivier Goffart]

On 2018-08-08 06:53, Taras Kushnir wrote:
> Hello
> 
> I’ve been refactoring giant pieces (like 50-60%) of one project's codebase and I’m concerned about validity/quality of the result. Except different kinds of tests I’m thinking about statistical metrics one of which would be to get a feel how Qt-specific parts of the project have changes.
> 
> Is there any way to produce statistics which signals got fired and how many times (+ the same for slots) automatically during any application runtime?
> (“any" way except of patching and recompiling Qt framework itself)


There is a way:
There is some exported private API from qobject_p.h that you can trivially 
re-declare in your project:


struct QSignalSpyCallbackSet
{
     typedef void (*BeginCallback)(QObject *caller, int signal_or_method_index, 
void **argv);
     typedef void (*EndCallback)(QObject *caller, int signal_or_method_index);
     BeginCallback signal_begin_callback,
                     slot_begin_callback;
     EndCallback signal_end_callback,
                 slot_end_callback;
};
void Q_CORE_EXPORT qt_register_signal_spy_callbacks(const QSignalSpyCallbackSet 
&callback_set);

extern QSignalSpyCallbackSet Q_CORE_EXPORT qt_signal_spy_callback_set;

https://code.woboq.org/qt5/qtbase/src/corelib/kernel/qobject_p.h.html#73


All you need to do is to call qt_register_signal_spy_callbacks to register the 
signal_begin_callback, and this will be called everytime a signal is emited. So 
you can gather some statistics from that.


-- 
Olivier

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