[RFC PATCH v2 02/16] apps: common: event_loop: Disable copy/move

[Jacopo Mondi]

Hi Barnabás

On Fri, Jan 24, 2025 at 09:23:47AM +0000, Barnabás Pőcze wrote:
> Hi
>
>
> 2025. január 22., szerda 10:03 keltezéssel, Jacopo Mondi <jacopo.mondi at ideasonboard.com> írta:
>
> > Hi Barnabás
> >
> > On Tue, Jan 14, 2025 at 06:21:56PM +0000, Barnabás Pőcze wrote:
> > > The compiler generated functions are not appropriate, so
> > > delete the copy/move constructor/assignment to avoid
> > > potential issues.
> > >
> > > Signed-off-by: Barnabás Pőcze <pobrn at protonmail.com>
> >
> > The class has this member
> > 	std::list<std::unique_ptr<Event>> events_;
> >
> > Is there a copy constructor generated for the class even if
> > unique_ptr<> do not provide one ?
>
> That list would indeed cause the copy constructor/assignment to be deleted,
> however, move constructor/assignment would still be generated, which would
> be incorrect since the owning `event_base` pointer is stored in a raw pointer.
> However, the class has an `std::mutex` member, so there are in fact no copy/move
> constructors/assignment operators defined by default.
>
> So this change does not really change much, my bad, this can be probably be ignored.
> Nonetheless, I have run into at least one situation in libcamera where a move
> constructor was defined by the compiler but semantically it was wrong. Specifically,
> it was `EventNotifier`; I am wondering if `Object` should disable copy/move altogether.
>
> In any case, I'd support it if libcamera would enforce the *rule of 0/5* more strictly.
> ( https://en.cppreference.com/w/cpp/language/rule_of_three )

Are you aware of any tooling that could help us detecting which
classes would need attention ?

>
>
> Regards,
> Barnabás Pőcze
>
> >
> > > ---
> > >  src/apps/common/event_loop.h | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/src/apps/common/event_loop.h b/src/apps/common/event_loop.h
> > > index d7d012c76..4e8dd0a46 100644
> > > --- a/src/apps/common/event_loop.h
> > > +++ b/src/apps/common/event_loop.h
> > > @@ -13,6 +13,8 @@
> > >  #include <memory>
> > >  #include <mutex>
> > >
> > > +#include <libcamera/base/class.h>
> > > +
> > >  #include <event2/util.h>
> > >
> > >  struct event_base;
> > > @@ -43,8 +45,11 @@ public:
> > >  			   std::function<void()> &&handler);
> > >
> > >  private:
> > > +	LIBCAMERA_DISABLE_COPY_AND_MOVE(EventLoop)
> > > +
> > >  	struct Event {
> > >  		Event(std::function<void()> &&callback);
> > > +		LIBCAMERA_DISABLE_COPY_AND_MOVE(Event)
> > >  		~Event();
> > >
> > >  		static void dispatch(int fd, short events, void *arg);
> > > --
> > > 2.48.0
> > >
> > >
> >