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

[Barnabás Pőcze]

2025. január 24., péntek 12:17 keltezéssel, Jacopo Mondi <jacopo.mondi at ideasonboard.com> írta:

> 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 ?

clang-tidy for example: https://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines/special-member-functions.html


Regards,
Barnabás Pőcze

> 
> >
> >
> > 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
> > > >
> > > >
> > >
>