[libcamera-devel] [PATCH 1/1] fix: pipeline handlers: Stop exponential explosive calls to createPipelineHandlers

[Laurent Pinchart]

Hello,

On Mon, Mar 06, 2023 at 10:39:59AM +0530, Umang Jain via libcamera-devel wrote:
> HI Sophie,
> 
> Thank you for the patch
> 
> On 3/6/23 4:36 AM, Sophie Friedrich via libcamera-devel wrote:
> > Currently the method `createPipelineHandlers` registered itself to the

We use "function" instead of "method" in libcamera, as the term "method"
comes from Java, and the C++ standard uses "function".

> > `devicesAdded` signal at the end of each call. As the Signal object
> > supports multiple non-unique listeners connected to it, the former
>
> s/listeners/slots maybe ?
>
> > method would be called exponentially often with each new emitted event
> > on `devicesAdded` (i.e. with udev plugging in a new camera)
> 
> indeed, quite a bug!

Oops, indeed.

> > By attaching the `createPipelineHandlers` function to `devicesAdded` during
> > the first call to it / init of the `CameraManager::Private` this effect
> > is prevented.
> 
> Would repharase a bit to :
> 
> Fix it by registering the createPipelineHandlers() slot to 

s/registering/connecting/

> `devicesAdded` signal in
> CameraManager::Private::init() instead. This will prevent the slot 
> getting registered

s/registered/connected/

> multiple times to the `devicesAdded` signal.
>
> > Signed-off-by: Sophie Friedrich <dev at flowerpot.me>
> 
> LGTM
> 
> Reviewed-by: Umang Jain <umang.jain at ideasonboard.com>

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

I'll apply the minor changes mentioned above locally, no need to submit
a v2.

> > ---
> >   src/libcamera/camera_manager.cpp | 3 +--
> >   1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/src/libcamera/camera_manager.cpp b/src/libcamera/camera_manager.cpp
> > index b1785f75..c1edefda 100644
> > --- a/src/libcamera/camera_manager.cpp
> > +++ b/src/libcamera/camera_manager.cpp
> > @@ -131,6 +131,7 @@ int CameraManager::Private::init()
> >   		return -ENODEV;
> >   
> >   	createPipelineHandlers();
> > +	enumerator_->devicesAdded.connect(this, &Private::createPipelineHandlers);
> >   
> >   	return 0;
> >   }
> > @@ -165,8 +166,6 @@ void CameraManager::Private::createPipelineHandlers()
> >   				<< "\" matched";
> >   		}
> >   	}
> > -
> > -	enumerator_->devicesAdded.connect(this, &Private::createPipelineHandlers);
> >   }
> >   
> >   void CameraManager::Private::cleanup()

-- 
Regards,

Laurent Pinchart