[libcamera-devel] [PATCH v2 3/5] libcamera: camera_manager: Introduce signals when a camera is added/removed

[Kieran Bingham]

Hi Umang,

On 13/05/2020 18:29, Umang Jain wrote:
> Emit 'cameraAdded' and 'cameraRemoved' from CameraManager to enable
> hotplug and hot-unplug support in appplications like QCam.

s/appplications/applications/


Hrm ... seeing cameraAdded and cameraRemoved, makes me think back to my
earlier signal name bikeshedding ;-) Perhaps that one should be
deviceAdded and deviceRemoved (was newDevicesFound?)

Anyway, let the bikeshedding happen on that patch instead ;-)

> Signed-off-by: Umang Jain <email at uajain.com>
> ---
>  include/libcamera/camera_manager.h |  6 +++++-
>  src/libcamera/camera_manager.cpp   | 34 +++++++++++++++++++++++++++---
>  src/libcamera/pipeline_handler.cpp |  2 +-
>  3 files changed, 37 insertions(+), 5 deletions(-)
> 
> diff --git a/include/libcamera/camera_manager.h b/include/libcamera/camera_manager.h
> index 079f848..366fa07 100644
> --- a/include/libcamera/camera_manager.h
> +++ b/include/libcamera/camera_manager.h
> @@ -13,6 +13,7 @@
>  #include <vector>
>  
>  #include <libcamera/object.h>
> +#include <libcamera/signal.h>
>  
>  namespace libcamera {
>  
> @@ -35,13 +36,16 @@ public:
>  	std::shared_ptr<Camera> get(dev_t devnum);
>  
>  	void addCamera(std::shared_ptr<Camera> camera, dev_t devnum);
> -	void removeCamera(Camera *camera);
> +	void removeCamera(std::shared_ptr<Camera> camera);
>  
>  	static const std::string &version() { return version_; }
>  
>  	void setEventDispatcher(std::unique_ptr<EventDispatcher> dispatcher);
>  	EventDispatcher *eventDispatcher();
>  
> +	Signal<std::shared_ptr<Camera>> cameraAdded;
> +	Signal<std::shared_ptr<Camera>> cameraRemoved;
> +
>  private:
>  	static const std::string version_;
>  	static CameraManager *self_;
> diff --git a/src/libcamera/camera_manager.cpp b/src/libcamera/camera_manager.cpp
> index a13cfe1..b9d2496 100644
> --- a/src/libcamera/camera_manager.cpp
> +++ b/src/libcamera/camera_manager.cpp
> @@ -186,7 +186,7 @@ void CameraManager::Private::addCamera(std::shared_ptr<Camera> &camera,
>  		}
>  	}
>  
> -	cameras_.push_back(std::move(camera));
> +	cameras_.push_back(camera);
>  
>  	if (devnum) {
>  		unsigned int index = cameras_.size() - 1;
> @@ -376,6 +376,32 @@ std::shared_ptr<Camera> CameraManager::get(dev_t devnum)
>  	return iter->second.lock();
>  }
>  
> +/**
> + * \brief Notify of a new camera added to the system

Missing the \var to reference the signal.

> + *
> + * This signal is emitted when a new camera is detected and successfully handled
> + * by the camera manager. The notification occurs alike for cameras detected
> + * when the manager is started with start() or when new cameras are later
> + * connected to the system. When the signal is emitted the new camera is already
> + * available from the list of cameras().
> + *
> + * The signal is emitted from the CameraManager thread. Applications shall
> + * minimize the time spent in the signal handler and shall in particular not
> + * perform any blocking operation.
> + */
> +
> +/**

And missing here too.

> + * \brief Notify of a new camera removed from the system
> + *
> + * This signal is emitted when a camera is removed from the system. When the
> + * signal is emitted the camera is not available from the list of cameras()
> + * anymore.
> + *
> + * The signal is emitted from the CameraManager thread. Applications shall
> + * minimize the time spent in the signal handler and shall in particular not
> + * perform any blocking operation.
> + */
> +
>  /**
>   * \brief Add a camera to the camera manager
>   * \param[in] camera The camera to be added
> @@ -395,6 +421,7 @@ void CameraManager::addCamera(std::shared_ptr<Camera> camera, dev_t devnum)
>  	ASSERT(Thread::current() == p_.get());
>  
>  	p_->addCamera(camera, devnum);
> +	cameraAdded.emit(camera);
>  }
>  
>  /**
> @@ -407,11 +434,12 @@ void CameraManager::addCamera(std::shared_ptr<Camera> camera, dev_t devnum)
>   *
>   * \context This function shall be called from the CameraManager thread.
>   */
> -void CameraManager::removeCamera(Camera *camera)
> +void CameraManager::removeCamera(std::shared_ptr<Camera> camera)
>  {
>  	ASSERT(Thread::current() == p_.get());
>  
> -	p_->removeCamera(camera);
> +	p_->removeCamera(camera.get());
> +	cameraRemoved.emit(camera);

Is there any race here, or potential problem emitting the signal with
the camera, after it's been removed from the CameraManager? (I
hope/expect not as it's using a shared_ptr ... But I haven't checked to
see if there are any implications caused by the removeCamera call)


>  }
>  
>  /**
> diff --git a/src/libcamera/pipeline_handler.cpp b/src/libcamera/pipeline_handler.cpp
> index 254d341..a9187e1 100644
> --- a/src/libcamera/pipeline_handler.cpp
> +++ b/src/libcamera/pipeline_handler.cpp
> @@ -555,7 +555,7 @@ void PipelineHandler::disconnect()
>  			continue;
>  
>  		camera->disconnect();
> -		manager_->removeCamera(camera.get());
> +		manager_->removeCamera(camera);
>  	}
>  
>  	cameras_.clear();
> 

-- 
Regards
--
Kieran