[libcamera-devel] [PATCH v2 09/14] libcamera: v4l2_device: Avoid copy of V4L2ControlInfo

[Jacopo Mondi]

Hi Laurent,

On Sat, Oct 12, 2019 at 09:44:02PM +0300, Laurent Pinchart wrote:
> The V4L2Device::listControls() method creates an instance of
> V4L2ControlInfo and then inserts it in the device's list of controls.
> The insertion uses std::map::emplace(), but passes the V4L2ControlInfo,
> resulting in a copy being performed (using the copy constructor of
> V4L2ControlInfo).
>
> Optimise this by really constructing the V4L2ControlInfo in-place. The
> use of std::piecewise_construct is required for gcc-5 that seems to have
> trouble with std::map::emplace() on non-copyable values in this case.

Thanks for fixing this, even if it will go away in next patches I
think

Acked-by: Jacopo Mondi <jacopo at jmondi.org>

Thanks
   j

>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/libcamera/v4l2_device.cpp | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> index fd4b9c6d5c62..3bd82ff23212 100644
> --- a/src/libcamera/v4l2_device.cpp
> +++ b/src/libcamera/v4l2_device.cpp
> @@ -352,8 +352,7 @@ void V4L2Device::listControls()
>  		    ctrl.flags & V4L2_CTRL_FLAG_DISABLED)
>  			continue;
>
> -		V4L2ControlInfo info(ctrl);
> -		switch (info.type()) {
> +		switch (ctrl.type) {
>  		case V4L2_CTRL_TYPE_INTEGER:
>  		case V4L2_CTRL_TYPE_BOOLEAN:
>  		case V4L2_CTRL_TYPE_MENU:
> @@ -364,12 +363,14 @@ void V4L2Device::listControls()
>  			break;
>  		/* \todo Support compound controls. */
>  		default:
> -			LOG(V4L2, Debug) << "Control type '" << info.type()
> +			LOG(V4L2, Debug) << "Control type '" << ctrl.type
>  					 << "' not supported";
>  			continue;
>  		}
>
> -		controls_.emplace(ctrl.id, info);
> +		controls_.emplace(std::piecewise_construct,
> +				  std::forward_as_tuple(ctrl.id),
> +				  std::forward_as_tuple(ctrl));
>  	}
>  }
>
> --
> Regards,
>
> Laurent Pinchart
>
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> libcamera-devel at lists.libcamera.org
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