[libcamera-devel] [RFC 0/2] android: Introduce CameraWorker

[Laurent Pinchart]

Hi Jacopo,

On Tue, Oct 06, 2020 at 06:06:35PM +0200, Jacopo Mondi wrote:
> This two small patches, sent as RFC mostly for comments on the design,
> implement a worker in the libcamera HAL that is used to handle synchronization
> fences before queueing a Request to the libcamera::Camera.
> 
> The camera framework provides, for each buffer part of a capture request
> an acquisition fence the camera HAL is supposed to wait on before using
> the buffer. The wait procedure cannot be performed in the Camera HAL thread, as
> the HAL runs in the global CameraManager thread.

All the operations exposed by the HAL to the camera service are run in
the camera service thread, not the libcamera CameraManager.

> As fences are handled through a simple poll, it would be possible to install
> a Notifier for each fence and handle their completion through a Signal in the
> CameraDevice. Although this would make the class over-complicated.
> 
> Introducing a worker that synchronously waits on fences using its own thread
> is a cleaner design a provides a cleaner interface for the CameraDevice.
> 
> The waitFence() function implementes the same mechanism as the libdrm provided
> sync_wait() function without introducing an explicit dependency in libcamera.
> 
> 
> Jacopo Mondi (2):
>   android: camera_worker: Introduce CameraWorker
>   android: camera_device: Queue request to Worker
> 
>  src/android/camera_device.cpp | 21 ++++------
>  src/android/camera_device.h   |  3 ++
>  src/android/camera_worker.cpp | 67 +++++++++++++++++++++++++++++++
>  src/android/camera_worker.h   | 75 +++++++++++++++++++++++++++++++++++
>  src/android/meson.build       |  1 +
>  5 files changed, 154 insertions(+), 13 deletions(-)
>  create mode 100644 src/android/camera_worker.cpp
>  create mode 100644 src/android/camera_worker.h

-- 
Regards,

Laurent Pinchart