android: camera_worker: Introduce CameraWorker

The Android 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. As the libcamera HAL runs in the camera service
thread, it is not possible to perform a synchronous wait there.

Introduce a CameraWorker class that runs an internal thread to wait
on a set of fences before queueing a capture request to the
libcamera::Camera.

Fences completion is handled through a simple poll, similar in
implementation to the sync_wait() function provided by libdrm.

Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

src/android/meson.build

@@ -21,6 +21,7 @@ android_hal_sources = files([
     'camera_metadata.cpp',
     'camera_ops.cpp',
     'camera_stream.cpp',
+    'camera_worker.cpp',
     'jpeg/encoder_libjpeg.cpp',
     'jpeg/exif.cpp',
 ])