[libcamera-devel] [RFC 1/2] android: camera_worker: Introduce CameraWorker

[Jacopo Mondi]

Hi Niklas,

On Wed, Oct 07, 2020 at 02:30:00PM +0200, Niklas Söderlund wrote:
> Hi Jacopo,
>
> Thanks for your work.
>
> On 2020-10-06 18:06:36 +0200, Jacopo Mondi wrote:
> > The CameraWork class creates a Worker instance and runs on an internal
> > thread. The worker waits on a set of fences before queueing a capture
> > requests to the the libcamera::Camera.
>
> I really like this solution!
>
> >
> > Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> > ---
> >  src/android/camera_worker.cpp | 67 +++++++++++++++++++++++++++++++
> >  src/android/camera_worker.h   | 75 +++++++++++++++++++++++++++++++++++
> >  src/android/meson.build       |  1 +
> >  3 files changed, 143 insertions(+)
> >  create mode 100644 src/android/camera_worker.cpp
> >  create mode 100644 src/android/camera_worker.h
> >
> > diff --git a/src/android/camera_worker.cpp b/src/android/camera_worker.cpp
> > new file mode 100644
> > index 000000000000..2bb94775a195
> > --- /dev/null
> > +++ b/src/android/camera_worker.cpp
> > @@ -0,0 +1,67 @@
> > +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> > +/*
> > + * Copyright (C) 2020, Google Inc.
> > + *
> > + * camera_worker.cpp - Process capture request on behalf of the Camera HAL
> > + */
> > +
> > +#include "camera_worker.h"
> > +
> > +#include <errno.h>
> > +#include <sys/poll.h>
> > +
> > +#include "camera_device.h"
> > +
> > +using namespace libcamera;
> > +
> > +CameraWorker::CameraWorker(const std::shared_ptr<Camera> &camera)
> > +	: camera_(camera), worker_(camera_.get())
> > +{
> > +	worker_.moveToThread(&thread_);
> > +	thread_.start();
> > +}
> > +
> > +void CameraWorker::queueRequest(std::unique_ptr<CaptureRequest> request)
> > +{
> > +	CaptureRequest *req = request.release();
> > +	worker_.invokeMethod(&Worker::processRequest, ConnectionTypeQueued, req);
> > +}
> > +
> > +int CameraWorker::Worker::waitFence(int fence)
> > +{
> > +	struct pollfd fds = { fence, POLLIN, 0 };
> > +	constexpr unsigned int timeoutMs = 300;
> > +	int ret;
> > +
> > +	do {
> > +		ret = poll(&fds, 1, timeoutMs);
> > +		if (ret == 0)
> > +			return -ETIME;
> > +
> > +		if (ret > 0) {
> > +			if (fds.revents & (POLLERR | POLLNVAL))
> > +				return -EINVAL;
> > +
> > +			return 0;
> > +		}
> > +	} while (ret == -1 && (errno == EINTR || errno == EAGAIN));
> > +
> > +	return ret;
> > +}
> > +
> > +void CameraWorker::Worker::processRequest(CaptureRequest *request)
> > +{
> > +	for (int fence : request->acquireFences_) {
> > +		if (fence == -1)
> > +			continue;
> > +
> > +		int ret = waitFence(fence);
> > +		if (ret < 0)
> > +			return;
> > +
> > +		close(fence);
> > +	}
>
> If you move this to a new function CaptureRequest::waitFences() you cold
> remove the friend statement :-)
>

How can I do so ? A CameraRequest is created by the CameraDevice and
moved to the CameraWorker. Then the CameraWorker schedules it on its
worker_ which runs in a dedicated thread (that's why it can wait
without interrupting the HAL thread).

Should I moveToThread() every CaptureRequest we receive ? It's
potentially a costly operation as it interrupts the thread's even
dispatcher and potentially moves messages from one queue to another.

I don't think it's worth it ?

> > +
> > +	camera_->queueRequest(request->request_);
> > +	delete request;
> > +}
> > diff --git a/src/android/camera_worker.h b/src/android/camera_worker.h
> > new file mode 100644
> > index 000000000000..24b176d6269c
> > --- /dev/null
> > +++ b/src/android/camera_worker.h
> > @@ -0,0 +1,75 @@
> > +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> > +/*
> > + * Copyright (C) 2020, Google Inc.
> > + *
> > + * camera_worker.h - Process capture request on behalf of the Camera HAL
> > + */
> > +#ifndef __ANDROID_CAMERA_WORKER_H__
> > +#define __ANDROID_CAMERA_WORKER_H__
> > +
> > +#include <memory>
> > +
> > +#include <libcamera/buffer.h>
> > +#include <libcamera/camera.h>
> > +#include <libcamera/object.h>
> > +#include <libcamera/request.h>
> > +#include <libcamera/stream.h>
> > +
> > +#include "libcamera/internal/thread.h"
> > +
> > +class CameraDevice;
> > +
> > +struct CaptureRequest {
> > +	CaptureRequest(libcamera::Request *request)
> > +		: request_(request)
> > +	{
> > +	}
> > +
> > +	void addBuffer(libcamera::Stream *stream,
> > +		       libcamera::FrameBuffer *buffer, int fence)
> > +	{
> > +		request_->addBuffer(stream, buffer);
> > +		acquireFences_.push_back(fence);
> > +	}
>
> If you move these to the .cpp file you can get away with forward
> declaration of most of the classes used.

Not really, as I can't forward declare symbols from a namespace.

>
> > +
> > +private:
> > +	friend class CameraWorker;
> > +
> > +	std::vector<int> acquireFences_;
> > +	libcamera::Request *request_;
> > +};
> > +
> > +class CameraWorker
> > +{
> > +public:
> > +	CameraWorker(const std::shared_ptr<libcamera::Camera> &camera);
> > +
> > +	void queueRequest(std::unique_ptr<CaptureRequest> request);
> > +
> > +private:
> > +	class Worker : public libcamera::Object
> > +	{
> > +	public:
> > +		Worker(libcamera::Camera *camera)
> > +			: camera_(camera)
> > +		{
> > +		}
> > +		~Worker()
> > +		{
> > +		}
> > +
> > +		void processRequest(CaptureRequest *request);
> > +
> > +	private:
> > +		int waitFence(int fence);
> > +
> > +		libcamera::Camera *camera_;
> > +	};
> > +
> > +	std::shared_ptr<libcamera::Camera> camera_;
>
> Could you not remove this and store a shared_ptr inside the Worker?
>

mmm, yes I probably should, there's no point in having the
shared_ptr<> here and passing the raw pointer to the worker.

Thanks
  j

> > +
> > +	Worker worker_;
> > +	libcamera::Thread thread_;
> > +};
> > +
> > +#endif /* __ANDROID_CAMERA_WORKER_H__ */
> > diff --git a/src/android/meson.build b/src/android/meson.build
> > index 802bb89afe57..b2b2293cf62d 100644
> > --- a/src/android/meson.build
> > +++ b/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',
> >  ])
> > --
> > 2.28.0
> >
> > _______________________________________________
> > libcamera-devel mailing list
> > libcamera-devel at lists.libcamera.org
> > https://lists.libcamera.org/listinfo/libcamera-devel
>
> --
> Regards,
> Niklas Söderlund