[libcamera-devel] [PATCH v4 7/9] android: camera_device: Add methods to get and return buffers

[Laurent Pinchart]

Hi Jacopo,

Thank you for the patch.

On Wed, Sep 30, 2020 at 03:27:05PM +0200, Jacopo Mondi wrote:
> Add two methods to the CameraDevice class to retrieve and return
> frame buffers associated to a stream from the memory pool reserved
> in libcamera.
> 
> Protect accessing the vector of FrameBuffer pointers with a
> per-pool mutex in the get and return buffer methods.
> 
> Reviewed-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> ---
>  src/android/camera_device.cpp | 34 +++++++++++++++++++++++++++++++++-
>  src/android/camera_device.h   | 11 +++++++++--
>  2 files changed, 42 insertions(+), 3 deletions(-)
> 
> diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
> index 07041dd916d5..2ebc3fcc336e 100644
> --- a/src/android/camera_device.cpp
> +++ b/src/android/camera_device.cpp
> @@ -8,6 +8,7 @@
>  #include "camera_device.h"
>  #include "camera_ops.h"
>  
> +#include <mutex>

You have that in camera_device.h already.

>  #include <sys/mman.h>
>  #include <tuple>
>  #include <vector>
> @@ -1402,11 +1403,42 @@ int CameraDevice::allocateBufferPool(Stream *stream)
>  	 * the HAL.
>  	 */
>  	for (const auto &frameBuffer : allocator_.buffers(stream))
> -		bufferPool_[stream].push_back(frameBuffer.get());
> +		bufferPool_[stream].buffers.push_back(frameBuffer.get());
>  
>  	return 0;
>  }
>  
> +libcamera::FrameBuffer *CameraDevice::getBuffer(libcamera::Stream *stream)
> +{
> +	if (bufferPool_.find(stream) == bufferPool_.end())
> +		return nullptr;
> +
> +	BufferPool *pool = &bufferPool_[stream];

	auto iter = bufferPool_.find(stream);
	if (iter == bufferPool_.end())
		return nullptr;

	BufferPool *pool = &iter->second;

to avoid a double lookup. Same below.

> +	std::lock_guard<std::mutex> locker(pool->mutex);
> +
> +	if (pool->buffers.empty()) {
> +		LOG(HAL, Error) << "Buffer underrun";
> +		return nullptr;
> +	}
> +
> +	FrameBuffer *buffer = pool->buffers.front();
> +	pool->buffers.erase(pool->buffers.begin());

Erasing an element at the front isn't nice, as all the elements will
have to move. Wouldn't it be better to use a std::queue ? Alternatively
you can use use back() and pop_back(), as we don't need to cycle through
buffers in order.

> +
> +	return buffer;
> +}
> +
> +void CameraDevice::returnBuffer(libcamera::Stream *stream,
> +				libcamera::FrameBuffer *buffer)
> +{
> +	if (bufferPool_.find(stream) == bufferPool_.end())
> +		return;
> +
> +	BufferPool *pool = &bufferPool_[stream];
> +	std::lock_guard<std::mutex> locker(pool->mutex);
> +
> +	pool->buffers.push_back(buffer);
> +}
> +
>  int CameraDevice::processCaptureRequest(camera3_capture_request_t *camera3Request)
>  {
>  	if (!camera3Request->num_output_buffers) {
> diff --git a/src/android/camera_device.h b/src/android/camera_device.h
> index c46610725e12..c91de367d7bd 100644
> --- a/src/android/camera_device.h
> +++ b/src/android/camera_device.h
> @@ -9,6 +9,7 @@
>  
>  #include <map>
>  #include <memory>
> +#include <mutex>
>  #include <tuple>
>  #include <vector>
>  
> @@ -166,8 +167,11 @@ protected:
>  	std::string logPrefix() const override;
>  
>  private:
> -	using FrameBufferPool = std::map<libcamera::Stream *,
> -					 std::vector<libcamera::FrameBuffer *>>;
> +	struct BufferPool {
> +		std::mutex mutex;
> +		std::vector<libcamera::FrameBuffer *> buffers;
> +	};
> +	using FrameBufferPool = std::map<libcamera::Stream *, BufferPool>;

I think I'd squash this patch with the previous one.

And wouldn't it be best to store the pool in the CameraStream class ?
The callers of allocateBufferPool(), getBuffer() and returnBuffer() all
have a pointer to the CameraStream.

>  
>  	CameraDevice(unsigned int id, const std::shared_ptr<libcamera::Camera> &camera);
>  
> @@ -198,6 +202,9 @@ private:
>  	std::tuple<uint32_t, uint32_t> calculateStaticMetadataSize();
>  	libcamera::FrameBuffer *createFrameBuffer(const buffer_handle_t camera3buffer);
>  	int allocateBufferPool(libcamera::Stream *stream);
> +	libcamera::FrameBuffer *getBuffer(libcamera::Stream *stream);
> +	void returnBuffer(libcamera::Stream *stream,
> +			  libcamera::FrameBuffer *buffer);
>  
>  	void notifyShutter(uint32_t frameNumber, uint64_t timestamp);
>  	void notifyError(uint32_t frameNumber, camera3_stream_t *stream);

-- 
Regards,

Laurent Pinchart