[libcamera-devel] [PATCH v2 09/13] libcamera: camera_manager: Run the camera manager in a thread

[Niklas Söderlund]

Hi Laurent,

Thanks for breaking this apart.

On 2020-01-22 22:57:19 +0200, Laurent Pinchart wrote:
> Relying on the application event loop to process all our internal events
> is a bad idea for multiple reasons. In many cases the user of libcamera
> can't provide an event loop, for instance when running through one of
> the adaptation layers. The Android camera HAL and V4L2 compatibility
> layer create a thread for this reason, and the GStreamer element would
> need to do so as well. Furthermore, relying on the application event
> loop pushes libcamera's realtime constraints to the application, which
> isn't manageable.
> 
> For these reasons it's desirable to always run the camera manager, the
> pipeline handlers and the cameras in a separate thread. Doing so isn't
> too complicated, it only involves creating the thread internally when
> starting the camera manager, and synchronizing a few methods of the
> Camera class. Do so as a first step towards defining the threading model
> of libcamera.
> 
> The event dispatcher interface is still exposed to applications, to
> enable cross-thread signal delivery if desired.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
> Changes since v1:
> 
> - Move "libcamera: camera_manager: Move private data members to private
>   implementation" and "libcamera: camera_manager: Return a copy of the
>   vector from cameras()" to separate patches
> ---
>  src/libcamera/camera_manager.cpp | 94 ++++++++++++++++++++++++++++++--
>  1 file changed, 88 insertions(+), 6 deletions(-)
> 
> diff --git a/src/libcamera/camera_manager.cpp b/src/libcamera/camera_manager.cpp
> index 5fc1bba974c6..11c333ccb4e0 100644
> --- a/src/libcamera/camera_manager.cpp
> +++ b/src/libcamera/camera_manager.cpp
> @@ -7,6 +7,7 @@
>  
>  #include <libcamera/camera_manager.h>
>  
> +#include <condition_variable>
>  #include <map>
>  
>  #include <libcamera/camera.h>
> @@ -28,33 +29,89 @@ namespace libcamera {
>  
>  LOG_DEFINE_CATEGORY(Camera)
>  
> -class CameraManager::Private
> +class CameraManager::Private : public Thread
>  {
>  public:
>  	Private(CameraManager *cm);
>  
>  	int start();
> -	void stop();
> -
>  	void addCamera(std::shared_ptr<Camera> &camera, dev_t devnum);
>  	void removeCamera(Camera *camera);
>  
> +	/*
> +	 * This mutex protects
> +	 *
> +	 * - initialized_ and status_ during initialization
> +	 * - cameras_ and camerasByDevnum_ after initialization
> +	 */
> +	Mutex mutex_;
>  	std::vector<std::shared_ptr<Camera>> cameras_;
>  	std::map<dev_t, std::weak_ptr<Camera>> camerasByDevnum_;
>  
> +protected:
> +	void run() override;
> +
>  private:
> +	int init();
> +	void cleanup();
> +
>  	CameraManager *cm_;
>  
> +	std::condition_variable cv_;
> +	bool initialized_;
> +	int status_;
> +
>  	std::vector<std::shared_ptr<PipelineHandler>> pipes_;
>  	std::unique_ptr<DeviceEnumerator> enumerator_;
>  };
>  
>  CameraManager::Private::Private(CameraManager *cm)
> -	: cm_(cm)
> +	: cm_(cm), initialized_(false)
>  {
>  }
>  
>  int CameraManager::Private::start()
> +{
> +	/* Start the thread and wait for initialization to complete. */
> +	Thread::start();
> +
> +	{
> +		MutexLocker locker(mutex_);
> +		cv_.wait(locker, [&] { return initialized_; });
> +	}

Do you not wish to copy status_ and use it bellow while the mutex is 
still locked?

With this issue resolved,

Reviewed-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>

> +
> +	/* If a failure happened during initialization, stop the thread. */
> +	if (status_ < 0) {
> +		exit();
> +		wait();
> +		return status_;
> +	}
> +
> +	return 0;
> +}
> +
> +void CameraManager::Private::run()
> +{
> +	LOG(Camera, Debug) << "Starting camera manager";
> +
> +	int ret = init();
> +
> +	mutex_.lock();
> +	status_ = ret;
> +	initialized_ = true;
> +	mutex_.unlock();
> +	cv_.notify_one();
> +
> +	if (ret < 0)
> +		return;
> +
> +	/* Now start processing events and messages. */
> +	exec();
> +
> +	cleanup();
> +}
> +
> +int CameraManager::Private::init()
>  {
>  	enumerator_ = DeviceEnumerator::create();
>  	if (!enumerator_ || enumerator_->enumerate())
> @@ -89,7 +146,7 @@ int CameraManager::Private::start()
>  	return 0;
>  }
>  
> -void CameraManager::Private::stop()
> +void CameraManager::Private::cleanup()
>  {
>  	/* TODO: unregister hot-plug callback here */
>  
> @@ -107,6 +164,8 @@ void CameraManager::Private::stop()
>  void CameraManager::Private::addCamera(std::shared_ptr<Camera> &camera,
>  				       dev_t devnum)
>  {
> +	MutexLocker locker(mutex_);
> +
>  	for (std::shared_ptr<Camera> c : cameras_) {
>  		if (c->name() == camera->name()) {
>  			LOG(Camera, Warning)
> @@ -126,6 +185,8 @@ void CameraManager::Private::addCamera(std::shared_ptr<Camera> &camera,
>  
>  void CameraManager::Private::removeCamera(Camera *camera)
>  {
> +	MutexLocker locker(mutex_);
> +
>  	auto iter = std::find_if(cameras_.begin(), cameras_.end(),
>  				 [camera](std::shared_ptr<Camera> &c) {
>  					 return c.get() == camera;
> @@ -232,7 +293,8 @@ int CameraManager::start()
>   */
>  void CameraManager::stop()
>  {
> -	p_->stop();
> +	p_->exit();
> +	p_->wait();
>  }
>  
>  /**
> @@ -242,10 +304,14 @@ void CameraManager::stop()
>   * Before calling this function the caller is responsible for ensuring that
>   * the camera manager is running.
>   *
> + * \context This function is \threadsafe.
> + *
>   * \return List of all available cameras
>   */
>  std::vector<std::shared_ptr<Camera>> CameraManager::cameras() const
>  {
> +	MutexLocker locker(p_->mutex_);
> +
>  	return p_->cameras_;
>  }
>  
> @@ -256,10 +322,14 @@ std::vector<std::shared_ptr<Camera>> CameraManager::cameras() const
>   * Before calling this function the caller is responsible for ensuring that
>   * the camera manager is running.
>   *
> + * \context This function is \threadsafe.
> + *
>   * \return Shared pointer to Camera object or nullptr if camera not found
>   */
>  std::shared_ptr<Camera> CameraManager::get(const std::string &name)
>  {
> +	MutexLocker locker(p_->mutex_);
> +
>  	for (std::shared_ptr<Camera> camera : p_->cameras_) {
>  		if (camera->name() == name)
>  			return camera;
> @@ -279,11 +349,15 @@ std::shared_ptr<Camera> CameraManager::get(const std::string &name)
>   * Before calling this function the caller is responsible for ensuring that
>   * the camera manager is running.
>   *
> + * \context This function is \threadsafe.
> + *
>   * \return Shared pointer to Camera object, which is empty if the camera is
>   * not found
>   */
>  std::shared_ptr<Camera> CameraManager::get(dev_t devnum)
>  {
> +	MutexLocker locker(p_->mutex_);
> +
>  	auto iter = p_->camerasByDevnum_.find(devnum);
>  	if (iter == p_->camerasByDevnum_.end())
>  		return nullptr;
> @@ -302,9 +376,12 @@ std::shared_ptr<Camera> CameraManager::get(dev_t devnum)
>   *
>   * \a devnum is used by the V4L2 compatibility layer to map V4L2 device nodes
>   * to Camera instances.
> + *
> + * \context This function shall be called from the CameraManager thread.
>   */
>  void CameraManager::addCamera(std::shared_ptr<Camera> camera, dev_t devnum)
>  {
> +	ASSERT(Thread::current() == p_.get());
>  
>  	p_->addCamera(camera, devnum);
>  }
> @@ -316,15 +393,20 @@ void CameraManager::addCamera(std::shared_ptr<Camera> camera, dev_t devnum)
>   * This function is called by pipeline handlers to unregister cameras from the
>   * camera manager. Unregistered cameras won't be reported anymore by the
>   * cameras() and get() calls, but references may still exist in applications.
> + *
> + * \context This function shall be called from the CameraManager thread.
>   */
>  void CameraManager::removeCamera(Camera *camera)
>  {
> +	ASSERT(Thread::current() == p_.get());
> +
>  	p_->removeCamera(camera);
>  }
>  
>  /**
>   * \fn const std::string &CameraManager::version()
>   * \brief Retrieve the libcamera version string
> + * \context This function is \a threadsafe.
>   * \return The libcamera version string
>   */
>  
> -- 
> Regards,
> 
> Laurent Pinchart
> 
> _______________________________________________
> libcamera-devel mailing list
> libcamera-devel at lists.libcamera.org
> https://lists.libcamera.org/listinfo/libcamera-devel

-- 
Regards,
Niklas Söderlund