[libcamera-devel] [PATCH v3 3/5] libcamera: camera_manager: Introduce signals when a camera is added/removed

[Umang Jain]

Emit 'newCameraAdded' and 'cameraRemoved' from CameraManager to enable
hotplug and hot-unplug support in appplication like QCam.

To avoid use-after-free race between the CameraManager and the
application, emit the 'cameraRemoved' with the shared_ptr version
of <Camera *>. This requires to change the function signature of
CameraManager::removeCamera() API.

Signed-off-by: Umang Jain <email at uajain.com>
---
 include/libcamera/camera_manager.h |  6 ++++-
 src/libcamera/camera_manager.cpp   | 36 +++++++++++++++++++++++++++---
 src/libcamera/pipeline_handler.cpp |  2 +-
 3 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/include/libcamera/camera_manager.h b/include/libcamera/camera_manager.h
index 079f848..365e286 100644
--- a/include/libcamera/camera_manager.h
+++ b/include/libcamera/camera_manager.h
@@ -13,6 +13,7 @@
 #include <vector>
 
 #include <libcamera/object.h>
+#include <libcamera/signal.h>
 
 namespace libcamera {
 
@@ -35,13 +36,16 @@ public:
 	std::shared_ptr<Camera> get(dev_t devnum);
 
 	void addCamera(std::shared_ptr<Camera> camera, dev_t devnum);
-	void removeCamera(Camera *camera);
+	void removeCamera(std::shared_ptr<Camera> camera);
 
 	static const std::string &version() { return version_; }
 
 	void setEventDispatcher(std::unique_ptr<EventDispatcher> dispatcher);
 	EventDispatcher *eventDispatcher();
 
+	Signal<std::shared_ptr<Camera>> newCameraAdded;
+	Signal<std::shared_ptr<Camera>> cameraRemoved;
+
 private:
 	static const std::string version_;
 	static CameraManager *self_;
diff --git a/src/libcamera/camera_manager.cpp b/src/libcamera/camera_manager.cpp
index 27064d2..bdd78f5 100644
--- a/src/libcamera/camera_manager.cpp
+++ b/src/libcamera/camera_manager.cpp
@@ -185,7 +185,7 @@ void CameraManager::Private::addCamera(std::shared_ptr<Camera> &camera,
 		}
 	}
 
-	cameras_.push_back(std::move(camera));
+	cameras_.push_back(camera);
 
 	if (devnum) {
 		unsigned int index = cameras_.size() - 1;
@@ -375,6 +375,34 @@ std::shared_ptr<Camera> CameraManager::get(dev_t devnum)
 	return iter->second.lock();
 }
 
+/**
+ * \var CameraManager::newCameraAdded
+ * \brief Notify of a new camera added to the system
+ *
+ * This signal is emitted when a new camera is detected and successfully handled
+ * by the camera manager. The notification occurs alike for cameras detected
+ * when the manager is started with start() or when new cameras are later
+ * connected to the system. When the signal is emitted the new camera is already
+ * available from the list of cameras().
+ *
+ * The signal is emitted from the CameraManager thread. Applications shall
+ * minimize the time spent in the signal handler and shall in particular not
+ * perform any blocking operation.
+ */
+
+/**
+ * \var CameraManager::cameraRemoved
+ * \brief Notify of a new camera removed from the system
+ *
+ * This signal is emitted when a camera is removed from the system. When the
+ * signal is emitted the camera is not available from the list of cameras()
+ * anymore.
+ *
+ * The signal is emitted from the CameraManager thread. Applications shall
+ * minimize the time spent in the signal handler and shall in particular not
+ * perform any blocking operation.
+ */
+
 /**
  * \brief Add a camera to the camera manager
  * \param[in] camera The camera to be added
@@ -394,6 +422,7 @@ void CameraManager::addCamera(std::shared_ptr<Camera> camera, dev_t devnum)
 	ASSERT(Thread::current() == p_.get());
 
 	p_->addCamera(camera, devnum);
+	newCameraAdded.emit(camera);
 }
 
 /**
@@ -406,11 +435,12 @@ void CameraManager::addCamera(std::shared_ptr<Camera> camera, dev_t devnum)
  *
  * \context This function shall be called from the CameraManager thread.
  */
-void CameraManager::removeCamera(Camera *camera)
+void CameraManager::removeCamera(std::shared_ptr<Camera> camera)
 {
 	ASSERT(Thread::current() == p_.get());
 
-	p_->removeCamera(camera);
+	p_->removeCamera(camera.get());
+	cameraRemoved.emit(camera);
 }
 
 /**
diff --git a/src/libcamera/pipeline_handler.cpp b/src/libcamera/pipeline_handler.cpp
index 53aeebd..9a1e6ff 100644
--- a/src/libcamera/pipeline_handler.cpp
+++ b/src/libcamera/pipeline_handler.cpp
@@ -555,7 +555,7 @@ void PipelineHandler::disconnect()
 			continue;
 
 		camera->disconnect();
-		manager_->removeCamera(camera.get());
+		manager_->removeCamera(camera);
 	}
 
 	cameras_.clear();
-- 
2.26.2