[PATCH v2] libcamera: camera_manager: Do not emit signals while holding lock

[Barnabás Pőcze]

Both `CameraManager::Private::{add,remove}Camera()` emit the
`camera{Added,Removed}` signals, respectively, while holding the
lock protecting the list of cameras.

This is problematic because if a callback tries to call `cameras()`,
then the same (non-recursive) lock would be locked again.

Furthermore, there is no real need to hold the lock while user code
is running, so release the lock as soon as possible.

Signed-off-by: Barnabás Pőcze <barnabas.pocze at ideasonboard.com>
Reviewed-by: Harvey Yang <chenghaoyang at chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
changes in v2:
  * indent scopes properly
  * drop `std::move()` calls


v1: https://patchwork.libcamera.org/patch/22905/
---
 src/libcamera/camera_manager.cpp | 44 +++++++++++++++++---------------
 1 file changed, 23 insertions(+), 21 deletions(-)

diff --git a/src/libcamera/camera_manager.cpp b/src/libcamera/camera_manager.cpp
index 87e6717ec..400109f12 100644
--- a/src/libcamera/camera_manager.cpp
+++ b/src/libcamera/camera_manager.cpp
@@ -202,24 +202,24 @@ void CameraManager::Private::addCamera(std::shared_ptr<Camera> camera)
 {
 	ASSERT(Thread::current() == this);

-	MutexLocker locker(mutex_);
+	{
+		MutexLocker locker(mutex_);

-	for (const std::shared_ptr<Camera> &c : cameras_) {
-		if (c->id() == camera->id()) {
-			LOG(Camera, Fatal)
-				<< "Trying to register a camera with a duplicated ID '"
-				<< camera->id() << "'";
-			return;
+		for (const std::shared_ptr<Camera> &c : cameras_) {
+			if (c->id() == camera->id()) {
+				LOG(Camera, Fatal)
+					<< "Trying to register a camera with a duplicated ID '"
+					<< camera->id() << "'";
+				return;
+			}
 		}
-	}

-	cameras_.push_back(std::move(camera));
-
-	unsigned int index = cameras_.size() - 1;
+		cameras_.push_back(camera);
+	}

 	/* Report the addition to the public signal */
 	CameraManager *const o = LIBCAMERA_O_PTR();
-	o->cameraAdded.emit(cameras_[index]);
+	o->cameraAdded.emit(camera);
 }

 /**
@@ -236,20 +236,22 @@ void CameraManager::Private::removeCamera(std::shared_ptr<Camera> camera)
 {
 	ASSERT(Thread::current() == this);

-	MutexLocker locker(mutex_);
+	{
+		MutexLocker locker(mutex_);

-	auto iter = std::find_if(cameras_.begin(), cameras_.end(),
-				 [camera](std::shared_ptr<Camera> &c) {
-					 return c.get() == camera.get();
-				 });
-	if (iter == cameras_.end())
-		return;
+		auto iter = std::find_if(cameras_.begin(), cameras_.end(),
+					 [camera](std::shared_ptr<Camera> &c) {
+						 return c.get() == camera.get();
+					 });
+		if (iter == cameras_.end())
+			return;
+
+		cameras_.erase(iter);
+	}

 	LOG(Camera, Debug)
 		<< "Unregistering camera '" << camera->id() << "'";

-	cameras_.erase(iter);
-
 	/* Report the removal to the public signal */
 	CameraManager *const o = LIBCAMERA_O_PTR();
 	o->cameraRemoved.emit(camera);
--
2.49.0