Declare rclcpp callbacks before the rcl entities (ros2#2024)

This is to ensure callbacks are destroyed last
on entities destruction, avoiding the gap in time
in which rmw entities hold a reference to a
destroyed function.

Signed-off-by: Mauro Passerino <mpasserino@irobot.com>

rclcpp/include/rclcpp/client.hpp

@@ -388,6 +388,13 @@ class ClientBase
   std::shared_ptr<rclcpp::Context> context_;
   rclcpp::Logger node_logger_;
 
+  std::recursive_mutex callback_mutex_;
+  // It is important to declare on_new_response_callback_ before
+  // client_handle_, so on destruction the client is
+  // destroyed first. Otherwise, the rmw client callback
+  // would point briefly to a destroyed function.
+  std::function<void(size_t)> on_new_response_callback_{nullptr};
+  // Declare client_handle_ after callback
   std::shared_ptr<rcl_client_t> client_handle_;
 
   std::atomic<bool> in_use_by_wait_set_{false};
@@ -396,9 +403,6 @@ class ClientBase
   bool use_intra_process_{false};
   IntraProcessManagerWeakPtr weak_ipm_;
   uint64_t intra_process_client_id_;
-
-  std::recursive_mutex callback_mutex_;
-  std::function<void(size_t)> on_new_response_callback_{nullptr};
 };
 
 template<typename ServiceT>

rclcpp/include/rclcpp/service.hpp

@@ -302,7 +302,6 @@ class ServiceBase
   // would point briefly to a destroyed function.
   std::function<void(size_t)> on_new_request_callback_{nullptr};
   // Declare service_handle_ after callback
-
   std::shared_ptr<rcl_service_t> service_handle_;
   bool owns_rcl_handle_ = true;
 

rclcpp/include/rclcpp/subscription_base.hpp

@@ -558,6 +558,14 @@ class SubscriptionBase : public std::enable_shared_from_this<SubscriptionBase>
   rclcpp::node_interfaces::NodeBaseInterface * const node_base_;
 
   std::shared_ptr<rcl_node_t> node_handle_;
+
+  std::recursive_mutex callback_mutex_;
+  // It is important to declare on_new_message_callback_ before
+  // subscription_handle_, so on destruction the subscription is
+  // destroyed first. Otherwise, the rmw subscription callback
+  // would point briefly to a destroyed function.
+  std::function<void(size_t)> on_new_message_callback_{nullptr};
+  // Declare subscription_handle_ after callback
   std::shared_ptr<rcl_subscription_t> subscription_handle_;
   std::shared_ptr<rcl_subscription_t> intra_process_subscription_handle_;
   rclcpp::Logger node_logger_;
@@ -580,9 +588,6 @@ class SubscriptionBase : public std::enable_shared_from_this<SubscriptionBase>
   std::atomic<bool> intra_process_subscription_waitable_in_use_by_wait_set_{false};
   std::unordered_map<rclcpp::QOSEventHandlerBase *,
     std::atomic<bool>> qos_events_in_use_by_wait_set_;
-
-  std::recursive_mutex callback_mutex_;
-  std::function<void(size_t)> on_new_message_callback_{nullptr};
 };
 
 }  // namespace rclcpp