feat: Added new CBGExecutor

Signed-off-by: Janosch Machowinski <[email protected]>

# Conflicts:
#	rclcpp/include/rclcpp/executor.hpp
#	rclcpp/src/rclcpp/executor.cpp
#	rclcpp/test/rclcpp/executors/test_executors.cpp

Author: Janosch Machowinski

rclcpp/CMakeLists.txt

@@ -63,6 +63,8 @@ set(${PROJECT_NAME}_SRCS
   src/rclcpp/executable_list.cpp
   src/rclcpp/executor.cpp
   src/rclcpp/executors.cpp
+  src/rclcpp/executors/cbg_executor.cpp
+  src/rclcpp/executors/detail/weak_executable_with_rcl_handle_cache.cpp
   src/rclcpp/executors/executor_entities_collection.cpp
   src/rclcpp/executors/executor_entities_collector.cpp
   src/rclcpp/executors/executor_notify_waitable.cpp

rclcpp/include/rclcpp/executor.hpp

@@ -485,7 +485,7 @@ class Executor
   RCLCPP_PUBLIC
   static void
   execute_subscription(
-    rclcpp::SubscriptionBase::SharedPtr subscription);
+    const rclcpp::SubscriptionBase::SharedPtr &subscription);
 
   /// Run timer executable.
   /**
@@ -503,7 +503,7 @@ class Executor
    */
   RCLCPP_PUBLIC
   static void
-  execute_service(rclcpp::ServiceBase::SharedPtr service);
+  execute_service(const rclcpp::ServiceBase::SharedPtr &service);
 
   /// Run service client executable.
   /**
@@ -512,7 +512,7 @@ class Executor
    */
   RCLCPP_PUBLIC
   static void
-  execute_client(rclcpp::ClientBase::SharedPtr client);
+  execute_client(const rclcpp::ClientBase::SharedPtr &client);
 
 protected:
   /// Block until more work becomes avilable or timeout is reached.