Revert "Add locking to protect the TimeSource::NodeState::node_base_ (ros2#2320)"

This reverts commit 07e90fd.

Author: jplapp

rclcpp/src/rclcpp/time_source.cpp

@@ -242,7 +242,6 @@ class TimeSource::NodeState final
     rclcpp::node_interfaces::NodeClockInterface::SharedPtr node_clock_interface,
     rclcpp::node_interfaces::NodeParametersInterface::SharedPtr node_parameters_interface)
   {
-    std::lock_guard<std::mutex> guard(node_base_lock_);
     node_base_ = node_base_interface;
     node_topics_ = node_topics_interface;
     node_graph_ = node_graph_interface;
@@ -287,14 +286,17 @@ class TimeSource::NodeState final
     parameter_subscription_ = rclcpp::AsyncParametersClient::on_parameter_event(
       node_topics_,
       [this](std::shared_ptr<const rcl_interfaces::msg::ParameterEvent> event) {
-        this->on_parameter_event(event);
+        if (node_base_ != nullptr) {
+          this->on_parameter_event(event);
+        }
+        // Do nothing if node_base_ is nullptr because it means the TimeSource is now
+        // without an attached node
       });
   }
 
   // Detach the attached node
   void detachNode()
   {
-    std::lock_guard<std::mutex> guard(node_base_lock_);
     // destroy_clock_sub() *must* be first here, to ensure that the executor
     // can't possibly call any of the callbacks as we are cleaning up.
     destroy_clock_sub();
@@ -331,7 +333,6 @@ class TimeSource::NodeState final
   std::thread clock_executor_thread_;
 
   // Preserve the node reference
-  std::mutex node_base_lock_;
   rclcpp::node_interfaces::NodeBaseInterface::SharedPtr node_base_{nullptr};
   rclcpp::node_interfaces::NodeTopicsInterface::SharedPtr node_topics_{nullptr};
   rclcpp::node_interfaces::NodeGraphInterface::SharedPtr node_graph_{nullptr};
@@ -469,14 +470,6 @@ class TimeSource::NodeState final
   // Callback for parameter updates
   void on_parameter_event(std::shared_ptr<const rcl_interfaces::msg::ParameterEvent> event)
   {
-    std::lock_guard<std::mutex> guard(node_base_lock_);
-
-    if (node_base_ == nullptr) {
-      // Do nothing if node_base_ is nullptr because it means the TimeSource is now
-      // without an attached node
-      return;
-    }
-
     // Filter out events on 'use_sim_time' parameter instances in other nodes.
     if (event->node != node_base_->get_fully_qualified_name()) {
       return;