Fix data race on 'on_parameter_event'

The callback 'on_parameter_event' was internally
accessing node_base_, which could be already destroyed.

This commit stores the node name, which is what
the callback wants to know, so we don't have to
access the node to obtain it.

rclcpp/include/rclcpp/time_source.hpp

@@ -142,6 +142,9 @@ class TimeSource
   // Store (and update on node attach) logger for logging.
   Logger logger_;
 
+  // Fully qualified node name
+  const char * node_name_;
+
   // QoS of the clock subscription.
   rclcpp::QoS qos_;
 

rclcpp/src/rclcpp/time_source.cpp

@@ -84,6 +84,7 @@ void TimeSource::attachNode(
   node_parameters_ = node_parameters_interface;
   // TODO(tfoote): Update QOS
 
+  node_name_ = node_base_->get_fully_qualified_name();
   logger_ = node_logging_->get_logger();
 
   // Though this defaults to false, it can be overridden by initial parameter values for the node,
@@ -297,7 +298,7 @@ void TimeSource::destroy_clock_sub()
 void TimeSource::on_parameter_event(const rcl_interfaces::msg::ParameterEvent::SharedPtr event)
 {
   // Filter out events on 'use_sim_time' parameter instances in other nodes.
-  if (event->node != node_base_->get_fully_qualified_name()) {
+  if (event->node != node_name_) {
     return;
   }
   // Filter for only 'use_sim_time' being added or changed.