`rcl_shutdown` is not thread-safe when used in both `signal_handler` and `Context.__exit__`.

[YuanYuYuan]

Bug report

We found this sporadic failure with rclpy (rolling) due to the race condition while calling rcl_shutdown. In this issue, the conflict happens if rmw_shutdown is slow so that rcutils_atomic_store on Thread 1 is set after the check rcl_context_is_valid on Thread 2. Therefore rcl_shutdown would be called twice and cause an error.

Analysis

• Thread 1

  • rclpy::shutdown_contexts
  • rcl_shutdown
  • check rcl_context_is_valid
  • rmw_shutdown // Slow
  • rcutils_atomic_store

• Thread 2

  • InitContextManger.__exit__
  • _try_shutdown
  • g_default_context.try_shutdown()
  • if self.__context.ok()
  • Context::ok() -> rcl_context_is_valid // If this passes
  • Context::shutdown() -> rcl_shutdown // , then this will run

Required Info:

• Operating System:
  • Ubuntu 24.04
• Installation type:
  • Docker
• Version or commit hash:
  • ros-rolling
• DDS implementation:
  • This bug is RMW independent. Any RMW implementation with a slow rmw_shutdown could lead to this issue.
• Client library (if applicable):
  • Both rcl and rclpy are rolling.
• Relevant issue: #1081