address context shutdown racy condition.

[fujitatomoya]

Description

replaces #3216

Fixes # (issue)

Is this user-facing behavior change?

Not really, it internally addresses the racy condition on context shutdown.

Did you use Generative AI?

Yes, Claude Fable 5.

Additional Information

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[fujitatomoya]

@jmachowinski @skyegalaxy

this is ABI compatible, so we can backport this to downstream distros. what do you think?

[fujitatomoya]

Pulls: #3217
Gist: https://gist.githubusercontent.com/fujitatomoya/3495a050d6d222a06e02762c94cd4d50/raw/3bace1d5b4ffe0c0803c7b8daadf115bcb379653/ros2.repos
BUILD args: --packages-above-and-dependencies rclcpp
TEST args: --packages-above rclcpp
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/20050

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[skyegalaxy]

lgtm for fixing this in previous distros in an ABI-compatible way, although IMO, I feel like the diff in https://github.com/ros2/rclcpp/pull/3216/changes is cleaner than introducing a g_contexts_in_shutdown.

My slight preference would be for if @fishitiny 's PR had targeted rolling and included the regression test added in this PR, and this g_contexts_in_shutdown variant was only used for backports, but not a big deal if we wanna merge as-is

[jmachowinski]

I agree this is more the back port and the other version was cleaner and should go into rolling

[fujitatomoya]

@jmachowinski @skyegalaxy

you are right. let's use this PR only for downstream branches, and address rolling with appropriate simple one. i will create the new PR for rolling and retarget this PR to lyrical.