Prevent executor race condition

[mjcarroll]

Description

This PR fixes a sporadic hang/deadlock in the camera_info_manager unit tests (https://ci.ros2.org/view/nightly/job/nightly_linux-aarch64_repeated/3582/testReport/junit/(root)/projectroot/camera_info_manager_unit_test/)

Root Cause

In tests/unit_test.cpp, the CameraInfoManagerTesting fixture spins an executor in a background thread during SetUp():

executor_thread = std::thread([this]() {executor->spin();});

And cancels/joins it during TearDown() :

executor->cancel();
executor_thread.join();

For very fast test cases, purely synchronous test cases the main thread completes and calls TearDown() almost immediately after SetUp(). This creates a race condition in rclcpp::Executor:

1. TearDown() calls executor->cancel() , setting the executor's internal spinning atomic flag to false .
2. The background thread subsequently starts executing spin() , which performs spinning.exchange(true) . This unconditionally
   sets spinning back to true .
3. The executor enters the spin loop and blocks on wait_for_work() indefinitely, as cancel() has already been called. The
   thread never joins, causing the test suite to hang.

Is this user-facing behavior change?

No (test code only).

Did you use Generative AI?

Yes, this pull request description and fix were prepared with the assistance of Gemini CLI.

Assisted-by: Gemini CLI:Gemini 3.5 Flash [run_command, view_file, grep_search, replace_file_content]

Additional Information

I think this is actually a valid race condition that we are going to potentially need to address in the executor?

[mjcarroll]

Pulls: #421
Gist: https://gist.githubusercontent.com/mjcarroll/531ec5be0745898904012fcabe99cca9/raw/052db77e388b9bd6c918eb2f3d36e7fd91782ba3/ros2.repos
BUILD args: --packages-up-to camera_info_manager
TEST args: --packages-select camera_info_manager --ctest-args --repeat until-fail:200
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/19409

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