Simple ros2 package to understand threads

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Running node

1. Single-thread test

In terminal A (also for the two belows)

ros2 run simple_thread_tester publisher_node

In terminal B

ros2 run simple_thread_tester single_thread_subscriber_node

2. Multi-thread reentrant callback group test

ros2 run simple_thread_tester multi_thread_reentrant_subscriber_node

3. Multi-thread mutually exclusive callback group test

ros2 run simple_thread_tester multi_thread_reentrant_subscriber_node
# If simulate mutex 
ros2 param set /subscriber_node use_mutex true