RIOT/tests/thread_priority_inversion

Priority Inversion

Scenario: A low priority thread holds a shared resource when a mid priority and a high priority thread become runnable. The high priority thread needs exclusive access to the resource the low priority one is holding and blocks. This mid priority thread does not compete with the other for resources but takes a long to complete. The scheduler must prefer the low priority thread over the mid priority thread while it is holding the resource the high priority thread is waiting for - otherwise the high priority thread effectively waits for the mid priority thread, which is an inversion of priority.

Output On Failure

main(): This is RIOT! (Version: ...)
low priority thread has started
low priority thread started to work on its task
high priority thread has started
mid priority thread has started
mid priority thread started to work on its task
    ... this ...
    ... takes ...
    ... bloody ...
    ... ages ...
    ... to ...
    ... complete ...
mid priority thread is done
low priority thread is done
high priority thread started to work on its task
high priority thread is done
==> Priority inversion occurred
TEST FAILED

Output On Success

main(): This is RIOT! (Version: ...)
low priority thread has started
low priority thread started to work on its task
high priority thread has started
low priority thread is done
high priority thread started to work on its task
high priority thread is done
mid priority thread has started
mid priority thread started to work on its task
    ... this ...
    ... takes ...
    ... bloody ...
    ... ages ...
    ... to ...
    ... complete ...
mid priority thread is done
TEST PASSED