RTEMS POSIX API User's Guide
There is one significant point of interpretation related to the RTEMS implementation of POSIX message queues:
What happens to threads already blocked on a message queue when the mode of that same message queue is changed from blocking to non-blocking?
The RTEMS POSIX implementation decided to unblock all waiting tasks
with an EAGAIN status just as if a non-blocking version of
the same operation had returned unsatisfied. This case is not
discussed in the POSIX standard and other implementations may have
chosen alternative behaviors.
RTEMS POSIX API User's Guide
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