rt 0.17.0

A real-time operating system capable of full preemption
Documentation 
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#include <rt/once.h>

void rt_once_call(struct rt_once *once, void (*fn)(void))
{
    if (rt_atomic_load(&once->done, RT_ATOMIC_ACQUIRE) == 0)
    {
        rt_mutex_lock(&once->mutex);
        // A mutex has acquire-release semantics, so we can load relaxed here.
        if (rt_atomic_load(&once->done, RT_ATOMIC_RELAXED) == 0)
        {
            fn();
            // This release pairs with the acquire in the fast path.
            rt_atomic_store(&once->done, 1, RT_ATOMIC_RELEASE);
        }
        rt_mutex_unlock(&once->mutex);
    }
}