- `g_iob_sem.semcount` must be equal to the total number of free IOBs.
It can also be negative if there are no free IOBs and there are threads
waiting for an IOB.
- g_throttle_sem.semcount represents the number of IOBs available for
throttled IOB allocations. Like any other semaphore, it should only go
negative if there is a thread waiting for it.
- Both semaphores are related to the same resource (free IOBs), hence,
they must be incremented/decremented simultaneously:
- Whenever a IOB buffer is freed, if a thread is waiting for a
non-throttled IOB or a thread is waiting for a throttled IOB and we
have at least `CONFIG_IOB_THROTTLE` buffers available, the IOB is put
in the committed list (`g_iob_committed`). Otherwise, it is put in the
common free list (`g_iob_freelist`).
- `g_iob_sem` is always incremented when an IOB buffer is freed, but
`g_throttle_sem` is incremented only if we have at least CONFIG_IOB_THROTTLE
buffers free.
- Both semaphores are posted with the schedule locked to avoid any
mismatches in the semaphores count.
- If a task is waiting for an IOB semaphore (`iob_allocwait`) is
awakened and would check the `g_iob_committed`. The highest priority
task waiting for a semaphore will be awakened first.
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