A way to solve this would be to have a transaction identifier into each
object descriptor, that is incremented each time the object's internal
state is altered (e.g. removal/insertion of some element from/to the
pendq and so on).

This works as long as the object descriptor itself can _not_ be deleted in the mean time.

IOW, "object->current_rev != prev_rev" makes sense only if "object" remains to be valid.

So it's not applicable to any native skin's primitives unless you have an additional mean to  determine that the object was deleted / or guarantee that it can't be deleted (e.g. reference counting).

In case of Jan's optimization it works as long as "nkpod" object is valid :

see comments below...

...
        /* Take a snapshot element-wise, restart if something changes
           underneath us. */

        while (holder) {
                xnthread_t *thread;
                xnsched_t *sched;
                xnticks_t period;
                int n;

                xnlock_get_irqsave(&nklock, s);          (1)

                if (nkpod->threadq_rev != rev)            (2)
                        goto restart;

                rev = nkpod->threadq_rev;                 (3)
...

btw, (3) doesn't make any sense. You can be there only when "nkpod->thread_rev == rev".

In fact, nkpod also can be NULL in (2) if xnpod_shutdown() was called (skin was unloaded) before (1). Although, it has quite low probability.



--
Philippe.


--
Best regards,
Dmitry Adamushko
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