Re: [PATCH 1/8] Introduce simple hazard pointers

[Boqun Feng]

On Wed, Jun 25, 2025 at 10:25:23AM -0400, Mathieu Desnoyers wrote:
> On 2025-06-24 23:10, Boqun Feng wrote:
> [...]
> > +
> > +static inline void shazptr_clear(struct shazptr_guard guard)
> > +{
> > +	/* Only clear the slot when the outermost guard is released */
> > +	if (likely(!guard.use_wildcard))
> > +		smp_store_release(guard.slot, NULL); /* Pair with ACQUIRE at synchronize_shazptr() */
> 
> How is the wildcard ever cleared ?
> 

The outermost shazptr_guard will have .use_wildcard being false, so it
will clear the wildcard. E.g.

	g1 = shazptr_acqure(a); // g1->use_wildcard is false
				// this cpu's hazptr slot is 'a'.
	g2 = shazptr_acqure(b); // g2->use_wildcard is true
				// this cpu's hazptr slot becomes
				// WILDCARD.

	shazptr_clear(g2);	// do nothing
	shazptr_clear(g1);	// clear this cpu's hazptr slot to NULL.

Regards,
Boqun

> Thanks,
> 
> Mathieu
> 
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com