Re: Buffer access rules, and a probable bug

Sorry for the delay.

On Tue, 3 Jul 2001, Tom Lane wrote:

> ncm@zembu.com (Nathan Myers) writes:
> 
> > Also, as hints, would it be Bad(tm) if an attempt to clear one failed?
> 
> Clearing hint bits is also an exclusive-lock-only operation.  Notice
> I specified that *setting* them is the only case allowed to be done
> with shared lock.

One problem though is that if you don't have a spin lock around the flag,
you can end up clearing it inadvertenty. i.e. two backends go to update
(different) bit flags. They each load the current value, and each set the
(different) bit they want to set. They then store the new value they each
have come up with. The second store will effectively clear the bit set in
the first store.

??

Take care,

Bill