Re: Move PinBuffer and UnpinBuffer to atomics

Andres Freund wrote:
> On 2016-03-28 15:46:43 +0300, Alexander Korotkov wrote:

> > @@ -932,8 +936,13 @@ ReadBuffer_common(SMgrRelation smgr, cha
> >  
> >      if (isLocalBuf)
> >      {
> > -        /* Only need to adjust flags */
> > -        bufHdr->flags |= BM_VALID;
> > +        /*
> > +         * Only need to adjust flags.  Since it's local buffer, there is no
> > +         * concurrency.  We assume read/write pair to be cheaper than atomic OR.
> > +         */
> > +        uint32 state = pg_atomic_read_u32(&bufHdr->state);
> > +        state |= BM_VALID;
> > +        pg_atomic_write_u32(&bufHdr->state, state);
> 
> I'm not a fan of repeating that comment in multiple places. Hm.

Perhaps a set of macros should be offered that do "read, set some flag,
write".  Then the comments can be attached to the macro instead of to
each callsite.

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
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