Horton

Re: valgrind versus pg_atomic_init()

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@lists.postgresql.org, Tom Lane <tgl@sss.pgh.pa.us>
Date: 2020-06-17T04:01:21Z
Lists: pgsql-hackers 
On Tue, Jun 16, 2020 at 08:35:58PM -0700, Andres Freund wrote:
> On June 16, 2020 8:24:29 PM PDT, Noah Misch <noah@leadboat.com> wrote:
> >Suppose the initializing process does:
> >
> >  pg_atomic_init_u64(&somestruct->atomic, 123);
> >  somestruct->atomic_ready = true;
> >
> >In released versions, any process observing atomic_ready==true will
> >observe
> >the results of the pg_atomic_init_u64().  After the commit from this
> >thread,
> >that's no longer assured.
> 
> Why did that hold true before? There wasn't a barrier in platforms already (wherever we know what 64 bit reads/writes have single copy atomicity).

You are right.  It didn't hold before.

Commits

  1. Avoid need for valgrind suppressions for pg_atomic_init_u64 on some platforms.