Re: [Valgrind-users] helgrind/drd annotations for one statement

[Julian S. <js...@ac...>]

On Tuesday, December 04, 2012, Patrick J. LoPresti wrote:
> There is no such thing as a benign data race.  Ever.

<soapbox>

Well said.  I couldn't have put any of this better myself.

Having spent a considerable amount of time working on Helgrind and then
using it to chase races in some big hairy C++ codes, I became very
skeptical of the "oh it's only a harmless race" arguments.  However,
I gave up shouting about it after a while since it just made me look
like a tiresome pedant hellbent on criticising people's clever go-faster-
by-avoiding-locking schemes.

IMO, the idea that some races are harmless is a dangerous myth that
we should try to stamp out.

I also noticed that threaded code that relies on unsynchronised
accesses is hard for newcomers to understand and reason about, so it
tends to be a maintenance hazard.

In some ways, the fact that the Intel architecture guarantees to
deliver stores in-order (x86-TSO), and is therefore somewhat tolerant
of such racery, is a disadvantage.  I think people would take this
stuff more seriously if racey code got trashed more often by machines
with memory systems that do reordering, such as Power7.

</soapbox>

J