Non-atomic ops allowed on shared variables?

Jonathan M Davis jmdavisProg at
Sat Dec 3 12:49:53 PST 2011

On Saturday, December 03, 2011 21:41:45 Andrej Mitrovic wrote:
> On 12/3/11, Jonathan M Davis <jmdavisProg at> wrote:
> > That page says that reads and writes are guaranteed to be atomic for
> > shared. It does _not_ say that something like ++threadsCount is
> > guaranteed to be atomic.
> Woops, sorry it was a typo. I meant page 411, not 413. It says it's an
> error there. Btw, I never said ++ was atomic, I've asked whether
> something has changed. IOW I thought perhaps this used to be an error
> but maybe it was changed to make increment/decrement to be atomic on
> shared variables. That's not the case of course..

Ah, okay. I had completely forgotten about that. That seems _very_ restrictive 
to me, and for it to work correctly, I would expect the compiler to have to be 
smart enough to realize when a synchronized  block is in use or a mutex is in 
use, and I don't see how it can be that smart across function calls (since if 
it isn't that smart, it forces you to use atomicOp even when it's completely 
unnecessary), so I don't see how that could possibly work without 
unnecessarily requiring you to use atomicOp all over the place.

I have no idea what the plan on this is at this point, and I'm very surprised 
that such a requirement was ever suggested. It's the kind of question that you 
may have to bring up in the main newsgroup if you want a good answer for it 
though, since the number of people who pay attention to d-learn is much lower, 
and I don't know if any of the key devs who _would_ know pay attention here.

- Jonathan M Davis

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