Messages in this thread | | | From | Oliver Neukum <> | Subject | Re: Uses for memory barriers | Date | Fri, 8 Sep 2006 23:46:20 +0200 |
| |
Am Freitag, 8. September 2006 23:26 schrieb Alan Stern: > On Fri, 8 Sep 2006, Oliver Neukum wrote: > > > It seems you are correct. > > Therefore the correct code on CPU 1 would be: > > > > y = -1; > > b = 1; > > //mb(); > > //x = a; > > while (y < 0) relax(); > > > > mb(); > > x = a; > > > > assert(x==1 || y==1); //??? > > > > And yes, it is confusing. I've been forced to change my mind twice. > > Again you have misunderstood. The original code was _not_ incorrect. I > was asking: Given the code as stated, would the assertion ever fail?
I claim the right to call code that fails its own assertions incorrect. :-)
> The code _was_ correct for my purposes, namely, to illustrate a technical > point about the behavior of memory barriers.
I would say that the code may fail the assertion purely based on the formal definition of a memory barrier. And do so in a subtle and inobvious way.
Regards Oliver - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |