On Sun, Aug 28, 2011 at 6:55 PM, Jeffrey Walton <noloa...@gmail.com> wrote: > On Sun, Aug 28, 2011 at 12:26 PM, Bart Van Assche <bvanass...@acm.org> wrote: >> On Sun, Aug 28, 2011 at 6:13 PM, Jeffrey Walton <noloa...@gmail.com> wrote: >>> (1) Never trust wikipedia. >> >> Reading your message makes me wonder whether you are familiar with the >> reason why memory barriers exist, > > I'm not aware that GCC will change the semantics of the program under > these conditions. I could be wrong, though.
What matters here is that without intervening memory barrier store instructions executed by one CPU may be observed in the opposite order by another CPU. This won't happen with x86 CPUs but can happen with e.g. PowerPC and ARM CPUs. When implementing the double-checked locking pattern, one has not only to be careful about instruction reordering by the compiler but also about reordering by the memory subsystem. >> something the Wikipedia authors of >> the page about double-checked locking clearly are aware of ? > > It does not change the fact that I do not trust wikipedia. I've found > too many mistakes of the years. :-) Bart. ------------------------------------------------------------------------------ EMC VNX: the world's simplest storage, starting under $10K The only unified storage solution that offers unified management Up to 160% more powerful than alternatives and 25% more efficient. Guaranteed. http://p.sf.net/sfu/emc-vnx-dev2dev _______________________________________________ Valgrind-users mailing list Valgrind-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/valgrind-users
