Alexander Terekhov wrote:
Dave Abrahams wrote:
on Tue Aug 23 2011, Alexander Terekhov <terekhov-AT-web.de> wrote:
Dave Abrahams wrote:
[... memory model ...]
It's not really different than locking. If you want to write to shared data, you need some way of making it not-a-race. It's just that when the data structure is small enough (like an int) you can make it atomic instead of putting a lock around it.
No.
All I'm saying here is that a C++11 default atomic int is equivalent to an int, coupled with an associated mutex, where accesses to the int are always protected by locking the associated mutex. If you're seriously disagreeing with *that*, please say explicitly on what grounds.
int i; mutex mi, int j; mutex mj;
mi.lock(); i = 1; mi.unlock();
mj.lock(); j = 2; mj.unlock();
can be transformed to
multi_lock(mi, mj); // deadlock free j = 2; i = 1; mi.unlock(); mj.unlock();
and thus result in reodering i = 1 and j = 2.
With C++11 default atomics (SC) for i and j such reodering is prohibited.
See also: http://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html regards, alexander.