Dave Abrahams wrote: [...]
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.
As it is with C++11 mutexes, IIUC.
Mutexes need only *acquire-release* semantics coupled with RMW(s) to result in *SC* for associated race-free data, as observed by another thread(s). C++11 default atomics are *SC* without mutexes (lockfree and all that stuff)... *SC* is more expansive than *acquire-release* in terms of sync on platforms such as:
If you have contrary evidence, please point to it.
http://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html (PowerPC) I mean: Load SC: hwsync; ld; cmp; bc; isync Store SC: hwsync; st alternative mappings: Load SC: ld; hwsync Store SC: lwsync; st; hwsync Note that *acquire-release* does NOT need *hw*sync: Load Acquire: ld; cmp; bc; isync Store Release: lwsync; st regards, alexander.