skaller <[EMAIL PROTECTED]> writes: > On Fri, 2007-10-26 at 07:58 -0700, Ian Lance Taylor wrote: > > skaller <[EMAIL PROTECTED]> writes: > > > > > As I understand it volatile is typically used as a 'hint' > > > to the compiler that there could be aliases it cannot see. > > > This is independent of the use suggesting asynchronous changes > > > in a hardware port for example, although the effect is the same. > > > > Not really. Volatile has a reasonably precise definition: it means > > that memory accesses must be done precisely as they are written in the > > program. They may not be coalesced, and they may not be moved. > > I understand that's the common meaning .. but the semantics > aren't specified for ISO C/C++.
Sure they are. In the C99 standard look at the definition of sequence points (5.1.2.3) and the definition of volatile (6.7.3). > > > [BTW I think this sucks, the need to synchronise ALL memory > > > on mutexing is far too heavy] > > > > It can not be avoided, for the reasons you describe. > > Of course it can be avoided easily if the memory model > allowed for local synchronisation sets, so the real problem > appears to be that Posix doesn't provide proper synchronisation > control. Or that POSIX only provides heavyweight synchronization. As I understand it, the draft C++0x memory model has acquire release semantics for annotated variables. Of course, it wouldn't help the originalk test case unless the global variable was annotated. Ian
