On 3/24/2014 9:53 AM, Koehne Kai wrote: > >> -----Original Message----- >> From: interest-bounces+kai.koehne=digia....@qt-project.org >> [mailto:interest-bounces+kai.koehne=digia....@qt-project.org] On Behalf Of >> Bob Hood >> Sent: Monday, March 24, 2014 4:49 PM >> To: Thiago Macieira; interest@qt-project.org >> Subject: Re: [Interest] QThread >> >> [...] >> I actually use the "volatile" tag to tell the compiler that it cannot >> optimize (i.e., >> make compile-time assumptions about) the variable that it decorates. >> Does std::atomic have the same meaning for optimizations? I can't get a >> clear >> picture of this by a (cursory) Google. > To cite > https://stackoverflow.com/questions/12878344/volatile-in-c11 > > " Now, let's look at what C++11 says about volatile int x;. If you put that > in there, and you have some other thread mess with x, you still have > undefined behavior. Volatile does not affect threading behavior. C++11's > memory model does not define reads or writes from/to x to be atomic, nor does > it require the memory barriers needed for non-atomic reads/writes to be > properly ordered. volatile has nothing to do with it one way or the other. > > Oh, your code might work. But C++11 doesn't guarantee it. > > What volatile tells the compiler is that it can't optimize memory reads from > that variable. However, CPU cores have different caches, and most memory > writes do not immediately go out to main memory. They get stored in that > core's local cache, and may be written... eventually."
Thanks a bunch, Kai. _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
