Gottlob Frege wrote:
On Thu, Aug 25, 2011 at 12:13 AM, Stephan T. Lavavej <stl@exchange.microsoft.com> wrote:
[Gottlob Frege]
1. I wish that C++11 atomics defaulted to acquire-on-read and release-on-write, and that's how I will almost always use them. It is also what java and C# use, I believe (on volatiles).
That doesn't solve the "independent reads, independent writes" problem, which is why the non-Standard semantics that VC8 gave volatile aren't really useful. (volatile: a multithreaded programmer's worst enemy.)
What's the "independent reads, independent writes" problem? I've probably heard, seen, or mistakenly had a bug due to it once, but don't know it by name.
IRIW is an example that highlights remote write atomicity: T1: X = 1; T2: Y = 1; T3: A = X; B = Y; T4: C = Y; D = X; A == 1 && B == 0 && C == 1 && D == 0 is possible without remote write atomicity. Another example is T1: X = 1; T2: if (X) Y = 1; T3: A = Y; B = X; A == 1 && B == 0 is possible without remote write atomicity. SC is basically "no local reordering" plus remote write atomicity. In 'modes' model, remote write atomicity is a separate mode apart from reordering. regards, alexander.