Re: Am I or Alexandrescu wrong about singletons?

James Kanze <>
Sun, 28 Mar 2010 15:25:46 CST
On Mar 26, 12:33 am, Herb Sutter <> wrote:

Please remember this: Standard ISO C/C++ volatile is useless
for multithreaded programming. No argument otherwise holds
water; at best the code may appear to work on some
compilers/platforms, including all attempted counterexamples
I've seen on this thread.

I agree with you in principle, but do be careful as to how you
formulate this. Standard ISO C/C++ is useless for multithreaded
programming, at least today. With or without volatile. And in
Standard ISO C/C++, volatile is useless for just about anything;
it was always intended to be mainly a hook for implementation
defined behavior, i.e. to allow things like memory-mapped IO
while not imposing excessive loss of optimizing posibilities

In theory, an implementation could define volatile in a way that
would make it useful in multithreading---I think Microsoft once
proposed doing so in the standard. In my opinion, this sort of
violates the original intention behind volation, which was that
volatile is applied to a single object, and doesn't affect other
objects in the code. But it's certainly something you could
argue both ways.


No. The reason that can't use volatiles for synchronization is that
they aren't synchronized (QED).

:-). And the reason their not synchronized is that
synchronization involves more than one variable, and that it was
never the intent of volatile to involve more than one variable.
(On a lot of modern processors, however, it would be impossible
to fully implement the original intent of volatile without
synchronization. The only instructions available on a Sparc,
for example, to ensure that a store instruction actually results
in a write to an external device is a membar. And that
synchronizes *all* accesses of the given type.)


(and it was a mistake to try to add those
guarantees to volatile in VC++).

Just curious: is that Microsoft talking, or Herb Sutter (or

James Kanze

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