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Re: [std-proposals] volatile is not well supported

From: Jason McKesson <jmckesson_at_[hidden]>
Date: Fri, 2 Sep 2022 19:27:43 -0400
On Fri, Sep 2, 2022 at 12:14 PM Phil Bouchard via Std-Proposals
<std-proposals_at_[hidden]> wrote:
> On 9/1/22 19:37, Charles Milette via Std-Proposals wrote:
> I believe you want an atomic<shared_ptr<int>>, not volatile.
> Ok actually I don't need the variable to be atomic, I just need it to be reloaded.

Reloaded for what purpose? If you're doing threading, then what you
want is "atomic", not "volatile". Volatile has absolutely no special
meaning with regard to inter-thread communication and offers no
guarantee that what you see will represent what was written by some
other thread at any point.

Using `volatile` for inter-thread communication has a history in
certain compilers, on certain CPUs, for many years. But those were the
days when C++ didn't have a threaded memory model. Now that it does,
we have a correct way that works on all compilers, on all CPUs they

And that way is not spelled "volatile".

> Also I wanted the entire struct to be volatile, not just a few fundamentals members.

You can make the whole object atomic (assuming that it is trivially
copyable). Though there may be a cost for doing atomic operations on
objects larger than the size of a word or so.

Received on 2022-09-02 23:28:19