Re: Protect bool on concurrent access

From:

Alberto Ganesh Barbati <AlbertoBarbati@libero.it>

Newsgroups:

comp.lang.c++.moderated

Date:

Fri, 30 May 2008 16:08:25 CST

Message-ID:

<vFV%j.88465$FR.323701@twister1.libero.it>

marlow.andrew@googlemail.com ha scritto:

Le Chaud Lapin wrote:

On May 28, 5:37 pm, Johan Torp <johan.t...@gmail.com> wrote:

I have a bool which will transition from false to true once. One
thread sets the bool to true (once), the other reads it every now and
then. I know C++03 and 0x has undefined behaviour, but in practice...
Is it necessary to protect such bools? Are there any known hardware/
platform/compilers which might cause problems?

So then it follows that there is no portable way to test the bool,
which means that any devised (correct) solution will rely on
mechanisms outside of Pure C++, which means that you might as well go
with full synchronization, which will invariably be more efficient in
time, and more regular in operation. :)

The C++0x standard library will include a whole bunch of atomic types
devoted precisely to fill this gap. It will be therefore possible to
solve the OP's problem in a portable way using std::atomic_bool.

Indeed. And I don't understand what makes bools so special. Surely any
variable that would potentially be shared between threads needs to be
protected in this way.

You will also have std::atomic_(integral), std::atomic_address and even
std::atomic<T>.

HTH,

Ganesh

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