Re: Protect bool on concurrent access
On May 28, 3:55 pm, rmauds...@googlemail.com wrote:
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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?
Johan
Yes, this will cause problems on multi-processor/multi-core machines.
You should mark the variable as volatile and use a memory fence to
make the value visible to the other threads. Under windows this can be
done using the InterlockedExchange() function.
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. :)
-Le Chaud Lapin-
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