Re: Am I or Alexandrescu wrong about singletons?

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Wed, 24 Mar 2010 05:34:54 CST

Message-ID:

<6ad512b8-7944-4c92-846f-d3dd52119176@g19g2000yqe.googlegroups.com>

On Mar 20, 7:13 am, red floyd <redfl...@gmail.com> wrote:

On Mar 19, 2:06 am, "Leigh Johnston" <le...@i42.co.uk> wrote:

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.

Agreed. I've seen this in non-threaded code with
memory-mapped I/O.

Which is a different issue. That's what volatile was designed
for: I think it still works for that on Intel architecture. (It
doesn't on Sparc, at least with g++ or Sun CC:-(.) Threading is
a different issue.

Note that volatile is still relevant for communications between
a signal handler and the main (single threaded) application. At
least according to the standard.

--
James Kanze

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