Re: Singleton_pattern and Thread Safety

James Kanze <>
Mon, 13 Dec 2010 02:12:31 -0800 (PST)
On Dec 10, 3:56 pm, Leigh Johnston <> wrote:

On 10/12/2010 15:29, James Kanze wrote:

On Dec 10, 1:16 pm, Leigh Johnston<> wrote:

On 10/12/2010 09:52, James Kanze wrote:

On Dec 9, 5:05 pm, Marcel M ller<> wrote:

Pallav singh wrote:


Note that the above still risks order of destruction issues;
it's more common to not destruct the singleton ever, with
something like:

      namespace {

      Singleton* ourInstance =&Singleton::instance();

          if (ourInstance == NULL)
              ourInstance = new Singleton;
          return *ourInstance;

(This solves both problems at once: initializing the variable
with a call to Singleton::instance and ensuring that the
singleton is never destructed.)

James "Cowboy" Kanze's OO designs includes objects that are never
destructed but leak instead?

And where do you see a leak?

Is that a serious question?

Yes. There's no memory leak in the code I posted. I've used it
in applications that run for years, without running out of

The only real difference between the two programs below is the amount of
memory leaked:

int main()
        int* p = new int;

int main()
        int* p = new int;
        p = new int;

Arguably, there's no memory leak in either. A memory leak
results in memory use that increases in time. That's the usual
definition of "leak" in English, applied to memory, and it's the
only "useful" definition; if the second line in the above were
in a loop, you would have a leak.

Other definitions of memory leak are possible---I've seen people
claim that you can't have a memory leak in Java because it has
garbage collection, for example. But such definitions are of no
practical use, and don't really correspond to the usual meaning.

A singular memory leak (one that is not repeated so doesn't
consume more and more memory as a program runs) is still
a memory leak.

I will ignore the predictable, trollish part of your reply.

In other words, you know that your position is indefensible, so
prefer to resort to name calling.

James Kanze

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