Re: Singleton_pattern and Thread Safety

From:
Leigh Johnston <leigh@i42.co.uk>
Newsgroups:
comp.lang.c++
Date:
Fri, 10 Dec 2010 16:42:19 +0000
Message-ID:
<lMmdna_nbsr-xZ_QnZ2dnUVZ8h-dnZ2d@giganews.com>
On 10/12/2010 15:56, Leigh Johnston wrote:

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

On Dec 10, 1:16 pm, Leigh Johnston<le...@i42.co.uk> wrote:

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

On Dec 9, 5:05 pm, Marcel M ller<news.5.ma...@spamgourmet.com> 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();

Singleton&
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?

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;
}

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.

/Leigh


Furthermore if you placed your singleton code into a DLL and the DLL was
continuously loaded and unloaded I think you would see plain evidence
that this is in fact a memory leak.

/Leigh

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