Re: Singleton_pattern and Thread Safety

Leigh Johnston <>
Mon, 13 Dec 2010 18:17:27 +0000
On 13/12/2010 11:45, James Kanze wrote:

On Dec 12, 2:55 pm, Leigh Johnston<> wrote:

On 12/12/2010 02:27, Joshua Maurice wrote:

On Dec 11, 6:00 pm, Leigh Johnston<> wrote:

On 12/12/2010 01:23, Joshua Maurice wrote:

On Dec 11, 5:19 pm, Tiib<> wrote:

On Dec 12, 2:30 am, Joshua Maurice<> wrote:

On Dec 11, 11:57 am, "Chris M. Thomasson"<> wrote:

"Leigh Johnston"<> wrote in message

On 11/12/2010 18:47, Chris M. Thomasson wrote:


One can instantiate multiple "Meyers Singletons" before creating any
threads to avoid any singleton related threading code. No object
destruction problems.

You continue to assert that a memory leak is bad a priori. The rest of
us in this thread disagree with that claim. Instead, we program to
tangible requirements, such as cost, time to market, meets (business)
use case. We also keep in mind less tangible but still important
considerations, like maintainability and reusability.

You are not listening. If you have multiple singletons using
Mr Kanze's method that "you all" agree with it is unspecified
as to the order of construction of these singletons across
multiple TUs; i.e. the method suffers the same problem as
ordinary global variables; it is no better than using ordinary
global variables modulo the lack of object destruction (which
is shite).

I'd suggest you read the code I posted first. It addresses the
order of initialization issues fully. (But of course, you're
not one to let actual facts bother you.)

The code you posted results in unspecified construction order of your
leaking singletons even though they are dynamically allocated if they
are defined in multiple TUs.

Unspecified construction order is anathema to maintainability
as the order could change as TUs are added or removed from
a project.

Unspecified constructor order of variables at namespace scope is
a fact of life in C++. That's why we use the singleton pattern
(which doesn't put the actual variable at namespace scope, but
allocates it dynamically).

A fact of life you seem to be ignoring; the order of construction of the
following is specified within a single TU but unspecified in relation to
globals defined in other TUs:

    foo global1;
    foo* global2 = new foo();
    foo global3; // global2 has been fully constructed (dynamically
allocated) before reaching here

Unspecified destructor order of variables with static lifetime
(namespace scope or not) is also a fact of life in C++. That's
why we don't destruct the variable we dynamically allocated.

Dynamic allocation is irrelevant here; construction order is unspecified
as you are initializing a global pointer with the result of a dynamic

It's called defensive programming. Or simply sound software
engineering. It's called avoiding undefined behavior, if you

As you are doing it wrong it is neither defensive programming nor sound


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