Re: question re. usage of "static" within static member functions of
a class
On Sep 8, 8:12 am, Paavo Helde <pa...@nospam.please.ee> wrote:
Francesco <entul...@gmail.com> kirjutas:
On 7 Set, 23:25, Paavo Helde <pa...@nospam.please.ee> wrote:
Pavel <dot_com_yahoo@paultolk_reverse.yourself> kirjutas:
Shrikumar wrote:
Thanks for the quick reply, Chris.
I was wondering about the static pointer part - I have always seen
static variables (that are not pointers) in use, but never a
static pointer (even if it is to guarantee that the singleton
always returns the *same* instance of the Class). Is a static
pointer (as in the instance function) a perfectly valid use of the
"static" keyword?
It is valid to declare pointers static if that's what you mean. On
a side note, I think they could avoid both using pointer and the
memory leak (which may be harmless in this case though) as follows:
{
static Data model;
return &model;
}
This brings along the destruction problems at the end of the program.
The singleton might be destroyed too early this way, when some code
still might need access to it. When created dynamically, this problem
does not occur, and the memory is reclaimed by the OS upon process
exit anyway, so there is no memory leak anyway. The singleton
destructor is not run in this case, so one should not put something
essential there.
Ahhhrgh! Thanks a lot for pointing this out - I was just stomping on
the same problem with my suggestion.
So then, if I got your post right Paavo: in order to circumvent the
destruction-order problem I should create the singleton instance as a
dynamic object _and_ I should not free it in the destructor -
otherwise I would be throwing in the destruction-order problem again.
Side question - once I'm there - is the following fine?
-------
Data& Data::instance() {
static Data* model = new Data();
return *model;
}
Yes I think this is fine, my singletons typically look alike.
Good to know, I suppose the following should be fine too:
-------
Data& Data::instance() {
static Data& model = *(new Data());
// or also, simply:
// static Data& model = *new Data;
return model;
}
-------
I recall someone who wrote "programming _IS_ decision making" ;-)
In addition, in case of multithreaded applications I usually call all
such instance() methods in the beginning of the program (or in the init
routine of a dynamically loaded library), in order to avoid potential
thread clash in the singleton creation. One could attempt to protect the
singleton creation by a static mutex, but then one would be back at the
statics destruction order problems.
Thank you for the further details about multi-threading, I'm adding
them to my "toolbox", along with all the good new things I'm learning
here on clc++.
Cheers,
Francesco