Re: Is Linux Unix?
Erik Steffl <steffl@bigfoot.com> wrote in message news:<2pUe5-6sD-3@gated-at.bofh.it>...
> Ryo Furue wrote:
[. . .]
> > That's a good question. In fact, most modern Unix/Linux systems allow
> > you to use as large stacksize as you like, roughly speaking. Although
> > the default stakesize limit is often set to a very low value, say, 2MB,
> > each user can raise the limit, unless the system administrator (root)
> > prohibits it. So, no. That feature in question is very useful.
> >
> > Some people believe that the stacksize limit should be kept low
> > (in other words, that you shouldn't use much stack), but, as far as
> > I know, nobody seems to be able to give a convincing argument for that
> > position. I suspect that the posision is just an inertia, a remnant
> > of an old habit. But, I'm ready to be convinced otherwise if somebody
> > has a good argument.
>
> stack is something you do not have control over and you have no
> information about, it's not good to use it for large data - you cannot
> figure out how big it is, how much you're using, there's nothing you can
> do if space cannot be allocated etc. (maybe you can figure some of it
> out but that would be compiler specific, I think)
>
> on the other hand when using malloc/free or new/delete you can do
> _something_ if there's not enough memory.
Right. But, that depends on your design goal. There are many applications
where the heap is the right choise for large data. But, there are others
where the stack is better.
First of all, there are many cases where the heap is the only choise, as
when your function needs to return the pointer to the space allocated
within it. So, the real choise arises in cases like this:
int f() {
//. . .
double workspace0[N]; // stack
double* workspace1 = new double[N]; // heap; Which is better?
//. . .
delete[] workspace1;
}
As you say, if there's _somthing_ to do when there is not enough memory,
the heap is the right choice. That "something" may be, and in many cases,
is, just to print an error message and quit.
If, on the other hand, you don't care if your program crashes in case
of memory shortage, the stack is the better choice. One obvious reason
is that the stack is the faster. Another is that you can forget about
'delete'ing the allocated space; deallocation is automatic for the stack.
Many scientific applications are like this: "If it doesn't run, it doesn't.
That's fine. Use a larger computer."
My point is that it's really is a choice. The fact is that in majority
of cases the heap is the better choise. But, I don't see any inherent
reason why you shouldn't use the stack for large data. I said the
stack-is-not-for-large-data is "inertia", but it may be better called
a myth.
By the way, I don't know how hard to keep track of stack use.
But, the stack is released when the function is finished. Isn't
it, then, harder to keep track of heap use? I've heard a lot about
"memory leak", which refers to forgetting to 'delete' allocated
heap memory. I'm yet to hear "stack leak" :)
Of course, I'm joking. Please don't take this seriously.
Cheers,
Ryo
Reply to: