Re: NSArray: Problem allocating memory on stack on windows

[Richard Frith-Macdonald]

On Thursday, October 9, 2003, at 11:09 AM, Roland Schwingel wrote:

> Hi....
>
> There is a problem with all the -initWithArray: and related methods.

> On windows stacksize is limited. So at present when calling 
> initWithArray
> with an array containing more then ~52100 elements stack runs out of 
> space
> and applications crashes (or behaves really silly, depending what gets 
> overwritten)
>
> The solution here to fix this would be to replace all that dynamic 
> array stuff
> with malloc()/free() calls.

We always knew this was a potential problem ... but didn't really 
expect to run into
it in practice (I guess the stack size on unix-like systems just tends 
to be a lot
bigger), so code like this only occasionally gets updated.

Simply replacing stack based memory management with heap based stuff is 
not
a good enough solution ... it's very slow.  Instead, what I do is a 
compromise ...

I select what seems a reasonable size (say a few thousand elements) and 
code
such that below this size we allocate memory on the stack, and above it 
we use
the heap.   The rationale being that, where we are dealing with large 
enough
amounts of data the overheads of heap management are proportionally 
smaller.

For instance, if -initWithArray: used malloc/free for an array 
containing just a
few objects, it would perhaps double the time taken by the array 
creation/initialisation,
but if it did it for an array containing 10000 objects, it would 
probably only
make a 1% difference.

Unfortunately, having two ways of dealing with the memory means more 
code,
and more chance of bugs ... so generally when adopting this scheme I 
initially
set the changeover point very small, so it's easy to exercise both 
schemes,
and only increase it when I'm confident both are working well.