Re: Array and memory usage

[Robert A Duff <bobduff@shell01.TheWorld.com>]

mheaney@on2.com (Matthew Heaney) writes:

> Robert A Duff <bobduff@shell01.TheWorld.com> wrote in message news:<wccr89ge7hw.fsf@shell01.TheWorld.com>...
> > 
> > If you use this trick on Windows, it will allocate backing store for all
> > that virtual memory.  I believe most Unix systems are smarter than that.
> > 
> > This trick is sometimes more efficient than linked lists for growable
> > data structures.  The links waste space, plus if you're not careful, the
> > list gets scattered all over the place, damaging cache behavior.  The
> > nice thing about arrays is that they are contiguous.
> 
> One thing you can on Windows is simply reserve the virtual memory for
> the array, without committing it to physical memory, and then use SEH
> ("structured exception handling") to handle the error.
> 
> The SEH mechanism supports resumption semantics, so you can handle the
> exception by committing the page you need, and then resuming from the
> spot from where the exception was raised.
> 
> This is documented in Jeff Richter's Programming Applications book.

I thought it happened automatically.  That is, if I say:

    X: array (1..100_000_000) of Integer;

it would allocate 400,000,000 bytes of virtual memory, but only allocate
physical pages on demand.  I believe that much works on Windows (without
calling windows-specific stuff like SEH).  (Windows 2000, Windows XP.)
The problem I found was that it allocated 400,000,000 bytes of backing
store, which was annoying.

Am I misinformed?

- Bob