18 Aug
2020
18 Aug
'20
2:43 a.m.
On Mon, 17 Aug 2020 at 21:34, Paul Winalski <paul.winalski(a)gmail.com> wrote:
On 8/17/20, Dibyendu Majumdar <mobile(a)majumdar.org.uk> wrote:
Unfortunately sbrk() is not portable (I am building on Windows with
MSVC too) and as far as I know was even removed from POSIX.
Yes, it only uses sbrk(). One consequence I think is that sbrk()
expands the process memory without invalidating existing use of memory
- so the code is able to periodically expand heap while retaining all
existing allocations.
If everyone does that, you can call other people's code without fear
of stepping on their memory when you allocate memory in your code.
Using a negative value to decrease the break is more problematic.
malloc() usually uses sbrk() to extend its heap.
When we ported DEC's GEM compilation system to Unix, I used sbrk() to
extend memory and built my own multiple heap allocation scheme on top
of that. I could have used malloc() to allocate the heap chunks, but
there was no point. Might as well cut out the middleman.
From Wikipedia:
sbrk and brk are considered
legacy even by 1997 standards (Single UNIX
Specification v2 or POSIX.1-1998).[5] They were removed in
POSIX.1-2001.[6]
Regards
Dibyendu