[4/4] ntdll: partially support HEAP_DISABLE_COALESCE_ON_FREE, allows us to detect use-after-free

[Dan Kegel]

Don't apply this one yet, just found a problem with it.

On Tue, Nov 24, 2009 at 6:20 PM, Dan Kegel <dank at kegel.com> wrote:
> This adds something like support for
> HEAP_DISABLE_COALESCE_ON_FREE.
> If the GlobalFlags registry entry has the
> 200000 bit set, freed blocks are set
> aside for a while rather than immediately
> being released for reuse.  This allows
> us to poison them and check for use-after-free
> or double-free errors, and report them as heap corruption.
>
> If you're running Valgrind, you get an immediate error
> and stack trace for any of these heap corruption events,
> which was the motivation for the patch series.
> But the patches are useful even without valgrind.
>
> The number of blocks kept out of circulation is
> 5000 by default, but can be set via an environment
> variable.  It ought to have a limit on number of bytes,
> too, but this seemed enough for the moment.
>