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Subject:	Re: Why does Cygwin not use MiCloneProcessAddressSpace() for fork()
To:	cygwin AT cygwin DOT com
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From:	Lionel Cons via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Lionel Cons <lionelcons1972 AT gmail DOT com>
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On Mon, 22 Sept 2025 at 12:49, Mark Liam Brown via Cygwin
<cygwin AT cygwin DOT com> wrote:
>
> On Mon, Sep 22, 2025 at 12:35 PM Mark Liam Brown
> <brownmarkliam AT gmail DOT com> wrote:
> >
> > Greetings!
> >
> > Why does Cygwin not use MiCloneProcessAddressSpace() for fork()? That
> > function was added for the Windows Services for UNIX, and it still
> > working in Windows 11.
>
> This is exposed to the userspace as NtCreateProcessEx() as documented
> in https://github.com/huntandhackett/process-cloning

That is the basis for RtlCloneUserProcess(), which AT&T UWIN and SFU use.

This is also the reason why UWIN runs circles around Cygwin in terms
of fork() performance, which directly affects performance of shell
scripts and /bin/make. That's also the reason we still have UWIN5 in
use, Cygwin has terrible fork() performance.


Lionel

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