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Subject: Re: Native posix_spawn() in Cygwin?
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From: Dan Shelton via Cygwin <cygwin AT cygwin DOT com>
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On Wed, 6 Mar 2024 at 01:08, Mark Geisert via Cygwin <cygwin AT cygwin DOT com> wrote:
>
> On 3/5/2024 2:42 PM, Dan Shelton via Cygwin wrote:
> > On Mon, 4 Mar 2024 at 07:45, Mark Geisert via Cygwin <cygwin AT cygwin DOT com> wrote:
> >>
> >> On 3/3/2024 7:27 PM, Dan Shelton via Cygwin wrote:
> [...]
> >>> strace does not help, as I need the Win32 calls BELOW posix_spawn(),
> >>> to see the implementation details.
> >>
> >> Check the source code, then. It's at:
> >>       https://cygwin.com/cgit/newlib-cygwin/tree/winsup/cygwin/fork.cc
> >>
> >> Look at line 587; there's the static function dofork(). Look at the
> >> thirty or so lines above that; there's both fork() and
> >> __posix_spawn_fork() calling dofork(). So both those user-level
> >> functions call into the exact same internals. (BTW __posix_spawn_fork()
> >> is called from posix_spawn(); the latter is in newlib and not Cygwin.)
> >>
> >> You can even see the reason it's done this way by reading the comment.
> >
> > Yes, but it is as I feared, Cygwin posix_spawn() does not use Win32
> > spawn() at all, and instead uses a rather inefficient vfork()
> > solution.
>
> Cygwin's vfork() is just a wrapper around fork(), so yes. But anyway...
>
> > posix_spawn() was added to POSIX so a Win32 implementation can use Win32 spawn()
>
> ...now I see what you're getting at:
>
> If posix_spawn() is intended to launch truly unrelated processes, with
> minimal or no coordination with the launching process, why can't it just
> use Windows' CreateProcess? I assume here that's what Win32 spawn() does.
>

I'm not sure, but I think this would benefit Cygwin greatly to
implement a native posix_spawn(). It should be faster and scale
better. Also the only stuff which do really need fork() are
bash/dash/ksh, and maybe daemon stuff like sshd.

Re CreateProcess: Maybe CreateProcess() breaks access token or newgrp support?

Does Cygwin do bounties (paid bug fixes), or Google Summer Of Code?

Dan
-- 
Dan Shelton - Cluster Specialist Win/Lin/Bsd

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