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Date: Tue, 5 Mar 2024 16:08:27 -0800
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Subject: Re: Native posix_spawn() in Cygwin?
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From: Mark Geisert via Cygwin <cygwin AT cygwin DOT com>
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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.

That's an interesting research question for somebody. If somebody steps 
up for that, great, otherwise as usual PTC.
Regards,

..mark


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