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Date: Mon, 17 Feb 2025 09:38:40 -0800 (PST)
To: cygwin@cygwin.com
cc: cygwin-patches@cygwin.com
Subject: Re: WinAPI spawn() not used by Cygwin posix_spawn()? Re: [PATCH]
 Cygwin: Add spawn family of functions to docs
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On Mon, 17 Feb 2025, Corinna Vinschen wrote:

> The requirements of posix_spawn and their helper functions are so
> that we can't easily fulfill them without doing the fork/exec
> twist.
>
> See https://man7.org/linux/man-pages/man3/posix_spawn.3.html.
> Windows CreateProcess() is not quite the same as Linux clone().
>
> However, if you think you can come up with a version only running the
> spawnve function and thus speed up Cygwin, feel free to send patches.

(based on my recollections rather than actually reading the docs again...)
Specifically, maybe the case where the attributes which are supposed to do
things effectively between fork and exec are not set could be fast-pathed
to use spawn/CreateProcess, and the more complex cases fall back to
fork/exec.  If the created process is also a Cygwin process, perhaps the
actions that are supposed to happen between fork and exec could happen in
the startup code (much like fork emulation).

Just brainstorming.

BTW, I vaguely remember an issue with GNU make in MSYS2, where we found
that making it *not* use posix_spawn made it faster.
https://github.com/msys2/MSYS2-packages/blob/a0902f1e21781022c5ceca44c64190998a62e048/make/PKGBUILD#L31-L32


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