Subject: Re: posix_spawn facility
From: "gs-cygwin.com--- via Cygwin" <[email-masked]>
To: [email-masked]
Cc: Bruno Haible <[email-masked]>
Date: Wed, 10 May 2023 04:59:24 -0400
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>

On Thu, Apr 20, 2023 at 03:14:59AM -0400, [email-masked] wrote:
> On Mon, Apr 17, 2023 at 08:44:51PM +0200, Bruno Haible via Cygwin wrote:
> > Btw, there are two more functions in the posix_spawn family meanwhile:
> >   * posix_spawn_file_actions_addchdir_np
> >     implemented by glibc [1], musl libc, macOS, FreeBSD [2], Solaris ≥ 11.3
> >     used by a few packages (Firefox, Chromium, Rust)
> >   * posix_spawn_file_actions_addfchdir_np
> >     implemented in glibc, musl libc
> >     but not used by any package so far [3].
> > 
> > The next POSIX will contain these functions (without the _np suffix).[4]
> > 
> > Bruno
> > 
> > [1] https://sourceware.org/bugzilla/show_bug.cgi?id=17405
> > [2] https://man.freebsd.org/cgi/man.cgi?query=posix_spawn_file_actions_adddup2&apropos=0&sektion=3&manpath=FreeBSD+11-current&format=html
> > [3] https://codesearch.debian.net/
> > [4] https://www.austingroupbugs.net/view.php?id=1208
> 
> With regards to [3] above, the next lighttpd release (lighttpd 1.4.70)
> will use posix_spawn_file_actions_addfchdir_np(), where available, for
> spawning CGI programs.
> 
> I have not yet tested under cygwin, but under Linux the overhead of
> initial CGI process creation can be greatly reduced by using
> posix_spawn() instead of fork(),execve().  The speedup is inversely
> proportional to how much work the target script performs (compared to
> the overhead of initial process creation).  On x86_64 Linux, running a
> minimal C program for CGI can be ~60% faster in lighttpd when using
> posix_spawn()!  When running a minimal /bin/sh program for CGI, the
> speedup is "only" ~20%!  (Those numbers were obtained from running
> h2load and weighttp microbenchmarks with the minimal CGI programs.)
> 
> minimal C program for CGI (compiled gcc -O3):
>   #include <unistd.h>
>   static const char resp[] = "Status: 200\n\n";
>   int main(void) { write(STDOUT_FILENO, resp, sizeof(resp)-1); return 0; }
> 
> minimal /bin/sh program for CGI:
>   #!/bin/sh
>   printf 'Status: 200\n\n'
> 
> Cheers, Glenn

lighttpd 1.4.70 has been released for cygwin and uses posix_spawn() when
running CGI programs.

Under cygwin 3.4.0, posix_spawn_file_actions_addfchdir_np() is not
detected and so not used, but once cygwin 3.5.0 is out, I'll rebuild the
lighttpd package on cygwin to take advantage of it.

Cheers, Glenn

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