Subject: Re: posix_spawn facility
From: "gs-cygwin.com--- via Cygwin" <[email-masked]>
To: Bruno Haible <[email-masked]>
Cc: [email-masked]
Date: Thu, 20 Apr 2023 03:14:50 -0400
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>

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

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