Using emacs' unexec to speed Python startup (was Re: [Python-Dev] Startup time)

[Jeff Epler]

O Sun, May 18, 2003 at 11:28:08PM -0400, Barry Warsaw wrote:
> Since it looks like you implemented the meat of it as a module, I 
> wonder if it couldn't be cleaned up (with the interrupt reset either 
> pulled in the extension or exposed to Python) and added to Python 2.3?

First off, I sure doubt that this feature could be truly made
"non-experimental" before 2.3 is released.  There was one "strange bug" so
far (the signal thing), though that was quickly solved (with another
change to the core Python source code).

Secondly, forcing all allocations to come from the heap instead of mmap'd
space may hurt performance.

Thirdly, the files implementing unexec itself, which come from fsf emacs,
are covered by the GNU GPL, which I think makes them unsuitable for
compiling into Python. (There's something called "dynodump" in Emacs that
appears to apply to ELF binaries which bears this license:
 * This source code is a product of Sun Microsystems, Inc. and is provided
 * for unrestricted use provided that this legend is included on all tape
 * media and as a part of the software program in whole or part.  Users
 * may copy or modify this source code without charge, but are not authorized
 * to license or distribute it to anyone else except as part of a product or
 * program developed by the user.
I wish I understood what "except as part of a product or program developed
by the user" meant--does that mean that Alice can't download Python
then give it to Bob if it includes dynodump?  After all, Alice didn't
develop it, she simply downloaded it.  The other dumpers in xemacs
seem to be GPL, and I think that the "portable undump" mentioned by
another poster is a placeholder for a project that isn't written yet:
http://www.xemacs.org/Architecting-XEmacs/unexec.html)

Fourthly, we'd have to duplicate whatever machinery chooses the correct
unexec implementation for the platform you're running on---there are lots to
choose from:
	unexaix.c     unexconvex.c  unexenix.c     unexnext.c    unexw32.c
	unexalpha.c   unexec.c      unexhp9k800.c  unexsni.c
	unexapollo.c  unexelf.c     unexmips.c     unexsunos4.c
(Of course, it's well known that only elf and win32 matter in these modern
times)

I'd be excited to see "my work" in Python, though the fact of the matter
is that I just tried this out because I was bored on a Sunday afternoon.

Jeff