GNU Emacs, SLIME, Allegro

For some reason, I decided that I just had to switch to GNU Emacs from XEmacs on my WinXP laptop. So I went and downloaded Emacs 22.1 for Windows and installed it.

Setting it up for Erlang was easy: I added this to C:\Documents and Settings\Parijat\.emacs:


;; Erlang:
;; Add the location of the elisp files to the load-path
(setq load-path (cons "C:/erl5.5.4/lib/tools-2.5.4/emacs" load-path))
;; set the location of the man page hierarchy
(setq erlang-root-dir "c:/erl5.5.4")
;; add the home of the erlang binaries to the exec-path
(setq exec-path (cons "c:/erl5.5.4/bin" exec-path))
;; load and eval the erlang-start package to set up everything else
(require 'erlang-start)


Now, to setup Common Lisp. I use Allegro CL 8.0 Free Express Edition. (Yes, one day I'll buy the full version and repay Franz, but only after getting myself Lisp Certified ;-)) I was following the instructions at http://www.franz.com/emacs/slime.lhtml and http://common-lisp.net/project/asdf-install/tutorial/setup.html .

This is what I did:

1. Opened up ACL and loaded asdf into it:


International Allegro CL Free Express Edition
8.0 [Windows] (Aug 17, 2007 22:59)
Copyright (C) 1985-2006, Franz Inc., Oakland, CA, USA. All Rights Reserved.

This development copy of Allegro CL is licensed to:
Trial User

CG version 1.81.2.23 / IDE version 1.80.2.21
Loaded options from C:\Documents and Settings\Parijat\My Documents\allegro-prefs.cl.

;; Optimization settings: safety 1, space 1, speed 1, debug 2.
;; For a complete description of all compiler switches given the current optimization settings
;; evaluate (EXPLAIN-COMPILER-SETTINGS).

[changing package from "COMMON-LISP-USER" to "COMMON-GRAPHICS-USER"]
CG-USER(1): (require :asdf)
; Fast loading C:\Program Files\acl80-express\code\ASDF.001
T



2. Then, downloaded asdf-install and unpacked it into "C:\Documents and Settings\Parijat\asdf-install" (the source tarball has several nested directories called asdf-install; the innnermost contains the .asd file, and that's the one I am referring to here).

3. Told asdf about this directory:

CG-USER(4): (pushnew "c:/Documents and Settings/Parijat/asdf-install/" asdf:*central-registry* :test #'equal)


and compiled and loaded asdf-install:

CG-USER(5): (asdf:operate 'asdf:compile-op 'asdf-install)
CG-USER(6): (asdf:operator 'asdf:load-op 'asdf-install)


4. Well, all this stuff was in the end to get SLIME. I went to http://common-lisp.net/project/slime/#downloading and found the link to the latest SLIME. Now, on Windows, it seems asdf-install can't download and install tarballs off net (at least on Allegro CL). Then I downloaded and put the slime tarball in C:\Temp. Then:

(setq asdf-install::*verify-gpg-signatures* nil)
(setq *cygwin-bash-program* "c:/cygwin/bin/bash.exe")


and then:


CG-USER(7): (asdf-install:install "C:/Temp/slime-2.0.tgz")


This did not work, complaining:


Warning: Cannot find tar command "C:\\PROGRA~1\\Cygwin\\bin\\bash.exe".
Error: Unable to extract tarball C:/Temp/slime-2.0.tgz.


It seems my mod to *cygwin-bash-program* did not take effect inside asdf. Wonder why. I even quit Allegro, restarted it, defined *cygwin-bash-program* before compiling and loading asdf-install. No luck. (One thing I did not try was to define asdf-install:*cygwin-bash-program* instead of vanilla *cygwin-bash-program*). So I just went and hardcoded tar-command() in installer.lisp to return "C:\\cygwin\\bin\\bash.exe".

Now the above command works.

5. The Franz documentation instructs me to start "mlisp.exe" or "alise.exe" LISP image (see next step). But my ACL 8.0 express did not come with these images; it only has "allegro-ansi.exe". So, following the README in the acl80-express directory, I create the images, by starting allegro-ansi.exe, and in the "Debug window", typing the following:

CG-USER(1): (build-lisp-image "sys:mlisp.dxl" :case-mode :case-sensitive-lower
:include-ide nil :restart-app-function nil
:restart-init-function nil)
CG-USER(2): (sys:copy-file "sys:allegro-ansi.exe" "sys:mlisp.exe")


Now, I have a mlisp.exe and mlisp.dxl. Sure enough, clicking on mlisp.exe launches a console LISP without the GUI.

6. Now I have to load slime into Emacs. According to the instructions on the Franz webpage, I created a file "C:\Documents and Settings\Parijat\.slime.lisp", with the contents:

(load "C:/Documents and Settings/Parijat/.asdf-install-dir/site/slime-2.0/swank-loader.lisp")

(sys:with-command-line-arguments (("p" :short port :required)
("ef" :long ef :required))
(restvar)
(swank::create-server :port (parse-integer port :junk-allowed nil)
:style :spawn
:dont-close t
:coding-system (or ef "latin-1")))


and added this to my .emacs:

;; Allegro LISP + SLIME
(push "c:/Documents and Settings/Parijat/.asdf-install-dir/site/slimw-2.0/" load-path)
(require 'slime)
(slime-setup)

(setq slime-multiprocessing t)
(setq *slime-lisp* "C:/Program Files/acl80-express/mlisp.exe")
(setq *slime-port* 4006)

(defun slime ()
(print "this is my slime")
(interactive)
(shell-command
(format "%s +B +cm -L \"c:/Documents and Settings/Parijat/.slime.lisp\" -- -p %s --ef %s &"
*slime-lisp* *slime-port*
slime-net-coding-system))
(delete-other-windows)
(while (not (ignore-errors (slime-connect "localhost" *slime-port*)))
(sleep-for 0.2)))


I restart emacs. I say "M-x slime". And wait. The mlisp.exe window shows up, but no connection.

I figure that the problem is in (swank:create-server :port ...) which is supposed to start the swank server, does not work. If I run it in the mlisp.exe window, the command does not return (okay, maybe it is not supposed to). I can't telnet to port 4006 on the localhost, though.

Puff!!! It used to be simpler.

Concurrency: Erlang vs Java

Its fashionable to extol the high-performance of Erlang concurrency these days. Programming Erlang, Section 8.11, has this problem:

Write a ring benchmark. Create N processes in a ring. Send a message
round the ring M times so that a total of N * M messages get
sent. Time how long this takes for different values of N and M.

Well, I copied off the Java program from here: http://www.sics.se/~joe/ericsson/du98024.html

And then I wrote this Erlang program:

-module(threadperftest).
-compile(export_all).

timeit() ->
 register(mainproc, self()),
 io:format(" Procs,  Mesgs, SpawnTotal,  SpawnProc,   RunTotal,    RunMesg~n", []),
 timeit_aux(1000, 1000, 10000),
 init:stop().

timeit_aux(NProcs, NMsgs, NProcsMax) ->
 if NProcs =<>
     main([NProcs, NMsgs]),
     timeit_aux(NProcs+1000, NMsgs, NProcsMax);
    true -> void
 end.
    
main([N, M]) ->
 {_, _W0} = statistics(wall_clock),
 FirstPid = spawn(fun loop0/0),
 % io:format("First: ~p~n", [FirstPid]),
 LastPid = setup(N-1, FirstPid),
 FirstPid ! LastPid,
 {_, W1} = statistics(wall_clock),
 LastPid ! M,
 receive
 stop ->
     void
 end,
 {_, W2} = statistics(wall_clock),
 io:format("~6B, ~6B, ~10g, ~10g, ~10g, ~10g~n", [N, M, W1*1.0, 1.0*W1/N, W2*1.0, W2*1000.0/(M*N+N)]).

setup(0, PrevPid) ->
 PrevPid;
setup(HowMany, PrevPid) ->
 Pid = spawn(fun() -> loop(PrevPid) end),
 % io:format("~p: Linking to: ~p~n", [Pid, PrevPid]),
 setup(HowMany - 1, Pid).

loop0() ->
 receive
 LinkedPid when is_pid(LinkedPid) ->
     % io:format("First: ~p: Linking to ~p~n", [self(), LinkedPid]),
     loop1(LinkedPid);
 X ->
     erlang:error({unknownMessageError, X, self()})
 end.

loop1(LinkedPid) ->
 receive
 M when is_integer(M), M > 0 ->
     % io:format("~p: Received: ~p~n", [self(), M]),
     LinkedPid ! (M-1),
     loop1(LinkedPid);
 M when is_integer(M), M =:= 0 ->
     % io:format("~p: Received: ~p, Terminating~n", [self(), M]),
     mainproc ! stop,
     done;
 X ->
     erlang:error({unknownMessageError, X, self()})
 end.
  
loop(LinkedPid) ->
 receive
 M when is_integer(M), M > 0 ->
     % io:format("~p: Received: ~p~n", [self(), M]),
     LinkedPid ! M,
     loop(LinkedPid);
 M when is_integer(M), M =:= 0 ->
     % io:format("~p: Received: ~p, Terminating~n", [self(), M]),
     LinkedPid ! M,
     done;
 X ->
     erlang:error({unknownMessageError, X, self()})
 end.

The performance is something like this (all times are in milliseconds, except the last one, which is in microseconds):

 Procs,  Mesgs, SpawnTotal,  SpawnProc,   RunTotal,    RunMesg
 1000,   1000, 0.00000e+0, 0.00000e+0,    266.000,   0.265734
 2000,   1000,    16.0000, 8.00000e-3,    562.000,   0.280719
 3000,   1000, 0.00000e+0, 0.00000e+0,    969.000,   0.322677
 4000,   1000, 0.00000e+0, 0.00000e+0,    1672.00,   0.417582
 5000,   1000,    15.0000, 3.00000e-3,    2469.00,   0.493307
 6000,   1000,    16.0000, 2.66667e-3,    3234.00,   0.538462
 7000,   1000,    16.0000, 2.28571e-3,    4015.00,   0.572998
 8000,   1000,    16.0000, 2.00000e-3,    4750.00,   0.593157
 9000,   1000,    31.0000, 3.44444e-3,    5469.00,   0.607060
10000,   1000,    31.0000, 3.10000e-3,    6375.00,   0.636863

The numbers in the RunMesg column are the time it takes to send one message from one process to another. Why is it increasing? Does the runtime have to do more work to find the target process?

Here is the Java output (program below):

 Procs,  Mesgs, SpawnTotal, SpawnProcs,   RunTotal,   RunMesg
  100,   1000,     16.000,      0.160,  15531.000,     15.531
  200,   1000,     62.000,      0.310,  27047.000,     27.047
  300,   1000,     94.000,      0.313,  37828.000,     37.828
  400,   1000,    125.000,      0.313,  46859.000,     46.859
  500,   1000,    141.000,      0.282,  54578.000,     54.578
  600,   1000,    203.000,      0.338,  60594.000,     60.594
  700,   1000,    234.000,      0.334,  65282.000,     65.282
  800,   1000,    406.000,      0.508,  68156.000,     68.156
  900,   1000,    484.000,      0.538,  69782.000,     69.782
 1000,   1000,    735.000,      0.735,  70015.000,     70.015

The last column is in milliseconds whereas for Erlang it was in microseconds, AND the number of procs is 100-1000, whereas for Erlang they were 1000-10,000.

Programming Erlang exercise problem: trouble in the concurrent universe?

Going through Programming Erlang, encountered this exercise problem in Section 8.11:

Write a function start(AnAtom, Fun) to register AnAtom as spawn(Fun). Make sure your program works correctly in the case when two parallel processes simultaneously evaluate start/2. In this case, you must guarantee that one of these processes succeeds and the other fails.

Here is my first solution, and it seems to compile and run.

-module(register_function).
-export([start/2]).

start(AnAtom, Fun) ->
  case whereis(AnAtom) of
       undefined -> register(AnAtom, spawn(Fun));
       _ -> error
  end.

Now, is there race condition in the above? I mean, consider Processes A and B both executing start/2:

1. Process A calls whereis(AnAtom) which evaluates to 'undefined';
   
2. Process B calls whereis(AnAtom) which evaluates to 'undefined';
3. Process A calls register(AnAtom, spawn(Fun)), which succeeds and returns true;
   
4. Process B calls register(AnAtom, spawn(Fun)), which fails as AnAtom has been registered

Superficially, we have satisfied the requirements of the problem: Process A succeeded and B failed. But the sinister problem is that spawn(...) has been called by both processes anyway. Thus we have two instances of Fun being executed, with one of them in an anonymous process that I, at least for now, don't know how to access.

Ironically, the problem seems to be because presumably register puts AnAtom in some "global" table. Exactly the kind of concurrency problem that Erlang tries to avoid.

How would this be solved? Here is an idea:

1. Create a "register_function" server;
2. start/2 sends a message to this server with AnAtom and Fun as contents
3. presumably the server processes one message at a time and the code between matching a message and executing some expressions is atomic with respect to other messages to the same server

Puff. You'd think Erlang would come with built in functionality for this. Is this important?

That free lunch that you were talking about....

Reading on BBC:

From his office in Nevada, entrepreneur Dennis Hope has spawned a multi-million-dollar property business selling plots of lunar real estate at $20 (£10) an acre.

This guy has made $9m till now.

Buyers include Hollywood stars, large corporations - including the Hilton and Marriot hotel chains - and even former US presidents Ronald Reagan and Jimmy Carter. George W Bush is also said to be a stake holder.

What drives me nuts is:

day. He allocates land by simply closing his eyes and pointing to a map of the Moon.

So, uh, who said there was no free lunch? I mean, by the time this guy's claims are challenged in court, he would have enjoyed much of that $9m.

Technorati Tags: greed stupid

Emacs and bitstream fonts

I use emacs on Ubuntu heavily and naturally want a nice font to use. I chose to use the "bitstream vera sans mono" font. Well, easy does it: Options->Customize Emacs->Specific Face: "default", and setting the value of "Font Family" to "bitstream-bitstream vera sans mono" and value of "Height" to "100" gave me the nice font that I wanted. "Custom" created the settings for me:

(custom-set-faces
;; custom-set-faces was added by Custom -- don't edit or cut/paste it!
;; Your init file should contain only one such instance.
'(default ((t (:inherit nil :stipple nil :background "gray12" :foreground "green" :inverse-video nil :box nil :strike-through nil :overline nil :underline nil :slant normal :weight normal :height 117 :width normal :family "bitstream vera sans mono")))))

I should mention that I am using the "color-scheme" package and using a nice looking color scheme. The color information probably comes from there.

But then I tried to create a new frame (C-x 5 2) and lo! the new frame had my old font. Reading the emacs faq gave the answer: I'd have to set the font again in the variable that determines the options for all new frames. So I set in my "~/.emacs":

(setq default-frame-alist
'((font . "-bitstream-bitstream vera sans mono-medium-r-normal--0-0-0-0-m-0-iso8859-1")))

and new frames would now have the specified font, which happens to be the same as the original. I wonder if it is a coincidence that the size of the font in new frames and initial matches, because I have not specified the height of the font in this variable.

This seems like a ugly way: why specify the font properties in two different places? So I commented out the face created by custom, and oops! new frames would have a background of white. So I had to undo the change and let the fonts be specified in two places. But at least the initial and new frames have the same good looking font.

Ubuntu Edgy and X11 font bogosity

Using Ubuntu Edgy recently. I'd installed the great bitstream vera fonts and could use them in gnome, but could not see them in X applications, in particular emacs.

Turned out that /etc/X11/xorg.conf had a wrong configuration for fonts. It originally said:

Section "Files"
FontPath "/usr/share/X11/fonts/misc"
FontPath "/usr/share/X11/fonts/cyrillic"
FontPath "/usr/share/X11/fonts/100dpi/:unscaled"
FontPath "/usr/share/X11/fonts/75dpi/:unscaled"
FontPath "/usr/share/X11/fonts.Type1"
FontPath "/usr/share/X11/fonts/100dpi"
FontPath "/usr/share/X11/fonts/75dpi"
FontPath "/usr/share/X11/fonts/misc"
# path to defoma fonts
FontPath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection

Turns out that the directory "/usr/share/X11/fonts" is wrong and should be "/usr/share/fonts/X11", I changed the section to:

Section "Files"
FontPath "/usr/share/fonts/X11/misc"
FontPath "/usr/share/fonts/X11/cyrillic"
FontPath "/usr/share/fonts/X11/100dpi/:unscaled"
FontPath "/usr/share/fonts/X11/75dpi/:unscaled"
FontPath "/usr/share/fonts/X11/Type1"
FontPath "/usr/share/fonts/X11/100dpi"
FontPath "/usr/share/fonts/X11/75dpi"
FontPath "/usr/share/fonts/X11/misc"
# path to defoma fonts
FontPath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
FontPath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/CID"
EndSection

Then I restarted X. But no go. xlsfonts would still not list the bitstream fonts.
The bitstream fonts were linked to from "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType". I went into that directory, and ran

$ sudo ttmkfdir -o fonts.dir -d .

Then I restarted X again. And yes, this time xlsfonts could see the bitstream fonts. So the problems were the wrong font paths and the fact that the fonts.dir file had not been created in the defoma directory. It seems that this is a new bug in Edgy.

Software is knowledge

People screaming about software engineering were pulling the wool over our eyes and trying to make a quick buck, all along, as we all suspected when we attended those boring software engineering classes in CS courses.

Robert Glass got it right. Software is NOT an artifact of engineering. Making software is not like making a bridge.

Software is an embodiment of knowledge. Executable knowledge. Knowledge that when pasted over some silicon and stimulated with electricity can cause things to happen. By itself very little beyond flipping voltage levels in areas of said silicon. But give it some tools (like a serial port, cable and lcd screen) and it can communicate. Give it more tools (serial port, cable, robot arm) and it can create physical changes in its environment.

Yeah, you got it. Software is less like a scalpel, more like a doctor.

Why the sudden light?

Well, I was trying to document high-availability solutions with MySQL. When going through the nitty-gritty of MySQL Cluster's limitations (no offense intended: it is probably a good product; I am not dissing the software) it occured to me that they warranted noting down, so that my team would not have to read so much should they deal with MySQL Cluster. I found myself writing a short note with a link to the original page for details, because I felt that I could not tell the whole truth in a shorter way, and copying and pasting would be a waste. So, my documentation is a little more than some summary notes peppered with links to the full documentation.

Anyone reading any code that tried to deal with the limitations above---written in an arguably already readable language---would still scratch their heads at why some weird stuff was being done. There would have to be comments explaining why this was done. The comment could be just a link to the MySQL documentation page. Or, it could have the full explanation, with the MySQL version in which said limitation lurked. Or both. The person reading the code would have to understand the documentation before they could say they understood the code.

The point is that: if there is good documentation about some topic, I can do little than point others to it and say "this is important". The documentation is the communication.

And the more important point is: you cannot claim to have understood a software unless you understand its intention and motivation. And in the above case, the motivation means reading the documentation. Most times, reading documentation means you come back with knowledge. In other words, to understand the software, you must, well, understand. Err.. I mean, you must acquire the knowledge the original developer had when creating the software.

Which brings me to a wicked question: the reason I was writing the original notes about clustering was so that not everyone in my team has to know the nitty-gritty and just know enough to design and write code to be handle clusters if we decided to use clusters. But it looks like no one can actually decide if the code will be right without having read the full documentation anyway.

What about code? That's worse. You now must understand the intention of the code. Then you must understand the motivation behind the code. To do that you must read the documentation.

Software is knowledge.

And my documentation is little more than a reminder note or a collection of related links.