Category: General

Categories
General Programming

Netscape; hindsight is foresight

I have been enjoying reading “Architects of the Web” (see it on my Amazon bookshelf), a collection of stories from the early days of Netscape, Yahoo and the like. Perhaps in an attempt to avoid the doom of repetition, I’ve been reading a lot of “software history” recently … Seattle Public Library has got plenty of cool books.

Chapter one follows the founding of Netscape, from the early days of NCSA Mosaic, the fortuitous meeting of Marc Andreessen and Jim Clark and the beginning of the browser wars. I remember this from first time around, but I didn’t really understand all of what was going on.

The book progresses to follow the start of the browser wars, AOL beginning to bundle IE, Netscape launching the communicator suite …

And then the Netscape part of the book ends.

What? The end? But what about the browser wars? Microsoft getting sued by their own government? The AOL buyout? The Time Warner merger? Open sourcing of mozilla? The doldrums of tangled source code? And finally the rise of firefox?

As I flipped back to the opening “acknowledgements” page, I suddenly understand.

It was written in December 1996.

OMG. This book is a history of the web from the world of 1996. They had no idea what was coming next. Napster was nearly three years away. iTunes and the DRM wars would wait another few years beyond that. Skype, blogs, Flickr and web2.0 weren’t even on the radar yet.

But then again, what would happen if I wrote a ‘history of the web’ book today? Twelve years from now, someone might pick it up and say “Wow, these guys had no idea that X, Y and Z were just around the corner”.

I remember during the early days of Napster, I thought “this is basically illegal and will get squished”. But it took me a while to understand that (although Napster itself would ultimately be doomed) a genie had came out from a bottle and wasn’t ever going back in. Napster itself would end up dead, but so would the “old way of thinking”. It maybe took over a decade, but now stores are selling DRM free digital music and making lots of money doing so. People voted with their feet and it’s hard to stop a crowd.

So it occurs to me that in order to have a chance of seeing the new X, Y and Z before they creep over the horizon, you probably want to try letting go some of your ‘immutable assumptions’ about the world, and see what’d change if the assumption didn’t hold any more. Here’s some which pop into my head: ‘you need to have a bank account to put your money into’, ‘computers are not disposable items’, ‘companies need to keep stuff secret from their competitors’. Coincidentally, I’m also reading a book about Einstein’s life (on my bookshelf) and he’s the posterchild for the the “what happens if we ignore this fundamental assumption” school of thought.

So I’m now wondering: which ‘truths’ will have their demise chronicled in the history books of the future?

Categories
General

RAID-1 sans disks

In preparation for a somewhat more dramatic future experiment, I’ve been trying out RAID-1 failure modes using linux’s loopback capabilities to avoid having to actually buy any more real hard drives. You can simulate drive failures, failover and easily see what the current disk contents are. It should go without saying that, if you have a real RAID system currently running, you probably don’t want to execute these commands without thinking a bit first:

# Creating and destroying disks from the safety of your own console
mkdir ~/raid; cd ~/raid

# Create two 10Mb files called disk0 and disk1
for d in 0 1; do dd if=/dev/zero of=disk${d} bs=1024 count=10240; done

# Make them available as block devices using the loopback device
for d in 0 1; do sudo losetup /dev/loop$d disk$d; done

# Combine the two 'disks' into a RAID-1 mirrored block device
# Using '--build' rather than '--create' means there is no device
# specific metadata, and so the contents of the disks will be identical
sudo mdadm --build --verbose /dev/md0 --level=1 --raid-devices=2 /dev/loop[01]

# Create a filesystem on our raid device and mount it
sudo mkfs.ext3 /dev/md0 
mkdir /tmp/raidmnt
sudo mount /dev/md0 /tmp/raidmnt
sudo chown $USER /tmp/raidmnt

# The contents of both disks change in unison
md5sum disk[01]
date > /tmp/raidmnt/datefile
sync
md5sum disk[01]

# If we mark one disk as failed, disk contents diverge
sudo mdadm --fail /dev/md0 /dev/loop0
date > /tmp/raidmnt/datefile
sync
md5sum disk[01]

# Remove the failed disk and readd it, and RAID1 will sync
sudo mdadm --remove /dev/md0 /dev/loop0
sudo mdadm --add /dev/md0 /dev/loop0
sleep 1
md5sum disk[01]

# Add a third (unused) disk into the system to test failover
dd if=/dev/zero of=disk2 bs=1024 count=10240
sudo losetup /dev/loop2 disk2
sudo mdadm --add /dev/md0 /dev/loop2
sudo mdadm --detail /dev/md0

# When one of original two disks fail, the new disk gets used
md5sum disk[012]
sudo mdadm --fail /dev/md0 /dev/loop0
date > /tmp/raidmnt/datefile
sync
md5sum disk[012]

# Tidy up the world
sudo umount /dev/md0
sudo mdadm -S /dev/md0
for x in /dev/loop[012]; do sudo losetup -d $x; done
rm -rf /tmp/raidmnt ~/raid
Categories
General

Reading mode for emacs

Reading lots of text on a computer isn’t the most fun thing in the world. I still like paper (or e-ink screens!). But computers still have the advantage of flexibility. I’ve tried some “alternative” reading methods like dictator before but didn’t like them much. I think a less radical approach is better. So, I’ve been hacking up a basic reading mode in emacs which just highlights a sentence at a time. I’ve found it pleasantly useful, especially for technical documents. Here’s the screenshot (code still in flux):

Sentence highlighting

Dead simple, but it keeps my mind focused.

Categories
General

Yi, the haskell editor

My latest shinything fascination is with Yi, an emacs-like editor written in Haskell. State! GUIs! Monads! What fun. It is entirely made of awesome.

It’s not the easiest program to start playing with, so I’ve written up some installation instructions and a beginner guide here. If you want to see what a real-world Haskell application looks like, yi is a great example.

Categories
General

The best programming book I’ve ever read: Beautiful Code

Beautiful Code is probably the best programming book I’ve read (and I’ve read a lot of them!).

Bookshops are filled with books about the mechanics of programming; “Learn X in N days”. But there are precious few books which manage to capture the thought processes and the wisdom of good programmers. Reading “Beautiful Code’ is like spending several hours in the pub in deep conversation with a bunch of really sharp programmers. If you care about programming, it’s a must-read.

When you write code, you make lots of decisions. Some are small scale, like whether to split a long conditional across two lines. Others are larger scale, like how to model concurrency in a large system. Ideally, each decision you make should be an informed one where you are aware of the trade-offs you are making. However, that thought process is rarely captured in source code. When another programmer reads your source in six months, they are probably going to wonder why you did it that particular way instead of different way.

So that’s the great thing about “Beautiful Code”. There are 33 articles, all written by programmers about systems they’ve built and care deeply about. The articles talk about the trade-offs and choices they made. Some articles focus on the design of small bits of software, such as Python’s dictionary implementation. Others focus on cool new techniques, such as Simon Peyton Jones’ article on transactional memory. There’s an amazing article about designing software for Stephen Hawking’s computer system (he can only operate a single input button). These are not trivial toy examples; they are real world systems with history and design.

There’s both a breadth and a depth to this book which really impresses me.

See Beautiful code at amazon.com or amazon.co.uk.