Flying the SR-71 Blackbird


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In April 1986, following an
attack on American soldiers
in a Berlin disco, President
Reagan ordered the bombing
of Muammar Qaddafi’s terrorist camps
in Libya. My duty was to fly over Libya
and take photos recording the damage
our F-111’s had inflicted. Qaddafi had
established a ‘line of death,’ a territorial
marking across the Gulf of Sidra,
swearing to shoot down any intruder
that crossed the boundary. On the
morning of April 15, I rocketed past
the line at 2,125 mph.
I was piloting the SR-71 spy plane,
the world’s fastest jet, accompanied
by Maj Walter Watson, the aircraft’s
reconnaissance systems officer (RSO).
We had crossed into Libya and were
approaching our final turn over the
bleak desert landscape when Walter
informed me that he was receiving missile
launch signals. I quickly increased
our speed, calculating the time it
would take for the weapons-most
likely SA-2 and SA-4 surface-to-air
missiles capable of Mach 5 - to reach
our altitude. I estimated that we could
beat the rocket-powered missiles to
the turn and stayed our course, betting
our lives on the plane’s performance.
After several agonizingly long seconds,
we made the turn and blasted
toward the Mediterranean ‘You might
want to pull it back,’ Walter suggested.
It was then that I noticed I still had the
throttles full forward. The plane was
flying a mile every 1.6 seconds, well
above our Mach 3.2 limit. It was the
fastest we would ever fly. I pulled the
throttles to idle just south of Sicily, but
we still overran the refueling tanker
awaiting us over Gibraltar.



Many hands make light work

A few years ago Tim Bray decided to
find out where things stood. He put a
computer on the Internet, which contained
over 200 million lines of text in
one very large file. Then he challenged
programmers to write a program to
do some simple things with this file,
such as finding the ten most common
lines, which matched certain patterns.
To give you a feel for the simplicity
of the task, Bray’s example program
employed one sequential thread of
execution and had 78 lines of code,
something you could hack up over
lunch.


import concurrent;

Shared memory can be pushed fairly
far, however. Instead of explicit locks,
Clojure and many newer languages use
an interesting technique called software
transactional memory. STM simulates a
sort of post-hoc, fine-grained, implicit
locking. Under this scheme semi-independent
workers, called threads, read
and write to a shared memory space
as though they were alone. The system
keeps a log of what they have read and
written. When a thread is finished the
system verifies that no data it read was
changed by any other. If so the changes
are committed.


Write more code

As odd as it sounds, the only way I
found to get through my fear of writing
code was to crank it out like it was
going out of style. The easiest way to
do this? Start new side projects and
contribute simple patches to Open
Source. Every time you write code,
you will learn something about the
code, your tools, or yourself. Did you
really think my 57 plus daily refactoring
posts were only about fixing bad
code? Nope, they are my sledgehammers
against coder’s block.