Modular SQL Queries with Unit Tests
I'm sure I'm not the only person on earth facing a complex and expensive analytical processing task. The one I've been working on for the past couple of years, runs on the GHTorrent 98.5 GB data set of GitHub process data. It comprises 99 SQL queries (2599 lines of SQL code in total) and takes more than 20 hours to run on a hefty server. To make the job's parts run efficiently and reliably I implemented simple-rolap, a bare-bones relational online analytical processing tool suite. To ensure the queries produce correct results, I wrote RDBUnit, a unit testing framework for relational database queries. Here is a quick overview on how to use the two.
Continue reading "Modular SQL Queries with Unit Tests"
The Road to Debugging Success
A colleague recently asked me how to debug a Linux embedded system that crashed in the Unix shell (and only there), when its memory got filled through the buffer cache. He added that when he emptied the buffer cache the crash no longer occurred.
Continue reading "The Road to Debugging Success"
First, Do No Harm
Let’s face it: not all software developers are superstar programmers (and, trust me, not all luminary developers program in a sane way.) This means that when we maintain existing code, we must be very careful to avoid breaking or degrading the system we work on. Why? Because a failure of a running system can affect operations, people, profits, property, and sometimes even lives. Here are the rules.
Continue reading "First, Do No Harm"
The Frictionless Development Environment Scorecard
The environment we work in as developers can make a tremendous difference on our productivity and well-being. I’ve often seen myself get trapped in an unproductive setup through a combination of inertia, sloth, and entropy. Sometimes I put-off investing in new, better tools, at other times I avoid the work required to automate a time-consuming process, and, also, as time goes by, changes in my environment blunt the edge of my setup. I thus occasionally enter into a state where my productivity suffers death by a thousand cuts. I’ve also seen the same situation when working with colleagues: cases where to achieve a simple task they waste considerable time and energy jumping through multiple hoops.
Continue reading "The Frictionless Development Environment Scorecard"
If estimating the time needed for implementing some software is difficult, coming up with a figure for the time required to debug it is nigh on impossible. Bugs can lurk in the most obscure corners of the system, or even in the crevices of third-party libraries and components. Ask some developers for a time estimate, and don’t be surprised if an experienced one snaps back, “I’ve found the bug when I’ve found the bug.” Thankfully, there are some tools that allow methodical debugging, thereby giving you a sense of progress and a visible target. A method I’ve come to appreciate over the past few months is differential debugging. Under it, you compare a known good system with the buggy one, working toward the problem source.
Continue reading "Differential Debugging"
Portability: Goodies vs. the hair shirt
“I don’t know what the language of the year 2000 will look like, but I know it will be called Fortran”
Continue reading "Portability: Goodies vs. the hair shirt"
Systems software is the low-level infrastructure that applications run on: the operating systems, language runtimes, libraries, databases, application servers, and many other components that churn our bits 24/7. It’s the mother of all code. In contrast to application software, which is constructed to meet specific use cases and business objectives, systems software should be able to serve correctly any reasonable workload. Consequently, it must be extremely reliable and efficient. When it works like that, it’s a mighty tool that lets applications concentrate on meeting their users’ needs. When it doesn’t, the failures are often spectacular. Let’s see how we go about creating such software.
Continue reading "Systems Software"
If I program in many high and low-level languages, but donít write systems code, I am a quiche programmer or a code monkey. And if my code runs without errors, and I know the complexity of all algorithms; and if my servers have hundreds of cores and gigabytes of RAM, but donít write systems code, I am nothing. And if I run the hippest kernel, and install the neatest apps, but donít write systems code, it profiteth me nothing.
Continue reading "Systems Code"
The Importance of Being Declarative
A declarative programming style focuses on what you want your program to do rather than how to perform the task. Through diverse programming techniques, libraries, and specialized languages, you end up with code that sidesteps nitty-gritty implementation details, dealing instead with a task’s big picture.
Continue reading "The Importance of Being Declarative"
APIs, Libraries, and Code
Let’s say you want to display a JPEG-compressed image, calculate Pearson’s correlation coefficient, parse an XML file, or create a key-value store. You can often choose between using the functionality of the application’s platform (Java EE or .NET), calling one of several available external libraries, or writing the code on your own. It isn’t an easy choice because you have many factors to consider. Specifically, you must take into account the task’s complexity, as well as the licensing, quality, and support of competing alternatives. See how you can narrow down your choice by eliminating alternatives at the earliest possible decision point.
Continue reading "APIs, Libraries, and Code"
Programming Languages vs. Fat Fingers
A substitution of a comma with a period in project Mercury's working Fortran code compromised the accuracy of the results, rendering them unsuitable for longer orbital missions.
How probable are such events and how does a programming language's design affect their likelihood and severity?
In a paper I recently presented at the
4th Annual International Workshop on Evaluation and Usability of Programming Languages and Tools
I showed results obtained by randomly perturbing similar programs written in
diverse languages to see whether the compiler or run-time system
would detect those changes as errors,
or whether these would end-up generating incorrect output.
Continue reading "Programming Languages vs. Fat Fingers"
How to Calculate an Operation's Memory Consumption
How can you determine how much memory is consumed by a specific
operation of a Unix program?
Valgrind's Massif subsystem could help you in this regard,
but it can be difficult to isolate a specific operation from
Here is another, simpler way.
Continue reading "How to Calculate an Operation's Memory Consumption"
Refactoring on the Cheap
The refactorings that a good integrated development environment can perform are impressive. Yet, there are many reasons to master some cheap-and-cheerful alternative approaches. First, there will always be refactorings that your IDE won’t support. Also, although your IDE might offer excellent refactoring support for some programming languages, it could fall short on others. Modern projects increasingly mix and match implementation languages, and switching to a specialized IDE for each language is burdensome and inefficient. Finally, IDE-provided refactorings resemble an intellectual straightjacket. If you only know how to use the ready-made refactorings, you’ll miss out on opportunities for other code improvements.
Continue reading "Refactoring on the Cheap"
This column is about a tool we no longer have: the continuous rise of the CPU clock frequency. We were enjoying this trend for decades, but in the past few years, progress stalled. CPUs are no longer getting faster because their makers can’t handle the heat of faster-switching transistors. Furthermore, increasing the CPU’s sophistication to execute our instructions more cleverly has hit the law of diminishing returns. Consequently, CPU manufacturers now package the constantly increasing number of transistors they can fit onto a chip into multiple cores—processing elements—and then ask us developers to put the cores to good use.
Continue reading "Faking it"
How I Dealt with Student Plagiarism
a colleague at the
NYU Stern School of Business,
received considerable media attention when,
in a blog post he subsequently removed,
he discussed how his aggressive use of plagiarism detection software
on student assignments poisoned the classroom atmosphere and
tanked his teaching evaluations.
As detailed in
a story posted on the Chronicle of Higher Education blog,
Mr. Ipeirotis proposes instead that professors should design assignments that
cannot be plagiarized.
Along these lines here are two methods I've used in the past.
Continue reading "How I Dealt with Student Plagiarism"
Code Verification Scripts
Which of my classes contain instance variables?
Which classes call the method
Continue reading "Code Verification Scripts"
but don't call the method
These and similar questions often come up when you want to verify
that your code is free from some errors.
For example, instance variable can be a problem in servlet classes.
Or you may have found a bug related to the
and you want to look for other places where this occurs.
Your IDE is unlikely to answer such questions,
and this is where a few lines in the Unix shell can save
you hours of frustration.
Choosing and Using Open Source Components
The developers of the SQLite open source database engine estimate that it’s deployed in roughly half a billion systems around the world (users include Airbus, Google, and Skype). Think of the hundreds of thousands of open source components, just one click away from you. If you know how to choose and use them effectively , your project can benefit mightily.
Continue reading "Choosing and Using Open Source Components"
Sure, you can write English right to left. You can also write software code to look like a disc or even a train (see www.ioccc.org/1988/westley.c and 1986/marshall.c). However, you can’t then complain when you have to fight with your magazine’s editor or production staff about accepting your column’s title for publication, or if your colleagues refuse to touch your code with a 10-foot pole. Writing code in a readable and consistent style is difficult, uninteresting, tedious, underappreciated, and, extremely important.
Continue reading "elytS edoC"
Farewell to Disks
A classic web-comic illustrates how idle Wikipedia browsing can lead us from the Tacoma Narrows Bridge to Fatal hilarity (and worse). The comic doesn’t show the path leading from A to B, and finding it is an interesting challenge—think how you would engineer a system that could answer such questions. I believe that this problem and a solution I’ll present demonstrate some programming tools and techniques that will become increasingly important in the years to come.
Continue reading "Farewell to Disks"
Sane vim Editing of Unicode Files
Being able to use plain alphabeitc keys as editing commands
is for many of us a great strength of the vi editor.
It allows us to edit without hunting for the placement of
the various movement keys on each particular keyboard,
and, most of the time,
without having to juggle in order to combine particular keys with
Continue reading "Sane vim Editing of Unicode Files"
However, this advantage can turn into a curse when editing files
using a non-ASCII keyboard layout.
When the keyboard input method is switched to another script
(Greek in my case, or, say, Cyrillic for others)
vi will stop responding to its normal commands, because it will
encounter unknown characters.
Here is how I've dealt with this problem.
Technical prose is almost immortal.
Continue reading "Code Documentation"
A generous car reviewer might praise a vehicle’s handling by writing that it turns as if it’s running on railroad tracks. Indeed, tracks offer guidance and support. When you run on tracks you can carry more weight, you can run faster, and you can’t get lost. That’s why engineers, from early childhood to old age, get hooked on trains. Can we get our software to run on tracks?
Continue reading "Software Tracks"
Applied Code Reading: Debugging FreeBSD Regex
When the code we're trying to
read is inscrutable,
inserting print statements and running various test cases can be
two invaluable tools.
Earlier today I fixed
a tricky problem in the FreeBSD regular expression library.
originally written by Henry Spencer in the early 1990s,
is by far the most complex I've ever encountered.
It implements sophisticated algorithms with minimal commenting.
Also, to avoid code repetition and increase efficiency,
the 1200 line long main part of the regular expression execution engine is
included in the compiled C code
three times after modifying various macros to adjust the code's behavior:
the first time the code targets small expressions and operates
with bit masks on long integers,
the second time the code handles larger expressions
by storing its data in arrays,
and the third time the code is also adjusted to handle multibyte characters.
Here is how I used test data and print statements to locate and fix the problem.
Continue reading "Applied Code Reading: Debugging FreeBSD Regex"
My colleague, who works for a major equipment vendor, was discussing how his employer was planning to lay off hundreds of developers over the coming months. “But I’m safe,” he said, “as I’m one of the two people in our group who really understand the code.” It seems that writing code that nobody else can comprehend can be a significant job security booster. Here’s some advice.
Continue reading "Job Security"
Applied Code Reading: GNU Plotutils
Robert, a UMLGraph user sent me an email
describing a problem with the
SVG output on Firefox.
I firmly believe that
code reading is a lot
easier than many think:
one can easily fix most software problems without detailed knowledge
of the underlying system.
I therefore decided to practice what I preach.
Continue reading "Applied Code Reading: GNU Plotutils"
A Tiny Review of Scala
Earlier today I finished reading the
Programming in Scala book.
My review of the book should appear soon in the
reviews.com site and the
ACM Computing Reviews.
Here I outline briefly my view of the
Continue reading "A Tiny Review of Scala"
Fixing the Orientation of JPEG Photographs
I used to fix the orientation of my photographs through an application
that would transpose the compressed JPEG blocks.
This had the advantage of avoiding the image degradation of a
decompression and a subsequent compression.
Continue reading "Fixing the Orientation of JPEG Photographs"
A Tiling Demo
Over the past (too many) days I've been preparing my presentation for the
At one point I wanted to show how loop tiling increases locality of reference
and therefore cache hits.
Surprisingly, I could not find a demo on the web, so I built one from scratch.
Here are two applets demonstrating memory accesses during a matrix raise to the
power of two operation.
Continue reading "A Tiling Demo"
Precision in Comments
As I was writing some code for the
refactoring browser today,
I reflected on the importance of writing precise and clear comments.
Continue reading "Precision in Comments"
Start With the Most Difficult Part
There’s not a lot you can change in the process of constructing a building. You must lay the foundation before you erect the upper floors, and you can’t paint without having the walls in place. In software, we’re blessed with more freedom.
Continue reading "Start With the Most Difficult Part"
The Information Train
The Information Train is a scientific
experiment that I presented at the
Wizards of Science 2009 contest over the past weekend.
The entry demonstrates how computers communicate with each other by
setting up a network in which a model train transfers a picture's pixels
from one computer to the other.
You can find
a video of the experiment
on YouTube, and, if you're interested, you can also download
the corresponding software and schematics from
this web page.
Continue reading "The Information Train"
What are the ingredients of robust, elegant, flexible, and maintainable software architecture?
Over the past couple of years, my colleague
and I worked
on answering this question through a collection of intriguing essays
from more than a dozen of today's leading software designers and architects.
Continue reading "Beautiful Architecture"
The World's Smallest Domain-Specific Language
Domain-specific languages, also known as little languages, allow us
to express knowledge in a form close to the problem at hand.
In contrast to general-purpose languages, like Java or C++,
they are specialized for a narrow domain.
Earlier today I wanted to initialize a rectangular array of Boolean
values to represent the stick figure of a human.
For that I devised a tiny domain-specific language (DSL) consisting of
two symbols (representing an on and an off pixel) and wrote its
commensurably simple interpreter.
Continue reading "The World's Smallest Domain-Specific Language"
A Well-Tempered Pipeline
I am studying the use of open source software in industry.
One way to obtain empirical data is to look at the operating systems and
browsers used by the Fortune 1000 companies by examining browser logs.
I obtained a list of the Fortune 1000 domains and wrote a pipeline
to summarize results by going through this site's access logs.
Continue reading "A Well-Tempered Pipeline"
The Value of Computing Paradigm Diversity
Today I wrote a combinatorial optimization algorithm to match members of
teams according to the psychological traits of each pair's members.
The program appeared to rearrange the initial random allocation of pairs
in a way that might match my specifications.
However, as I'll use this allocation for an experiment that I'll be able
to perform only once, I realized that I wanted to carefully verify the results.
How does one verify the operation of such a program?
Continue reading "The Value of Computing Paradigm Diversity"
A Look at Zero-Defect Code
National Security Agency
has released a case study showing how to
develop zero-defect code in a cost-effective manner.
The researchers of the project conclude that,
if adopted widely, the practices advocated in the case study
could help make commercial software programs more reliable and less vulnerable.
I examined a small part of the case study's code, and was not impressed.
Continue reading "A Look at Zero-Defect Code"
Suspend Windows from the Command Line
I used to leave my computer up all night, but I've come to realize that this
is ecologically unsound.
Now I suspend it before going to sleep, but this missed running
a daily job that used to run at 03:00 am.
The job marks my students' exercises and send me email with the next day's
I thus decided to schedule the task to wakeup my computer at 3:00 am,
run the job, and then suspend it again.
The Windows scheduler allows you to specify a wakeup option,
but not a subsequent suspend.
Furthermore, it seems that Windows lacks a way to suspend from the
command line (while maintaining the ability to hibernate), and the
only free tools on the web are distributed in executable form,
so I ended writing a small tool myself.
Continue reading "Suspend Windows from the Command Line"
Web Services Come of Age
For years I've reacted to the hype surrounding web services with skepticism.
I found SOAP, WSDL, and UDDI to be too complex and brittle for wide deployment,
and I also wondered what types of services could be better provided over the
web rather than locally.
A new excellent developer site,
answers both of my concerns.
Continue reading "Web Services Come of Age"
Saving the Editor's History
I recently spent a few days writing some tricky bit-twiddling code to
implement a radix tree.
I found myself making many programming mistakes, and I thought it would be
interesting to study them, examine their contributing factors, and
think how each of them could be prevented.
Continue reading "Saving the Editor's History"
The Way We Program
If the code and the comments disagree, then both are probably wrong.
Continue reading "The Way We Program"
The tools and processes we use to transform our system’s source code into an application we can deploy or ship were always important, but nowadays they can mean the difference between success and failure. The reasons are simple: larger code bodies, teams that are bigger, more fluid, and wider distributed, richer interactions with other code, and sophisticated tool chains. All these mean that a slapdash software build process will be an endless drain on productivity and an embarrassing source of bugs, while a high-quality one will give us developers more time and traction to build better software.
Continue reading "Software Builders"
Over the past few days I worked over a large code body correcting various
accumulated errors and style digressions.
When I finished I wanted to see who wrote the original lines.
(It turned out I was not entirely innocent.)
Continue reading "Assigning Responsibility"
A Minute Minute Minder
Today I delivered the opening
at the 4th Panhellenic Conference on Computer Science Education.
For a number of reasons (more on that later) I wanted to keep track of
my progress during the presentation.
For this I put together a minute minder that displayed the
time from the presentation's start and the slide I should be in.
I could thus adjust my pace to finish as planned.
Continue reading "A Minute Minute Minder"
Using and Abusing XML
Words are like leaves; and where they most abound,
Much fruit of sense beneath is rarely found.
— Alexander Pope
I was recently gathering GPS coordinates and cell identification data, researching the algorithms hiding behind Google’s “My Location” facility.
While working on this task, I witnessed the great interoperability benefits we get from XML. With a simple 140-line script, I converted the data I gathered into a de facto standard, the XML-based GPS-exchange format called GPX. Then, using a GPS-format converter, I converted my data into Google Earth’s XML data format A few mouse clicks later, I had my journeys and associated cell tower switchovers beautifully superimposed on satellite pictures and maps.
Continue reading "Using and Abusing XML"
The Mysterious TreeMap Type Signature
For my lecture notes on file handling
I wrote a small Java program to display the number of characters
that fall in each
and got bitten by an unexpected
a wizard of Java Generics, kindly provided me with an explanation
of the JDK design,
which I'd like to share.
Continue reading "The Mysterious TreeMap Type Signature"
Metaprogramming, using programs to manipulate other programs, is as old as programming. From self-modifying machine code in early computers to expressions involving partially applied functions in modern functional-programming languages, metaprogramming is an essential part of an advanced programmer’s arsenal.
Continue reading "Rational Metaprogramming"
The Relativity of Performance Improvements
Today, after receiving a 1.7MB daily security log message containing
thousands of ssh failed login attempts from bots around the
world, I decided I had enough.
I enabled IPFW to a FreeBSD system I maintain, and added a script
to find and block the offending IP addresses.
In the process I improved the script's performance.
The results of the improvement were unintuitive.
Continue reading "The Relativity of Performance Improvements"
Curing MIDlet Bluetooth Disconnects
Over the last few days I've been writing a
to collect GPS coordinates and cell identifiers.
I'm doing this
in an effort to look at what algorithms might be needed
in order to implement something similar to Google's
Here is a Google Earth example of the data I'm collecting.
I reached a point where I was collecting all the information I needed,
but the program was often plagued by random disconnections of the Bluetooth
link to the GPS.
Continue reading "Curing MIDlet Bluetooth Disconnects"
Many Ways to Skin a Window
Every couple of years,
users of a Microsoft Windows application I wrote a long time ago
start complaining that the application crashes when they exit from it.
Every time it turns out that the reason is a Windows message that tells
the application's main window to close
in a way that was not originally foreseen.
Continue reading "Many Ways to Skin a Window"
A box of crayons and a big sheet of paper provides a more expressive medium for kids than computerized paint programs.
— Clifford Stoll
This column came to life as I was trying to devise an algorithm for
analyzing initializers for C arrays and structures. At the time I was
using the CScout
refactoring browser to look for possible differences
between closed and open source code. I had already processed the
Linux, FreeBSD, and Windows research kernel source codel and only the
OpenSolaris kernel remained. Unlikethe other three code bases, Sun’s
code didn’t appear to use any exotic compiler extensions, so
CScout uncomplainingly devoured one file after the next. Then, after
aspproximately six hours of processing and 80 percent along the way,
it reported a syntax error.
Continue reading "On Paper"
A Programmer's Bookshelf
A first year student at a nearby university wrote to me asking for
advice on becoming a hacker
definition, he clarified).
He sent me a laundry-list of 18 programming languages he aimed to learn
by the time he graduated, and asked for other recommendations.
I've learned a lot from reading books,
so I compiled two reading lists for him.
Continue reading "A Programmer's Bookshelf"
Abstraction and Variation
“Master, a friend told me today that I should never use the editor’s copy-paste functions when programming,” said the young apprentice. “I thought the whole point of programming tools was to make our lives easier,” he continued.
The Master stroked his long grey beard and pressed the busy button on his phone. This was going to be one of those long, important discussions.
Continue reading "Abstraction and Variation"
Palindromic Palindrome Checking
Stan Kelly-Bootle's column in the April 2007
ACM Queue, titled
Ode or Code? — Programmers Be Mused!,
was as always very enjoyable.
However, I found its ending,
a C function that returns true when given a palindromic string
(e.g. ABCCBA), anticlimactic.
The function given is recursive; I was expecting it to be palindromic.
How difficult can it be to write such a function?
Continue reading "Palindromic Palindrome Checking"
Using the Open-Sourced Java Platform
Having access to a system's source code is liberating.
I've felt this since I first laid my eyes on the source code of the
9th Edition Unix in 1988, and I saw this again as I used the freshly
open-sourced Java platform
to implement a UMLGraph
feature that has been bugging me for more than a month.
Continue reading "Using the Open-Sourced Java Platform"
Knowledge is power.
—Sir Francis Bacon
The ultimate source of truth regarding a program is its execution. When a program runs everything comes to light: correctness, CPU and memory utilization, even interactions with buggy libraries, operating systems, and hardware. Yet, this source of truth is also fleeting, rushing into oblivion at the tune of billions of instructions per second. Worse, capturing that truth can be a tricky, tortuous, or downright treacherous affair.
Continue reading "I Spy"
Software Development Productivity Award
Yesterday, at the
17th annual Jolt Product Excellence and Productivity Awards
Code Quality: The Open Source Perspective won a Software Development Productivity Award
in the Technical Books category.
Continue reading "Software Development Productivity Award"
Software Rejuvenation is Counterproductive
In the February issue of the Computer magazine
Grottke and Trivedi propose four strategies for
fighting bugs that are difficult to detect and reproduce.
operation and replicating software are indeed time-honored and practical
solutions. When coupled with appropriate logging, they may allow an
application to continue functioning, while also alerting its maintainers
that something is amiss. On the other hand, the proposal to restart
applications at regular intervals (rejuvenation as the authors call
it), doesn't allow us to find latent bugs, sweeping them instead under
the carpet. This lowers the bar on the quality we expect from software,
and will doubtless result in a higher density of bugs and increasingly
complicated failure modes.
Continue reading "Software Rejuvenation is Counterproductive"
A Peek at Beautiful Code
An exciting new book is about to hit the shelves,
and I consider myself very lucky to be among its contributors.
subtitled "leading programmers explain how they think",
contains 33 chapters where contributors describe some code
they consider noteworthy.
Although I don't consider myself worthy of the book's subtitle,
I love coding, and
I'm extremely happy that code is taking the leading role among such an
Here is the complete table of the book's contents.
Continue reading "A Peek at Beautiful Code"
The Escape of a Small Program
C. A. R. Hoare's
Law of Large Programs states that
inside every large program is a small program struggling to get out.
The parking receipt I got yesterday returning from a
SQO-OSS meeting proves this fact.
Continue reading "The Escape of a Small Program"
The Return of Performance Engineering and Trendy Programmers
In the 1950s, when processor cycle times were measured in microseconds,
algorithm design and clever programming could make or break an application.
These fields continued to be popular in the 1960s and 1970s, because
widespread computers were used to attack ever larger problems.
Programming was a hip and trendy occupation.
Today's $500 computers operating on GHz clocks allow anybody who has
(just about) mastered the syntax of a programming language to write
code that drives dynamic web sites serving hundreds of transactions each
Managers consider code a commodity, and enrollments to computer science
degrees are dwindling.
However, change is in the air.
Continue reading "The Return of Performance Engineering and Trendy Programmers"
Research in Domain Specific Languages
My research colleague
is working on better programming support for domain specific languages (DSLs).
Today he claimed that DSLs were hyped during 1998-2002,
and now interest has waned.
Continue reading "Research in Domain Specific Languages"
When I set out to apply CScout
on the Linux kernel source code, I
discovered that it failed to correctly expand a couple of C macros,
causing the analysis to fail. This prompted me to reimplement CScout's
macro expansion using a
precise functional specification,
the code's severe degradation in time performance, and finally tidy up
the optimized code mess.
Continue reading "Code Finessing"
Cross compiling software on a host platform to run on a different
target used to be an exotic stunt to be performed by
the brave and desperate.
One had first to configure and build the compiler, assembler, archiver,
and linker for the different architecture, then cross-build the other
architecture's libraries, and finally the software.
This week, while preparing a new release of the
CScout refactoring browser
I realized that what was once a feat is nowadays a routine operation.
Continue reading "Cross Compiling"
Choosing a Collection: A Discussion with Kent Beck
Recently I reviewed the mansucript of Kent Beck's upcoming
book Implementation Patterns.
I will certainly put it in the list of books any professional programmer
When discussing collections (containers in C++ STL parlance),
Kent mentions that
his overall strategy for performance coding with collections is to use the
simplest possible implementation at first and pick a more specialized collection
class when it becomes necessary.
My view is that
we should choose the most efficient implementation from the start.
With prepackaged collections this doesn't have any cost associated with
it, and it avoids nasty surprises when a dataset increases beyond the
size the programmer envisaged.
I added a comment to that effect in my review, and later I sent him
an email with a supporting citation, which
kindled an interesting exchange.
I reproduce our email exchange here, with his permission.
Continue reading "Choosing a Collection: A Discussion with Kent Beck"
The Verbosity of Object-Oriented Code
As I refactored a piece of code from an imperative to an
object-oriented style I increased its clarity and reusability,
but I also trippled its size.
This worries me.
Continue reading "The Verbosity of Object-Oriented Code"
UML Class Diagrams from C++ Code
I needed a UML class diagram of the classes I use in the implementation of
CScout refactoring browser.
I drew the last such diagram on paper about four years ago, so it was
definitely out of date.
I always say that whenever possible documentation should be automatically
generated from the code, so I decided to automate the task.
Continue reading "UML Class Diagrams from C++ Code"
Open Source and Professional Advancement
Doing really first-class work, and knowing it, is as good as wine, women (or men) and song put together.
— Richard Hamming
I recently participated in an online discussion regarding the advantages of the various certification programs. Some voiced skepticism regarding how well one can judge a person's knowledge through answers to narrowly framed multiple choice questions. My personal view is that the way a certification's skills are examined is artificial to the point of uselessness. In practice I often find solutions to problems by looking for answers on the web. Knowing where and how to search for an answer is becoming the most crucial problem-solving skill, yet typical certification exams still test rote learning. Other discussants suggested that certification was a way to enter into a job market where employers increasingly asked for experience in a specific technology. My reaction to that argument was that open source software development efforts offer us professionals a new and very valuable way to obtain significant experience in a wide range of areas. In this column I'll describe how we can advance professionally by contributing to open source projects.
Continue reading "Open Source and Professional Advancement"
Choosing a Programming Language
A language that doesn't have everything is actually easier to program in than some that do.
— Dennis M. Ritchie
Computer languages fascinate me. Like a living person, each one has its own history, personality, interests, and quirks. Once you've learned one, you can use it again after years of neglect, and it's like reconnecting with an old friend: you can continue discussions from the point they were broken off years before. For a task I recently faced I adopted a language I hadn't used for 15 years, and felt enlightened.
Continue reading "Choosing a Programming Language"
Debuggers and Logging Frameworks
As soon as we started programming, we found to our surprise that it wasn't as easy to get programs right as we had thought. Debugging had to be discovered.
— Maurice Wilkes discovers debugging, 1949
The testing, diagnostic, and repair equipment of many professions is horrendously expensive. Think of logic analyzers, CAT scanners, and dry docks. For us the cost of debuggers and logging frameworks is minimal; some of them are even free. All we need to become productive, is to invest some time and effort to learn how to use these tools in the most efficient and effective way.
Continue reading "Debuggers and Logging Frameworks"
Xerces v Flex
What is the fastest way to process and XML file?
I was faced with this question when I recently wanted to
process a 452GiB XML file; for this amount of data speed matters.
Some obvious choices were XML libraries, hand-crafted code, and
lexical analyzer generators.
Continue reading "Xerces v Flex"
Code Quality: The Open Source Perspective
My new book
Code Quality: The Open Source Perspective
three years after I started writing it.
The book owes more to open source software than any of the books
dealing with Linux, PHP, Apache, Perl or any other book covering
a specific technology.
Continue reading "Code Quality: The Open Source Perspective"
Efficiency Will Always Matter
Many claim that today's fast CPUs and large memory capacities make
time-proven technologies that efficiently harness a computer's power irrelevant.
I beg to differ, and my experience in the last three days demonstrated
that technologies that originated in the 70s still have their place today.
Continue reading "Efficiency Will Always Matter"
Although only a few may originate a policy, we are all able to judge it.
— Pericles of Athens
Popular folklore has our profession's use of the word bug originating from a real insect found in an early electromechanical computer. Indeed, on September 9th of 1947 the Harvard Mark II operators did find a moth obstructing a relay's contacts. They removed it and dutifully taped it in the machine's logbook. However, engineers were using the term "bug" many decades before that incident. For example, in a 1878 letter Edison used the term referring to the faults and difficulties he was facing while moving from an invention's intuition to a commercialisable product.
Continue reading "Bug Busters"
A General-Purpose Swap Macro
A couple of days ago I came up with a general-purpose macro for swapping
values in C programs.
My colleague Panagiotis Louridas suggested an improvement, and
this prompted me to see the two macros got compiled.
Continue reading "A General-Purpose Swap Macro"
If STL Had Been Designed by a Committee
I've been reading on XML schema, and it's embarrassingly obvious
that it has been designed by a committee.
Continue reading "If STL Had Been Designed by a Committee"
How to Sort Three Numbers
Quick: how do you sort three numbers in ascending order?
Continue reading "How to Sort Three Numbers"
Supporting Java's Foreach Construct
Java 1.5 supports a new
construct for iterating over collections.
The construct can be used on arrays and on all classes in Java's Collection
I searched the internet for an example on how to make my own
classes iterable with this construct, but could not find an example.
Continue reading "Supporting Java's Foreach Construct"
C++0X Enhancement: Rational Metaprogramming
In a recent article
presented the evolution of C++ toward the 0X standard, and asked the C++
community for ideas regarding C++ enhancements.
This is a proposal to add to C++ support for rational metaprogramming.
Continue reading "C++0X Enhancement: Rational Metaprogramming"
GCC Obfuscated Code
For years I've struggled to understand the
GNU compiler collection internals,
I am ashamed to say, without much success.
I always thought that the subject was intrinsically too complicated
for me, but after struggling to understand a two line gcc
code snippet of a fairly simple operation for more than two minutes,
I realized that the code style may have something to do with my problems.
Continue reading "GCC Obfuscated Code"
C++0X Enhancement: Packaged Libraries
In a recent article
presented the evolution of C++ toward the 0X standard, and asked the C++
community for ideas regarding C++ enhancements.
This is a proposal to add to C++ support for using packaged libraries,
and a standardizing a library distribution format.
Continue reading "C++0X Enhancement: Packaged Libraries"
Tool Writing: A Forgotten Art?
Merely adding features does not make it easier for users to do things—it just makes the manual thicker. The right solution in the right place is always more effective than haphazard hacking.
— Brian W. Kernighan and Rob Pike
In 1994 Chidamber and Kemerer defined a set of six simple metrics for object-oriented programs. Although the number of object-oriented metrics swelled to above 300 in the years that followed, I had a case where I preferred to use the original classic metric set for clarity, consistency, and simplicity. Surprisingly, none of the six open-source tools I found and tried to use fitted the bill. Most tools calculated only a subset of the six metrics, some required tweaking to make them compile, others had very specific dependencies on other projects (for example Eclipse), while others were horrendously inefficient. Although none of the tools I surveyed managed to calculate correctly the six classic Chidamber and Kemerer metrics in a straightforward way, most of them included numerous bells and whistles, such as graphical interfaces, XML output, and bindings to tools like ant and Eclipse.
Continue reading "Tool Writing: A Forgotten Art?"
XML Abstraction at the Wrong Level
Over the last month I've encountered two applications
that use XML at the wrong level of abstraction.
Instead of tailoring the schema to their needs, they
use a very abstract schema, and encode their elements
at a meta level within the XML data.
This approach hinders the verification and manipulation of the corresponding
Continue reading "XML Abstraction at the Wrong Level"
Today's Dynamic is Tomorrow's Static
Today at the IEEE Software's
editorial and advisory board
meeting, the issue of service-oriented architectures came up.
Robert Glass wondered whether this was the upcoming fad,
following structured programming and object-oriented programming,
to which Stan Rifkin replied that service-oriented architectures
are a lot more dynamic.
Interestingly, the previous approaches, which we today consider as
static, were also thought-off as dynamic in their day.
Continue reading "Today's Dynamic is Tomorrow's Static"
Warum einfach, wenns auch kompliziert geht?
(Why make it simple, when you can also make it complicated?)
Consider the task of associating code with specific data
Using a multi-way conditional can be error-prone, because
the data values become separated by the code.
It can also be inefficient in the cases where we have to use cascading
Continue reading "Warum einfach, wenns auch kompliziert geht?"
else if statements, instead of a
which the compiler can optimize into a hash table.
In C I would use an array containing values and function pointers.
My understanding is that the Java approach involves using the
Strategy pattern: a separate class for each case,
and an interface "to rule them all".
Ordnung muss sein
A free-form translation of the above German phrase (orderliness must exist)
would be that orderliness is not negotiable.
In the domain of information technology I find this motto particularly
Continue reading "Ordnung muss sein"
Java Makes Scripting Languages Irrelevant?
Simplicity does not precede complexity, but follows it.
— Alan J. Perlis
In computing we often solve a complex problem by adding another level of indirection. As an example, on Unix file systems an index node, or inode, data structure allows files to be allocated concurrently and sparsely, and yet still provide an efficient random access capability. When we want to customize large and complex systems or express fluid and rapidly changing requirements a common tool we employ is to add a scripting layer on top of the corresponding system. An early instance of this approach was employed in Dan Murphy's TECO editor developed on the DEC PDP-1 computer in 1962–63: its command language also doubled as an arcane (to put it politely) macro language.
Continue reading "Java Makes Scripting Languages Irrelevant?"
The Efficiency of Java and C++, Revisited
A number of people worked on replicating the results and optimizing
the programs I listed in my earlier blog entry.
Continue reading "The Efficiency of Java and C++, Revisited"
Macro-based Substitutions in Source Code
A friends asks:
"How can one easily replace a method call (which can contain
arguments with brackets in its invocation code) with a simple
Continue reading "Macro-based Substitutions in Source Code"
Measuring the Effect of Shared Objects
For the Code Quality
book I am writing I wanted to measure the memory savings of
On a lightly loaded web server these amounted to 80MB,
on a more heavilly loaded shell access machine these ammounted
Continue reading "Measuring the Effect of Shared Objects"
Code Reading Example: the Linux Kernel Load Calculation
A colleague's Linux machine was exhibiting a very high load value,
for no obvious reason.
I wanted to make him point the kernel debugger on the routine calculating
It has been more than 7 years since the last time I worked on a Linux
so I had to find my way around from first principles.
This is an annotated and slightly edited version of what I did.
Continue reading "Code Reading Example: the Linux Kernel Load Calculation"
Book Review: C++ Coding Standards
A number of years ago, reading Koenig's and Moo's
Ruminations on C++  I made a wish for more of the
same, updated to reflect current C++ practice.
My wish has come true.
C++ Coding Standards: 101 Rules, Guidelines, and Best Practices
by Herb Sutter and Andrei Alexandrescu 
is an indispensable book for all serious C++ programmers.
Continue reading "Book Review: C++ Coding Standards"
Cracker Code Review
According to a popular myth, crackers are computer whiz kids:
brilliant software developers who run circles around their
"peers" in the corporate world.
When my undergraduate student Achilleas Anagnostopoulos sent me a
to the source code of the
Microsoft GDIPlus.DLL JPEG Parsing Engine Buffer Overflow
exploit, I decided to test the myth
by performing a code review of the exploit's source code.
The results are not flattering for the exploit's developers:
no self-respecting professional would ever write production code of
such an abysmally low quality.
Continue reading "Cracker Code Review"
Digital Data Makes Anything Possible
Once data becomes digital anything and everything becomes possible.
Consider arranging the books on your bookshelf by the color of
Continue reading "Digital Data Makes Anything Possible"
When editing documents or code, my not so agile fingers, often trigger
a movement or search command that accidentally throws me to a random
location in the text I am editing.
How can I return back?
Amazingly, I noticed I am using exactly the same trick for returning back
on both the vim editor I use for most of
my editing tasks, and Microsoft Word I use for collaborating with many
Continue reading "Continous Bookmarking"
The hypot() Mystery
I was writing a section for the
followup volume, and wanted to demonstrate the pitfalls of
using homebrewn mathematical functions instead of the library
As an example, I chose to compare the C library
Continue reading "The hypot() Mystery"
sqrt(x * x, y * y).
I created a plot of "unit in last place" (ulp) error values between
the two functions, which demonstrated how the error increased for larger
values of y.
Patching Framework III
I needed to read some old files I wrote in 1992 using the Ashton-Tate
Framework III program.
Unfortunately, trying to run the program under Windows XP resulted in a
Continue reading "Patching Framework III"
Divide overflow" error.
A bit of searching on the web revealed that the problem was related
to the system's speed (1.6GHz).
Apparently, Framework tries to calculate the speed of the machine
by dividing a fixed number with a loop counter;
on modern machines this results in the overflow.
Optimizing ppp and Code Quality
While debugging a problem of my ppp connection I noticed that
ppp was apparently doing a protocol lookup (with a file open,
read, close sequence) for every packet it read.
This is an excerpt from the strace log, one of my
favourite debugging tools.
Continue reading "Optimizing ppp and Code Quality"
Computer Languages Form an Ecosystem
(This is a copy of an
article I posted on
slashdot on March 15th,
in response to a discussion titled
C Alive and Well Thanks to Portable.NET.
Many posters argued that the C language is dead.
I add my response here, because one month after its original slashdot submission,
I am still getting web site hits from it.)
Continue reading "Computer Languages Form an Ecosystem"
Binary File Similarity Checking
How can one determine whether two binary files
(for example, executable images) are somehow similar?
I started writing a program to perform this task.
Such a program could be useful for determing
whether a vendor had included GNU
Public License (GPL)
code in a propriatary product, violating the GPL license.
After writing about 20 lines, I realized that I needed an accurate
definition of similarity than the vague
"the two files contain a number of identical subsequences"
I had in mind.
Continue reading "Binary File Similarity Checking"
A Unix-based Logic Analyzer
A circuit I was designing was behaving in unexpected ways:
the output of a wireless serial receiver based on Infineon's TDA5200
was refusing to drive an LS TTL load.
To debug the problem I needed an oscilloscope or a logic analyzer,
but I had none.
I searched the web and located
software to convert the PC's parallel port to a logic analyzer.
I downloaded the 900K program, but that was not the end.
Unfortunately the design of Windows 2000 does not allow direct access
to the I/O ports, so I also downloaded
a parallel port device driver and a program to give the appropriate privileges to other
Finally, I also downloaded from a third site the Borland runtime libraries
required by the logic analyzer.
Needless to say that the combination refused to work.
Continue reading "A Unix-based Logic Analyzer"
Well-behaved Web Applications
Very few web-based applications are designed to match the
As a result they are often irritating, counteproductive,
or simply unusable.
During the last two months I've been working on an
IEEE Software theme issue titled "developing with
open source software".
Most of my work is performed over the
IEEE Computer Society
The application is an almost perfect example of everything that
is often wrong with such interfaces.
Continue reading "Well-behaved Web Applications"
Code Reading: The Open Source Perspective
In July 2000, while working on a paper on the use of slicing for
choosing parts of an application to develop in a scripting language
(don't ask), I found myself searching open-source programs for
motivating examples, and experimenting with a tool for annotating the
corresponding source code. At some point, a loud click sound in my mind
brought to my attention the fact that although most books and courses
teach us how to program, we actually spend most of our time reading code
others have written. I reasoned that by applying my annotation tool on
open source software I could write a book to present the ideas,
techniques, and tools that go behind code reading.
Continue reading "Code Reading: The Open Source Perspective"