Free Training For Laid-Off Developers

Like many areas in the United States, Seattle has recently been hit with layoffs and downsizing in our industry. So it’s quite timely that Steve McConnell’s company Construx, in the Seattle area, is offering free training for laid-off software workers:

After listening to doom and gloom economic reports for the past few months, we decided we would try to do something to brighten our little corner of the world. Here’s our official press release about it:

Construx Software has designated 25% of its public seminar seats free of charge to software workers who have been laid off. Construx seminars help software professionals improve their technical and managerial skills. Seminar attendees will be more effective when they reenter the workforce. Construx hopes this program will help laid-off software workers reenter the workforce more quickly.

Please read the full article for more details.

I’m very pleased to report that this program will include my next U.S. Effective Concurrency seminar which will be held in Bellevue, WA on July 27-30, 2009. I’ll blog about that seminar again as we get closer, but it’s on the Construx calendar now.

I hope that this will be helpful to some people, and I look forward to seeing some of you in Bellevue.

Aside: Please Be Professional

One problem with offering things for free is that people don’t always value them. I was surprised to learn that a surprising number of people who’ve asked for and received this free admission at Construx have been no-shows.

The following should go without saying, but here it is: As a courtesy to Construx and to other attendees, please don’t sign up unless you intend to come, and if something comes up that prevents you from attending please notify Construx. Otherwise, you may be taking the place of someone who would have liked to attend in your place (seating is limited), and Construx is out the cost of food (they provide breakfast and lunch) and printed color binders and such that go to waste.

Other Free Materials

Most of you know that virtually all the articles and columns I’ve ever written have always been available for free on my own website or via magazine websites (modulo some link rot, sigh). These include all the Effective Concurrency articles, and my C++-focused “Guru of the Week” and magazine articles.

The only things I’ve written that aren’t legally freely available are the final texts of my books, including translations, to which the publishing company owns the copyright; but the books are based on the same freely-available English articles, and Addison-Wesley/Pearson has never had any issue with those staying available, so the basic material is all there.

But there’s news on the “final book contents” front, too, at least in English: Once my current book(s) on Effective Concurrency is done, Jim Hyslop and I plan to compile a book of the C++ Conversations articles we coauthored in C++ Report and C/C++ Users Journal (thanks again for your patience, Jim!) and I also plain to write a second edition of Exceptional C++ – and both books will be updated for C++0x, which is now feature-complete and undergoing its first round of international review. It’s quite interesting just how often using C++0x language and library features (from lambdas to shared_ptrs and concurrency) really help solve the old problems in even more elegant and robust ways… and I’m sure we’ll throw in a couple of new problems and solutions too. My goal is to post these books’ draft Items, perhaps in the form of blog entries, as we write them. But I’m also working with the publisher to see if perhaps we could even post the very final Items in that format with their permission. I’ll post more news about that as there’s something to say.

Effective Concurrency: Sharing Is the Root of All Contention

This month’s Effective Concurrency column, “Sharing Is the Root of All Contention”, is now live on DDJ’s website.

This article aims to address the root cause behind some frequently made assertions: Statements like “locks kill scalability” and “CAS kills scalability” are mostly true but focus on symptoms rather than causes; and others such as “reader/writer mutexes are great for scalability” at minimum need some heavy qualification.

From the article:

Quick: What fundamental principle do all of the following have in common?

Two children drawing with crayons.

Three customers at Starbucks adding cream to their coffee.

Four processes running on a CPU core.

Five threads updating an object protected by a mutex.

Six threads running on different processors updating the same lock-free queue.

Seven modules using the same reference-counted shared object.

Answer: In each case, multiple users share a resource that requires coordination because not everyone can use it simultaneously — and such sharing is the root cause of all resulting contention that will degrade everyone’s performance. (Note: The only kind of shared resource that doesn’t create contention is one that inherently requires no synchronization because all users can use it simultaneously without restriction, which means it doesn’t fall into the description above. For example, an immutable object can have its unchanging bits be read by any number of threads or processors at any time without synchronization.)

In this article, I’ll deliberately focus most of the examples on one important case, namely mutable (writable) shared objects in memory, which are an inherent bottleneck to scalability on multicore systems. But please don’t lose sight of the key point, namely that "sharing causes contention" is a general principle that is not limited to shared memory or even to computing.

The Inherent Costs of Sharing

Here’s the issue in one sentence: Sharing fundamentally requires waiting and demands answers to expensive questions. …

Aside: This will be in the first electronic-only Dr. Dobb’s Report, and I’m going to have to get used to Dobb’s being electronic-only. One consequence of this change that I just discovered today is that an article can go online hours after I correct the proofs. That may seem like it shouldn’t be surprising in the days of blogs, but a magazine isn’t (or at least wasn’t) like a blog. When I wrote for magazines like C++ Report in the late 1990s, the time between submitting the final column manuscript and seeing it in print was about two to three months, depending on the magazine. Since the mid-2000s with Dobb’s, it’s been only one month from proofs to print — and Dobb’s could have posted the online versions even sooner, but held them back to be semi-synced with the print magazine. Now that the print constraint has disappeared, apparently I can (and, today, did) start work on a Friday morning to find the Dobb’s proofs I corrected the night before already on the web. Nifty. (And thanks again, Deirdre!)

I hope you enjoy it. Finally, here are links to previous Effective Concurrency columns and the DDJ print magazine issue in which they first appeared:

The Pillars of Concurrency (Aug 2007)

How Much Scalability Do You Have or Need? (Sep 2007)

Use Critical Sections (Preferably Locks) to Eliminate Races (Oct 2007)

Apply Critical Sections Consistently (Nov 2007)

Avoid Calling Unknown Code While Inside a Critical Section (Dec 2007)

Use Lock Hierarchies to Avoid Deadlock (Jan 2008)

Break Amdahl’s Law! (Feb 2008)

Going Superlinear (Mar 2008)

Super Linearity and the Bigger Machine (Apr 2008)

Interrupt Politely (May 2008)

Maximize Locality, Minimize Contention (Jun 2008)

Choose Concurrency-Friendly Data Structures (Jul 2008)

The Many Faces of Deadlock (Aug 2008)

Lock-Free Code: A False Sense of Security (Sep 2008)

Writing Lock-Free Code: A Corrected Queue (Oct 2008)

Writing a Generalized Concurrent Queue (Nov 2008)

Understanding Parallel Performance (Dec 2008)

Measuring Parallel Performance: Optimizing a Concurrent Queue (Jan 2009)

volatile vs. volatile (Feb 2009)

Sharing Is the Root of All Contention (Mar 2009)

Income in Perspective: 2 Bppl @ $3/day

I just saw a CNN headline that read: “Young workers scrimp to live on $15/wk.” Before reading further, what do you think: Is that stunning and shocking? Or shockingly typical?

The story turned out to be a piece about white-collar workers in China trying to live frugally, spending only 100 Yuan on travel and food during the workweek to conserve funds. Of course, the workers’ actual total expenses and income are higher, because that $15/week figure doesn’t include weekend expenses and other major costs like rent. Even so, the story is considered newsworthy here, and is probably a shock to a number of readers in the western world.

But the headline wouldn’t surprise readers who are familiar with the approximate distribution of income/GDP/wealth in the world.

To illustrate, here are two personal data points from 2006, when my wife and I traveled to Kenya and Zambia to visit friends:

Income: In Kenya, we were told that being a staff worker at a safari lodge is considered a good job. What does it pay? About $2 per day, for long hours and six-day weeks. This isn’t unusual; in about 30 countries, including Kenya, more than half of the population earns under $2 per day. An estimated two billion people – 30% of the world’s population – live on an income of less than $3 per day. And $3 per day is about what the attention-grabbing CNN headline implies, though the actual story behind that headline is much less bad.
Cost of living: But what happens when we consider, not just dollar-for-dollar comparisons, but purchasing power? Isn’t it less expensive to live in less-developed countries? Yes, it usually is, especially for shelter and services – there’s been some talk lately on the U.S. news about retiring in Mexico as a way for older people to save money in this economy – but the difference for the same quality goods is often less than one might think. In Lusaka, the capital of Zambia, we found there were only three grocery stores [*] having similar goods to what we would expect to find in a U.S.-style Safeway, although of course the Zambian stores were much smaller than U.S. stores (more the size of a medium Trader Joe’s) and offered far less selection diversity (something like a factor of 20 fewer varieties or brands). When we visited one of the stores, I picked up a few Western-style items, totaled the price and converted to U.S. dollars in my head, and found that those comparable products in Lusaka cost nearly the same as we would have paid for the same items in Seattle. Our local friend replied: “Right, nobody who lives here would ever think of buying a can of soda pop.” Certainly not when a can of Coke costs a day’s wage for many people, and doesn’t confer any significant nutritional benefit.

The gulf between the western- and world-median standards of living is, simply put, vast – and growing. The standard of living that’s normal for most of the planet’s population is well nigh unimaginable to many of us in the western world, and even for those of us who’ve been there, it’s one thing to see it and quite another to really understand what such a life would be like. I don’t claim to.

[*] They might well be the only such stores in the country, not just the capital.