Postponed: Effective Concurrency Europe

Right now I should be at 40,000 feet somewhere over Baffin Island on my way to Stockholm for Effective Concurrency Europe, but instead I’m in bed with a fever that I’ve had since Wednesday night and still unable to talk. The organizer and I have been staying in touch with flu updates every few hours to see if lots of “TLC and OTC” (tender loving care and over-the-counter drugs) could get me well enough to fly and push through teaching for three days; that usually works, but this time it’s a really nasty one, and we have to postpone.

I’m sorry to have to disappoint this week and for any inconvenience this will surely cause some of you, and I hope that you’ll understand. The organizer has already emailed everyone who has registered to notify you of the cancellation of this week’s dates (this post partly serves as a backup to that email), and we’ll keep you posted as we reschedule. The response has exceeded expectations by a good margin, and I’m grateful for your strong interest and planning to take time away from your schedules to come and talk concurrency with me. I’m still very much looking forward to seeing you there in the near future. (And minus potentially spreading wicked germs.)

Best wishes to you and yours,

Herb

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.

Effective Concurrency Seminar in Europe: March 16-18, Stockholm, Sweden

A number of people have asked whether I will be teaching my Effective Concurrency seminar in Europe. The answer is yes:

Effective Concurrency (Europe) will be held on March 16-18, 2009, in Stockholm, Sweden. This is my only public European seminar in 2009. I’ll cover the following topics:

Fundamentals: Define basic concurrency goals and requirements • Understand applications’ scalability needs • Key concurrency patterns
Isolation — Keep work separate: Running tasks in isolation and communicate via async messages • Integrating multiple messaging systems, including GUIs and sockets • Building responsive applications using background workers • Threads vs. thread pools
Scalability — Re-enable the Free Lunch: When and how to use more cores • Exploiting parallelism in algorithms • Exploiting parallelism in data structures • Breaking the scalability barrier
Consistency — Don’t Corrupt Shared State: The many pitfalls of locks–deadlock, convoys, etc. • Locking best practices • Reducing the need for locking shared data • Safe lock-free coding patterns • Avoiding the pitfalls of general lock-free coding • Races and race-related effects
High Performance Concurrency: Machine architecture and concurrency • Costs of fundamental operations, including locks, context switches, and system calls • Memory and cache effects • Data structures that support and undermine concurrency • Enabling linear and superlinear scaling
Migrating Existing Code Bases to Use Concurrency
Near-Future Tools and Features

I hope to see some of you there!

From the "we know what they meant, but it’s not what they said" department

While walking our dogs recently, we came across several of these signs — ironically, in front of our neighborhood school.

Effective Concurrency: volatile vs. volatile

This month’s Effective Concurrency column, “volatile vs. volatile”, is now live on DDJ’s website and also appears in the print magazine. (As a historical note, it’s DDJ’s final print issue, as I mentioned previously.)

This article aims to answer the frequently asked question: “What does volatile mean?” The short answer: “It depends, do you mean Java/.NET volatile or C/C++ volatile?” From the article:

What does the volatile keyword mean? How should you use it? Confusingly, there are two common answers, because depending on the language you use volatile supports one or the other of two different programming techniques: lock-free programming, and dealing with ‘unusual’ memory.

Adding to the confusion, these two different uses have overlapping requirements and impose overlapping restrictions, which makes them appear more similar than they are. Let’s define and understand them clearly, and see how to spell them correctly in C, C++, Java and C# — and not always as volatile. …

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)

Answer to "16 Technologies": Engelbart and the Mother of All Demos

A few days ago I posted a challenge to name the researcher/team and approximate year each of the following 16 important technologies was first demonstrated. In brief, they were:

The personal computer for dedicated individual use all day long.
The mouse.
Internetworks.
Network service discovery.
Live collaboration and desktop/app sharing.
Hierarchical structure within a file system and within a document.
Cut/copy/paste, with drag-and-drop.
Paper metaphor for word processing.
Advanced pattern search and macro search.
Keyword search and multiple weighted keyword search.
Catalog-based information retrieval.
Flexible interactive formatting and line drawing.
Hyperlinks within a document and across documents.
Tagging graphics, and parts of graphics, as hyperlinks.
Shared workgroup document collaboration with annotations etc.
Live shared workgroup collaboration with live audio/video teleconference in a window.

A single answer to all of the above: Doug Engelbart and his ARC team, in what is now known as “The Mother of All Demos”, on Monday, December 9, 1968.

Last month, we marked the 40th anniversary of the famous Engelbart Demo, a truly unique “Eureka!” moment in the history of computing. 40 years go, Engelbart and his visionary team foresaw — and prototyped and demonstrated — many essential details of what we take for granted as our commonplace computing environment today, including all of the above-listed technologies, most of them demonstrated for the first time in that talk.

This talk would be noteworthy and historic just for being the first time a “mouse” was shown and called by that name. Yet the mouse was just one of over a dozen important innovations to be compellingly presented with working prototype implementations.

Note: Yes, some of the individual technologies have earlier theoretical roots. I deliberately phrased the question to focus on implementations because it’s great to imagine a new idea, but it isn’t engineering until we prove it can work by actually building it. For example, consider hypertext: Vannevar Bush’s Memex, vintage 1945, was a theorectical “proto-hypertext” system but it unfortunately remained theoretical, understandably so given the nascent state of computers at the time. Project Xanadu, started in 1960, pursued similar ideas but wasn’t demonstrated until 1972. The Engelbart Demo was the first time that hypertext was publicly shown in a working form, together with a slew of other important working innovations that combined to deliver an unprecedented tour de force. What made it compelling wasn’t just the individual ideas, but the working demonstrations to show that the ideas worked and how they could combine and interact in wonderful ways.

Recommended viewing

You can watch the 100-minute talk here (Stanford University) in sections with commentary, and here (Google Video) all in one go.

16 Important Technologies: Who demonstrated each one first?

We enjoy such an abundance of computing riches that it’s easy to take wonderful technological ideas for granted. Yet so many of the pieces of our modern computing experience that we consider routine today were at one time unimaginable. After all, back in the early days of computing, we were still discovering what these newfangled room-filling gadgets might eventually become capable of — who could have known then what using computers would be like today?

Of course, we have these technologies today because some visionaries did know, did imagine them… and, best of all, built and demonstrated them.

Hence today’s challenge:

Quiz: For each of the following 16 technologies that have become commonplace in our modern computing experience, give the researcher/team and approximate year that a working prototype was first demonstrated. How many can you answer without a web search?

The personal computer for dedicated individual use, that one person can have at their disposal all day long. (Hint: Before the Altair in 1975 and Apple I in 1976.)
Mouse input with a graphical pointer. (Hint: Before the Xerox Alto at Xerox PARC in 1973.)
Internetworks across campuses and cities. (Hint: Before Ethernet at Xerox PARC (again) in 1973.)
Discovery of ‘who’s got what service’ in an internetwork.
Using internetworks for live collaboration, not just file sharing. (Hint: Before RDP and others.)
Hierarchical structure within a file system and within a document. (Hint: Before Unix.)
Cut/copy/paste, with drag-and-drop.
Paper metaphor for word processing, starting with a blank piece of paper and the applying formatting and navigating levels in the structure of text.
Advanced pattern search and macro search within documents. (Hint: Before MIT’s Emacs.)
Keyword search and multiple weighted keyword search. (Hint: Long before Google (alternate link).)
Information retrieval through indirect construction of a catalog.
Flexible interactive formatting and line drawing.
Hyperlinks within a document and across documents, and “jumping on a link” to navigate. (Hint: Before Tim Berners-Lee invented the World Wide Web in 1989-1990.) (Hint’: Yes, before HyperCard too.)
Tagging graphics, and parts of graphics, as hyperlinks. (Hint: Before Flickr.)
Workgroup collaboration on a document, including collaborative annotations, allowing members of a group to use and modify a document. (Hint: Before Lotus Notes and Ward Cunningham’s Wikis.)
The next step up from that: Live collaboration on a document with screen sharing on the two writers’ computers so they can see what the other is doing — with live audio/video teleconference in a window at the same time. (Hint: Not Skype or LiveMeeting.)

The 2008 Media Inflection: Meet Dr. Web, the New Gorilla

[edited 2009.01.15 to add link to DDJ’s announcement]

2008 was quite a year, full of landmark events that were certainly historic, if not always welcome.

If I had to pick one technology-related highlight from the past year, it would be this: A notable inflection point in the ongoing shift from traditional media to the web. Given that that tide is still in progress, why single out 2008? I think we’ll look back at 2008, especially the fourth quarter, as a turning point when the web became an A-list media outlet and first started to beat up, and even replace, major legacy competitors in newspapers, technical magazines, movies, and TV. An inflection point, if you will, where the web clearly stopped being the pencil-necked upstart, and visibly emerged as the new gorilla flexing its advertising-revenue-pumped-up muscles and kicking sand on the others.

In 2008, and particularly in the last month, the web began to outright replace some existing newspapers and technology and programming magazines.

December 2008: The first two major city newspapers go web-only or web-mostly. The Detroit News and The Detroit Free Press announced truncated print editions and reduced print delivery. Newspapers in several other cities seem likely to follow fairly soon.
As of January 2009: PC Magazine is going “digital only.” After the January issue, the print magazine will disappear. Instead, the content will appear exclusively on the web.
As of January 2009: Dr. Dobb’s Journal is permanently suspending print publication and going web-only. Some of the content will be available as a new “Dr. Dobb’s Report” section of InformationWeek. My Effective Concurrency column will continue, and I’ll continue to blog when new columns go live on the web, so if you’re reading the column via this blog nothing will significantly change for you.

As of next month, the only major technical programmer’s trade magazines still available in print, that I know of, are platform- and technology-specific ones like asp.netPRO and MSDN Magazine — and even those increasingly feature online-only content. For example, from MSDN Mag’s January 2009 editor’s note:

As we continue to grow our coverage to keep pace with the rapidly expanding set of technologies, we will often offer content exclusively online at msdn.microsoft.com/magazine. So please check in frequently!

Gotta love RSS (and Atom etc.): Every text feed is like a magazine or newspaper column, every blogger a columnist. Every audio/video podcast feed is like a radio or TV series, or a radio station or TV channel. And our feed reader is the new magazine/newspaper, as we subscribe to columnists to make our personal custom newsmagazine. But RSS readers, along with RSS-consuming clients like iTunes, are more — they’re our personal selection, not only of the columns we want to read (on whatever topics we want, including the funnies section), but also of the media we want to hear and watch. It’s increasingly our way to choose the text, audio, and video we want all together. Who knew that a large chunk of the coming media convergence would come in the shape of RSS readers?

And other media are feeling the pressure from Dr. Web, the new gorilla:

This week (late December 2008), even cable operator Time Warner pushed web delivery for TV. Time Warner has had various contract disputes with Viacom and some local stations. But as part of the dispute:
During October-December 2008, Netflix’s Watch Instantly has started to turn into a juggernaut. It’s interesting enough that you can watch 12,000+ movies and TV shows streamed over the net to your PC at high quality. As of October 2008, you can get them on your Mac. As of November 2008, on your Xbox. As of December 2008, on your TiVo. As noted in one recent article:

And I won’t even get started on SaaS: hosted rich GUI apps served up on the web, for example the December 2008 (again) announcement about Office Online.

Yes, don’t forget 2008, especially December 2008: The month the first major newspapers moved mostly to the web and abandoned print at least partly; the month that PC Magazine and Dr. Dobb’s suspended print publication and went web-only; the month Netflix Watch Instantly arrived in the living room on TiVos after hitting Xboxes a fortnight before; the month cable provider Time Warner threatened to tell people to watch TV on the net; and the month even Microsoft announced their intent to deliver significant Office web applications.

I for one welcome Dr. Web, our new Gorilla and media overlord!

Besides, what choice do I have?