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!
While walking our dogs recently, we came across several of these signs — ironically, in front of our neighborhood school.
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)
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.
- 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.
You can watch the 100-minute talk here (Stanford University) in sections with commentary, and here (Google Video) all in one go.
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.)