DDJ posted the next Effective Concurrency column a couple of weeks earlier than usual. You can find it here: “Lock-Free Code: A False Sense of Security”, just went live on DDJ’s site, and also appears in the print magazine.
This is a special column in a way, because I rarely critique someone else’s published code. However, mere weeks ago DDJ itself published an article with fundamentally broken code that tried to show how to write a simplified lock-free queue. I corresponded with the author, Petru Marginean, and his main reviewer, Andrei Alexandrescu, to discuss the problems, and they have patched the code somewhat and added a disclaimer to the article. But the issues need to be addressed, and so Petru kindly let me vivisect his code in public in this column (and the next, not yet available, which will show how to do it right).
From the article:
[Lock-free code is] hard even for experts. It’s easy to write lock-free code that appears to work, but it’s very difficult to write lock-free code that is correct and performs well. Even good magazines and refereed journals have published a substantial amount of lock-free code that was actually broken in subtle ways and needed correction.
To illustrate, let’s dissect some peer-reviewed lock-free code that was published here in DDJ just two months ago …
I hope you enjoy it. (Note: Yes, the title is a riff on Tom Cargill’s classic article “Exception Handling: A False Sense of Security”, one of Scott Meyers’ five “Most Important C++ Non-Book Publications…Ever”.)
Finally, here are links to previous Effective Concurrency columns (based on the magazine print issue dates):
| August 2007 | The Pillars of Concurrency |
| September 2007 | How Much Scalability Do You Have or Need? |
| October 2007 | Use Critical Sections (Preferably Locks) to Eliminate Races |
| November 2007 | Apply Critical Sections Consistently |
| December 2007 | Avoid Calling Unknown Code While Inside a Critical Section |
| January 2007 | Use Lock Hierarchies to Avoid Deadlock |
| February 2008 | Break Amdahl’s Law! |
| March 2008 | Going Superlinear |
| April 2008 | Super Linearity and the Bigger Machine |
| May 2008 | Interrupt Politely |
| June 2008 | Maximize Locality, Minimize Contention |
| July 2008 | Choose Concurrency-Friendly Data Structures |
| August 2008 | The Many Faces of Deadlock |
| September 2008 | “Lock-Free Code: A False Sense of Security” |
Sutter’s Mill 