Bryan M. Cantrill

Real-world concurrency

What does the proliferation of concurrency mean for the software you develop?

Hidden in Plain Sight

In December 1997, Sun Microsystems had just announced its new flagship machine: a 64-processor symmetric multiprocessor supporting up to 64 gigabytes of memory and thousands of I/O devices. As with any new machine launch, Sun was working feverishly on benchmarks to prove the machine’s performance. While the benchmarks were generally impressive, there was one in particular that was exhibiting unexpectedly low performance. The benchmark machine would occasionally become mysteriously distracted: Benchmark activity would practically cease, but the operating system kernel remained furiously busy. After some number of minutes spent on unknown work, the operating system would suddenly right itself: Benchmark activity would resume at full throttle and run to completion. Those running the benchmark could see that the machine was on course to break the world record, but these minutes-long periods of unknown kernel activity were enough to be the difference between first and worst.

A Pioneer's Flash of Insight

In the May/June issue of Queue, Eric Allman wrote a tribute to Jim Gray, mentioning that Queue would be running some of Jim’s best works in the months to come. I’m embarrassed to confess that when this idea was first discussed, I assumed these papers would consist largely of Jim’s seminal work on databases showing only that I (unlike everyone else on the Queue editorial board) never knew Jim. In an attempt to learn more about both his work and Jim himself, I attended the tribute held for him at UC Berkeley in May.