Friday, June 08, 2007

Concurrency Buzz

There's been quite a buzz lately in the programming blogsphere about concurrent programming. I think the software world is paying increasing attention to concurrent programming (and Erlang) due to the following reasons:

- The apparent decline of Moor's law coupled with the rise of multi-core CPUs.
- The "traditional" (i.e. shared-memory based concurrency) employed by most languages is flawed: it's too hard to grasp, it's too error-prone, and it's not multi-core friendly.
- Joe Armstrong's book, Programming Erlang has made Erlang accessible to a wide audience.
- Reddit.

There's more to Erlang style concurrency than lightweight processes and message passing. I don't expect other (popular) languages to fully gain Erlang-style concurrency (not soon, at least) because to do so they would have to adopt the following combination of traits:

- A scheduler that uses a mixture of lightweight processes and system threads (SMP Erlang spawns a system thread per CPU).
- Immutable variables.
- General avoidance of long blocking calls to native code in libraries.
- A garbage collector that utilizes per-process heaps to avoid freezing the entire VM during sweeps.
- A revised approach to error handling based on supervision trees and non-defensive coding.
- Web servers, database drivers, libraries, tools, etc. that actually use the new concurrency primitives.

As the saying goes, never say "never"... :)

Does that mean that you need Erlang to make your applications utilize available CPUs on multi-core machines? Of course not. However, when 80 core machines start appearing in our data centers in a few years, at least some people will take comfort in Joe Armstrong's statement:

"Your Erlang program should just run N times faster on an N core processor"

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