Armstrong Thesis (Chapter 2)

As part of the reading list for CS527 this semester, our class has recently began reading the thesis of Joe Armstrong. The thesis is about building reliable software assuming that there will be hardware and/or software errors present.

For this week's reading we focused on Chapter 2 which introduces the architectural model being proposed. The chapter begins by introducing the original problem domain (telecom switching systems requiring essentially 24/7 operation with the ability to be updated while running). Oh wait ... did I mention that we are also going to assume that there will be hardware & software errors and that the system has to be able to work around such issues? Not an easy task!

Armstrong approaches the problem through the use of what he calls "concurrency oriented programming languages" (COPLs). COPLs typcially consist of and must support the concept of processes to serve as isolation boundaries. Communication between processes is achieved through message passing. Message delivery is guaranteed in-order between two endpoints, but is not guaranteed reliable. The other key feature is that processes must be able to detect failures of other processes and react accordingly. Armstrong introduces the Erlang language as one such implementation.

The remainder of the chapter discusses library support of Erlang for things like stable storage (storage that survives a crash) and various behaviours that assist with building these systems.

In subsequent weeks we will be reading additional chapters from Armstrong's thesis. If chapter 2 is any indication, this seems like it will be a good read.