The Read Copy Update Pattern in the Linux Kernel

In the August meeting, Julian Brown gave a short talk introducing Lock-Free Architectures. In this presentation, he continued the theme by looking somewhat more deeply at the Read, Copy, Update strategy. This approach is used in the Linux kernel and other places to allow manipulation of important data structures in a multi-threaded system, without the need for locks.

This strategy is built on top of some of the primitives Julian introduced last time (like CAS).

Some of the most important features of this strategy are that readers can continue to access the data structure even while it is being updated. Just as importantly, updates using this strategy do not force the readers to fail and retry.

Julian's presentation is available.

Two Color 3D Printing with Perl

Since there was quite a bit of extra time after Julian's talk, G. Wade Johnson did the presentation that he had scheduled for last month. As a hobby, Wade has been doing 3D printing for a while. Most common desktop FDM printers are limited to one material/color at a time. There are a few technical solutions, but they are much more expensive and finicky.

As part of a project, Wade needed to be able to change colors on a print after a certain height. The design was a flat plate with a raised brim and text.

He develops most of his designs using OpenSCAD. That program converts a text description of the design into an STL file. Another program, Slic3r converts that format into the G-code file that drives the printer.

Since G-code is a text format, it is pretty easy to use Perl to find the point where we want to separate the design. His program separates the design into two parts. The base of the design is written to one file, along with some housekeeping code that moves the nozzle out of the way to allow changing the filament to a new color. A second file contains a small amount of code to restore the printer to the state where it can print again and then contains the rest of the design.

Much discussion ensued regarding the details and realities of 3D printing.

We had 9 people attending this month. As always, we'd like to thank cPanel, Inc. for providing the meeting space and food for the group.