Sponsored Feature: Multi-Threading Goo!: A Programmer's Diary

Author: by Staff

In the latest Intel-sponsored feature, part of the Gamasutra Visual Computing microsite, Goo! developer Tommy Refenes of PillowFort matches wits with multi-threading in four gripping acts -- and emerges victorious. Refenes begins by describing his initial attitude to threading, one which proved a poor choice: he dedicated a thread to the specific tasks of collision, only calling that thread's functions when needed and keeping it in a nonfunctioning loop otherwise. Here, he explains his mistake: "The model of having two threads sleeping and waiting for work (at least in the way in which they were waiting) was horrible. The threads waited in an infinite loop for work, and if they didn't find any, they performed a Sleep(0) and then continued waiting for work. At the time, I thought the Sleep(0) would free the processor enough so that other threads running elsewhere on the OS would be scheduled efficiently. Boy, was I wrong. The work check loop had the two processors constantly running at 90 percent to 100 percent capacity- an absolute waste of time. To understand why, picture this scenario. Let's say you are in charge of five construction workers tasked with paving a road. You know that you will need at least two of them to lay blacktop and at least the remaining three to grade the road, dig the ditches, and so on. Being the efficient supervisor that you are, you wouldn't think of allowing the two workers that need to lay the blacktop to sleep in the middle of the road until the blacktop is ready to be laid. No, to work as efficiently as possible, you would put all five of them to work grading and then all five paving." Refenes goes on to describe how he then created a new custom multi-threaded collision engine -- which he once again threw away and rewrote since that version of the game would not run on single-core machines. By the end of Act 4, he has programming another engine, one which dynamically scales based on the number of cores available. You can now read the full feature, which includes specific technical details and visual aids.