Starcraft AI blog

Earlier, I pointed out 2 rare game-over bugs in Steamhammer 2.3. It turns out that there are 2 other serious bugs in this version, which are not rare; they are causing a good proportion of the bot’s losses.

One is a bug in turning gas collection on and off. The bug can turn off gas collection even when the bot needs gas to continue production, causing a production freeze that can last for the rest of the game (not likely to be long with no production). It may have been introduced when I refactored the code for gas decisions. The other is a bug that cancels vital hatcheries (and perhaps other buildings) for no apparent reason. I suspect an error in one of the emergency “uh oh, no drones!” or “panic! I need those resources back NOW!” tests. There are other possibilities.

Critical bugs go straight to the top of my list.

The bugs also point out a weakness in Steamhammer’s design: Decentralized decision making. Decision rules that take direct action are scattered through the code. Of course a bug in any rule can cause bad behavior; that’s inevitable. The weak point of the design is that the separate rules, sometimes far away from each other in the code, have to cooperate so they don’t override each other’s decisions. The gas collection bug is clearly a coordination bug; one rule says “I need gas for the next production item” and some other rule is incorrectly overriding the decision, “nah, I wanna turn off gas.”

Compare the unit mix decision, which is made using a more indirect method: Rules collect evidence, then in a second stage the evidence is weighed and the decision is made. The evidence is explicit, so bugs are easier to trace, and evidence-collecting rules do not need to cooperate with each other, they only need to weight their evidence consistently. Machine learning systems conventionally follow this collect evidence, then decide paradigm as a matter of course.