Getting To Know Parallelism

Abstract

Every morning the first thing that X does is make tea for herself. She first turns on the stove and then while the stove ring is heating up, she pours water from the faucet into the kettle. She then places the kettle on the stove ring, now nicely hot, and while the water is being heated she puts tea bags into the teapot; she then pours milk from the milk carton into a milk jug and then puts the milk jug into the microwave oven. After the water starts to boil she pours water into teapot. And while the tea “gathers strength” in the teapot, she presses the time button on the microwave to start warming the milk. After the milk is warmed she first pours tea from the teapot into a teacup and then adds milk from the warmed milk jug to the tea in the cup. This tiny, humdrum, comforting, domestic scenario X enacts every morning has many (but not all) of the ingredients of a situation that involves the scope and limits of parallel processing. More precisely, the art of making tea as practiced by X entails a blend of both sequential and parallel events. We note that certain events can take place in parallel (or concurrently) because they do not interfere with one another; for example, the heating of the stove and the pouring of water into the kettle. But other events must be sequentially ordered either because they interfere with one another or because one event must complete before the other can begin. The kettle can be placed on the stove ring only after it has been filled with water; water can be poured into the teapot only after the water has boiled. But notice also that there is some flexibility in the ordering of X’s actions. She can defer turning on the stove until after the kettle is placed on the stove ring; she can alter the ordering of pouring water into the teapot and placing teabags into the pot; she could defer warming the milk in the microwave until the tea has brewed.