Phases

The Roller Coaster Problem The Roller Coaster Problem, introduced by Allen Downey in “The Little Book of Semaphores,” demonstrates multi-phase synchronization and cyclic barriers. It’s a perfect model for batch processing systems where work happens in coordinated phases. The Scenario A roller coaster ride has: A car with capacity C passengers Passengers continuously arriving and queuing The car cycles through: board → ride → unboard → repeat The rules: Car waits until exactly C passengers are ready Passengers can’t board until car is empty Car can’t run until full Passengers must unboard before new passengers board Process repeats indefinitely The Challenge: Three-Phase Coordination Each ride has three synchronized phases: ...