Schrödinger's Cat and RCU (Well, Structured Procrastination, Actually)

davecb writes "Paul E. McKenney, one of the Linux RCU implementors, addresses the problem of synchronization using structured deferral on, what else, Mr Schrödinger's famous cat. Courtesy of deferral/procrastination, the cat can be both alive and dead at the same time. 'In this example, Schrödinger would like to construct an in-memory database to keep track of the animals in his zoo. Births would of course result in insertions into this database, while deaths would result in deletions. The database is also queried by those interested in the health and welfare of Schrödinger's animals. Schrödinger has numerous short-lived animals such as mice, resulting in high update rates. In addition, there is a surprising level of interest in the health of Schrödinger's cat, so much so that Schrödinger sometimes wonders whether his mice are responsible for most of these queries. Regardless of their source, the database must handle the large volume of cat-related queries without suffering from excessive levels of contention. Both accesses and updates are typically quite short, involving accessing or mutating an in-memory data structure, and therefore synchronization overhead cannot be ignored.'"