Advanced: Disruptor, Actor, False Sharing

Two threads alternate output (1,A,2,B,3,C) by sharing a boolean flag protected with synchronized, wait(), and notify(), where each thread flips the flag after printing and wakes the other.

False sharing is a performance problem where two threads writing to independent variables on the same CPU cache line cause constant cross-core cache invalidation, degrading throughput by 10-100x even though no data is actually shared.

Spinning trades CPU cycles to avoid a context switch, so it helps only for very short waits on an available core; use Thread.onSpinWait to hint the CPU, and block instead when the wait is long or cores are scarce.

The Disruptor is a lock-free, pre-allocated ring buffer coordinated by sequences and barriers under a single-writer rule, giving millions of events per second without BlockingQueue lock and allocation overhead.

An actor owns private state, receives asynchronous immutable messages into a mailbox, and processes them one at a time, so shared mutable state and locks disappear entirely.