How does the JVM implement volatile variables and atomic operations?

1. Volatile Variables

• Memory Barrier: The JVM inserts a "Memory Barrier" (Fence) instruction.
• Visibility: Forces the thread to read/write directly from Main Memory instead of CPU cache.
• No Caching: Prevents instruction reordering around the volatile variable.

2. Atomic Operations

• CAS (Compare-And-Swap): Most atomic classes (AtomicInteger, etc.) use CPU-level CAS instructions.
• CPU Instruction: It's a single, indivisible CPU instruction that checks if the value is what we expect; if yes, it updates it.
• Non-blocking: Unlike synchronized, CAS is non-blocking (optimistic locking).