How atomics work in Java?
#atomics #concurrency
Java atomics java.util.concurrent.atomic package has a set of classes that support lock-free thread-safe programming on
single variables (values or arrays). Common classes like AtomicInteger or AtomicBoolean are implemented by calling Unsafe or VarHandle methods (depending on the Java version) which are in general just system calls with extra safety steps. The AtomicIntegerArray or AtomicReferenceArray classes further extend atomic operation support to arrays of these types, but they are still have limitations of memory contention.
Atomic operations are very special and provide only limited support. C, C++, Rust, and Swift have relaxed atomics. Relaxed atomics do not create happens-before edges and therefore have no synchronizing effect. Java has VarHandle's “plain” mode. JavaScript has non-atomic accesses to the SharedArrayBuffer (the only shared memory).
