Go

Defines the scope as concurrency within a single process on a single machine, then connects shared variables, shared memory, message passing, language concurrency semantics, and hardware implementation.

Continues with counter and counter + ready to explain how read-write locks allow concurrent readers, comparing Java's Lock API, Go sync.RWMutex, and the situation in CPython.

Continues with counter++ to explain how mutexes provide atomicity, visibility, and ordering, then compares Java synchronized, Go sync.Mutex, and CPython threading.Lock.

Moves from hardware memory models back to the language layer: why languages need their own concurrency semantics, and what Java, Go, and CPython guarantee to concurrent programs.

Starting from the von Neumann architecture and instruction execution, this article follows count++ down to the hardware-level problems of atomicity, visibility, and ordering.

Uses the counter + ready example to explain the visibility and ordering guarantees of Java volatile, and why Go and Python do not have an equivalent volatile keyword.

Follows Java AtomicInteger, Go sync/atomic, and CPython's internal atomic operations to see how Atomic RMW reaches the compiler, runtime, and CPU.

Continues with counter and ready to explain the atomicity, visibility, and ordering guarantees of atomic operations, then compares the public semantics in Java, Go, and CPython.