How can a variable be changed from multiple threads without synchronization primitives? What are atomic operations and how are they related to multithreading?

Modifying a variable from multiple threads without using synchronization primitives (such as lock, Mutex) can be done using atomic operations. Atomic operations are those that are executed entirely, indivisibly, without interruptions, which guarantees correctness when accessed concurrently from different threads.

In C#, there is a class Interlocked that provides methods for atomic modification of variables, such as Interlocked.Increment, Interlocked.CompareExchange, and others. They allow safe modification of int, long, and reference type variables without explicit locks.

Example:

int counter = 0;

// In multiple threads
Interlocked.Increment(ref counter); // atomically increases counter by 1

Thus, atomic operations ensure data correctness in a multithreaded environment without the overhead of locks, preventing race conditions.