What are non-blocking algorithms?

Non-blocking algorithms allow multiple threads to perform operations concurrently without the need to block each other. This is achieved through the use of atomic operations and the prevention of race conditions.

Key characteristics:

• Deadlock freedom: Threads do not wait for each other indefinitely.
• Liveness: Guarantee that some operation will eventually complete. There are three levels of liveness:
  • Obstruction-free: A thread can always perform an operation if it works in isolation.
  • Lock-free: Guarantee that at least one thread will perform an operation within a finite number of steps (global progress).
  • Wait-free: Guarantee that every thread will perform an operation within a finite number of steps (individual progress).

Examples in Java:

• java.util.concurrent.atomic package (e.g., AtomicInteger, AtomicReference).
• Some implementations of collections from java.util.concurrent (e.g., ConcurrentHashMap).

Atomic operations such as Compare-and-Swap (CAS) are the foundation of lock-free algorithms.

// Example of using AtomicInteger
import java.util.concurrent.atomic.AtomicInteger;

public class NonBlockingCounter {
    private final AtomicInteger count = new AtomicInteger(0);

    public int increment() {
        // Atomically increments the value by 1
        return count.incrementAndGet();
    }

    public int getCount() {
        return count.get();
    }
}