How is synchronization carried out to prevent simultaneous processing of events of one entity by multiple consumers?

To prevent concurrent processing of events of the same entity by multiple consumers in Java, various synchronization mechanisms are used:

1. Locks — using synchronized or classes from java.util.concurrent.locks (e.g., ReentrantLock) to ensure exclusive access to a resource.

2. Use of atomic operations — classes from java.util.concurrent.atomic allow performing operations without locks, reducing the likelihood of race conditions.

3. Queue and message broker mechanisms — for example, using JMS, Kafka, or RabbitMQ with consumer configuration so that an event is processed by only one consumer (e.g., through partitioning or consumer groups).

4. Optimistic locking — storing the entity's version and checking it before updating to avoid conflicts.

5. Using ConcurrentHashMap or other thread-safe collections to manage entity states.

6. Distributed Locking — in distributed systems, external services (e.g., Redis with Redlock, Zookeeper) are used to coordinate access.

Example using ReentrantLock:

import java.util.concurrent.locks.ReentrantLock;

public class EntityProcessor {
    private final ReentrantLock lock = new ReentrantLock();

    public void processEvent(Event event) {
        lock.lock();
        try {
            // process event
        } finally {
            lock.unlock();
        }
    }
}