Kas saaksid anda näite Java olukorrast, kus kasutatakse pessimisti blokki, et vältida konfliktide tekkimist andmetele juurdepääsul?

Pessimistic locking in Java is often used when it is necessary to ensure that data will not be modified by other threads during the execution of a critical operation. For example, when working with a database via JPA/Hibernate, you can use the lock() method with the PESSIMISTIC_WRITE lock mode to prevent concurrent modifications of the same record:

EntityManager em = ...;
EntityTransaction tx = em.getTransaction();
tx.begin();

// Get object with write lock
MyEntity entity = em.find(MyEntity.class, id, LockModeType.PESSIMISTIC_WRITE);

// Make changes
entity.setValue(newValue);

// Save changes
em.persist(entity);
tx.commit();

In this example, until the transaction is completed, other transactions attempting to acquire a lock on the same record will wait, preventing conflicts and ensuring data integrity.