example.java

// Example of the executor service
class UserRepository implements Closeable {

    private FileStore fileStore;
    private ConcurrentHashMap<UUID, User> cache = new ConcurrentHashMap<>();
    private ReadWriteLock lock = new ReentrantReadWriteLock();
    private ExecutorService executors = Executors.newFixedThreadPool(2);
 
    UserRepository(FileStore fnileStore) {
        this.fileStore = fileStore;
    }

    @Override
    public CompletableFuture<Void> saveUser(User user) {
        return CompletableFuture.runAsync(() -> {
            lock.writeLock().lock();
            fileStore.write(user.getId(), user);
            cache.put(user.getId(), user);
            lock.writeLock().unlock();
        }, executors);
    }

    @Override
    public void close()  {
   executors.isShutdown()
});