[동시성 처리] synchronized vs Reentrant Lock - 실습

실습

💡synchronized

https://annovation.tistory.com/509

동시성 이슈 해결방법[2] - synchronized

 

💡Reentrant Lock

• 기본 사용법

private final ReentrantLock lock = new ReentrantLock();

public void method() {
    lock.lock();
    try {
        // 비즈니스 로직
    } finally {
        lock.unlock();
    }
}

 

• HubEleven 프로젝트 적용 실습

@Service
@RequiredArgsConstructor
public class StockServiceImpl implements StockService {

    private final StockRepository stockRepository;
    private final ProductRepository productRepository;

    private final ReentrantLock lock = new ReentrantLock();

	... (생략) ...

    @Override
    @Transactional
    public StockResult decreaseStock(StockRequests.Decrease request) {

        lock.lock();
        try {
            Product product = getProductOrThrow(request.productId());

            Stock stock = getStockOrThrow(request.productId());

            stock.decreaseQuantity(request.quantity());

            return StockResult.from(stock, product.getName());
        } finally {
            lock.unlock();
        }
    }
}

 

✅ 한계 : MSA 와 같은 멀티 서버에서는 무용지물

 

멀티 서버 구성 예시

Server A → JVM A → Heap A → Object A(모니터 A)
Server B → JVM B → Heap B → Object B(모니터 B)

• Server A에서 synchronized/ReentrantLock으로 임계영역을 막아도
• Server B에서는 완전히 별개의 락이라 동시에 들어올 수 있음

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참고 자료

1) Oracle Docs : ReentrantLock

https://docs.oracle.com/javase/17/docs/api/java.base/java/util/concurrent/locks/ReentrantLock.html

Overview (Java SE 17 & JDK 17)