隨記

說明

Shared mutable state between threads must be properly synchronised. Service beans (singletons by default in Spring) must not store request-scoped mutable state in instance fields.

為什麼重要

  • Data races — concurrent modification causes unpredictable behaviour
  • Heisenbugs — race conditions are nearly impossible to reproduce locally
  • State corruption — partial writes visible to other threads

Enforcement

IS2_INCONSISTENT_SYNC — field is sometimes synchronised and sometimes not.

正例

@Service
public class OrderService {
    // ✅ immutable or thread-safe state only
    private final OrderRepository orderRepository;

    // ✅ request-scoped state passed as method parameter
    public Order process(OrderRequest request) {
        // ...
    }
}

反例

@Service
public class OrderService {
    private Order currentOrder; // ❌ mutable shared state in singleton

    public void process(OrderRequest request) {
        this.currentOrder = orderRepository.findById(request.getId()); // ❌ data race
    }
}