ShopEase — Module 32: Solving Inventory Overselling with Concurrency Control

In an e-commerce application, multiple users can try to purchase the same product at exactly the same time.
This creates a common backend problem: Race Conditions.
The Problem
Suppose a product has only 10 items in stock.
Now imagine 50 users place an order simultaneously.
Without proper concurrency handling, multiple threads may read the same stock value before any of them updates it:
Stock = 10
→ Thread 1 reads 10
→ Thread 2 reads 10
→ Thread 3 reads 10
→ ...
→ Multiple threads try to purchase
The result can be incorrect stock updates and overselling, where the system accepts more orders than the available inventory.
This is a serious problem for an e-commerce backend.
The Solution
In ShopEase, I implemented Concurrency, Multithreading & Database Locking to handle these situations safely.
The inventory update process now uses:

• Multithreading for concurrent request testing
• Optimistic Locking using @version
• Pessimistic Locking using @lock(LockModeType.PESSIMISTIC_WRITE)
• Database row locking with FOR UPDATE
• Atomic stock deduction
• Proper transaction handling With pessimistic locking, when one transaction is updating a product's stock, other transactions have to wait instead of modifying the same row simultaneously. 50-Thread Stress Testing To verify the implementation, I performed concurrent testing with 50 threads trying to purchase the same product. The test focused on: 50 concurrent requests → Stock validation → Locking → Atomic deduction → Order result The important result was: No negative stock. No overselling. Concurrent requests handled safely. What This Module Solved The main problem solved in this module was protecting inventory from race conditions during simultaneous purchases. This makes the ShopEase backend more reliable when multiple users interact with the same product at the same time. Key Takeaway Concurrency isn't just about running multiple threads. In a real e-commerce system, it is about making sure that multiple operations happening simultaneously still produce a correct and consistent result. Tech Stack: Java • Spring Boot • Spring Data JPA • Hibernate • MariaDB • Multithreading • Optimistic Locking • Pessimistic Locking #Java #SpringBoot #Concurrency #Multithreading #DatabaseLocking #Hibernate #MariaDB #BackendDevelopment #ShopEase