#27 stock: race condition solution 3 - redis(lettuce)

stock/build.gradle

@@ -20,6 +20,7 @@ repositories {
 
 dependencies {
     implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
+    implementation 'org.springframework.boot:spring-boot-starter-data-redis'
     implementation 'org.springframework.boot:spring-boot-starter-web'
     compileOnly 'org.projectlombok:lombok'
     runtimeOnly 'com.mysql:mysql-connector-j'

stock/src/main/java/com/example/stock/facade/LettuceLockStockFacade.java

@@ -0,0 +1,28 @@
+package com.example.stock.facade;
+
+import com.example.stock.repository.RedisLockRepository;
+import com.example.stock.service.StockService;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Component;
+import org.springframework.transaction.annotation.Transactional;
+
+@Component
+@RequiredArgsConstructor
+public class LettuceLockStockFacade {
+
+    private final RedisLockRepository redisLockRepository;
+
+    private final StockService stockService;
+
+    public void decrease(Long id, Long quantity) throws InterruptedException {
+        while (!redisLockRepository.lock(id)) {
+            Thread.sleep(100);
+        }
+
+        try {
+            stockService.decrease(id, quantity);
+        } finally {
+            redisLockRepository.unlock(id);
+        }
+    }
+}

stock/src/main/java/com/example/stock/repository/RedisLockRepository.java

@@ -0,0 +1,28 @@
+package com.example.stock.repository;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.data.redis.core.RedisTemplate;
+import org.springframework.stereotype.Component;
+
+import java.time.Duration;
+
+@Component
+@RequiredArgsConstructor
+public class RedisLockRepository {
+
+    private final RedisTemplate<String, String> redisTemplate;
+
+    public Boolean lock(Long key) {
+        return redisTemplate
+                .opsForValue()
+                .setIfAbsent(generateKey(key), "lock", Duration.ofMillis(3_000));
+    }
+
+    public Boolean unlock(Long key) {
+        return redisTemplate.delete(generateKey(key));
+    }
+
+    private String generateKey(Long key) {
+        return key.toString();
+    }
+}

stock/src/test/java/com/example/stock/facade/LettuceLockStockFacadeTest.java

@@ -0,0 +1,63 @@
+package com.example.stock.facade;
+
+import com.example.stock.domain.Stock;
+import com.example.stock.repository.StockRepository;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+@SpringBootTest
+class LettuceLockStockFacadeTest {
+    @Autowired
+    private LettuceLockStockFacade lettuceLockStockFacade;
+
+    @Autowired
+    private StockRepository stockRepository;
+
+    @BeforeEach
+    public void before() {
+        Stock stock = new Stock(1L, 100L);
+
+        stockRepository.saveAndFlush(stock);
+    }
+
+    @AfterEach
+    public void after() {
+        stockRepository.deleteAll();
+    }
+
+    @Test
+    public void 동시에_100개의_요청_lettuce() throws InterruptedException {
+        int threadCount = 100;
+        ExecutorService executorService = Executors.newFixedThreadPool(32);
+
+        CountDownLatch latch = new CountDownLatch(threadCount);
+
+        for (int i = 0; i < threadCount; i++) {
+            executorService.submit(() -> {
+                try {
+                    lettuceLockStockFacade.decrease(1L, 1L);
+                } catch (InterruptedException e) {
+                    throw new RuntimeException(e);
+                } finally {
+                    latch.countDown();
+                }
+            });
+        }
+
+        latch.await();
+
+        Stock stock = stockRepository.findById(1L).orElseThrow();
+
+        // 100 - (1 * 100) = 0
+        assertEquals(0L, stock.getQuantity());
+    }
+}