#27 stock: race condition solution 1 - java syncronized

stock/src/main/java/com/example/stock/service/StockProxyService.java

@@ -0,0 +1,17 @@
+package com.example.stock.service;
+
+import com.example.stock.domain.Stock;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+@RequiredArgsConstructor
+public class StockProxyService {
+
+    private final StockService stockService;
+
+    public synchronized void decrease(Long id, Long quantity) {
+        stockService.decrease(id, quantity);
+    }
+}

stock/src/test/java/com/example/stock/service/StockServiceTest.java

@@ -20,6 +20,9 @@ class StockServiceTest {
     @Autowired
     private StockService stockService;
 
+    @Autowired
+    private StockProxyService stockProxyService;
+
     @Autowired
     private StockRepository stockRepository;
 
@@ -69,4 +72,29 @@ class StockServiceTest {
         // 100 - (1 * 100) = 0
         assertEquals(0L, stock.getQuantity());
     }
+
+    @Test
+    public void 동시에_100개의_요청_Proxy() 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 {
+                    stockProxyService.decrease(1L, 1L);
+                } finally {
+                    latch.countDown();
+                }
+            });
+        }
+
+        latch.await();
+
+        Stock stock = stockRepository.findById(1L).orElseThrow();
+
+        // 100 - (1 * 100) = 0
+        assertEquals(0L, stock.getQuantity());
+    }
 }