[사전과제] 재고 관리 및 현재 주문 정보 동시성 문제 해결

app/src/main/java/org/example/BeforeOrderServiceJava.java

@@ -0,0 +1,53 @@
+package org.example;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+public class BeforeOrderServiceJava {
+
+
+
+    // 상품 DB
+    private final Map<String, Integer> productDatabase = new ConcurrentHashMap<>() {
+    };
+    // 가장 최근 주문 정보를 저장하는 DB
+    private final ThreadLocal<ConcurrentMap<String, OrderInfo>> latestOrderDatabase = ThreadLocal.withInitial(ConcurrentHashMap::new);
+
+    public BeforeOrderServiceJava() {
+        // 초기 상품 데이터
+        productDatabase.put("apple", 100);
+        productDatabase.put("banana", 50);
+        productDatabase.put("orange", 75);
+    }
+
+    // 주문 처리 메서드
+    public void order(String productName, int amount) {
+
+        productDatabase.compute(productName, (key, stock) -> {
+            try {
+                Thread.sleep(1); // 동시성 이슈 유발을 위한 인위적 지연
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new RuntimeException(e);
+            }
+
+            if (stock != null && stock >= amount) {
+                System.out.println("Current Thread : " + Thread.currentThread().getName() +
+                        " - CurrentStock : " + stock + " - Order : " + amount);
+
+                latestOrderDatabase.get().put(productName, new OrderInfo(productName, amount, System.currentTimeMillis()));
+
+
+                return stock - amount;
+            } else {
+                throw new IllegalStateException("재고 부족");
+            }
+        });
+    }
+
+    // 재고 조회
+    public int getStock(String productName) {
+        return productDatabase.getOrDefault(productName, 0);
+    }
+}

app/src/main/java/org/example/OrderInfo.java

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+package org.example;
+
+public class OrderInfo {
+    public String productName;
+    public Integer amount;
+    public Long timestamp;
+
+    public OrderInfo(String productName, int amount, Long timestamp) {
+        this.productName = productName;
+        this.amount = amount;
+        this.timestamp = timestamp;
+    }
+}

app/src/test/java/org/example/BeforeOrderServiceJavaTest.java

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+package org.example;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+
+class BeforeOrderServiceJavaTest {
+
+    private final BeforeOrderServiceJava service = new BeforeOrderServiceJava();
+
+    @Test
+    void testConcurrentOrdersCauseStockMismatch() throws InterruptedException {
+        String productName = "apple";
+        int initialStock = service.getStock(productName);
+
+        int orderAmount = 8;
+        int threadCount = 100;
+
+        ExecutorService executor = Executors.newFixedThreadPool(threadCount);
+        CountDownLatch latch = new CountDownLatch(threadCount);
+
+        // 각 스레드에서 주문을 수행하는 작업 생성
+        for (int i = 0; i < threadCount; i++) {
+            executor.execute(() -> {
+                try {
+                    service.order(productName, orderAmount);
+                }catch (Exception e){
+                    System.out.println("Thread: " + Thread.currentThread().getName() + " - " + e.getMessage());
+                }
+                finally {
+                    latch.countDown(); // 작업 완료 후 카운트 감소
+                }
+            });
+        }
+
+        // 모든 스레드가 작업을 완료할 때까지 대기
+        latch.await();
+        executor.shutdown();
+
+        // 최종 재고 값 확인
+        int expectedStock = initialStock % orderAmount;
+        int actualStock = service.getStock(productName);
+
+        System.out.println("Expected Stock: " + expectedStock + ", Actual Stock: " + actualStock);
+
+        // 동시성 이슈로 인해 재고가 맞지 않는 경우를 확인
+        assertNotEquals(expectedStock, actualStock, "재고 불일치 발생!");
+    }
+}