From 7757cb7a0d87f09a2585f71b4cc93724aca35ca4 Mon Sep 17 00:00:00 2001
From: rmsxo200 <78577092+rmsxo200@users.noreply.github.com>
Date: Thu, 2 Jan 2025 09:41:38 +0900
Subject: [PATCH] =?UTF-8?q?=EC=82=AC=EC=A0=84=EA=B3=BC=EC=A0=9C?=
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---
 week0/BeforeOrderService.java     | 58 +++++++++++++++++++++++++++++++
 week0/BeforeOrderServiceTest.java | 53 ++++++++++++++++++++++++++++
 week0/OrderInfo.java              | 16 +++++++++
 3 files changed, 127 insertions(+)
 create mode 100644 week0/BeforeOrderService.java
 create mode 100644 week0/BeforeOrderServiceTest.java
 create mode 100644 week0/OrderInfo.java

diff --git a/week0/BeforeOrderService.java b/week0/BeforeOrderService.java
new file mode 100644
index 0000000..e8b9b59
--- /dev/null
+++ b/week0/BeforeOrderService.java
@@ -0,0 +1,58 @@
+package com.hanghae.radis.service;
+
+import com.hanghae.radis.model.OrderInfo;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+public class BeforeOrderService {
+    // 상품 DB (공유 자원의 동시성 이슈 해결을 위해 ConcurrentMap 사용)
+    private final ConcurrentMap<String, Integer> productDatabase = new ConcurrentHashMap<>();
+    // 가장 최근 주문 정보를 저장하는 DB
+    private final Map<String, OrderInfo> latestOrderDatabase = new HashMap<>();
+
+    public BeforeOrderService() {
+        // 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) {
+        try {
+            Thread.sleep(1); // 동시성 이슈 유발을 위한 인위적 지연
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new RuntimeException(e);
+        }
+        
+        //스레드 안전성을 보장하기 위해 특정 키에 대한 연산을 원자적으로 수행하는 compute 사용
+        productDatabase.compute(productName, (key, value) -> {
+            if (value >= amount) {
+                //주문 정보 화면 출력
+                System.out.println(Thread.currentThread().getName() + " 주문정보 : \n"
+                        + productName + ": " + amount + " 건, 현재 수량: " + value + " , 판매 후 수량: " + (value - amount));
+                
+                //주문 성공시 최신 주문내역 저장
+                latestOrderDatabase.put(productName, new OrderInfo(productName, amount, System.currentTimeMillis()));
+
+                return value - amount; // 상품수가 주문량보다 많을 경우 업데이트
+            } else {
+                return value; // 아닐 경우 상품수 유지
+            }
+        });
+    }
+
+    // 재고 조회
+    public int getStock(String productName) {
+        return productDatabase.getOrDefault(productName, 0);
+    }
+
+    // 최근 주문 조회
+    public OrderInfo getLatestOrder(String productName) {
+        return latestOrderDatabase.getOrDefault(productName, null);
+    }
+}
diff --git a/week0/BeforeOrderServiceTest.java b/week0/BeforeOrderServiceTest.java
new file mode 100644
index 0000000..a36458d
--- /dev/null
+++ b/week0/BeforeOrderServiceTest.java
@@ -0,0 +1,53 @@
+package com.hanghae.radis.service;
+
+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;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class BeforeOrderServiceTest {
+    private final BeforeOrderService service = new BeforeOrderService();
+
+    @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);
+                } 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);
+        System.out.println("최근 주문 ["
+                + "상품명: " + service.getLatestOrder(productName).getProductName()
+                + ", 상품수: " +  service.getLatestOrder(productName).getAmount() + " 건]");
+
+        // 재고 일치 여부 확인
+        assertEquals(actualStock, expectedStock);
+    }
+}
diff --git a/week0/OrderInfo.java b/week0/OrderInfo.java
new file mode 100644
index 0000000..e42bd24
--- /dev/null
+++ b/week0/OrderInfo.java
@@ -0,0 +1,16 @@
+package com.hanghae.radis.model;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Getter
+@Setter
+@NoArgsConstructor
+@AllArgsConstructor
+public class OrderInfo {
+    private String productName;
+    private Integer amount;
+    private Long timestamp;
+}