[사전과제] 동시성 제어

.gitignore

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+HELP.md
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/

build.gradle

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+plugins {
+    id 'java'
+    id 'org.springframework.boot' version '3.4.1'
+    id 'io.spring.dependency-management' version '1.1.7'
+}
+
+group = 'com.example'
+version = '0.0.1-SNAPSHOT'
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation 'org.springframework.boot:spring-boot-starter-web'
+    testImplementation 'org.springframework.boot:spring-boot-starter-test'
+    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
+}
+
+tasks.named('test') {
+    useJUnitPlatform()
+}

settings.gradle

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+rootProject.name = 'redis_1st_pre'

src/main/java/com/example/threadsafepractice/OrderServiceWithConcurrentHashMap.java

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+package com.example.threadsafepractice;
+
+import java.util.concurrent.ConcurrentHashMap;
+
+public class OrderServiceWithConcurrentHashMap {
+    // 상품 DB
+    private final ConcurrentHashMap<String, Integer> productDatabase = new ConcurrentHashMap<>();
+    // 가장 최근 주문 정보를 저장하는 DB
+    private final ConcurrentHashMap<String, OrderInfo> latestOrderDatabase = new ConcurrentHashMap<>();
+
+    public OrderServiceWithConcurrentHashMap() {
+        // 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, currentStock) -> {
+            if (currentStock == null) {
+                throw new IllegalArgumentException("상품이 존재하지 않습니다.");
+            }
+
+            try {
+                Thread.sleep(1); // 동시성 이슈 유발을 위한 인위적 지연
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new RuntimeException(e);
+            }
+
+            if (currentStock >= amount) {
+                System.out.printf("Thread %d 주문 정보:\n", Thread.currentThread().threadId());
+                System.out.printf("%8s: %d 건 ([%d])\n", productName, 1, amount);
+
+                productDatabase.put(productName, currentStock - amount);
+                latestOrderDatabase.put(productName, new OrderInfo(productName, amount, System.currentTimeMillis()));
+                return currentStock - amount; // 기존 재고에서 주문 수량 차감
+            }
+            System.out.println("[ERROR] 재고 부족: " + productName);
+            return currentStock; // 차감할 수 없으면 기존 재고 유지
+        });
+    }
+
+    public static class OrderInfo {
+        public OrderInfo(String productName, int amount, long orderTime) {
+        }
+    }
+
+    // 재고 조회
+    public int getStock(String productName) {
+        return productDatabase.getOrDefault(productName, 0);
+    }
+}

src/main/java/com/example/threadsafepractice/OrderServiceWithReentrantLock.java

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+package com.example.threadsafepractice;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.locks.ReentrantLock;
+
+public class OrderServiceWithReentrantLock {
+
+    // 상품 DB (공유 자원)
+    private final Map<String, Integer> productDatabase = new HashMap<>();
+    private final Map<String, OrderInfo> latestOrderDatabase = new HashMap<>();
+
+    // ReentrantLock 객체 추가
+    private final ReentrantLock lock = new ReentrantLock();
+
+    public OrderServiceWithReentrantLock() {
+        // 초기 상품 데이터 설정
+        productDatabase.put("apple", 100);
+        productDatabase.put("banana", 50);
+        productDatabase.put("orange", 75);
+    }
+
+    // ReentrantLock을 사용하여 동기화된 주문 처리 메서드
+    public void order(String productName, int amount) {
+        lock.lock(); // 락 획득 (스레드 간 경합 방지)
+        try {
+            // 재고 체크 및 감소 로직
+            Integer currentStock = productDatabase.getOrDefault(productName, 0);
+
+            try {
+                Thread.sleep(1); // 동시성 이슈 유발을 위한 인위적 지연
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new RuntimeException(e);
+            }
+
+            if (currentStock >= amount) {
+                System.out.printf("Thread %d 주문 정보:\n", Thread.currentThread().threadId());
+                System.out.printf("%8s: %d 건 ([%d])\n", productName, 1, amount);
+
+                // 재고 감소
+                productDatabase.put(productName, currentStock - amount);
+                latestOrderDatabase.put(productName, new OrderInfo(productName, amount, System.currentTimeMillis()));
+            } else {
+                System.out.println("[ERROR] 재고 부족: " + productName);
+            }
+        } finally {
+            lock.unlock(); // 락 해제 (데드락 방지)
+        }
+    }
+
+    public static class OrderInfo {
+        public OrderInfo(String productName, int amount, long orderTime) {
+        }
+    }
+
+    // 재고 조회 메서드
+    public int getStock(String productName) {
+        lock.lock(); // 락 획득
+        try {
+            return productDatabase.getOrDefault(productName, 0);
+        } finally {
+            lock.unlock(); // 락 해제
+        }
+    }
+}

src/main/resources/application.properties

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+spring.application.name=thread-safe-practice

src/test/java/com/example/threadsafepractice/OrderServiceWithConcurrentHashMapTest.java

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+package com.example.threadsafepractice;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import org.junit.jupiter.api.Test;
+
+class OrderServiceWithConcurrentHashMapTest {
+
+    private final OrderServiceWithConcurrentHashMap service = new OrderServiceWithConcurrentHashMap();
+
+    @Test
+    void testConcurrentOrdersHandlesStockCorrectly() 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);
+
+        // 동시성 이슈 없이 재고가 일치하는 것을 확인
+        assertEquals(expectedStock, actualStock);
+    }
+
+}

src/test/java/com/example/threadsafepractice/OrderServiceWithReentrantLockTest.java

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+package com.example.threadsafepractice;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import org.junit.jupiter.api.Test;
+
+class OrderServiceWithReentrantLockTest {
+
+    private final OrderServiceWithReentrantLock service = new OrderServiceWithReentrantLock();
+
+    @Test
+    void testConcurrentOrdersHandlesStockCorrectly() 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);
+
+        // 동시성 이슈 없이 재고가 일치하는 것을 확인
+        assertEquals(expectedStock, actualStock);
+    }
+
+}