Multithreading

import java.util.concurrent.*;
import java.util.concurrent.locks.*;

public class MultithreadingExample {

    // 1. Thread 클래스 상속
    static class MyThread extends Thread {
        private String name;

        public MyThread(String name) {
            this.name = name;
        }

        @Override
        public void run() {
            System.out.println("스레드 " + name + " 시작");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
            System.out.println("스레드 " + name + " 완료");
        }
    }

    // 2. Runnable 인터페이스 구현 (권장)
    static class MyRunnable implements Runnable {
        @Override
        public void run() {
            System.out.println("Runnable 실행: " +
                Thread.currentThread().getName());
        }
    }

    // 3. synchronized를 사용한 동기화
    static class Counter {
        private int count = 0;
        private final Object lock = new Object();

        // 메서드 전체 동기화
        public synchronized void incrementSync() {
            count++;
        }

        // 블록 동기화 (더 세밀한 제어)
        public void incrementBlock() {
            synchronized (lock) {
                count++;
            }
        }

        public int getCount() { return count; }
    }

    // 4. ReentrantLock 사용 (더 유연한 락)
    static class BetterCounter {
        private int count = 0;
        private final ReentrantLock lock = new ReentrantLock();

        public void increment() {
            lock.lock();
            try {
                count++;
            } finally {
                lock.unlock();  // 반드시 finally에서 해제
            }
        }

        // tryLock으로 데드락 방지
        public boolean tryIncrement() {
            if (lock.tryLock()) {
                try {
                    count++;
                    return true;
                } finally {
                    lock.unlock();
                }
            }
            return false;
        }
    }

    public static void main(String[] args) throws Exception {
        // 5. ExecutorService (실무 권장 패턴)
        ExecutorService executor = Executors.newFixedThreadPool(4);

        // Runnable 실행
        executor.execute(() -> System.out.println("Task 1"));

        // Callable로 결과 반환
        Future future = executor.submit(() -> {
            Thread.sleep(1000);
            return "Task 완료";
        });

        System.out.println("결과: " + future.get());  // 블로킹

        // CompletableFuture (Java 8+, 비동기 체이닝)
        CompletableFuture.supplyAsync(() -> "Hello")
            .thenApply(s -> s + " World")
            .thenAccept(System.out::println)
            .join();

        executor.shutdown();
        executor.awaitTermination(5, TimeUnit.SECONDS);
    }
}