java 并发编程学习笔记（一）之 并发基础

                                              并发基础

• 并发小测试

java.util.concurrent.Semaphore 类

public class SemTest {
    /**
     * Semaphore 通常用来控制同时有多少个线程在运行
     */
    private static Semaphore semaphore = new Semaphore(1);
    // private static Semaphore semaphore = new Semaphore(3);
    static class car implements Runnable {


        @Override
        public void run() {
            try {
                semaphore.acquire();
                System.out.println(Thread.currentThread().getName() + "start ");
                System.out.println(Thread.currentThread().getName() + "end");
                semaphore.release();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        ExecutorService service = Executors.newCachedThreadPool();
        Thread thread = new Thread(new car(), "小汽车1");
        Thread thread2 = new Thread(new car(), "小汽车2");
        Thread thread3 = new Thread(new car(), "小汽车3");
        List<Thread> list = new ArrayList<Thread>();
        list.add(thread);
        list.add(thread2);
        list.add(thread3);
        for (int i = 0; i < list.size(); i++) {
            service.execute(list.get(i));
        }
    }
}

@Slf4j
public class CountExample {

    private static int threadTotal =  1;
    private static int clientTotal = 5000;

    private static  long count = 0;

    public static void main(String[] args) {
        ExecutorService exec = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        for (int index = 0; index < clientTotal; index++) {
            exec.execute(() -> {

                try {
                    semaphore.acquire();
                    add();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
            });
        }
        exec.shutdown();
        log.info("count:{}", count);
    }

    private static void add() {
        count++;
    }
}

并发： 多个线程操作相同的资源，保证线程安全，合理使用资源

高并发: 服务器同时处理很多请求，提高程序性能