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

文章来源: blog.csdn.net，作者：血煞风雨城2018，版权归原作者所有，如需转载，请联系作者。

原文链接：blog.csdn.net/qq_31905135/article/details/84143986