多线程并发安全计数器实现限流(三) 加锁实现计数器

一、加锁实现计数器

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public class CounterSync implements Counter {       volatile int i = 0; // 本质是修改内存中某一个变量的值       public synchronized int incr() {         return i++;     }       public int decr() {         return i--;     }       @Override     public int get() {         return i;     } }

　　

二、测试

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public static void main(String[] args) throws InterruptedException {         final Counter ct = new CounterSync();           //模拟多线程场景         CountDownLatch countDownLatch = new CountDownLatch(2);           for (int i = 0; i < 2; i++) {             new Thread(() -> {                 long begin = System.nanoTime();                 for (int j = 0; j < 10000; j++) {                     ct.incr();                 }                 System.out.println("done...运算时间： " + (System.nanoTime() - begin));                 countDownLatch.countDown();             }).start();         }           countDownLatch.await();         System.out.println("计数器最终结果: " + ct.get());         // 预期结果应该 --- 20000     }

　　

三、打印结果

done...运算时间： 1173900
done...运算时间： 803900
计数器最终结果: 20000