Java长整形原子操作测试

怼烎@ 2023-02-13 08:52 12阅读 0赞

package com.example;
    
    import java.util.concurrent.Semaphore;
    import java.util.concurrent.atomic.AtomicLong;
    
    import org.junit.jupiter.api.Test;
    
    /**
     * 原子操作测试：值类型操作如++非原子性，CPU内有高速缓存，多线程非安全 java.util.concurrent.atomic包下对应有原子操作封装类 以AtomicLong自增为例，CPU消耗远远高于long自增(约2个数量级)
     * 
     * @author yeqiang
     * @since 5/28/20 8:58 AM
     */
    public class AtomicOptTest {
        static final long INC_LOOP_COUNT = 100000000l;
        static final Semaphore semaphore = new Semaphore(0);
    
        static long counter = 0l;
        static AtomicLong atomicLong = new AtomicLong(0l);
        Runnable counterIncFailFun = new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < INC_LOOP_COUNT; i++) {
                    counter++;
                }
                semaphore.release();
            }
        };
    
        Runnable counterIncSuccFun = new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < INC_LOOP_COUNT; i++) {
                    atomicLong.addAndGet(1);
                }
                semaphore.release();
            }
        };
    
        /**
         * 失败的测试
         * 
         * @throws InterruptedException
         */
        @Test
        public void testMultiThreadCounterIncFail() throws InterruptedException {
            int THREAD_COUNT = 2;
            long result = INC_LOOP_COUNT * THREAD_COUNT;
    
            for (int i = 0; i < THREAD_COUNT; i++) {
                Thread t = new Thread(counterIncFailFun);
                t.start();
            }
    
            semaphore.acquire(THREAD_COUNT);
            System.out.println(counter);
    
        }
    
        @Test
        public void testMultiThreadCounterIncSucc() throws InterruptedException {
    
            int THREAD_COUNT = 2;
            long result = INC_LOOP_COUNT * THREAD_COUNT;
    
            for (int i = 0; i < THREAD_COUNT; i++) {
                Thread t = new Thread(counterIncSuccFun);
                t.start();
            }
    
            semaphore.acquire(THREAD_COUNT);
            System.out.println(atomicLong.get());
    
        }
    }

运行结果

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hrbmFydXRv_size_16_color_FFFFFF_t_70][]

结果说明：

1. 普通java long类型++操作不能保证多线程安全，由于CPU缓存，运行速度极快，CPU消耗低

2. AtomicLong addAndGet()方法具备原子性，保证结果安全，但CPU消耗极大，耗时是long ++的两个数量级

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hrbmFydXRv_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/2020052810185230.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hrbmFydXRv,size_16,color_FFFFFF,t_70