volatile 关键字 和 i++ 原子性

 1 package com.mozq.multithread;
 2 
 3 /**
 4  * 深入理解Java虚拟机 volatile 关键字 和 i++ 原子性。
 5  */
 6 public class VolatileTest {
 7     public static volatile int race = 0;
 8 
 9     private static final int THREADS_COUNT = 20;
10 
11     public static void main(String[] args) {
12         Thread[] threads = new Thread[THREADS_COUNT];
13         for(int i = 0; i < THREADS_COUNT; i++){
14             threads[i] = new Thread(()-> {//自增 10000 次
15                 for (int j = 0; j < 10000; j++) {
16                     race++;
17                 }
18             });
19             threads[i].start();
20         }
21         //等待所有线程执行完毕
22         for(int i = 0; i < THREADS_COUNT; i++){
23             try {
24                 threads[i].join();
25             } catch (InterruptedException e) {
26                 e.printStackTrace();
27             }
28         }
29 
30         System.out.println(race);
31     }
32     /*
33     javap -v VolatileTest.class
34     使用 javap 工具生成字节码指令信息，发现自增操作对应多条字节码指令，一条字节码至少对应一条机器指令，所以自增对应多条机器指令。
35     更严谨的说法应该验证自增操作和汇编指令间的对应关系。可以使用 PrintAssembly 工具生成对应汇编指令。
36     public static void increase();
37     descriptor: ()V
38     flags: ACC_PUBLIC,ACC_STATIC
39     Code:
40       stack=2,locals=0,args_size=0
41          0: getstatic     #2                  // Field race:I
42          3: iconst_1
43          4: iadd
44          5: putstatic     #2                  // Field race:I
45     */
46 }

 1 package com.mozq.multithread;
 2 
 3 import java.util.concurrent.BlockingQueue;
 4 import java.util.concurrent.LinkedBlockingQueue;
 5 import java.util.concurrent.atomic.AtomicReference;
 6 import java.util.concurrent.locks.LockSupport;
 7 // CAS自定义锁及模拟高并发测试 https://blog.csdn.net/LiuRenyou/article/details/92996001#CountDownLatch_54
 8 public class ExclusiveLock {
 9     AtomicReference<Thread> sign = new AtomicReference();
10     BlockingQueue<Thread> waiter = new LinkedBlockingQueue();
11 
12     public  void lock(){
13         Thread thread = Thread.currentThread();
14         while(!sign.compareAndSet(null,thread)){
15             waiter.add(thread);
16             //这里不可以用wait notify，因为notify不能唤醒指定的线程，只能用LockSupport
17             LockSupport.park();
18             waiter.remove(thread);
19         }
20     }
21 
22     public void unlock(){
23         if(sign.compareAndSet(Thread.currentThread(),null)){
24             Object[] arrs = waiter.toArray();
25             for (Object obj:arrs) {
26                 LockSupport.unpark((Thread)obj);
27             }
28         }
29     }
30 }