Java线程安全 关于原子性与volatile的试验
Posted
tags:
篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了Java线程安全 关于原子性与volatile的试验相关的知识,希望对你有一定的参考价值。
1. 变量递增试验
1 static /*volatile*/ int shared=0;//volatile也无法保证++操作的原子性 2 static synchronized int incrShared(){//不加synchronized的话,shared最终结果值小于预期 3 return ++shared; 4 } 5 public static void testIncrShared(String[] args) throws InterruptedException { 6 shared=0; 7 Thread[] thrds = new Thread[20]; 8 for(int j=0;j<thrds.length;j++){ 9 thrds[j] = new Thread(new Runnable() { 10 @Override 11 public void run() { 12 for(int k=0;k<1000;k++){ 13 System.out.println(incrShared()); 14 } 15 } 16 }); 17 } 18 for(int j=0;j<thrds.length;j++){ 19 thrds[j].start(); 20 } 21 for(int j=0;j<thrds.length;j++){ 22 thrds[j].join(); 23 } 24 System.out.println(shared); 25 }
2. volatile试验
1 static /*volatile*/ int a0,a1;//这里加volatile的话,可以避免r0==r1==0的结果 2 static /*volatile*/ int r0,r1;//这里即使加volatile,也无法避免r0==r1==0的结果 3 public static void testVolatile(String[] args) throws InterruptedException { 4 int[] a=new int[2]; 5 int[] r=new int[2]; 6 final int SLEEP=10; 7 final Object lock=new Object(); 8 Runnable run1=new Runnable() { 9 @Override 10 public void run() { 11 try { 12 Thread.sleep(SLEEP); 13 } catch (InterruptedException e) { 14 e.printStackTrace(); 15 } 16 //synchronized (lock) {//加锁也可以建立happens-before关系,避免r0==r1==0的结果 17 a0=1; 18 //} 19 r1=a1; 20 } 21 }; 22 Runnable run2=new Runnable() { 23 @Override 24 public void run() { 25 try { 26 Thread.sleep(SLEEP); 27 } catch (InterruptedException e) { 28 e.printStackTrace(); 29 } 30 //synchronized (lock) { 31 a1=1; 32 //} 33 r0=a0; 34 } 35 }; 36 Thread thrd1; 37 Thread thrd2; 38 39 int i; 40 int[][] acnt=new int[2][2]; 41 int[][] rcnt=new int[2][2]; 42 for(i=0;i<10000;i++){ 43 a0=a1=0; 44 r0=r1=0; 45 thrd1 = new Thread(run1); 46 thrd2 = new Thread(run2); 47 48 thrd1.start(); 49 thrd2.start(); 50 51 thrd1.join(); 52 thrd2.join(); 53 54 a[0]=a0; 55 a[1]=a1; 56 r[0]=r0; 57 r[1]=r1; 58 System.out.println(i); 59 System.out.println(Arrays.toString(a)); 60 System.out.println(Arrays.toString(r)); 61 acnt[a[0]][a[1]]++; 62 rcnt[r[0]][r[1]]++; 63 } 64 System.out.println(Arrays.deepToString(acnt)); 65 System.out.println(Arrays.deepToString(rcnt)); 66 }
3. volatile试验2
1 static boolean shouldStop=false; 2 public static void testVolatile2(String[] args) throws InterruptedException { 3 shouldStop=false; 4 Runnable run1=new Runnable() { 5 @Override 6 public void run() { 7 int i=0; 8 while (!shouldStop) {//无法读取到线程2修改后的shouldStop值,导致无限循环 9 i++; 10 //System.out.println(i);//如果调用其他函数的话,就又可以读取到shouldStop的最新值了 11 } 12 } 13 }; 14 Runnable run2=new Runnable() { 15 @Override 16 public void run() { 17 try { 18 Thread.sleep(10); 19 } catch (InterruptedException e) { 20 e.printStackTrace(); 21 } 22 shouldStop=true; 23 } 24 }; 25 Thread thrd1; 26 Thread thrd2; 27 28 int i; 29 int[][] acnt=new int[2][2]; 30 int[][] rcnt=new int[2][2]; 31 for(i=0;i<100;i++){ 32 thrd1 = new Thread(run1); 33 thrd2 = new Thread(run2); 34 35 thrd1.start(); 36 thrd2.start(); 37 38 thrd2.join(); 39 System.out.println(i); 40 System.out.println(shouldStop); 41 thrd1.join(); 42 43 } 44 }
以上是关于Java线程安全 关于原子性与volatile的试验的主要内容,如果未能解决你的问题,请参考以下文章