5 还有网站的域,哪有深圳网站页面设计,济南建设工程信息网,wordpress做的网站缓存缓存行#xff1a;缓存行越大#xff0c;局部性空间效率越高#xff0c;但读取时间慢缓存行越小#xff0c;局部性空间效率越低#xff0c;但读取时间快取一个折中值#xff0c;目前多用#xff1a;64字节public class CacheLinePadding { //执行时间在4s左右public…缓存缓存行缓存行越大局部性空间效率越高但读取时间慢缓存行越小局部性空间效率越低但读取时间快取一个折中值目前多用64字节public class CacheLinePadding { //执行时间在4s左右public volatile static long[] arrnew long[2];public static void main(String[] args) throws Exception{Thread t1new Thread(()-{for (long i0;i 10_0000_0000L;i){arr[0]i;}});Thread t2new Thread(()-{for (long i0;i 10_0000_0000L;i){arr[1]i;}});t1.start();t2.start();final long start System.nanoTime();t1.join();t2.join();final long end System.nanoTime();System.out.println((end-start)/1000000);}}public class T02_CacheLinePadding { //执行在2s左右public volatile static long[] arrnew long[16];public static void main(String[] args) throws Exception{Thread t1new Thread(()-{for (long i0;i 10_0000_0000L;i){arr[0]i;}});Thread t2new Thread(()-{for (long i0;i 10_0000_0000L;i){arr[8]i;}});t1.start();t2.start();final long start System.nanoTime();t1.join();t2.join();final long end System.nanoTime();System.out.println((end-start)/1000000);}}缓存行对齐对于有些特别敏感的数字会存在线程高竞争的访问为了保证不发生伪共享可以使用缓存航对齐的编程方式JDK7中很多采用long padding提高效率eg:JDK8加入了Contended注解(实验)需要加上JVM -XX:-RestrictContendedpublic class T03_CacheLinePading {Contendedvolatile long x;Contendedvolatile long y;public static void main(String[] args) throws Exception{ //0.6sT03_CacheLinePading t3new T03_CacheLinePading();Thread t1new Thread(()-{for (long i0;i 1_0000_0000L;i){t3.xi;}});Thread t2new Thread(()-{for (long i0;i 1_0000_0000L;i){t3.yi;}});t1.start();t2.start();final long start System.nanoTime();t1.join();t2.join();final long end System.nanoTime();System.out.println((end-start)/1000000);}}乱序执行/*** CPU的乱序执行*/public class DisorderTest {private static int x0,y0;private static int a0,b0;//第44448次 (0,0)public static void main(String[] args) throws InterruptedException {int i 0;for (; ; ) {i;x 0;y 0;a 0;b 0;Thread one new Thread(new Runnable() {public void run() {//由于线程one先启动下面这句话让它等一等线程two. 读着可根据自己电脑的实际性能适当调整等待时间.shortWait(100000);a 1;x b;}});Thread other new Thread(new Runnable() {public void run() {b 1;y a;}});one.start();other.start();one.join();other.join();String result 第 i 次( x , y );if (x 0 y 0) {System.err.println(result);break;} else {//System.out.println(result);}}}public static void shortWait(long interval){long start System.nanoTime();long end;do{end System.nanoTime();}while(start interval end);}}禁止乱序CPU层面Intel - 原语(mfence lfence sfence) 或者锁总线JVM层级8个hanppens-before原则 4个内存屏障 (LL LS SL SS)as-if-serial : 不管硬件什么顺序单线程执行的结果不变看上去像是serial合并写Write Combining Buffer一般是4个字节由于ALU速度太快所以在写入L1的同时写入一个WC Buffer满了之后再直接更新到L2
