java.util.Random and concurrent.ThreadLocalRandom contrast

xindoo 2021-01-22 12:45:22
java.util.random java util random concurrent.threadlocalrandom

Recently, I met a demand in my work , We need to filter out part of the traffic with a certain probability , Think about it Random 了 , Because it's in a multithreaded environment , I also made it a point to confirm Random Whether multithreading can work normally ,Random The implementation of is also relatively simple , When initializing, use the current event to initialize a random number seed , And then each time you take a value, you use this seed with some MagicNumber operation , And update the seed . The core is this next Function of , Whether you call nextDouble still nextInt still nextBoolean,Random The bottom is all about this next(int bits).

 protected int next(int bits) {
long oldseed, nextseed;
AtomicLong seed = this.seed;
do {
oldseed = seed.get();
nextseed = (oldseed * multiplier + addend) & mask;
} while (!seed.compareAndSet(oldseed, nextseed));
return (int)(nextseed >>> (48 - bits));

In order to ensure that each generation of random number under multithreading is different ,next() Make sure that seed The update of is atomic operation , So use the AtomicLong Of compareAndSet(), This method calls the sum.misc.Unsafe Of compareAndSwapLong(), That's what people often hear CAS, This is a native Method , It can guarantee that the atom is updated by one number .

since Random Meet my needs , It can run normally under multithreading , So I used it directly random, Later on codeReview in , Colleagues put forward to use concurrent.ThreadLocalRandom To replace Random. I had a problem right in my head , since random It's thread safe , Why? concurrent There's another one in the package random. stay oracle Of jdk A sentence was found in the document

use of ThreadLocalRandom rather than shared Random objects in concurrent programs will typically encounter much less overhead and contention. Use of ThreadLocalRandom is particularly appropriate when multiple tasks (for example, each a ForkJoinTask) use random numbers in parallel in thread pools.

The main idea is to use ThreadLocalRandom More suitable for multithreading , It can greatly reduce the performance overhead and resource contention under multithreading . Since it's said in the document that it's awesome , How much performance improvement can there be ? I did a simple test . Test environment :24 nucleus CPU, jdk8, Each randomly generated 100000 individual double Count ,, Test under different number of threads respectively rando and ThreadLocalRandom Running time of , The data are as follows


ThreadLocalRandom Although there are fluctuations , But it's basically flat , and random As the number of threads increases, it keeps increasing , stay 1000 There is a hundred times performance gap between the two threads . But here's a phenomenon that people can't understand , Why? random It takes time to 500 It's a thread and it falls down , This has been the case many times , So it's not an accident .

I also tested it in my notebook , My laptop is dual core i7,ThreadLocalRandom and Random The biggest performance gap is 100 times , I found that my laptop runs faster than the company server ( The data are as follows ).... I'm on one, too 1 Core Alibaba cloud ECS I tested it. , According to the truth 1 The core technology , Even multithreading starts serially , but ThreadLocalRandom and Random stay 1000 In the case of two threads, there are also 6 Times the performance gap .

since ThreadLocalRandom In multithreading, it's so awesome , How on earth does it work ? Let's look at the source code , Its core code is this

 final long nextSeed() {
Thread t; long r; // read and update per-thread seed
UNSAFE.putLong(t = Thread.currentThread(), SEED,
r = UNSAFE.getLong(t, SEED) + GAMMA);
return r;

start ThreadLocalRandom Is to set a separate random number seed for each thread , In this way, there will be no resource contention when multiple threads update a number at the same time , Trade space for time . The last attached Random and ThreadLocalRandom Performance test code for

import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
public class RandomTest {
private static Random random = new Random();
private static final int N = 100000;
// Random from java.util.concurrent.
private static class TLRandom implements Runnable {
public void run() {
double x = 0;
for (int i = 0; i < N; i++) {
x += ThreadLocalRandom.current().nextDouble();
// Random from java.util
private static class URandom implements Runnable {
public void run() {
double x = 0;
for (int i = 0; i < N; i++) {
x += random.nextDouble();
public static void main(String[] args) {
for (int threadNum = 50; threadNum <= 2000; threadNum += 50) {
ExecutorService poolR = Executors.newFixedThreadPool(threadNum);
long RStartTime = System.currentTimeMillis();
for (int i = 0; i < threadNum; i++) {
poolR.execute(new URandom());
try {
poolR.awaitTermination(100, TimeUnit.SECONDS);
} catch (InterruptedException e) {
String str = "" + threadNum +"," + (System.currentTimeMillis() - RStartTime)+",";
ExecutorService poolTLR = Executors.newFixedThreadPool(threadNum);
long TLRStartTime = System.currentTimeMillis();
for (int i = 0; i < threadNum; i++) {
poolTLR.execute(new TLRandom());
try {
poolTLR.awaitTermination(100, TimeUnit.SECONDS);
} catch (InterruptedException e) {
System.out.println(str + (System.currentTimeMillis() - TLRStartTime));

Participation of this paper Tencent cloud media sharing plan , You are welcome to join us , share .


  1. 【计算机网络 12(1),尚学堂马士兵Java视频教程
  2. 【程序猿历程,史上最全的Java面试题集锦在这里
  3. 【程序猿历程(1),Javaweb视频教程百度云
  4. Notes on MySQL 45 lectures (1-7)
  5. [computer network 12 (1), Shang Xuetang Ma soldier java video tutorial
  6. The most complete collection of Java interview questions in history is here
  7. [process of program ape (1), JavaWeb video tutorial, baidu cloud
  8. Notes on MySQL 45 lectures (1-7)
  9. 精进 Spring Boot 03:Spring Boot 的配置文件和配置管理,以及用三种方式读取配置文件
  10. Refined spring boot 03: spring boot configuration files and configuration management, and reading configuration files in three ways
  11. 精进 Spring Boot 03:Spring Boot 的配置文件和配置管理,以及用三种方式读取配置文件
  12. Refined spring boot 03: spring boot configuration files and configuration management, and reading configuration files in three ways
  13. 【递归,Java传智播客笔记
  14. [recursion, Java intelligence podcast notes
  15. [adhere to painting for 386 days] the beginning of spring of 24 solar terms
  16. K8S系列第八篇(Service、EndPoints以及高可用kubeadm部署)
  17. K8s Series Part 8 (service, endpoints and high availability kubeadm deployment)
  18. 【重识 HTML (3),350道Java面试真题分享
  19. 【重识 HTML (2),Java并发编程必会的多线程你竟然还不会
  20. 【重识 HTML (1),二本Java小菜鸟4面字节跳动被秒成渣渣
  21. [re recognize HTML (3) and share 350 real Java interview questions
  22. [re recognize HTML (2). Multithreading is a must for Java Concurrent Programming. How dare you not
  23. [re recognize HTML (1), two Java rookies' 4-sided bytes beat and become slag in seconds
  24. 造轮子系列之RPC 1:如何从零开始开发RPC框架
  25. RPC 1: how to develop RPC framework from scratch
  26. 造轮子系列之RPC 1:如何从零开始开发RPC框架
  27. RPC 1: how to develop RPC framework from scratch
  28. 一次性捋清楚吧,对乱糟糟的,Spring事务扩展机制
  29. 一文彻底弄懂如何选择抽象类还是接口,连续四年百度Java岗必问面试题
  30. Redis常用命令
  31. 一双拖鞋引发的血案,狂神说Java系列笔记
  32. 一、mysql基础安装
  33. 一位程序员的独白:尽管我一生坎坷,Java框架面试基础
  34. Clear it all at once. For the messy, spring transaction extension mechanism
  35. A thorough understanding of how to choose abstract classes or interfaces, baidu Java post must ask interview questions for four consecutive years
  36. Redis common commands
  37. A pair of slippers triggered the murder, crazy God said java series notes
  38. 1、 MySQL basic installation
  39. Monologue of a programmer: despite my ups and downs in my life, Java framework is the foundation of interview
  40. 【大厂面试】三面三问Spring循环依赖,请一定要把这篇看完(建议收藏)
  41. 一线互联网企业中,springboot入门项目
  42. 一篇文带你入门SSM框架Spring开发,帮你快速拿Offer
  43. 【面试资料】Java全集、微服务、大数据、数据结构与算法、机器学习知识最全总结,283页pdf
  44. 【leetcode刷题】24.数组中重复的数字——Java版
  45. 【leetcode刷题】23.对称二叉树——Java版
  46. 【leetcode刷题】22.二叉树的中序遍历——Java版
  47. 【leetcode刷题】21.三数之和——Java版
  48. 【leetcode刷题】20.最长回文子串——Java版
  49. 【leetcode刷题】19.回文链表——Java版
  50. 【leetcode刷题】18.反转链表——Java版
  51. 【leetcode刷题】17.相交链表——Java&python版
  52. 【leetcode刷题】16.环形链表——Java版
  53. 【leetcode刷题】15.汉明距离——Java版
  54. 【leetcode刷题】14.找到所有数组中消失的数字——Java版
  55. 【leetcode刷题】13.比特位计数——Java版
  56. oracle控制用户权限命令
  57. 三年Java开发,继阿里,鲁班二期Java架构师
  58. Oracle必须要启动的服务
  59. 万字长文!深入剖析HashMap,Java基础笔试题大全带答案
  60. 一问Kafka就心慌?我却凭着这份,图灵学院vip课程百度云