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feat: 限流算法示例
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‎codes/java-distributed/java-rate-limit/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>io.github.dunwu.javatech</groupId>
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<artifactId>java-rate-limit</artifactId>
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<version>1.0.0</version>
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<packaging>jar</packaging>
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<name>${project.artifactId}</name>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<java.version>1.8</java.version>
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<maven.compiler.source>${java.version}</maven.compiler.source>
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<maven.compiler.target>${java.version}</maven.compiler.target>
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</properties>
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<dependencies>
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<dependency>
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<groupId>cn.hutool</groupId>
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<artifactId>hutool-all</artifactId>
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<version>5.8.25</version>
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</dependency>
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<dependency>
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<groupId>org.projectlombok</groupId>
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<artifactId>lombok</artifactId>
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<version>1.18.30</version>
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</dependency>
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<dependency>
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<groupId>ch.qos.logback</groupId>
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<artifactId>logback-classic</artifactId>
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<version>1.2.3</version>
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<optional>true</optional>
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</dependency>
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</dependencies>
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</project>

‎codes/java-distributed/java-rate-limit/src/main/java/io/github/dunwu/distributed/ratelimit/FixedWindowRateLimiter.java‎

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package io.github.dunwu.distributed.ratelimit;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicLong;
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/**
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* 固定时间窗口限流算法
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*
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* @author <a href="mailto:[email protected]">Zhang Peng</a>
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* @date 2024-01-18
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*/
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public class FixedWindowRateLimiter implements RateLimiter {
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/**
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* 允许的最大请求数
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*/
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private final long maxPermits;
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/**
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* 窗口期时长
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*/
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private final long periodMillis;
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/**
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* 窗口期截止时间
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*/
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private long lastPeriodMillis;
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/**
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* 请求计数
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*/
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private AtomicLong count = new AtomicLong(0);
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public FixedWindowRateLimiter(long qps) {
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this(qps, 1000, TimeUnit.MILLISECONDS);
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}
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public FixedWindowRateLimiter(long maxPermits, long period, TimeUnit timeUnit) {
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this.maxPermits = maxPermits;
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this.periodMillis = timeUnit.toMillis(period);
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this.lastPeriodMillis = System.currentTimeMillis() + this.periodMillis;
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}
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@Override
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public synchronized boolean tryAcquire(int permits) {
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long now = System.currentTimeMillis();
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if (lastPeriodMillis <= now) {
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this.lastPeriodMillis = now + this.periodMillis;
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count = new AtomicLong(0);
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}
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if (count.get() + permits <= maxPermits) {
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count.addAndGet(permits);
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return true;
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} else {
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return false;
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}
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}
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}

‎codes/java-distributed/java-rate-limit/src/main/java/io/github/dunwu/distributed/ratelimit/LeakyBucketRateLimiter.java‎

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package io.github.dunwu.distributed.ratelimit;
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import java.util.concurrent.atomic.AtomicLong;
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/**
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* 漏桶限流算法
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*
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* @author <a href="mailto:[email protected]">Zhang Peng</a>
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* @date 2024-01-18
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*/
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public class LeakyBucketRateLimiter implements RateLimiter {
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/**
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* QPS
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*/
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private final int qps;
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/**
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* 桶的容量
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*/
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private final long capacity;
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/**
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* 计算的起始时间
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*/
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private long beginTimeMillis;
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/**
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* 桶中当前的水量
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*/
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private final AtomicLong waterNum = new AtomicLong(0);
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public LeakyBucketRateLimiter(int qps, int capacity) {
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this.qps = qps;
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this.capacity = capacity;
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}
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@Override
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public synchronized boolean tryAcquire(int permits) {
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// 如果桶中没有水，直接放行
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if (waterNum.get() == 0) {
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beginTimeMillis = System.currentTimeMillis();
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waterNum.addAndGet(permits);
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return true;
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}
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// 计算水量
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long leakedWaterNum = ((System.currentTimeMillis() - beginTimeMillis) / 1000) * qps;
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long currentWaterNum = waterNum.get() - leakedWaterNum;
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waterNum.set(Math.max(0, currentWaterNum));
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// 重置时间
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beginTimeMillis = System.currentTimeMillis();
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if (waterNum.get() + permits < capacity) {
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waterNum.addAndGet(permits);
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return true;
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} else {
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return false;
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}
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}
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}

‎codes/java-distributed/java-rate-limit/src/main/java/io/github/dunwu/distributed/ratelimit/RateLimiter.java‎

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package io.github.dunwu.distributed.ratelimit;
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/**
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* 限流器
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*
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* @author <a href="mailto:[email protected]">Zhang Peng</a>
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* @date 2024-01-18
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*/
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public interface RateLimiter {
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boolean tryAcquire(int permits);
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}

‎codes/java-distributed/java-rate-limit/src/main/java/io/github/dunwu/distributed/ratelimit/RateLimiterDemo.java‎

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package io.github.dunwu.distributed.ratelimit;
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import cn.hutool.core.thread.ThreadUtil;
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import cn.hutool.core.util.RandomUtil;
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import lombok.extern.slf4j.Slf4j;
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import java.util.concurrent.CountDownLatch;
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import java.util.concurrent.ExecutorService;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicInteger;
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/**
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* 限流器示例
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*
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* @author <a href="mailto:[email protected]">Zhang Peng</a>
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* @date 2024-01-18
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*/
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@Slf4j
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public class RateLimiterDemo {
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public static void main(String[] args) {
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// ============================================================================
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int qps = 20;
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System.out.println("======================= 固定时间窗口限流算法 =======================");
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FixedWindowRateLimiter fixedWindowRateLimiter = new FixedWindowRateLimiter(qps);
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testRateLimit(fixedWindowRateLimiter, qps);
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System.out.println("======================= 滑动时间窗口限流算法 =======================");
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SlidingWindowRateLimiter slidingWindowRateLimiter = new SlidingWindowRateLimiter(qps, 10);
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testRateLimit(slidingWindowRateLimiter, qps);
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System.out.println("======================= 漏桶限流算法 =======================");
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LeakyBucketRateLimiter leakyBucketRateLimiter = new LeakyBucketRateLimiter(qps, 100);
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testRateLimit(leakyBucketRateLimiter, qps);
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System.out.println("======================= 令牌桶限流算法 =======================");
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TokenBucketRateLimiter tokenBucketRateLimiter = new TokenBucketRateLimiter(qps, 100);
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testRateLimit(tokenBucketRateLimiter, qps);
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}
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private static void testRateLimit(RateLimiter rateLimiter, int qps) {
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AtomicInteger okNum = new AtomicInteger(0);
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AtomicInteger limitNum = new AtomicInteger(0);
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ExecutorService executorService = ThreadUtil.newFixedExecutor(10, "限流测试", true);
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long beginTime = System.currentTimeMillis();
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int threadNum = 4;
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final CountDownLatch latch = new CountDownLatch(threadNum);
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for (int i = 0; i < threadNum; i++) {
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executorService.submit(() -> {
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try {
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batchRequest(rateLimiter, okNum, limitNum, 1000);
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} catch (Exception e) {
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log.error("发生异常!", e);
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} finally {
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latch.countDown();
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}
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});
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}
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try {
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latch.await(10, TimeUnit.SECONDS);
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long endTime = System.currentTimeMillis();
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long gap = endTime - beginTime;
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log.info("限流 QPS: {} -> 实际结果：耗时 {} ms，{} 次请求成功，{} 次请求被限流，实际 QPS: {}",
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qps, gap, okNum.get(), limitNum.get(), okNum.get() * 1000 / gap);
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if (okNum.get() == qps) {
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log.info("限流符合预期");
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}
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} catch (Exception e) {
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log.error("发生异常!", e);
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} finally {
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executorService.shutdown();
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}
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}
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private static void batchRequest(RateLimiter rateLimiter, AtomicInteger okNum, AtomicInteger limitNum, int num)
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throws InterruptedException {
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for (int j = 0; j < num; j++) {
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if (rateLimiter.tryAcquire(1)) {
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log.info("请求成功");
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okNum.getAndIncrement();
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} else {
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log.info("请求限流");
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limitNum.getAndIncrement();
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}
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TimeUnit.MILLISECONDS.sleep(RandomUtil.randomInt(0, 10));
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}
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}
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}

‎codes/java-distributed/java-rate-limit/src/main/java/io/github/dunwu/distributed/ratelimit/SlidingWindowRateLimiter.java‎

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package io.github.dunwu.distributed.ratelimit;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicLong;
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/**
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* 滑动时间窗口限流算法
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*
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* @author <a href="mailto:[email protected]">Zhang Peng</a>
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* @date 2024-01-18
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*/
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public class SlidingWindowRateLimiter implements RateLimiter {
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/**
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* 允许的最大请求数
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*/
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private final long maxPermits;
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/**
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* 窗口期时长
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*/
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private final long periodMillis;
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/**
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* 分片窗口期时长
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*/
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private final long shardPeriodMillis;
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/**
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* 窗口期截止时间
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*/
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private long lastPeriodMillis;
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/**
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* 分片窗口数
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*/
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private final int shardNum;
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/**
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* 请求总计数
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*/
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private final AtomicLong totalCount = new AtomicLong(0);
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/**
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* 分片窗口计数列表
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*/
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private final List<AtomicLong> countList = new LinkedList<>();
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public SlidingWindowRateLimiter(long qps, int shardNum) {
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this(qps, 1000, TimeUnit.MILLISECONDS, shardNum);
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}
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public SlidingWindowRateLimiter(long maxPermits, long period, TimeUnit timeUnit, int shardNum) {
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this.maxPermits = maxPermits;
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this.periodMillis = timeUnit.toMillis(period);
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this.lastPeriodMillis = System.currentTimeMillis();
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this.shardPeriodMillis = timeUnit.toMillis(period) / shardNum;
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this.shardNum = shardNum;
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for (int i = 0; i < shardNum; i++) {
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countList.add(new AtomicLong(0));
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}
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}
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@Override
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public synchronized boolean tryAcquire(int permits) {
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long now = System.currentTimeMillis();
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if (now > lastPeriodMillis) {
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for (int shardId = 0; shardId < shardNum; shardId++) {
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long shardCount = countList.get(shardId).get();
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totalCount.addAndGet(-shardCount);
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countList.set(shardId, new AtomicLong(0));
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lastPeriodMillis += shardPeriodMillis;
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}
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}
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int shardId = (int) (now % periodMillis / shardPeriodMillis);
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if (totalCount.get() + permits <= maxPermits) {
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countList.get(shardId).addAndGet(permits);
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totalCount.addAndGet(permits);
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return true;
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} else {
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return false;
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}
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}
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}

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