《 面试又翻车了》这次竟然和 Random 有关？（下）

/**
 * 源码版本：JDK 11
 */
public int nextInt(int bound) {
    if (bound <= 0)
        throw new IllegalArgumentException(BAD_BOUND);
    // 根据老种子生成新种子
    int r = mix32(nextSeed());
    int m = bound - 1;
    // 根据新种子计算算出随机数
    if ((bound & m) == 0) // power of two
        r &= m;
    else { // reject over-represented candidates
        for (int u = r >>> 1;
             u + m - (r = u % bound) < 0;
             u = mix32(nextSeed()) >>> 1)
            ;
    }
    return r;
}

/**
 * 源码版本：JDK 11
 */
final long nextSeed() {
    Thread t; long r; // read and update per-thread seed
    // 把当前线程作为参数生成一个新种子
    U.putLong(t = Thread.currentThread(), SEED,
              r = U.getLong(t, SEED) + GAMMA);
    return r;
}
@HotSpotIntrinsicCandidate
public native void putLong(Object o, long offset, long x);

// 声明多线程
ExecutorService service = Executors.newCachedThreadPool();
// 共享 ThreadLocalRandom
ThreadLocalRandom threadLocalRandom = ThreadLocalRandom.current();
for (int i = 0; i < 10; i++) {
    // 多线程执行随机数并打印结果
    service.submit(() -> {
        System.out.println(Thread.currentThread().getName() + ":" + threadLocalRandom.nextInt(10));
        ;
    });
}

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
/**
 * JDK：11
 * Windows 10 I5-4460/16G
 */
@BenchmarkMode(Mode.Throughput) // 测试类型：吞吐量
//@Threads(16)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
public class RandomExample {
    public static void main(String[] args) throws RunnerException {
        // 启动基准测试
        Options opt = new OptionsBuilder()
                .include(RandomExample.class.getSimpleName()) // 要导入的测试类
                .warmupIterations(5) // 预热 5 轮
                .measurementIterations(10) // 度量10轮
                .forks(1)
                .build();
        new Runner(opt).run(); // 执行测试
    }
    /**
     * Random 性能测试
     */
    @Benchmark
    public void randomTest() {
        Random random = new Random();
        for (int i = 0; i < 10; i++) {
            // 生成 0-9 的随机数
            random.nextInt(10);
        }
    }
    /**
     * ThreadLocalRandom 性能测试
     */
    @Benchmark
    public void threadLocalRandomTest() {
        ThreadLocalRandom threadLocalRandom = ThreadLocalRandom.current();
        for (int i = 0; i < 10; i++) {
            threadLocalRandom.nextInt(10);
        }
    }
}