Question

我遇到了番石榴RateLimiter的问题。我使用RateLimiter.create（1.0）创建RateLimiter（“每秒1次允许”）并在每个周期调用rateLimiter.acquire（），但是当我测试运行时，我得到以下结果：

Average: 1232.0 Diff since last: 2540
Average: 1180.0 Diff since last: 258
Average: 1159.0 Diff since last: 746
Average: 1151.0 Diff since last: 997
Average: 1144.0 Diff since last: 1004

平均值是它平均睡眠的毫秒数，diff是自上次打印以来经过的毫秒数。平均而言没关系，它不允许我的代码每秒运行超过一次。但有时（正如你所看到的）它每秒运行不止一次。

你知道为什么吗？我错过了什么吗？

生成上述输出的代码：

private  int numberOfRequests;
private Date start;
private long last;
private boolean first = true;
private void sleep() {
    numberOfRequests++;
    if(first) {
        first = false;
        start = new Date();
    }

    rateLimiter.acquire();

    long current = new Date().getTime();
    double num = (current -start.getTime()) / numberOfRequests;
    System.out.println("Average: "+ num + " Diff since last: " + (current - last));
    last = current;
}

Answer 1

您的基准测试似乎存在缺陷 - 当我尝试复制它时，我发现非常接近每秒一次采集。这是我的基准：

public class RateLimiterDemo {
  public static void main(String[] args) {
    StatsAccumulator stats = new StatsAccumulator();
    RateLimiter rateLimiter = RateLimiter.create(1.0);
    rateLimiter.acquire(); // discard initial permit
    for (int i = 0; i < 10; i++) {
      long start = System.nanoTime();
      rateLimiter.acquire();
      stats.add((System.nanoTime() - start) / 1_000_000.0);
    }
    System.out.println(stats.snapshot());
  }
}

示例运行打印：

Stats{count=10, mean=998.9071456, populationStandardDeviation=3.25398397901304, min=989.303887, max=1000.971085}

差异几乎全部归因于基准开销（填充StatsAccumulator并计算时间增量）。

即使这个基准也存在缺陷（尽管我认为它不那么严重）。创建accurate benchmark 非常难，而简单的基准测试基准测试通常要么不准确，要么更糟糕，不能反映在生产环境中测试的代码的实际性能。 / p>

番石榴RateLimiter经常运行

1 个答案: