Question

我正在使用Guava 18.0 RateLimiter：

public static void simpleTst() throws Exception{
    RateLimiter lt = RateLimiter.create(2);
    _log.info("Acquired one " + lt.tryAcquire());
    _log.info("Acquired two " + lt.tryAcquire());
}

输出结果为：

: 08 16:22:10 PST.INFO1*RateLimiterTst~simpleTst@37: Acquired one true
: 08 16:22:10 PST.INFO1*RateLimiterTst~simpleTst@38: Acquired two false

指定12的许可数量：

public static void simpleTst() throws Exception{
    RateLimiter lt = RateLimiter.create(2);
    _log.info("Acquired one " + lt.tryAcquire(12));
    _log.info("Acquired two " + lt.tryAcquire());
}

输出结果为：

: 08 16:22:36 PST.INFO1*RateLimiterTst~simpleTst@37: Acquired one true
: 08 16:22:36 PST.INFO1*RateLimiterTst~simpleTst@38: Acquired two false

为什么会这样？

Answer 1

第一个例子的行为是预期的，因为：

// we request 2 permit per seconds
RateLimiter lt = RateLimiter.create(2);
_log.info("Acquired one " + lt.tryAcquire());

// waiting 1/2 second we will be able to get the second permit
Thread.sleep(500);
_log.info("Acquired two " + lt.tryAcquire());

输出结果为：

Acquired one true
Acquired two true

来自番石榴文档：

返回的RateLimiter确保平均不超过 permitPerSecond在任何给定的秒内发出，持续请求平稳分布在每一秒。

第二个例子的行为也是预期的，因为要成功获得第二个“获取”的单一许可我们需要等待大约6秒（= 12/2）

// we request 2 permit per seconds
RateLimiter lt = RateLimiter.create(2);

// trying to acquire 12 permits
_log.info("Acquired one " + lt.tryAcquire(12));

// waiting 12 / 2 seconds in order to be able to get the second permit
Thread.sleep(6000);
_log.info("Acquired two " + lt.tryAcquire());

输出结果为：

Acquired one true
Acquired two true

尝试获取等待时间少于6秒的最后一个许可证将失败，这就是示例中lt.tryAcquire()返回false的原因。

Answer 2

如果您将应用程序睡眠1毫秒，它将返回true和true。

番石榴Ratelimiter tryAcquire仅对第一次调用（任意数量的许可）返回true？

2 个答案: