java – Guava Ratelimiter tryAcquire仅对第一次调用(任意数量的许可)返回true？

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

输出是：

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

将许可证数量指定为12：

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

输出是：

: 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？

// 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());

输出是：

Acquired one true
Acquired two true

来自番石榴文档：

The returned RateLimiter ensures that on average no more than
permitsPerSecond are issued during any given second, with sustained
requests being smoothly spread over each second.

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());

输出是：

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,这就是为什么示例中的lt.tryAcquire()返回false.