Java限流策略

﹏ヽ暗。殇╰゛Y 2022-05-28 07:29 205阅读 0赞

## 概要 ##

在大数据量高并发访问时，经常会出现服务或接口面对暴涨的请求而不可用的情况，甚至引发连锁反映导致整个系统崩溃。此时你需要使用的技术手段之一就是限流，当请求达到一定的并发数或速率，就进行等待、排队、降级、拒绝服务等。在限流时，常见的两种算法是漏桶和令牌桶算法算法。

## 限流算法 ##

令牌桶(Token Bucket)、漏桶(leaky bucket)和计数器算法是最常用的三种限流的算法。

### 1. 令牌桶算法 ###

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令牌桶算法的原理是系统会以一个恒定的速度往桶里放入令牌，而如果请求需要被处理，则需要先从桶里获取一个令牌，当桶里没有令牌可取时，则拒绝服务。 当桶满时，新添加的令牌被丢弃或拒绝。

#### 令牌桶算法示例 ####

Guava RateLimiter 提供了令牌桶算法可用于平滑突发限流策略。  
该示例为每秒中产生5个令牌，每200毫秒会产生一个令牌。  
limiter.acquire() 表示消费一个令牌。当桶中有足够的令牌时，则直接返回0，否则阻塞，直到有可用的令牌数才返回，返回的值为阻塞的时间。

### 2. 漏桶算法 ###

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它的主要目的是控制数据注入到网络的速率，平滑网络上的突发流量，数据可以以任意速度流入到漏桶中。漏桶算法提供了一种机制，通过它，突发流量可以被整形以便为网络提供一个稳定的流量。 漏桶可以看作是一个带有常量服务时间的单服务器队列，如果漏桶为空，则不需要流出水滴，如果漏桶（包缓存）溢出，那么水滴会被溢出丢弃。

### 3. 计数器限流算法 ###

计数器限流算法也是比较常用的，主要用来限制总并发数，比如数据库连接池大小、线程池大小、程序访问并发数等都是使用计数器算法。

#### 使用计数器限流示例1 ####

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      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">try</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">{ </code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,130,0);">//处理核心逻辑</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">TimeUnit.SECONDS.sleep(</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,153,0);">1</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">);</code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println(</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:#0000FF;">"--"</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">+System.currentTimeMillis()/</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,153,0);">1000</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">);</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">catch</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">(InterruptedException e) { </code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">e.printStackTrace();</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">finally</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">{ </code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">count.decrementAndGet();</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

使用AomicInteger来进行统计当前正在并发执行的次数，如果超过域值就简单粗暴的直接响应给用户，说明系统繁忙，请稍后再试或其它跟业务相关的信息。

> 弊端：使用 AomicInteger 简单粗暴超过域值就拒绝请求，可能只是瞬时的请求量高，也会拒绝请求。

#### 使用计数器限流示例2 ####

<table style="border:1px solid #C0C0C0;width:1017px;background:none;float:none;height:auto;line-height:1.1em;margin:0px;padding:0px;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
 <tbody style="background:none;float:none;height:auto;line-height:1.1em;margin:0px;padding:0px;vertical-align:baseline;width:auto;min-height:auto;"> 
  <tr style="background:none;border-top:0px;float:none;height:auto;line-height:1.1em;margin:0px;padding:0px;vertical-align:baseline;width:auto;min-height:auto;"> 
   <td style="border-color:#C0C0C0;padding:3px;border-collapse:collapse;font-size:12px;background:none;float:none;height:auto;line-height:1.1em;margin:0px;vertical-align:baseline;width:35px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(175,175,175);"> 
    <div style="background:rgb(244,244,244) none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      1 
    </div> 
    <div style="background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      2 
    </div> 
    <div style="background:rgb(244,244,244) none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      3 
    </div> 
    <div style="background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      4 
    </div> 
    <div style="background:rgb(244,244,244) none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      5 
    </div> 
    <div style="background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      6 
    </div> 
    <div style="background:rgb(244,244,244) none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      7 
    </div> 
    <div style="background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      8 
    </div> 
    <div style="background:rgb(244,244,244) none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      9 
    </div> 
    <div style="background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      10 
    </div> 
    <div style="background:rgb(244,244,244) none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      11 
    </div> 
    <div style="background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      12 
    </div> 
    <div style="background:rgb(244,244,244) none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      13 
    </div> 
    <div style="background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      14 
    </div> 
    <div style="background:rgb(244,244,244) none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      15 
    </div> 
    <div style="background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      16 
    </div> 
    <div style="background:rgb(244,244,244) none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      17 
    </div> 
    <div style="background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      18 
    </div> 
    <div style="background:rgb(244,244,244) none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      19 
    </div> 
    <div style="background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;height:auto;line-height:1.8em;margin:0px;padding:0px .5em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
      20 
    </div></td> 
   <td style="border-color:#C0C0C0;padding:3px;border-collapse:collapse;font-size:12px;background:none;float:none;height:auto;line-height:1.1em;margin:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;"> 
    <div style="background:none;border:0px;float:none;height:auto;line-height:1.1em;margin:0px;padding:0px;vertical-align:baseline;width:auto;min-height:auto;"> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">class</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">CountRateLimiterDemo2 { </code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
       &nbsp; 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">private</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">static</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">Semaphore semphore =&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">new</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">Semaphore(</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,153,0);">5</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">);</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;">
       &nbsp; 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">static</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">void</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">exec() { </code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">if</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">(semphore.getQueueLength()&gt;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,153,0);">100</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">){ </code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println(</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:#0000FF;">"当前等待排队的任务数大于100，请稍候再试..."</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">);</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">try</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">{ </code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">semphore.acquire();</code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,130,0);">// 处理核心逻辑</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">TimeUnit.SECONDS.sleep(</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,153,0);">1</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">);</code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println(</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:#0000FF;">"--"</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">+ System.currentTimeMillis() /&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,153,0);">1000</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">);</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">catch</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">(InterruptedException e) { </code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">e.printStackTrace();</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">finally</code>&nbsp; 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">{ </code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">semphore.release();</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background:rgb(244,244,244) none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background-image:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px 1em;vertical-align:baseline;width:auto;min-height:auto;white-space:nowrap;"> 
      <code style="background:none;border:0px;float:none;height:auto;line-height:1.8em;margin:0px;padding:0px;vertical-align:baseline;width:auto;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

使用Semaphore信号量来控制并发执行的次数，如果超过域值信号量，则进入阻塞队列中排队等待获取信号量进行执行。如果阻塞队列中排队的请求过多超出系统处理能力，则可以在拒绝请求。

> 相对Atomic优点：如果是瞬时的高并发，可以使请求在阻塞队列中排队，而不是马上拒绝请求，从而达到一个流量削峰的目的。

[1240]: /images/20220528/4880b6c3a78e4d7f9cc3c51a1557b75d.png
[1240 1]: /images/20220528/3512d43f80424aee8608a967873dcb5d.png