/*
* Copyright 2008-2009 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package net.hasor.rsf.address.route.flowcontrol.speed;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.concurrent.atomic.AtomicInteger;
/**
* 描述：线程安全的令牌桶限流器，时间窗刷新误差为毫秒级。 定义有效的限流器需要满足：
* <ol>
* <li>速率rate > 0，单位为次数/秒
* <li>时间窗timeWindow >= 1，单位为毫秒
* <li>峰值peak >= rate * timeWindow / 1000.0
* </ol>
*/
public class QoSBucket {
protected Logger logger = LoggerFactory.getLogger(getClass());
private static final int DEFAULT_RATE = 50;
private static final int DEFAULT_PEAK = 100;
private static final int DEFAULT_TIMEWINDOW = 1000;
private int rate; // 稳态中，每秒允许的调用次数
private int peak; // 突发调用峰值的上限，即令牌桶容量
private int timeWindow; // 令牌桶刷新最小间隔，单位毫秒
private AtomicInteger tokens; // 当前可用令牌数量
private volatile long lastRefreshTime; // 下一次刷新令牌桶的时间
private volatile double leftDouble;
//
//
public QoSBucket() {
this(DEFAULT_RATE, DEFAULT_PEAK, DEFAULT_TIMEWINDOW);
}
public QoSBucket(int rate, int peak, int timeWindow) {
this.rate = rate;
this.peak = peak;
this.timeWindow = timeWindow;
double initialToken = rate * timeWindow / 1000d;
//初始的token为零不合理， 改为1。
this.tokens = initialToken >= 1 ? new AtomicInteger((int) initialToken) : new AtomicInteger(1);
//增加此保存值，是为了double转int时候的不精确；如果不累及这个误差，累计的接过会非常大。
this.leftDouble = initialToken - Math.floor(initialToken);
this.lastRefreshTime = System.currentTimeMillis();
}
/** 检查令牌前，首先更新令牌数量 */
public boolean check() {
long now = System.currentTimeMillis();
if (now > lastRefreshTime + timeWindow) {// 尝试更新令牌数量
int currentValue = tokens.get();
double interval = (now - lastRefreshTime) / 1000d;
double addedDouble = interval * rate;
int added = (int) addedDouble; // 最大值为Integer.MAX_VALUE
if (added > 0) {
double addedPlusDouble = leftDouble + (addedDouble - added);
int addPlus = (int) addedPlusDouble;
added += addPlus;
int newValue = currentValue + added;
newValue = (newValue > currentValue && newValue < peak) ? newValue : peak;
if (tokens.compareAndSet(currentValue, newValue)) {
lastRefreshTime = now;// 更新成功后，设置新的刷新时间
leftDouble = addedPlusDouble - addPlus;
if (logger.isDebugEnabled()) {
logger.debug("[QoSBucket] Updated done: [{}] -> [{}], refresh time: {}.", currentValue, newValue, now);
}
}
}
}
int value = tokens.get();// 尝试获得一个令牌
boolean flag = false; // 是否获得到一个令牌
while (value > 0 && !flag) {
flag = tokens.compareAndSet(value, value - 1);
value = tokens.get();
}
if (logger.isDebugEnabled() && !flag) {
logger.debug("QoSBucket: get token failed, tokens[" + tokens.get() + "]");
}
return flag;
}
@Override
public String toString() {
return "QoSBucket [tokens=" + tokens + ", rate=" + rate + ", peak=" + peak + ", timeWindow=" + timeWindow + "]";
}
/**
* 限流器有效性验证。限流器的配置必须满足以下条件：
* <ol>
* <li>速率rate、峰值peak配置为大于0
* <li>时间窗timeWindow不小于1
* <li>峰值不小于速率与时间窗的乘积
* </ol>
* @return true/false
*/
public boolean validate() {
if (rate <= 0 || peak <= 0 || timeWindow < 1) {
return false;
}
if (peak < (rate * timeWindow / 1000F)) {
return false;
}
return true;
}
}