Ribbon的RandomRule和RoundRobinRule 原
Ribbon的RandomRule和RoundRobinRule 原
克虏伯
发布于 2019-10-06 20:58:20
发布于 2019-10-06 20:58:20
Ribbon的版本是2.3.0.release.
１.RandomRule
图1
图1所示，RandomRule继承AbstractLoadBalancerRule，调用choose(Object)时，调用内部方法choose(ILoadBalancer lb, Object key)，如下List-1
List-1
public Server choose(ILoadBalancer lb, Object key) {
if (lb == null) {
return null;
} else {
Server server = null;
while(server == null) {
if (Thread.interrupted()) {
return null;
}
List<Server> upList = lb.getReachableServers();
List<Server> allList = lb.getAllServers();
int serverCount = allList.size();
if (serverCount == 0) {
return null;
}
int index = this.chooseRandomInt(serverCount);
server = (Server)upList.get(index);
if (server == null) {
Thread.yield();
} else {
if (server.isAlive()) {
return server;
}
server = null;
Thread.yield();
}
}
return server;
}
}
protected int chooseRandomInt(int serverCount) {
return ThreadLocalRandom.current().nextInt(serverCount);
}- 通过ILoadBalancer获取所有的服务，如果服务个数是０则直返回null
- 调用chooseRandomInt方法，参数是服务个数，这样返回的随机值是在0与服务数之间，有趣的是出于多线程安全的考虑，使用了java.util.concurrent.ThreadLocalRandom#current来获取随机值
- 如果服务是alive，则返回改服务
2.RoundRobinRule
图2
RoundRobinRule是轮循算法实现，choose(Object)方法会调用choose(ILoadBalancer lb, Object key)，如下List-2所示
List-2
private AtomicInteger nextServerCyclicCounter;
public RoundRobinRule() {
this.nextServerCyclicCounter = new AtomicInteger(0);
}
public RoundRobinRule(ILoadBalancer lb) {
this();
this.setLoadBalancer(lb);
}
public Server choose(ILoadBalancer lb, Object key) {
if (lb == null) {
log.warn("no load balancer");
return null;
} else {
Server server = null;
int count = 0;
while(true) {
if (server == null && count++ < 10) {
List<Server> reachableServers = lb.getReachableServers();
List<Server> allServers = lb.getAllServers();
int upCount = reachableServers.size();
int serverCount = allServers.size();
if (upCount != 0 && serverCount != 0) {
int nextServerIndex = this.incrementAndGetModulo(serverCount);
server = (Server)allServers.get(nextServerIndex);
if (server == null) {
Thread.yield();
} else {
if (server.isAlive() && server.isReadyToServe()) {
return server;
}
server = null;
}
continue;
}
log.warn("No up servers available from load balancer: " + lb);
return null;
}
if (count >= 10) {
log.warn("No available alive servers after 10 tries from load balancer: " + lb);
}
return server;
}
}
}
private int incrementAndGetModulo(int modulo) {
int current;
int next;
do {
current = this.nextServerCyclicCounter.get();
next = (current + 1) % modulo;
} while(!this.nextServerCyclicCounter.compareAndSet(current, next));
return next;
}很重要的一个类属性是AtomicInteger nextServerCyclicCounter，通过它来实现轮循。
- ILoadBalancer获取所有的服务列表
- 之后调用incrementAndGetModulo方法，参数是服务个数，incrementAndGetModulo方法中用CAS来实现线程安全，获得服务的下标
- 得到服务Server后，判断是否是alive和ReadyToServe，则返回；如果循坏了10次还没有找到，则log打印warn日志提示
这个实现是简单的轮循，没有实现有权重的RoundRibbon。
Reference
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