Ribbon中BestAvailableRule和RetryRule的使用方法

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Ribbon的版本是2.3.0.release.

1.BestAvailableRule

图1

ClientConfigEnabledRoundRobinRule如下所示，定义了一个类属性RoundRobinRule，choose方法中调用RoundRobinRule进行选择，所以这里面的是轮循算法。

List-1.1

public class ClientConfigEnabledRoundRobinRule extends AbstractLoadBalancerRule {    RoundRobinRule roundRobinRule = new RoundRobinRule();    public ClientConfigEnabledRoundRobinRule() {    }    public void initWithNiwsConfig(IClientConfig clientConfig) {        this.roundRobinRule = new RoundRobinRule();    }    public void setLoadBalancer(ILoadBalancer lb) {        super.setLoadBalancer(lb);        this.roundRobinRule.setLoadBalancer(lb);    }    public Server choose(Object key) {        if (this.roundRobinRule != null) {            return this.roundRobinRule.choose(key);        } else {            throw new IllegalArgumentException("This class has not been initialized with the RoundRobinRule class");        }    }}

BestAvailableRule继承了ClientConfigEnabledRoundRobinRule，内部实现如下List-1.2，遍历所有的服务提供者，选择并发量最小的那个服务。

List-1.2

private LoadBalancerStats loadBalancerStats;public Server choose(Object key) {    if (this.loadBalancerStats == null) {        return super.choose(key);    } else {        List serverList = this.getLoadBalancer().getAllServers();        int minimalConcurrentConnections = 2147483647;        long currentTime = System.currentTimeMillis();        Server chosen = null;        Iterator var7 = serverList.iterator();        while(var7.hasNext()) {            Server server = (Server)var7.next();            ServerStats serverStats = this.loadBalancerStats.getSingleServerStat(server);            if (!serverStats.isCircuitBreakerTripped(currentTime)) {                int concurrentConnections = serverStats.getActiveRequestsCount(currentTime);                if (concurrentConnections < minimalConcurrentConnections) {                    minimalConcurrentConnections = concurrentConnections;                    chosen = server;                }            }        }        if (chosen == null) {            return super.choose(key);        } else {            return chosen;        }    }}public void setLoadBalancer(ILoadBalancer lb) {    super.setLoadBalancer(lb);    if (lb instanceof AbstractLoadBalancer) {        this.loadBalancerStats = ((AbstractLoadBalancer)lb).getLoadBalancerStats();    }}

choose方法重新了父类中的choose方法，

1. 获取服务列表，遍历服务

2. 通过ServerStats获取当前服务实例的并发连接数，如下List-3所示，并发连接数不是0，且当前时间与上次有效更改时间间隔在范围内，则返回当前并发连接数。

3. 遍历所有的服务提供者后，如果得到的server是null，则调用父类的choose方法，用RoundRobin算法进行选择。

List-1.3

public int getActiveRequestsCount(long currentTime) {    int count = this.activeRequestsCount.get();    if (count == 0) {        return 0;    } else if (currentTime - this.lastActiveRequestsCountChangeTimestamp <= (long)(activeRequestsCountTimeout.get() * 1000) && count >= 0) {        return count;    } else {        this.activeRequestsCount.set(0);        return 0;    }}

2.RetryRule

图2

RetryRule的实现比较简单，基于RoundRobinRule，如下List-2.1所示

List-2.1

public class RetryRule extends AbstractLoadBalancerRule {    IRule subRule = new RoundRobinRule();    long maxRetryMillis = 500L;    ...    public Server choose(ILoadBalancer lb, Object key) {        long requestTime = System.currentTimeMillis();        long deadline = requestTime + this.maxRetryMillis;        Server answer = null;        answer = this.subRule.choose(key);        if ((answer == null || !answer.isAlive()) && System.currentTimeMillis() < deadline) {            InterruptTask task = new InterruptTask(deadline - System.currentTimeMillis());            while(!Thread.interrupted()) {                answer = this.subRule.choose(key);                if (answer != null && answer.isAlive() || System.currentTimeMillis() >= deadline) {                    break;                }                Thread.yield();            }            task.cancel();        }        return answer != null && answer.isAlive() ? answer : null;    }    ...

RetryRule中choose(Object key)调用choose(ILoadBalancer lb, Object key)，

1. 当前时间加上maxRetryMillis得到deadline，即截止时间

2. 用subRule获取服务server，如果服务有效则直接返回该服务

3. 构造InterruptTask，它里面有个Timer定时任务，如List-2.2。之后循坏，只要当前线程没有被interrupt，则用subRule的RoundRobin算法选择一个服务实例，如果这个服务有效或者当前时间过了截止时间则跳出循坏

4. 如果步骤３中得到的服务实例无效，且当前时间在截止时间之内，则调用Thread.yield()，让出线程资源给其它线程

通过源码可知，RetryRule在subRule.choose获得无效的服务实例后，仅仅是再次再次用subRule获取服务实例，并不会一直尝试下去，即尝试一次。

List-2.2

public class InterruptTask extends TimerTask {    static Timer timer = new Timer("InterruptTimer", true);    protected Thread target = null;    public InterruptTask(long millis) {        this.target = Thread.currentThread();        timer.schedule(this, millis);    }    public boolean cancel() {        try {            return super.cancel();        } catch (Exception var2) {            return false;        }    }    public void run() {        if (this.target != null && this.target.isAlive()) {            this.target.interrupt();        }    }    ...

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