注册中心 Eureka 源码解析 —— 应用实例注册发现 （四）之自我保护机制

// AbstractInstanceRegistry.java
/**
* 期望最小每分钟续租次数
*/
protected volatile int numberOfRenewsPerMinThreshold;
/**
* 期望最大每分钟续租次数
*/
protected volatile int expectedNumberOfRenewsPerMin;

// AbstractInstanceRegistry.java
public void evict(long additionalLeaseMs) {

   if (!isLeaseExpirationEnabled()) {
       logger.debug("DS: lease expiration is currently disabled.");
       return;
   }

   // ... 省略过期租约逻辑
}

// PeerAwareInstanceRegistryImpl.java
@Override
public boolean isLeaseExpirationEnabled() {
   if (!isSelfPreservationModeEnabled()) {
       // The self preservation mode is disabled, hence allowing the instances to expire.
       return true;
   }
   return numberOfRenewsPerMinThreshold > 0 && getNumOfRenewsInLastMin() > numberOfRenewsPerMinThreshold;
}

// EurekaBootStrap.java
protected void initEurekaServerContext() throws Exception {

    // ... 省略其它代码

    // 【2.2.10】从其他 Eureka-Server 拉取注册信息
    // Copy registry from neighboring eureka node
    int registryCount = registry.syncUp();
    registry.openForTraffic(applicationInfoManager, registryCount);

    // ... 省略其它代码
}

// PeerAwareInstanceRegistryImpl.java
@Override
public void openForTraffic(ApplicationInfoManager applicationInfoManager, int count) {
   // Renewals happen every 30 seconds and for a minute it should be a factor of 2.
   this.expectedNumberOfRenewsPerMin = count * 2;
   this.numberOfRenewsPerMinThreshold =
           (int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());

   // ... 省略其它代码
}   

// PeerAwareInstanceRegistryImpl.java
private void scheduleRenewalThresholdUpdateTask() {
   timer.schedule(new TimerTask() {
                      @Override
                      public void run() {
                          updateRenewalThreshold();
                      }
                  }, serverConfig.getRenewalThresholdUpdateIntervalMs(),
           serverConfig.getRenewalThresholdUpdateIntervalMs());
}

// AbstractInstanceRegistry.java
/**
* 自我保护机锁
*
* 当计算如下参数时使用：
*  1. {@link #numberOfRenewsPerMinThreshold}
*  2. {@link #expectedNumberOfRenewsPerMin}
*/
protected final Object lock = new Object();

private void updateRenewalThreshold() {
   try {
       // 计算 应用实例数
       Applications apps = eurekaClient.getApplications();
       int count = 0;
       for (Application app : apps.getRegisteredApplications()) {
           for (InstanceInfo instance : app.getInstances()) {
               if (this.isRegisterable(instance)) {
                   ++count;
               }
           }
       }
       // 计算 expectedNumberOfRenewsPerMin 、 numberOfRenewsPerMinThreshold 参数
       synchronized (lock) {
           // Update threshold only if the threshold is greater than the
           // current expected threshold of if the self preservation is disabled.
           if ((count * 2) > (serverConfig.getRenewalPercentThreshold() * numberOfRenewsPerMinThreshold)
                   || (!this.isSelfPreservationModeEnabled())) {
               this.expectedNumberOfRenewsPerMin = count * 2;
               this.numberOfRenewsPerMinThreshold = (int) ((count * 2) * serverConfig.getRenewalPercentThreshold());
           }
       }
       logger.info("Current renewal threshold is : {}", numberOfRenewsPerMinThreshold);
   } catch (Throwable e) {
       logger.error("Cannot update renewal threshold", e);
   }
}

// 
public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {

    // ... 省略无关代码

    // The lease does not exist and hence it is a new registration
    // 【自我保护机制】增加 `numberOfRenewsPerMinThreshold` 、`expectedNumberOfRenewsPerMin`
    synchronized (lock) {
         if (this.expectedNumberOfRenewsPerMin > 0) {
             // Since the client wants to cancel it, reduce the threshold
             // (1
             // for 30 seconds, 2 for a minute)
             this.expectedNumberOfRenewsPerMin = this.expectedNumberOfRenewsPerMin + 2;
             this.numberOfRenewsPerMinThreshold =
                     (int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
         }
     }

     // ... 省略无关代码
}

// PeerAwareInstanceRegistryImpl.java
@Override
public boolean cancel(final String appName, final String id,
                     final boolean isReplication) {
   // ... 省略无关代码

   synchronized (lock) {
        if (this.expectedNumberOfRenewsPerMin > 0) {
               // Since the client wants to cancel it, reduce the threshold (1 for 30 seconds, 2 for a minute)
               this.expectedNumberOfRenewsPerMin = this.expectedNumberOfRenewsPerMin - 2;
               this.numberOfRenewsPerMinThreshold = (int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
        }
   }

   // ... 省略无关代码
}