[原创] Eureka源码剖析之五：服务下线

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Eureka源码剖析之一：初始化-启动

Eureka源码剖析之二：服务注册

Eureka源码剖析之三：服务拉取

Eureka源码剖析之四：服务续约

    /**
     * 注销服务，调用client的cancel服务，往里面看也就是调用了服务端的http delete 请求进行服务下线
     */
    void unregister() {
        // It can be null if shouldRegisterWithEureka == false
        if(eurekaTransport != null && eurekaTransport.registrationClient != null) {
            try {
                logger.info("Unregistering ...");
                EurekaHttpResponse<Void> httpResponse = eurekaTransport.registrationClient.cancel(instanceInfo.getAppName(), instanceInfo.getId());
                logger.info(PREFIX + appPathIdentifier + " - deregister  status: " + httpResponse.getStatusCode());
            } catch (Exception e) {
                logger.error(PREFIX + appPathIdentifier + " - de-registration failed" + e.getMessage(), e);
            }
        }
    }

    @Override
    public EurekaHttpResponse<Void> cancel(String appName, String id) {
        String urlPath = "apps/" + appName + '/' + id;
        ClientResponse response = null;
        try {
            Builder resourceBuilder = jerseyClient.resource(serviceUrl).path(urlPath).getRequestBuilder();
            addExtraHeaders(resourceBuilder);
            response = resourceBuilder.delete(ClientResponse.class);
            return anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
        } finally {
            if (logger.isDebugEnabled()) {
                logger.debug("Jersey HTTP DELETE {}/{}; statusCode={}", serviceUrl, urlPath, response == null ? "N/A" : response.getStatus());
            }
            if (response != null) {
                response.close();
            }
        }
    }

    @PreDestroy
    @Override
    public synchronized void shutdown() {
        if (isShutdown.compareAndSet(false, true)) {
            logger.info("Shutting down DiscoveryClient ...");
            // 注销服务状态的监听器
            if (statusChangeListener != null && applicationInfoManager != null) {
                applicationInfoManager.unregisterStatusChangeListener(statusChangeListener.getId());
            }
            // 取消定时器任务，关闭线程池等
            cancelScheduledTasks();

            // 服务实例以及被注册，那么设置实例状态为DOWN，并且进行注销操作
            if (applicationInfoManager != null && clientConfig.shouldRegisterWithEureka()) {
                applicationInfoManager.setInstanceStatus(InstanceStatus.DOWN);
                unregister();
            }
            // 关闭eurekaTransport
            if (eurekaTransport != null) {
                eurekaTransport.shutdown();
            }
            // 关闭监控
            heartbeatStalenessMonitor.shutdown();
            registryStalenessMonitor.shutdown();

            logger.info("Completed shut down of DiscoveryClient");
        }
    }

    // DiscoveryManager调用了DiscveryClient的shutdown方法，这里就是服务下线的入口
    public void shutdownComponent() {
        if (discoveryClient != null) {
            try {
                discoveryClient.shutdown();
                discoveryClient = null;
            } catch (Throwable th) {
                logger.error("Error in shutting down client", th);
            }
        }
    }

    // 服务端提供的对外服务下线接口
    @DELETE
    public Response cancelLease(
            @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
        boolean isSuccess = registry.cancel(app.getName(), id,
                "true".equals(isReplication));

        if (isSuccess) {
            logger.debug("Found (Cancel): " + app.getName() + " - " + id);
            return Response.ok().build();
        } else {
            logger.info("Not Found (Cancel): " + app.getName() + " - " + id);
            return Response.status(Status.NOT_FOUND).build();
        }
    }

    // 服务端下线入口
    @Override
    public boolean cancel(final String appName, final String id,
                          final boolean isReplication) {
        // 调用父类cancel方法，将实例信息添加到最近下线队列、最近变更队列，并且使本地缓存失效操作
        if (super.cancel(appName, id, isReplication)) {
            // 服务端集群之间进行Cancel同步操作
            replicateToPeers(Action.Cancel, appName, id, null, null, isReplication);
            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());
                }
            }
            return true;
        }
        return false;
    }

    // 最终调用这个方法进行实例信息移除
    protected boolean internalCancel(String appName, String id, boolean isReplication) {
        try {
            // 读锁
            read.lock();
            // 取消（下线）计数
            CANCEL.increment(isReplication);
            // 获取续约实例
            Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
            Lease<InstanceInfo> leaseToCancel = null;
            if (gMap != null) {
                leaseToCancel = gMap.remove(id);
            }
            // 添加到近期取消队列
            recentCanceledQueue.add(new Pair<Long, String>(System.currentTimeMillis(), appName + "(" + id + ")"));
            // 移除实例状态
            InstanceStatus instanceStatus = overriddenInstanceStatusMap.remove(id);
            if (instanceStatus != null) {
                logger.debug("Removed instance id {} from the overridden map which has value {}", id, instanceStatus.name());
            }
            if (leaseToCancel == null) {
                // 续约实例不存在，返回false
                CANCEL_NOT_FOUND.increment(isReplication);
                logger.warn("DS: Registry: cancel failed because Lease is not registered for: {}/{}", appName, id);
                return false;
            } else {
                // 续约实例执行取消操作：设置剔除时间
                leaseToCancel.cancel();
                InstanceInfo instanceInfo = leaseToCancel.getHolder();
                String vip = null;
                String svip = null;
                if (instanceInfo != null) {
                    // 设置实例行为为delete
                    instanceInfo.setActionType(ActionType.DELETED);
                    // 添加到近期变化队列
                    recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel));
                    instanceInfo.setLastUpdatedTimestamp();
                    vip = instanceInfo.getVIPAddress();
                    svip = instanceInfo.getSecureVipAddress();
                }
                // 使响应缓存失效
                invalidateCache(appName, vip, svip);
                logger.info("Cancelled instance {}/{} (replication={})", appName, id, isReplication);
                return true;
            }
        } finally {
            // 释放读锁
            read.unlock();
        }
    }