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服務(wù)下線的大致流程圖

??下面這張圖很簡單地描述了Server端服務(wù)下線的大致流程：

服務(wù)下線.jpg

服務(wù)下線Server端實(shí)現(xiàn)源碼分析

??Eureka服務(wù)實(shí)現(xiàn)是通過Server端InstanceResource 類 cancelLease 方法來實(shí)現(xiàn)服務(wù)下線操作，下面我們來看看具體實(shí)現(xiàn)代碼：

@DELETE
public Response cancelLease(
        @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
    try {
        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();
        }
    } catch (Throwable e) {
        logger.error("Error (cancel): {} - {}", app.getName(), id, e);
        return Response.serverError().build();
    }
}

??由上可見，調(diào)用了registry.cancel()方法，我們接著往下看

@Override
public boolean cancel(final String appName, final String id,
                      final boolean isReplication) {
    if (super.cancel(appName, id, isReplication)) {
        // 向其他Server同步服務(wù)下線信息
        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;
}

??由上面我們可以發(fā)現(xiàn)，如果調(diào)用super.cancel(appName, id, isReplication)成功，則會(huì)調(diào)用replicateToPeers方法向Server端同步發(fā)送服務(wù)下線消息。我們接著看super.cancel(appName, id, isReplication)的具體實(shí)現(xiàn)：

@Override
public boolean cancel(String appName, String id, boolean isReplication) {
    return internalCancel(appName, id, isReplication);
}

??在父類的cancel方法中調(diào)用了internalCancel(appName, id, isReplication)來實(shí)現(xiàn)，因此我們繼續(xù)往下看：

protected boolean internalCancel(String appName, String id, boolean isReplication) {
    try {
        read.lock();
        CANCEL.increment(isReplication);
        Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
        Lease<InstanceInfo> leaseToCancel = null;
        if (gMap != null) {
            // 刪除服務(wù)租約信息
            leaseToCancel = gMap.remove(id); 
        }
        synchronized (recentCanceledQueue) {
            // 添加進(jìn)隊(duì)列，方便其他客戶端進(jìn)行批量更新
            recentCanceledQueue.add(new Pair<Long, String>(System.currentTimeMillis(), appName + "(" + id + ")"));
        }
        //刪除客戶端狀態(tài)信息
        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) {
            CANCEL_NOT_FOUND.increment(isReplication);
            logger.warn("DS: Registry: cancel failed because Lease is not registered for: {}/{}", appName, id);
            return false;
        } else {
            leaseToCancel.cancel();
            InstanceInfo instanceInfo = leaseToCancel.getHolder();
            String vip = null;
            String svip = null;
            if (instanceInfo != null) {
                instanceInfo.setActionType(ActionType.DELETED);
                recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel));
                instanceInfo.setLastUpdatedTimestamp();
                vip = instanceInfo.getVIPAddress();
                svip = instanceInfo.getSecureVipAddress();
            }
            // 刪除緩存信息，并重新加載實(shí)例信息，初始化讀寫緩存
            invalidateCache(appName, vip, svip);
            logger.info("Cancelled instance {}/{} (replication={})", appName, id, isReplication);
            return true;
        }
    } finally {
        read.unlock();
    }
}

總結(jié)：
??參考上面internalCancel方法的源碼，以及之前整體調(diào)用的方法，我們可以發(fā)現(xiàn)服務(wù)續(xù)約整體的流程大致可以分為以下幾步：
???? $\color{red}{1.刪除服務(wù)租約信息}$
???? $\color{red}{2.將下線的服務(wù)放進(jìn)隊(duì)列里，方便其他Client的增量更新操作}$
???? $\color{red}{3.刪除服務(wù)狀態(tài)信息}$
???? $\color{red}{4.刪除緩存信息}$ (注意：清除的是讀寫緩存的數(shù)據(jù))
???? $\color{red}{5.向其他Server同步發(fā)送服務(wù)下線消息}$