private class FDConnectionListener implements TransportConnectionListener {
        @Override
        public void onNodeConnected(DiscoveryNode node) {
        }
        @Override
        public void onNodeDisconnected(DiscoveryNode node) {
            handleTransportDisconnect(node);
        }
    }

private?void?innerStart(final?DiscoveryNode masterNode) {
        this.masterNode = masterNode;
        this.retryCount = 0;
        this.notifiedMasterFailure.set(false);
        // 嘗試連接master節(jié)點(diǎn)
        try {
            transportService.connectToNode(masterNode);
        } catch (final Exception e) {
            // 連接失敗通知masterNode失敗
            notifyMasterFailure(masterNode, "failed to perform initial connect [" + e.getMessage() + "]");
            return;
        }
　　　　//關(guān)閉之前的masterping，重啟新的masterping
        if (masterPinger != null) {
            masterPinger.stop();
        }
        this.masterPinger = new MasterPinger();
        // 周期之后啟動(dòng)masterPing，這里并沒(méi)有周期啟動(dòng)masterPing，只是設(shè)定了延遲時(shí)間。
        threadPool.schedule(pingInterval, ThreadPool.Names.SAME, masterPinger);
    }

private void notifyMasterFailure(final DiscoveryNode masterNode, final String reason) {
        if (notifiedMasterFailure.compareAndSet(false, true)) {
            threadPool.generic().execute(new Runnable() {
                @Override
                public void run() {
　　　　　　　　　　　　//通知所有l(wèi)istener master丟失
                    for (Listener listener : listeners) {
                        listener.onMasterFailure(masterNode, reason);
                    }
                }
            });
            stop("master failure, " + reason);
        }
    }

private class MasterPinger implements Runnable {
        private volatile boolean running = true;
        public void stop() {
            this.running = false;
        }
        @Override
        public void run() {
            if (!running) {
                // return and don't spawn...
                return;
            }
            final DiscoveryNode masterToPing = masterNode;
   final MasterPingRequest request = new MasterPingRequest(clusterService.localNode().id(), masterToPing.id(), clusterName);
            final TransportRequestOptions options = options().withType(TransportRequestOptions.Type.PING).withTimeout(pingRetryTimeout);
            transportService.sendRequest(masterToPing, MASTER_PING_ACTION_NAME, request, options, new BaseTransportResponseHandler<MasterPingResponseResponse>() {
                        @Override
                        public MasterPingResponseResponse newInstance() {
                            return new MasterPingResponseResponse();
                        }
                        @Override
                        public void handleResponse(MasterPingResponseResponse response) {
                            if (!running) {
                                return;
                            }
                            // reset the counter, we got a good result
                            MasterFaultDetection.this.retryCount = 0;
                            // check if the master node did not get switched on us..., if it did, we simply return with no reschedule
                            if (masterToPing.equals(MasterFaultDetection.this.masterNode())) {
                                // 啟動(dòng)新的ping周期
                                threadPool.schedule(pingInterval, ThreadPool.Names.SAME, MasterPinger.this);
                            }
                        }
                        @Override
                        public void handleException(TransportException exp) {
                            if (!running) {
                                return;
                            }
                            synchronized (masterNodeMutex) {
                                // check if the master node did not get switched on us...
                                if (masterToPing.equals(MasterFaultDetection.this.masterNode())) {
                                    if (exp instanceof ConnectTransportException || exp.getCause() instanceof ConnectTransportException) {
                                        handleTransportDisconnect(masterToPing);
                                        return;
                                    } else if (exp.getCause() instanceof NoLongerMasterException) {
                                        logger.debug("[master] pinging a master {} that is no longer a master", masterNode);
                                        notifyMasterFailure(masterToPing, "no longer master");
                                        return;
                                    } else if (exp.getCause() instanceof NotMasterException) {
                                        logger.debug("[master] pinging a master {} that is not the master", masterNode);
                                        notifyMasterFailure(masterToPing, "not master");
                                        return;
                                    } else if (exp.getCause() instanceof NodeDoesNotExistOnMasterException) {
                                        logger.debug("[master] pinging a master {} but we do not exists on it, act as if its master failure", masterNode);
                                        notifyMasterFailure(masterToPing, "do not exists on master, act as master failure");
                                        return;
                                    }
                                    int retryCount = ++MasterFaultDetection.this.retryCount;
                                    logger.trace("[master] failed to ping [{}], retry [{}] out of [{}]", exp, masterNode, retryCount, pingRetryCount);
                                    if (retryCount >= pingRetryCount) {
                                        logger.debug("[master] failed to ping [{}], tried [{}] times, each with maximum [{}] timeout", masterNode, pingRetryCount, pingRetryTimeout);
                                        // not good, failure
                                        notifyMasterFailure(masterToPing, "failed to ping, tried [" + pingRetryCount + "] times, each with  maximum [" + pingRetryTimeout + "] timeout");
                                    } else {
                                         // resend the request, not reschedule, rely on send timeout
                                        transportService.sendRequest(masterToPing, MASTER_PING_ACTION_NAME, request, options, this);
                                    }
                                }
                            }
                        }
            );
        }
    }

protected void handleTransportDisconnect(DiscoveryNode node) {
　　　　//這里需要同步
        synchronized (masterNodeMutex) {
　　　　　　　　//master 已經(jīng)換成其它節(jié)點(diǎn)，就沒(méi)必要再連接
            if (!node.equals(this.masterNode)) {
                return;
            }
            if (connectOnNetworkDisconnect) {
                try {
　　　　　　　　　　　　//嘗試再次連接
                    transportService.connectToNode(node);
                    // if all is well, make sure we restart the pinger
                    if (masterPinger != null) {
                        masterPinger.stop();
                    }
　　　　　　　　　　　　//連接成功啟動(dòng)新的masterping
                    this.masterPinger = new MasterPinger();
                    // we use schedule with a 0 time value to run the pinger on the pool as it will run on later
                    threadPool.schedule(TimeValue.timeValueMillis(0), ThreadPool.Names.SAME, masterPinger);
                } catch (Exception e) {
　　　　　　　　　　　　//連接出現(xiàn)異常，啟動(dòng)master節(jié)點(diǎn)丟失通知
                    logger.trace("[master] [{}] transport disconnected (with verified connect)", masterNode);
                    notifyMasterFailure(masterNode, "transport disconnected (with verified connect)");
                }
            } else {
　　　　　　　　　　//不需要重連，通知master丟失。
                logger.trace("[master] [{}] transport disconnected", node);
                notifyMasterFailure(node, "transport disconnected");
            }
        }
    }