聊聊nacos-server的PushService

序

本文主要研究一下 nacos server 的 PushService

PushService

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/push/PushService.java

@Component
public class PushService implements ApplicationContextAware, ApplicationListener<ServiceChangeEvent> {

    @Autowired
    private SwitchDomain switchDomain;

    private ApplicationContext applicationContext;

    private static final long ACK_TIMEOUT_NANOS = TimeUnit.SECONDS.toNanos(10L);

    private static final int MAX_RETRY_TIMES = 1;

    private static volatile ConcurrentMap<String, Receiver.AckEntry> ackMap
        = new ConcurrentHashMap<String, Receiver.AckEntry>();

    private static ConcurrentMap<String, ConcurrentMap<String, PushClient>> clientMap
        = new ConcurrentHashMap<String, ConcurrentMap<String, PushClient>>();

    private static volatile ConcurrentHashMap<String, Long> udpSendTimeMap = new ConcurrentHashMap<String, Long>();

    public static volatile ConcurrentHashMap<String, Long> pushCostMap = new ConcurrentHashMap<String, Long>();

    private static int totalPush = 0;

    private static int failedPush = 0;

    private static ConcurrentHashMap<String, Long> lastPushMillisMap = new ConcurrentHashMap<>();

    private static DatagramSocket udpSocket;

    private static Map<String, Future> futureMap = new ConcurrentHashMap<>();
    private static ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor(new ThreadFactory() {
        @Override
        public Thread newThread(Runnable r) {Thread t = new Thread(r);
            t.setDaemon(true);
            t.setName("com.alibaba.nacos.naming.push.retransmitter");
            return t;
        }
    });

    private static ScheduledExecutorService udpSender = Executors.newSingleThreadScheduledExecutor(new ThreadFactory() {
        @Override
        public Thread newThread(Runnable r) {Thread t = new Thread(r);
            t.setDaemon(true);
            t.setName("com.alibaba.nacos.naming.push.udpSender");
            return t;
        }
    });

    static {
        try {udpSocket = new DatagramSocket();

            Receiver receiver = new Receiver();

            Thread inThread = new Thread(receiver);
            inThread.setDaemon(true);
            inThread.setName("com.alibaba.nacos.naming.push.receiver");
            inThread.start();

            executorService.scheduleWithFixedDelay(new Runnable() {
                @Override
                public void run() {
                    try {removeClientIfZombie();
                    } catch (Throwable e) {Loggers.PUSH.warn("[NACOS-PUSH] failed to remove client zombie");
                    }
                }
            }, 0, 20, TimeUnit.SECONDS);

        } catch (SocketException e) {Loggers.SRV_LOG.error("[NACOS-PUSH] failed to init push service");
        }
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {this.applicationContext = applicationContext;}

    //......

    public static void removeClientIfZombie() {

        int size = 0;
        for (Map.Entry<String, ConcurrentMap<String, PushClient>> entry : clientMap.entrySet()) {ConcurrentMap<String, PushClient> clientConcurrentMap = entry.getValue();
            for (Map.Entry<String, PushClient> entry1 : clientConcurrentMap.entrySet()) {PushClient client = entry1.getValue();
                if (client.zombie()) {clientConcurrentMap.remove(entry1.getKey());
                }
            }

            size += clientConcurrentMap.size();}

        if (Loggers.PUSH.isDebugEnabled()) {Loggers.PUSH.debug("[NACOS-PUSH] clientMap size: {}", size);
        }

    }

    //......
}

• PushService 实现了 ApplicationContextAware、ApplicationListener<ServiceChangeEvent> 接口；它有两个 ScheduledExecutorService，一个用于 retransmitter，一个用于 udpSender；其 static 代码块创建了一个 deamon 线程执行 Receiver，同时注册了一个定时任务执行 removeClientIfZombie，它会遍历 clientMap，移除 zombie 的 client

Receiver

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/push/PushService.java

    public static class Receiver implements Runnable {
        @Override
        public void run() {while (true) {byte[] buffer = new byte[1024 * 64];
                DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

                try {udpSocket.receive(packet);

                    String json = new String(packet.getData(), 0, packet.getLength(), Charset.forName("UTF-8")).trim();
                    AckPacket ackPacket = JSON.parseObject(json, AckPacket.class);

                    InetSocketAddress socketAddress = (InetSocketAddress) packet.getSocketAddress();
                    String ip = socketAddress.getAddress().getHostAddress();
                    int port = socketAddress.getPort();

                    if (System.nanoTime() - ackPacket.lastRefTime > ACK_TIMEOUT_NANOS) {Loggers.PUSH.warn("ack takes too long from {} ack json: {}", packet.getSocketAddress(), json);
                    }

                    String ackKey = getACKKey(ip, port, ackPacket.lastRefTime);
                    AckEntry ackEntry = ackMap.remove(ackKey);
                    if (ackEntry == null) {
                        throw new IllegalStateException("unable to find ackEntry for key:" + ackKey
                            + ", ack json:" + json);
                    }

                    long pushCost = System.currentTimeMillis() - udpSendTimeMap.get(ackKey);

                    Loggers.PUSH.info("received ack: {} from: {}:, cost: {} ms, unacked: {}, total push: {}",
                        json, ip, port, pushCost, ackMap.size(), totalPush);

                    pushCostMap.put(ackKey, pushCost);

                    udpSendTimeMap.remove(ackKey);

                } catch (Throwable e) {Loggers.PUSH.error("[NACOS-PUSH] error while receiving ack data", e);
                }
            }
        }

        //......

        public static class AckPacket {
            public String type;
            public long lastRefTime;

            public String data;
        }
    }

• Receiver 实现了 Runnable 接口，其 run 方法使用 while true 循环来执行 udpSocket.receive，之后解析 AckPacket，从 ackMap 移除该 ackKey，更新 pushCostMap，同时从 udpSendTimeMap 移除该 ackKey

PushClient

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/push/PushService.java

    public class PushClient {
        private String namespaceId;
        private String serviceName;
        private String clusters;
        private String agent;
        private String tenant;
        private String app;
        private InetSocketAddress socketAddr;
        private DataSource dataSource;
        private Map<String, String[]> params;

        public Map<String, String[]> getParams() {return params;}

        public void setParams(Map<String, String[]> params) {this.params = params;}

        public long lastRefTime = System.currentTimeMillis();

        public PushClient(String namespaceId,
                          String serviceName,
                          String clusters,
                          String agent,
                          InetSocketAddress socketAddr,
                          DataSource dataSource,
                          String tenant,
                          String app) {
            this.namespaceId = namespaceId;
            this.serviceName = serviceName;
            this.clusters = clusters;
            this.agent = agent;
            this.socketAddr = socketAddr;
            this.dataSource = dataSource;
            this.tenant = tenant;
            this.app = app;
        }

        public DataSource getDataSource() {return dataSource;}

        public PushClient(InetSocketAddress socketAddr) {this.socketAddr = socketAddr;}

        public boolean zombie() {return System.currentTimeMillis() - lastRefTime > switchDomain.getPushCacheMillis(serviceName);
        }

        @Override
        public String toString() {
            return "serviceName:" + serviceName
                + ", clusters:" + clusters
                + ", ip:" + socketAddr.getAddress().getHostAddress()
                + ", port:" + socketAddr.getPort()
                + ", agent:" + agent;
        }

        public String getAgent() {return agent;}

        public String getAddrStr() {return socketAddr.getAddress().getHostAddress() + ":" + socketAddr.getPort();
        }

        public String getIp() {return socketAddr.getAddress().getHostAddress();}

        @Override
        public int hashCode() {return Objects.hash(serviceName, clusters, socketAddr);
        }

        @Override
        public boolean equals(Object obj) {if (!(obj instanceof PushClient)) {return false;}

            PushClient other = (PushClient) obj;

            return serviceName.equals(other.serviceName) && clusters.equals(other.clusters) && socketAddr.equals(other.socketAddr);
        }

        public String getClusters() {return clusters;}

        public void setClusters(String clusters) {this.clusters = clusters;}

        public String getNamespaceId() {return namespaceId;}

        public void setNamespaceId(String namespaceId) {this.namespaceId = namespaceId;}

        public String getServiceName() {return serviceName;}

        public void setServiceName(String serviceName) {this.serviceName = serviceName;}

        public String getTenant() {return tenant;}

        public void setTenant(String tenant) {this.tenant = tenant;}

        public String getApp() {return app;}

        public void setApp(String app) {this.app = app;}

        public InetSocketAddress getSocketAddr() {return socketAddr;}

        public void refresh() {lastRefTime = System.currentTimeMillis();
        }
    }

• PushClient 封装了要推送的目标服务地址等信息，它提供了 zombie 方法来判断目标服务是否 zombie，它判断距离 lastRefTime 的时间差是否超过 switchDomain 指定的该 serviceName 的 PushCacheMillis( 默认为 10 秒 )，超过则判定为 zombie

PushService.onApplicationEvent

@Component
public class PushService implements ApplicationContextAware, ApplicationListener<ServiceChangeEvent> {

    //......

    @Override
    public void onApplicationEvent(ServiceChangeEvent event) {Service service = event.getService();
        String serviceName = service.getName();
        String namespaceId = service.getNamespaceId();

        Future future = udpSender.schedule(new Runnable() {
            @Override
            public void run() {
                try {Loggers.PUSH.info(serviceName + "is changed, add it to push queue.");
                    ConcurrentMap<String, PushClient> clients = clientMap.get(UtilsAndCommons.assembleFullServiceName(namespaceId, serviceName));
                    if (MapUtils.isEmpty(clients)) {return;}

                    Map<String, Object> cache = new HashMap<>(16);
                    long lastRefTime = System.nanoTime();
                    for (PushClient client : clients.values()) {if (client.zombie()) {Loggers.PUSH.debug("client is zombie:" + client.toString());
                            clients.remove(client.toString());
                            Loggers.PUSH.debug("client is zombie:" + client.toString());
                            continue;
                        }

                        Receiver.AckEntry ackEntry;
                        Loggers.PUSH.debug("push serviceName: {} to client: {}", serviceName, client.toString());
                        String key = getPushCacheKey(serviceName, client.getIp(), client.getAgent());
                        byte[] compressData = null;
                        Map<String, Object> data = null;
                        if (switchDomain.getDefaultPushCacheMillis() >= 20000 && cache.containsKey(key)) {org.javatuples.Pair pair = (org.javatuples.Pair) cache.get(key);
                            compressData = (byte[]) (pair.getValue0());
                            data = (Map<String, Object>) pair.getValue1();

                            Loggers.PUSH.debug("[PUSH-CACHE] cache hit: {}:{}", serviceName, client.getAddrStr());
                        }

                        if (compressData != null) {ackEntry = prepareAckEntry(client, compressData, data, lastRefTime);
                        } else {ackEntry = prepareAckEntry(client, prepareHostsData(client), lastRefTime);
                            if (ackEntry != null) {cache.put(key, new org.javatuples.Pair<>(ackEntry.origin.getData(), ackEntry.data));
                            }
                        }

                        Loggers.PUSH.info("serviceName: {} changed, schedule push for: {}, agent: {}, key: {}",
                            client.getServiceName(), client.getAddrStr(), client.getAgent(), (ackEntry == null ? null : ackEntry.key));

                        udpPush(ackEntry);
                    }
                } catch (Exception e) {Loggers.PUSH.error("[NACOS-PUSH] failed to push serviceName: {} to client, error: {}", serviceName, e);

                } finally {futureMap.remove(UtilsAndCommons.assembleFullServiceName(namespaceId, serviceName));
                }

            }
        }, 1000, TimeUnit.MILLISECONDS);

        futureMap.put(UtilsAndCommons.assembleFullServiceName(namespaceId, serviceName), future);

    }

    //......

    public void serviceChanged(Service service) {
        // merge some change events to reduce the push frequency:
        if (futureMap.containsKey(UtilsAndCommons.assembleFullServiceName(service.getNamespaceId(), service.getName()))) {return;}

        this.applicationContext.publishEvent(new ServiceChangeEvent(this, service));
    }

    //......    
}

• onApplicationEvent 会处理 ServiceChangeEvent，它会注册一个延时任务并将该 future 放入 futureMap；该延时任务会从 clientMap 获取指定 namespaceId, serviceName 的 clients；然后遍历 clients 判断是否是 zombie，如果是的话则移除该 client，否则创建 Receiver.AckEntry，然后执行 udpPush(ackEntry)，最后从 futureMap 移除该 future；serviceChanged 方法提供给外部调用发布 ServiceChangeEvent

PushService.udpPush

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/push/PushService.java

@Component
public class PushService implements ApplicationContextAware, ApplicationListener<ServiceChangeEvent> {

    //......

    public static class Receiver implements Runnable {
        //......

        public static class AckEntry {public AckEntry(String key, DatagramPacket packet) {
                this.key = key;
                this.origin = packet;
            }

            public void increaseRetryTime() {retryTimes.incrementAndGet();
            }

            public int getRetryTimes() {return retryTimes.get();
            }

            public String key;
            public DatagramPacket origin;
            private AtomicInteger retryTimes = new AtomicInteger(0);
            public Map<String, Object> data;
        }

        //......
    }    

    private static Receiver.AckEntry udpPush(Receiver.AckEntry ackEntry) {if (ackEntry == null) {Loggers.PUSH.error("[NACOS-PUSH] ackEntry is null.");
            return null;
        }

        if (ackEntry.getRetryTimes() > MAX_RETRY_TIMES) {Loggers.PUSH.warn("max re-push times reached, retry times {}, key: {}", ackEntry.retryTimes, ackEntry.key);
            ackMap.remove(ackEntry.key);
            udpSendTimeMap.remove(ackEntry.key);
            failedPush += 1;
            return ackEntry;
        }

        try {if (!ackMap.containsKey(ackEntry.key)) {totalPush++;}
            ackMap.put(ackEntry.key, ackEntry);
            udpSendTimeMap.put(ackEntry.key, System.currentTimeMillis());

            Loggers.PUSH.info("send udp packet:" + ackEntry.key);
            udpSocket.send(ackEntry.origin);

            ackEntry.increaseRetryTime();

            executorService.schedule(new Retransmitter(ackEntry), TimeUnit.NANOSECONDS.toMillis(ACK_TIMEOUT_NANOS),
                TimeUnit.MILLISECONDS);

            return ackEntry;
        } catch (Exception e) {Loggers.PUSH.error("[NACOS-PUSH] failed to push data: {} to client: {}, error: {}",
                ackEntry.data, ackEntry.origin.getAddress().getHostAddress(), e);
            ackMap.remove(ackEntry.key);
            udpSendTimeMap.remove(ackEntry.key);
            failedPush += 1;

            return null;
        }
    }

    //......
}

• udpPush 方法会根据 Receiver.AckEntry 的信息进行判断，如果其重试次数大于 MAX_RETRY_TIMES 则终止 push，将其从 ackMap、udpSendTimeMap 中移除；如果可以重试则将其 ackEntry.key 放入 ackMap 及 udpSendTimeMap，然后执行 udpSocket.send(ackEntry.origin) 及 ackEntry.increaseRetryTime()，并注册 Retransmitter 的延时任务；如果出现异常则将其从 ackMap、udpSendTimeMap 移除

Retransmitter

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/push/PushService.java

    public static class Retransmitter implements Runnable {
        Receiver.AckEntry ackEntry;

        public Retransmitter(Receiver.AckEntry ackEntry) {this.ackEntry = ackEntry;}

        @Override
        public void run() {if (ackMap.containsKey(ackEntry.key)) {Loggers.PUSH.info("retry to push data, key:" + ackEntry.key);
                udpPush(ackEntry);
            }
        }
    }

• Retransmitter 实现了 Runnable 方法，其 run 方法在 ackMap 包含 ackEntry.key 的条件下执行 udpPush 重试

小结

• PushService 实现了 ApplicationContextAware、ApplicationListener<ServiceChangeEvent> 接口
• 其 static 代码块创建了一个 deamon 线程执行 Receiver，同时注册了一个定时任务执行 removeClientIfZombie，它会遍历 clientMap，移除 zombie 的 client
• 其 onApplicationEvent 会处理 ServiceChangeEvent，它会注册一个延时任务并将该 future 放入 futureMap；该延时任务会从 clientMap 获取指定 namespaceId, serviceName 的 clients；然后遍历 clients 判断是否是 zombie，如果是的话则移除该 client，否则创建 Receiver.AckEntry，然后执行 udpPush(ackEntry)，最后从 futureMap 移除该 future；serviceChanged 方法提供给外部调用发布 ServiceChangeEvent

doc

• PushService