zk系列-c++下zookeeper使用实例

ZooKeeper是一个分布式的，开放源码的分布式应用程序协调服务。分布式应用可以使用它来实现诸如：统一命名服务、配置管理、分布式锁服务、集群管理等功能。公司常用到的是Java服务集群的管理。

1.函数介绍

//create a handle to used communicate with zookeeper
zhandle_t *zookeeper_init(const char *host, watcher_fn fn, int recv_timeout, const clientid_t *clientid, void *context, int flags)
//create a node synchronously
int zoo_create(zhandle_t *zh, const char *path, const char *value,int valuelen,
   const struct ACL_vector *acl, int flags,char *path_buffer, int path_buffer_len);
//lists the children of a node synchronously.
int zoo_wget_children(zhandle_t *zh, const char *path, watcher_fn watcher, void* watcherCtx, struct String_vector *strings)
//close the zookeeper handle and free up any resources.
int zookeeper_close(zhandle_t *zh)

2.实例

用上面3个函数，就能创建一个简单的集群管理。

数据存储结构为

服务端向Zk注册服务

//连接zk
void ZkRegistry::ConnectZK() {
  if (zhandle_) {
    zookeeper_close(zhandle_);
  }
  int count = 0;
  do {
    ++count;
    zhandle_ = zookeeper_init(zk_hosts_.c_str(),InitWatcher, timeout_, NULL, NULL, 0);
  } while (!connected_ && count < ZK_MAX_CONNECT_TIMES);

  if (count >= ZK_MAX_CONNECT_TIMES) {
    SLOG_WARN("ZkRegistry::Init --> connect host " << zk_hosts_ << " over max times:" << count);
    return;
  }
}

//发布服务，建立临时节点
void ZkRegistry::PublishService() {
  if (zhandle_ == NULL) {
    ConnectZK();
  }
  string server_path = PING_SERVER + "/" + PingConfig::instance().get_index() + "/"
    + GetIp() + ":" + PingConfig::instance().get_port();
  char res_path[128];
  int rc = zoo_create(zhandle_, server_path.c_str(), GetIp().c_str(), GetIp().size(),
      &ZOO_OPEN_ACL_UNSAFE, ZOO_EPHEMERAL, res_path, 128);
  if (rc) {
    SLOG_INFO("ZkRegistry::PublishService --> zoo_create() path=" << server_path << "," << zerror(rc));
  }
}

//每隔10s注册一次服务
void ZkRegistry::run() {
  while(true) {
    SLOG_INFO("publish service");
    ConnectZK();
    PublishService();
    sleep(10);
  }
}

void ZkRegistry::InitWatcher(zhandle_t *zh, int type, int state, const char *path, void *watcher_ctx) {
  if (state == ZOO_CONNECTED_STATE) {
    connected_ = true;
    SLOG_INFO("InitWatcher() ZOO_CONNECTED_STATE");
  } else if (state == ZOO_AUTH_FAILED_STATE) {
    SLOG_INFO("InitWatcher() ZOO_AUTH_FAILED_STATE");
  } else if (state == ZOO_EXPIRED_SESSION_STATE) {
    SLOG_INFO("InitWatcher() ZOO_EXPIRED_SESSION_STATE");
  } else if (state == ZOO_CONNECTING_STATE) {
    SLOG_INFO("InitWatcher() ZOO_CONNECTING_STATE");
  } else if (state == ZOO_ASSOCIATING_STATE) {
    SLOG_INFO("InitWatcher() ZOO_ASSOCIATING_STATE");
  }
}

客户端获取服务列表

//连接zk server
void ZkClient::ConnectZK() {
  cout << "ZkClient::ConnectZK" << endl;
  if (zhandle_) {
    zookeeper_close(zhandle_);
  }
  zhandle_ = NULL;
  connected_ = false;

  int count = 0;
  do {
    ++count;
    zhandle_ = zookeeper_init(zk_hosts_.c_str(), InitWatcher, timeout_, NULL, NULL, 0);
    sleep(5 * ONE_SECONDS);
  } while (!connected_ && count < ZK_MAX_CONNECT_TIMES);

  if (count >= ZK_MAX_CONNECT_TIMES){
    cout << "ZkClient::Init --> connecting zookeeper host: " << zk_hosts_ << " over times: " << count << endl;
  }
}
//更新服务列表，冷备和热备
void ZkClient::Update() {
  cout << "ZkClient::Update" << endl;
  if (zhandle_ == NULL || connected_ == false) {
    Init();
  }
  //获得服务份数
  struct String_vector str_vec;
  int ret = zoo_wget_children(zhandle_, PING_SERVER.c_str(), ServiceWatcher, NULL, &str_vec);
  if (ret) {
    cout << "Update --> read path:" << PING_SERVER << " wrong, " << zerror(ret) << endl;
    return;
  }

  //获得各份服务ip:port
  for (int i = 0; i < str_vec.count; ++i) {
    struct String_vector node_vec;
    string path = PING_SERVER + "/" + str_vec.data[i];
    int ret = zoo_wget_children(zhandle_, path.c_str(), ServiceWatcher, NULL, &node_vec);
    cout << "Update --> path:" << path << ", ret:" << ret << ", node's size:" << node_vec.count << endl;
    if (ret || node_vec.count != 1) {
      continue;
    }
    ....
  }
}
//监控服务变化
void ZkClient::ServiceWatcher(zhandle_t *zh, int type, int state, const char *path, void *watcherCtx) {
  cout << "type:" << type << endl;
  cout << "state:" << state << endl;
  cout << "path:" << path << endl;
//  cout << "watcherCtx:" << (char*)watcherCtx << endl;
  cout << "ZOO_CHILD_EVENT:" << ZOO_CHILD_EVENT << endl;
  if (ZOO_CHILD_EVENT == type) {
    cout << "ServiceWatcher ZOO_CHILD_EVENT" << endl;
    ZkClient::Instance().Update();//更新服务列表    
  }
}

服务端会每隔一段时间重新注册自己；

客户端在第一次与zk建立连接获取服务列表时，注册监听函数。zk当节点发生变化时，通知客户端，客户端重新获取服务列表，并注册事件。