Zookeeper C++编程实战之主备切换

默认zookeeper日志输出到stderr，
可以调用zoo_set_log_stream(FILE*)设置输出到文件中
还可以调用zoo_set_debug_level(ZooLogLevel)控制日志级别！！！

类CZookeeperHelper提供基于zookeeper的主备切换接口和读取数据等接口：
https://github.com/eyjian/libmooon/blob/master/include/mooon/net/zookeeper_helper.h

使用示例：

class CMyApplication: public mooon::net::CZookeeperHelper
{
public:
    CMyApplication(const char* data);
    void stop() { _stop = true; }
    void run();
    void wait();

private:
    void work();

private:
    virtual void on_zookeeper_session_connected(const char* path);
    virtual void on_zookeeper_session_connecting(const char* path);
    virtual void on_zookeeper_session_expired(const char *path);
    virtual void on_zookeeper_session_event(int state, const char *path);
    virtual void on_zookeeper_event(int type, int state, const char *path);

private:
    volatile bool _stop;
    std::string _master_path; 用来竞争master的zookeeper节点路径
    std::string _master_data; 成功竞争为master时，写入_master_path的数据，主备应当提供不同的数据，以方便判断自己是否处于主状态
};

int main(int argc, char* argv[])
{
    try
    {
        mooon::sys::g_logger = mooon::sys::create_safe_logger();
        const std::string zk_nodes = "127.0.0.1:2181";
        const int session_timeout_seconds = 1;

        CMyApplication myapp(argv[1]);
        myapp.create_session(zk_nodes, session_timeout_seconds);
        myapp.run();
        myapp.wait();

        return 0;
    }
    catch (mooon::sys::CSyscallException& ex)
    {
        fprintf(stderr, "%s
", ex.str().c_str());
        exit(1);
    }
    catch (mooon::utils::CException& ex)
    {
        fprintf(stderr, "%s
", ex.str().c_str());
        exit(1);
    }
}

CMyApplication::CMyApplication(const char* data)
    : _stop(false)
{
    _master_path = "/tmp/a";
    if (data != NULL)
        _master_data = data;
}

void CMyApplication::run()
{
    启动时竞争master，
    在成为master之前不能进入工作状态
    while (!_stop)
    {
        int zk_errcode;
        std::string zk_errmsg;

        if (race_master(_master_path, _master_data, &zk_errcode, &zk_errmsg))
        {
            成为master后，
            要让原来的master有足够时间退出master状态
            MYLOG_INFO("Race master at %s with %s successfully, sleep for 10 seconds to let the old master quit
", _master_path.c_str(), _master_data.c_str());
            mooon::sys::CUtils::millisleep(10000);
            MYLOG_INFO("Start working now
");

            work();
            if (!_stop)
            {
                退出work()，表示需要重新竞争master
                MYLOG_INFO("Turn to slave from master at %s with %s successfully, stop working now
", _master_path.c_str(), _master_data.c_str());
            }
        }
        else
        {
            如果node_exists_exception()返回true，表示已有master，
            即_master_path已存在，返回false为其它错误，应将错误信息记录到日志
            if (node_exists_exception(zk_errcode))
            {
                MYLOG_INFO("A master exists
");
            }
            else
            {
                MYLOG_ERROR("Race master at %s with %s failed: (state:%d)(errcode:%d)%s
", _master_path.c_str(), _master_data.c_str(), get_state(), zk_errcode, zk_errmsg.c_str());
                if (invalid_handle_exception(zk_errcode))
                {
                    MYLOG_INFO("To recreate session
");
                    recreate_session();
                }
            }

            休息2秒后再尝试，不要过频重试，一般情况下1~10秒都是可接受的
            mooon::sys::CUtils::millisleep(2000);
        }
    }

    MYLOG_INFO("Exit now
");
}

void CMyApplication::wait()
{
}

void CMyApplication::work()
{
    要及时检查is_connected()，以防止master失效后同时存在两个master
    while (!_stop && !is_session_expired())
    {
        mooon::sys::CUtils::millisleep(2000);
        MYLOG_INFO("Working with state:33[1;33m%d33[m ...
", get_state());
    }
}

void CMyApplication::on_zookeeper_session_connected(const char* path)
{
    MYLOG_INFO("[33[1;33mon_zookeeper_session_connected33[m] path: %s
", path);

    const std::string zk_parent_path = "";
    const std::string zk_node_name = "test";
    const std::string zk_node_data = "123";

    try
    {
        create_node(zk_parent_path, zk_node_name, zk_node_data, ZOO_EPHEMERAL);
        MYLOG_INFO("Create %s/%s ok
", zk_parent_path.c_str(), zk_node_name.c_str());
    }
    catch (mooon::utils::CException& ex)
    {
        MYLOG_ERROR("Create %s/%s failed: %s
", zk_parent_path.c_str(), zk_node_name.c_str(), ex.str().c_str());
    }
}

void CMyApplication::on_zookeeper_session_connecting(const char* path)
{
    MYLOG_INFO("[33[1;33mon_zookeeper_session_connecting33[m] path: %s
", path);
}

void CMyApplication::on_zookeeper_session_expired(const char *path)
{
    MYLOG_INFO("[33[1;33mon_zookeeper_session_expired33[m] path: %s
", path);
    //exit(1); 最安全的做法，在这里直接退出，通过重新启动方式再次竞争master
}

void CMyApplication::on_zookeeper_session_event(int state, const char *path)
{
    MYLOG_INFO("[33[1;33mon_zookeeper_session_event33[m][state:%d] path: %s
", state, path);
}

void CMyApplication::on_zookeeper_event(int type, int state, const char *path)
{
    MYLOG_INFO("[33[1;33mon_zookeeper_event33[m][type:%d][state:%d] path: %s
", type, state, path);

    if (type == 3)
    {
        const int data_size = mooon::SIZE_4K;
        const bool keep_watch = true;
        std::string zk_data;
        const int n = get_zk_data(path, &zk_data, data_size, keep_watch);
        printf("(%d/%zd)%s
", n, zk_data.size(), zk_data.c_str());
    }
}