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\n", ex.str().c_str());
exit(1);
}
catch (mooon::utils::CException& ex)
{
fprintf(stderr, "%s\n", 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\n", _master_path.c_str(), _master_data.c_str());
mooon::sys::CUtils::millisleep(10000);
MYLOG_INFO("Start working now\n"); 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\n", _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\n");
}
else
{
MYLOG_ERROR("Race master at %s with %s failed: (state:%d)(errcode:%d)%s\n", _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\n");
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\n");
} 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:\033[1;33m%d\033[m ...\n", get_state());
}
} void CMyApplication::on_zookeeper_session_connected(const char* path)
{
MYLOG_INFO("[\033[1;33mon_zookeeper_session_connected\033[m] path: %s\n", 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\n", zk_parent_path.c_str(), zk_node_name.c_str());
}
catch (mooon::utils::CException& ex)
{
MYLOG_ERROR("Create %s/%s failed: %s\n", 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("[\033[1;33mon_zookeeper_session_connecting\033[m] path: %s\n", path);
} void CMyApplication::on_zookeeper_session_expired(const char *path)
{
MYLOG_INFO("[\033[1;33mon_zookeeper_session_expired\033[m] path: %s\n", 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("[\033[1;33mon_zookeeper_session_event\033[m][state:%d] path: %s\n", state, path);
} void CMyApplication::on_zookeeper_event(int type, int state, const char *path)
{
MYLOG_INFO("[\033[1;33mon_zookeeper_event\033[m][type:%d][state:%d] path: %s\n", 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", n, zk_data.size(), zk_data.c_str());
}
}