1.基本介绍

通知/协调机制通常有两种方式。

• 系统调度模式：操作人员发送通知实际是通过控制台改变某个节点的状态，然后Zookeeper将这些变化发送给注册了这个节点的Watcher的所有客户端。
• 工作汇报模式：这个情况是每个工作进程都在某个目录下创建一个临时节点，并携带工作的进度数据。这样汇总的进程可以监控目录子节点的变化获得工作进度的实时的全局情况。

总的来说，利用Zookeeper的watcher注册和异步通知功能，通知的发送者创建一个节点，并将通知的数据写入的该节点；通知的接受者则对该节点注册watch，当节点变化时，就算作通知的到来。

场景实践

通过上面的说明，其实实现还是非常容易的。看下关键的几个地方：

• g_monitor_child:变量等于0标识只监控节点，等于1标识监控所有子节点。
• show_notify(zh,g_path);：打印接受到的通知
• show_list(zh,g_path);：打印所有子节点的进度

再来看监控函数：

void zktest_watcher_g(zhandle_t* zh, int type, int state, const char* path, void* watcherCtx)  
{  
    //监控节点数据变化
    if(type == ZOO_CHANGED_EVENT &&
       state == ZOO_CONNECTED_STATE &&
       g_monitor_child == 0){

        show_notify(zh,g_path);
    //监控子节点个数变化
    }else if(type == ZOO_CHILD_EVENT &&
            state == ZOO_CONNECTED_STATE &&
            g_monitor_child == 1){

        show_list(zh,g_path);
    //监控子节点数据变化
    }else if(type == ZOO_CHANGED_EVENT &&
            state == ZOO_CONNECTED_STATE &&
            g_monitor_child == 1){

        show_list(zh,g_path);
    }
}

下面是完整的代码：

#include<stdio.h>  
#include<string.h>  
#include<unistd.h>
#include"zookeeper.h"  
#include"zookeeper_log.h"  

char g_host[512]= "172.17.0.36:2181";  
char g_path[512]= "/Notify";
int g_monitor_child = 0;

//watch function when child list changed
void zktest_watcher_g(zhandle_t* zh, int type, int state, const char* path, void* watcherCtx);
void show_notify(zhandle_t *zkhandle,const char *path);
//show all process ip:pid
void show_list(zhandle_t *zkhandle,const char *path);

void print_usage();
void get_option(int argc,const char* argv[]);

/**********unitl*********************/  
void print_usage()
{
    printf("Usage : [notify] [-h] [-c] [-p path][-s ip:port] \n");
    printf("        -h Show help\n");
    printf("        -p path\n");
    printf("        -c monitor the child nodes\n");
    printf("        -s zookeeper server ip:port\n");
    printf("For example:\n");
    printf("notify -s172.17.0.36:2181 -p /Notify\n");
}

void get_option(int argc,const char* argv[])
{
    extern char    *optarg;
    int            optch;
    int            dem = 1;
    const char    optstring[] = "hcp:s:";


    while((optch = getopt(argc , (char * const *)argv , optstring)) != -1 )
    {
        switch( optch )
        {
        case 'h':
            print_usage();
            exit(-1);
        case '?':
            print_usage();
            printf("unknown parameter: %c\n", optopt);
            exit(-1);
        case ':':
            print_usage();
            printf("need parameter: %c\n", optopt);
            exit(-1);
        case 'c':
            g_monitor_child = 1;
            break;
        case 's':
            strncpy(g_host,optarg,sizeof(g_host));
            break;
        case 'p':
            strncpy(g_path,optarg,sizeof(g_path));
            break;
        default:
            break;
        }
    }
} 
void zktest_watcher_g(zhandle_t* zh, int type, int state, const char* path, void* watcherCtx)  
{  
  /*
    printf("watcher event\n");  
    printf("type: %d\n", type);  
    printf("state: %d\n", state);  
    printf("path: %s\n", path);  
    printf("watcherCtx: %s\n", (char *)watcherCtx);  
  */

    if(type == ZOO_CHANGED_EVENT &&
       state == ZOO_CONNECTED_STATE &&
       g_monitor_child == 0){

        show_notify(zh,g_path);
    }else if(type == ZOO_CHILD_EVENT &&
            state == ZOO_CONNECTED_STATE &&
            g_monitor_child == 1){

        show_list(zh,g_path);
    }else if(type == ZOO_CHANGED_EVENT &&
            state == ZOO_CONNECTED_STATE &&
            g_monitor_child == 1){

        show_list(zh,g_path);
    }
} 
void show_notify(zhandle_t *zkhandle,const char *path)
{
    char notify_buffer[1024]={0};
    int  notify_len = sizeof(notify_buffer);

    int ret = zoo_get(zkhandle,g_path,1,notify_buffer,¬ify_len,NULL);
    if(ret != ZOK){
        fprintf(stderr,"failed to get the data of path %s!\n",g_path);
    }else{
        printf("Notice:%s\n",notify_buffer);
    }
}
void show_list(zhandle_t *zkhandle,const char *path)
{

    struct String_vector children;
    int i = 0;
    int ret = zoo_get_children(zkhandle,path,1,&children);

    if(ret == ZOK){
        char child_path[512] ={0};
        char notify_buffer[1024] = {0};
        int notify_len = sizeof(notify_buffer);

        printf("--------------\n");
        for(i = 0; i < children.count; ++i){
            sprintf(child_path,"%s/%s",g_path,children.data[i]);
            ret = zoo_get(zkhandle,child_path,1,notify_buffer,¬ify_len,NULL);
            if(ret != ZOK){
                fprintf(stderr,"failed to get the data of path %s!\n",child_path);
            }else{
                printf("%s:%s\n",children.data[i],notify_buffer);
            }
        }
    }else{
        fprintf(stderr,"failed to get the children of path %s!\n",path);
    }

    for(i = 0; i < children.count; ++i){
        free(children.data[i]);
        children.data[i] = NULL;
    }
}

int main(int argc, const char *argv[])  
{  
    int timeout = 30000;  
    char path_buffer[512];  
    int bufferlen=sizeof(path_buffer);  

    zoo_set_debug_level(ZOO_LOG_LEVEL_WARN); //设置日志级别,避免出现一些其他信息  

    get_option(argc,argv);

    zhandle_t* zkhandle = zookeeper_init(g_host,zktest_watcher_g, timeout, 0, (char *)"Notify Test", 0);  

    if (zkhandle ==NULL)  
    {  
        fprintf(stderr, "Error when connecting to zookeeper servers...\n");  
        exit(EXIT_FAILURE);  
    }  

    int ret = zoo_exists(zkhandle,g_path,0,NULL); 
    if(ret != ZOK){
        ret = zoo_create(zkhandle,g_path,"1.0",strlen("1.0"),  
                          &ZOO_OPEN_ACL_UNSAFE,0,  
                          path_buffer,bufferlen);  
        if(ret != ZOK){
            fprintf(stderr,"failed to create the path %s!\n",g_path);
        }else{
            printf("create path %s successfully!\n",g_path);
        }
    }

    if(ret == ZOK && g_monitor_child == 0){
        show_notify(zkhandle,g_path);
    }else if(ret == ZOK && g_monitor_child == 1){
        show_list(zkhandle,g_path);
    }

    getchar();

    zookeeper_close(zkhandle); 

    return 0;
}

程序由3个参数选项

• -s:指定Zookeeper的服务器的ip:port
• -p:指定要监控的路径，默认为/Notify
• -c:使用此项表示监控子节点列表

如 notify -s172.17.0.36:2181 -p /Notify
当你在客户端修改数据的时候，程序就能收到对应的通知了。