Zookeeper場景實踐：（5）分佈式通知/協調

1.基本介紹

通知/協調機制通常有兩種方式。

• 系統調度模式：操作人員發送通知實際是通過控制檯改變某個節點的狀態，然後Zookeeper將這些變化發送給註冊了這個節點的Watcher的所有客戶端。
• 工作彙報模式：這個情況是每個工作進程都在某個目錄下創建一個臨時節點，並攜帶工作的進度數據。這樣彙總的進程可以監控目錄子節點的變化獲得工作進度的實時的全局情況。

總的來說，利用Zookeeper的watcher註冊和異步通知功能，通知的發送者創建一個節點，並將通知的數據寫入的該節點；通知的接受者則對該節點註冊watch，當節點變化時，就算作通知的到來。

場景實踐

通過上面的說明，其實實現還是非常容易的。看下關鍵的幾個地方：

• g_monitor_child:變量等於0標識只監控節點，等於1標識監控所有子節點。
• show_notify(zh,g_path);：打印接受到的通知
• show_list(zh,g_path);：打印所有子節點的進度

再來看監控函數：

void zktest_watcher_g(zhandle_t* zh, int type, int state, const char* path, void* watcherCtx)  
{  
    //監控節點數據變化
    if(type == ZOO_CHANGED_EVENT &&
       state == ZOO_CONNECTED_STATE &&
       g_monitor_child == 0){

        show_notify(zh,g_path);
    //監控子節點個數變化
    }else if(type == ZOO_CHILD_EVENT &&
            state == ZOO_CONNECTED_STATE &&
            g_monitor_child == 1){

        show_list(zh,g_path);
    //監控子節點數據變化
    }else if(type == ZOO_CHANGED_EVENT &&
            state == ZOO_CONNECTED_STATE &&
            g_monitor_child == 1){

        show_list(zh,g_path);
    }
}

下面是完整的代碼：

#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); //設置日誌級別,避免出現一些其他信息  

    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個參數選項

• -s:指定Zookeeper的服務器的ip:port
• -p:指定要監控的路徑，默認爲/Notify
• -c:使用此項表示監控子節點列表

如 notify -s172.17.0.36:2181 -p /Notify
當你在客戶端修改數據的時候，程序就能收到對應的通知了。