第五步：tracker全局变量g_groups初始化(part 2)--tracker_mem_init_groups函数分析

|-----tracker_mem_init
        |-----init_pthread_lock（mem_thread_lock）
        |-----init_pthread_lock（mem_file_lock）
        |-----tracker_open_changlog_file
        |-----tracker_mem_init_groups

在上一节提到的tracker_mem_init函数中，tracker_mem_init_groups函数被这样调用

return tracker_mem_init_groups(&g_groups);//初始化g_groups全局变量

tracker_mem_init_groups函数被用来初始化全局变量g_groups，g_groups是一个FDFSGroups结构的变量，该结构构造如下：

typedef struct
{
    int alloc_size; //alloc group count   //记录一次分配的group个数
    int count; //group count   //记录现在的groups中的group个数
    FDFSGroupInfo **groups; //指向group指针数组
    FDFSGroupInfo **sorted_groups; //groups order by group_name  //指向sorted_group指针数组
    FDFSGroupInfo *pStoreGroup; //the group to store uploaded files  //上传文件的store group
    int current_write_group; //current group index to upload file  //上传文件的store group的index
    byte store_lookup; //store to which group, from conf file   //
    byte store_server; //store to which storage server, from conf file
    byte download_server; //download from which storage server, from conf file
    byte store_path; //store to which path, from conf file
    char store_group[FDFS_GROUP_NAME_MAX_LEN + 1];
} FDFSGroups

FDFSGroups结构维护着分布式系统所有group的信息，FDFSGroups结构包含FDFSGroupInfo结构的指针，该结构构造如下：

typedef struct
{
    char group_name[FDFS_GROUP_NAME_MAX_LEN + 1];
    int64_t free_mb; //free disk storage in MB
    int alloc_size; //alloc storage count   //一次增加个数
    int count; //total server count    //一个group中，总共的server的数目
    int active_count; //active server count  //活动的server数目
    int storage_port; //storage server port    //端口
    int storage_http_port; //storage http server port    //http端口
    FDFSStorageDetail **all_servers; //all storage servers
    FDFSStorageDetail **sorted_servers; //storages order by ip addr
    FDFSStorageDetail **active_servers; //storages order by ip addr
    FDFSStorageDetail *pStoreServer; //for upload priority mode

#ifdef WITH_HTTPD
    FDFSStorageDetail **http_servers; //storages order by ip addr
    int http_server_count; //http server count
    int current_http_server; //current http server index
#endif

    int current_read_server; //current read storage server index
    int current_write_server; //current write storage server index

    int store_path_count; //store base path count of each storage server

    /* subdir_count * subdir_count directories will be auto created
       under each store_path (disk) of the storage servers
    */
    int subdir_count_per_path;

    int **last_sync_timestamps;//row for src storage, col for dest storage

    int chg_count; //current group changed count
    time_t last_source_update; //last source update timestamp
    time_t last_sync_update; //last synced update timestamp
} FDFSGroupInfo

FDFSGroupInfo结构表示分布式存储系统中的单个group的信息，FDFSGroupInfo结构又包含了FDFSStorageDetail结构，该结构的构造如下：

typedef struct StructFDFSStorageDetail
{
    char status;  //当前存储的状态
    char ip_addr[IP_ADDRESS_SIZE];  //ip地址
    char domain_name[FDFS_DOMAIN_NAME_MAX_SIZE];  //当前存储的域名
    char version[FDFS_VERSION_SIZE];  //版本

    struct StructFDFSStorageDetail *psync_src_server;
    time_t sync_until_timestamp;

    time_t join_time; //storage join timestamp (create timestamp)
    time_t up_time; //startup timestamp
    int64_t total_mb; //total disk storage in MB
    int64_t free_mb; //free disk storage in MB
    int64_t changelog_offset; //changelog file offset

    int64_t *path_total_mbs; //total disk storage in MB
    int64_t *path_free_mbs; //free disk storage in MB

    int store_path_count; //store base path count of each storage server
    int subdir_count_per_path;
    int upload_priority; //storage upload priority

    int storage_port; //storage server port
    int storage_http_port; //storage http server port

    int current_write_path; //current write path index

    int chg_count; //current server changed counter
    FDFSStorageStat stat;

#ifdef WITH_HTTPD
    int http_check_last_errno;
    int http_check_last_status;
    int http_check_fail_count;
    char http_check_error_info[256];
#endif
} FDFSStorageDetail

FDFSStorageDetail表示分布式系统中的一个storage的结构，通过对上面三个结构的分析，对理清groups、group、storage的三者之间的关系很重要

tracker_mem_init_groups内部的函数调用结构如下：
tracker_mem_init_groups
    |-----tracker_load_data
tracker_mem_init_groups在内部先分配了全局变量g_groups的groups的空间，再调用tracker_load_data函数分配相关group与storage的空间

//初始化group的空间
static int tracker_mem_init_groups(FDFSGroups *pGroups)
{
    int result;
    FDFSGroupInfo **ppGroup;
    FDFSGroupInfo **ppGroupEnd;

    pGroups->alloc_size = TRACKER_MEM_ALLOC_ONCE; //每次分配2个group的空间
    pGroups->count = 0;//group数目置0
    pGroups->current_write_group = 0;//upload group的index置0
    pGroups->pStoreGroup = NULL;//当前upload group为null
    pGroups->groups = (FDFSGroupInfo **)malloc( \  //为groups分配空间，groups指向的是一个group的指针数组
            sizeof(FDFSGroupInfo *) * pGroups->alloc_size);
    if (pGroups->groups == NULL)
    {
        logCrit("file: "__FILE__", line: %d, " \
            "malloc %d bytes fail!", __LINE__, \
            (int)sizeof(FDFSGroupInfo *) * pGroups->alloc_size);
        return errno != 0 ? errno : ENOMEM;
    }

    memset(pGroups->groups, 0, \  //把groups指向的数组空间置0
        sizeof(FDFSGroupInfo *) * pGroups->alloc_size);

    ppGroupEnd = pGroups->groups + pGroups->alloc_size;//指向group指针数组末尾的下一个节点
    for (ppGroup=pGroups->groups; ppGroup<ppGroupEnd; ppGroup++)
    {
        *ppGroup = (FDFSGroupInfo *)malloc(sizeof(FDFSGroupInfo));//为group指针数组的每个元素分配一个group的空间
        if (*ppGroup == NULL)
        {
            logCrit("file: "__FILE__", line: %d, " \
                "malloc %d bytes fail!", \
                __LINE__, (int)sizeof(FDFSGroupInfo));
            return errno != 0 ? errno : ENOMEM;
        }

        memset(*ppGroup, 0, sizeof(FDFSGroupInfo));
    }

    pGroups->sorted_groups = (FDFSGroupInfo **) \//为sorted_groups分配空间，sorted_groups指向的是一个group的指针数组
            malloc(sizeof(FDFSGroupInfo *) * pGroups->alloc_size);
    if (pGroups->sorted_groups == NULL)
    {
        free(pGroups->groups);
        pGroups->groups = NULL;

        logCrit("file: "__FILE__", line: %d, " \
            "malloc %d bytes fail!", __LINE__, \
            (int)sizeof(FDFSGroupInfo *) * pGroups->alloc_size);
        return errno != 0 ? errno : ENOMEM;
    }

    memset(pGroups->sorted_groups, 0, \  //把sorted_groups指向的数组空间置0
        sizeof(FDFSGroupInfo *) * pGroups->alloc_size);

    if ((result=tracker_load_data(pGroups)) != 0) //从配置文件中加载group与server的数据
    {
        return result;
    }

    return 0;
}

下图展示出了，在执行函数tracker_load_data函数之前，g_groups的初始化状态


程序给groups指针数组分配了空间，并给数组中的每个指针分配了空间，而对sorted_groups指针数组，只分配了数组空间，数组中的每个元素还未分配空间
下一节将详细分析tracker_load_data函数，该函数继续为全局变量g_gruoup中的元素分配空间