Mosquitto-1.5.4源码分析，主题订阅的数据结构及SUBSCRIBE的函数跳转关系

更新时间：2022-05-29 02:01:15

1.4.x之前的版本可以参考博客，使用的是树来实现：

mosquito从版本1.5.x开始，主题订阅的数据结构有变化。采用哈希表来存储。每一层都有一个哈希表来存储。

/src/database.c

这里初始化了两个主题，一个是业务主题“”，为空；另一个是系统主题“$SYS”

函数sub__add_hier_entry很重要，新增哈希key-value都靠它来实现。

int db__open(struct mosquitto__config *config, struct mosquitto_db *db)
{
    struct mosquitto__subhier *subhier;
    if(!config || !db) return MOSQ_ERR_INVAL;
    db->last_db_id = 0;
    db->contexts_by_id = NULL;
    db->contexts_by_sock = NULL;
    db->contexts_for_free = NULL;
#ifdef WITH_BRIDGE
    db->bridges = NULL;
    db->bridge_count = 0;
#endif
    // Initialize the hashtable
    db->clientid_index_hash = NULL;
    db->subs = NULL;
    subhier = sub__add_hier_entry(NULL, &db->subs, "", strlen(""));//业务子树根节点
    if(!subhier) return MOSQ_ERR_NOMEM;
    subhier = sub__add_hier_entry(NULL, &db->subs, "$SYS", strlen("$SYS"));//系统子树根节点
    if(!subhier) return MOSQ_ERR_NOMEM;
subs.c，会创建内存
child = mosquitto__malloc(sizeof(struct mosquitto__subhier));
struct mosquitto__subhier *sub__add_hier_entry(struct mosquitto__subhier *parent, struct mosquitto__subhier **sibling, const char *topic, size_t len)
{
    struct mosquitto__subhier *child;
    assert(sibling);
    child = mosquitto__malloc(sizeof(struct mosquitto__subhier));
    if(!child){
  log__printf(NULL, MOSQ_LOG_ERR, "Error: Out of memory.");
  return NULL;
    }
    child->parent = parent;
    child->topic_len = len;
    if(UHPA_ALLOC_TOPIC(child) == 0){
  child->topic_len = 0;
  mosquitto__free(child);
  log__printf(NULL, MOSQ_LOG_ERR, "Error: Out of memory.");
  return NULL;
    }else{
  strncpy(UHPA_ACCESS_TOPIC(child), topic, child->topic_len+1);
    }
    child->subs = NULL;
    child->children = NULL;
    child->retained = NULL;
    if(child->topic_len+1 > sizeof(child->topic.array)){
  if(child->topic.ptr){
    HASH_ADD_KEYPTR(hh, *sibling, child->topic.ptr, child->topic_len, child);
  }else{
    mosquitto__free(child);
    return NULL;
  }
    }else{
  HASH_ADD(hh, *sibling, topic.array, child->topic_len, child);
    }
    return child;
}