// 命令队列结构体
typedef struct multiState {
// 命令队列
multiCmd *commands;     /* Array of MULTI commands */

// 命令的个数
int count;              /* Total number of MULTI commands */

// 以下两个参数暂时没有用到，和主从复制有关
int minreplicas;        /* MINREPLICAS for synchronous replication */
time_t minreplicas_timeout; /* MINREPLICAS timeout as unixtime. */
} multiState;

// 监视键值函数
/* Watch for the specified key */
void watchForKey(redisClient *c, robj *key) {
list *clients = NULL;
listIter li;
listNode *ln;
watchedKey *wk;

// 是否已经监视该键值
/* Check if we are already watching for this key */
listRewind(c->watched_keys,&li);
while((ln = listNext(&li))) {
wk = listNodeValue(ln);
if (wk->db == c->db && equalStringObjects(key,wk->key))
return; /* Key already watched */
}

// 获取监视该键值的客户端链表
/* This key is not already watched in this DB. Let’s add it */
clients = dictFetchValue(c->db->watched_keys,key);
// 如果不存在链表，需要新建一个
if (!clients) {
clients = listCreate();
dictAdd(c->db->watched_keys,key,clients);
incrRefCount(key);
}

// 尾插法。将客户端添加到链表尾部
listAddNodeTail(clients,c);

// 将监视键添加到 redisClient.watched_keys 的尾部
/* Add the new key to the list of keys watched by this client */
wk = zmalloc(sizeof(*wk));
wk->key = key;
wk->db = c->db;
incrRefCount(key);
listAddNodeTail(c->watched_keys,wk);
}

// REDIS_DIRTY_CAS 更改的时候会设置此标记
c->flags |= REDIS_DIRTY_CAS;
}
}

// 执行队列中的所有命令
/* Exec all the queued commands */
unwatchAllKeys(c); /* Unwatch ASAP otherwise we’ll waste CPU cycles */

// 保存当前的命令，一般为 MULTI，在执行完所有的命令后会恢复。
orig_argv = c->argv;
orig_argc = c->argc;
orig_cmd = c->cmd;

addReplyMultiBulkLen(c,c->mstate.count);

for (j = 0; j < c->mstate.count; j++) {
// 命令队列中的命令被赋值给当前的命令
c->argc = c->mstate.commands[j].argc;
c->argv = c->mstate.commands[j].argv;
c->cmd = c->mstate.commands[j].cmd;

// 遇到包含写操作的命令需要将 MULTI 命令写入 AOF 文件
/* Propagate a MULTI request once we encounter the first write op.
* This way we’ll deliver the MULTI/…./EXEC block as a whole and
* both the AOF and the replication link will have the same consistency
* and atomicity guarantees. */
if (!must_propagate && !(c->cmd->flags & REDIS_CMD_READONLY)) {
execCommandPropagateMulti(c);
must_propagate = 1;
}

// 调用 call() 执行
call(c,REDIS_CALL_FULL);

// 这几句是多余的
/* Commands may alter argc/argv, restore mstate. */
c->mstate.commands[j].argc = c->argc;
c->mstate.commands[j].argv = c->argv;
c->mstate.commands[j].cmd = c->cmd;
}

// 恢复当前的命令，一般为 MULTI
c->argv = orig_argv;
c->argc = orig_argc;
c->cmd = orig_cmd;

// 事务已经执行完毕，清理与此事务相关的信息，如命令队列和客户端标记
discardTransaction(c);
/* Make sure the EXEC command will be propagated as well if MULTI
* was already propagated. */
if (must_propagate) server.dirty++;

……
}