Redis源码阅读笔记-命令的接收和执行过程(二)

曾经终败给现在 2022-01-14 23:43 255阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

接着上一篇[Redis源码阅读笔记-命令的接收和执行过程(一)][Redis_-]，主要写`processCommand()`的调用过程，和`call()`是如何调用各个命令的执行函数的。

## `processCommand()` ##

`processCommand()`主要作用是判断命令的类型和简单判断参数数量，并对机器状态（内存限制，磁盘，主从状态等）和命令类型进行判断，看是否能调用命令，最后调用`call()`来真正调用各命令的执行函数。

// server.c 
    
    /* If this function gets called we already read a whole
     * command, arguments are in the client argv/argc fields.
     * processCommand() execute the command or prepare the
     * server for a bulk read from the client.
     *
     * If C_OK is returned the client is still alive and valid and
     * other operations can be performed by the caller. Otherwise
     * if C_ERR is returned the client was destroyed (i.e. after QUIT). */
    int processCommand(client *c) {
        /* The QUIT command is handled separately. Normal command procs will
         * go through checking for replication and QUIT will cause trouble
         * when FORCE_REPLICATION is enabled and would be implemented in
         * a regular command proc. */
        // 检查是否是退出命令
        if (!strcasecmp(c->argv[0]->ptr,"quit")) {
            addReply(c,shared.ok);
            c->flags |= CLIENT_CLOSE_AFTER_REPLY;
            return C_ERR;
        }
    
        /* Now lookup the command and check ASAP about trivial error conditions
         * such as wrong arity, bad command name and so forth. */
        // 从命令字典中判断c->argv[0]->ptr中是否是正确的命令
        // 命令集保存在server.commands中，这是一个redis的字典结构
        // 在initServerConfig()的时候通过populateCommandTable()函数将命令集添加进字典中
        c->cmd = c->lastcmd = lookupCommand(c->argv[0]->ptr);
        // c->cmd 是一个redisCommand的结构，其中proc是一个函数指针，指向对应命令的操作
        if (!c->cmd) {
            // 命令不在命令集中，返回错误信息给客户端
    
            flagTransaction(c);
            sds args = sdsempty();
            int i;
            for (i=1; i < c->argc && sdslen(args) < 128; i++)
                args = sdscatprintf(args, "`%.*s`, ", 128-(int)sdslen(args), (char*)c->argv[i]->ptr);
            addReplyErrorFormat(c,"unknown command `%s`, with args beginning with: %s",
                (char*)c->argv[0]->ptr, args);
            sdsfree(args);
            return C_OK;
        } else if ((c->cmd->arity > 0 && c->cmd->arity != c->argc) ||
                   (c->argc < -c->cmd->arity)) {
            // 命令在命令集中
            // 但是命令需要参数，且argc中的参数数量不等于命令所需的，或者少于所需要
            // 返回错误信息给客户端
            flagTransaction(c);
            addReplyErrorFormat(c,"wrong number of arguments for '%s' command",
                c->cmd->name);
            return C_OK;
        }
    
        /* Check if the user is authenticated */
        // 检查客户端连接是否已经登录验证（设置了需要验证的话）
        if (server.requirepass && !c->authenticated && c->cmd->proc != authCommand)
        {
            flagTransaction(c);
            addReply(c,shared.noautherr);
            return C_OK;
        }
    
        /* If cluster is enabled perform the cluster redirection here.
         * However we don't perform the redirection if:
         * 1) The sender of this command is our master.
         * 2) The command has no key arguments. */
        // 如果启动了集群，则进行集群的重定向
        // 下面两种情况不重定向:
        // 1. 命令时Master节点发送过来的
        // 2. 命令没有关键参数
        if (server.cluster_enabled && // 集群是否启动
            !(c->flags & CLIENT_MASTER) && // 非Master节点的命令
            !(c->flags & CLIENT_LUA && 
              server.lua_caller->flags & CLIENT_MASTER) && // 非Mater节点的lua函数
            !(c->cmd->getkeys_proc == NULL && c->cmd->firstkey == 0 && 
              c->cmd->proc != execCommand)) // 命令有关键参数
        {
            int hashslot;
            int error_code;
            // getNodeByQuery获取为该命令服务的节点，并获取错误代码和哈希槽
            clusterNode *n = getNodeByQuery(c,c->cmd,c->argv,c->argc,
                                            &hashslot,&error_code);
            if (n == NULL || n != server.cluster->myself) {
                if (c->cmd->proc == execCommand) {
                    discardTransaction(c);
                } else {
                    flagTransaction(c);
                }
                // 命令重定向到节点
                clusterRedirectClient(c,n,hashslot,error_code);
                return C_OK;
            }
        }
    
        /* Handle the maxmemory directive.
         *
         * First we try to free some memory if possible (if there are volatile
         * keys in the dataset). If there are not the only thing we can do
         * is returning an error. */
        // 如果有限定最大使用内存
        // 则先尝试释放内存，如果内存不足则返回OOM错误
        if (server.maxmemory) {
            // 检查和尝试释放内存
            // 原理是，zmalloc.c中会有一个used_memory的全局变量，来记录redis申请了多少内存
            // PS: AOF的缓冲区和slaves的输出缓冲并不会算入已使用内存中
            // 当内存不够时，freeMemoryIfNeeded()会根据设置的最大内存规则区尝试释放内存
            int retval = freeMemoryIfNeeded();
            /* freeMemoryIfNeeded may flush slave output buffers. This may result
             * into a slave, that may be the active client, to be freed. */
            if (server.current_client == NULL) return C_ERR;
    
            /* It was impossible to free enough memory, and the command the client
             * is trying to execute is denied during OOM conditions? Error. */
            if ((c->cmd->flags & CMD_DENYOOM) && retval == C_ERR) {
                flagTransaction(c);
                addReply(c, shared.oomerr);
                return C_OK;
            }
        }
    
        /* Don't accept write commands if there are problems persisting on disk
         * and if this is a master instance. */
        // 同时满足3个条件:
        //    1. 磁盘存在问题，aof等写操作失败
        //    2. 本机是master主机
        //    3. 命令属于写操作
        // 则会返回错误
        if (((server.stop_writes_on_bgsave_err &&
              server.saveparamslen > 0 &&
              server.lastbgsave_status == C_ERR) ||
              server.aof_last_write_status == C_ERR) &&
            server.masterhost == NULL &&
            (c->cmd->flags & CMD_WRITE ||
             c->cmd->proc == pingCommand))
        {
            flagTransaction(c);
            if (server.aof_last_write_status == C_OK)
                addReply(c, shared.bgsaveerr);
            else
                addReplySds(c,
                    sdscatprintf(sdsempty(),
                    "-MISCONF Errors writing to the AOF file: %s\r\n",
                    strerror(server.aof_last_write_errno)));
            return C_OK;
        }
    
        /* Don't accept write commands if there are not enough good slaves and
         * user configured the min-slaves-to-write option. */
        // 如果同时满足
        //     1. 本机是master
        //     2. 用户配置了 min-slaves-to-write 的选项
        //     3. 命令属于写操作
        //     4. 可用的 slaves 数量少于 repl_min_slaves_to_write 所需要的数量
        // 则返回错误
        if (server.masterhost == NULL &&
            server.repl_min_slaves_to_write &&
            server.repl_min_slaves_max_lag &&
            c->cmd->flags & CMD_WRITE &&
            server.repl_good_slaves_count < server.repl_min_slaves_to_write)
        {
            flagTransaction(c);
            addReply(c, shared.noreplicaserr);
            return C_OK;
        }
    
        /* Don't accept write commands if this is a read only slave. But
         * accept write commands if this is our master. */
        // 如果同时满足
        //    1. 本机是 slave
        //    2. 本机是 只读 的slave
        //    3. client不是来自 master
        //    4. client的命令属于写操作
        // 则返回错误
        if (server.masterhost && server.repl_slave_ro &&
            !(c->flags & CLIENT_MASTER) &&
            c->cmd->flags & CMD_WRITE)
        {
            addReply(c, shared.roslaveerr);
            return C_OK;
        }
    
        /* Only allow SUBSCRIBE and UNSUBSCRIBE in the context of Pub/Sub */
        // 如果client是消息订阅的连接
        // 只允许以下操作: 
        //    * ping
        //    * subscribe
        //    * unsubscribe
        //    * psubscribe
        //    * punsubscribe
        if (c->flags & CLIENT_PUBSUB &&
            c->cmd->proc != pingCommand &&
            c->cmd->proc != subscribeCommand &&
            c->cmd->proc != unsubscribeCommand &&
            c->cmd->proc != psubscribeCommand &&
            c->cmd->proc != punsubscribeCommand) {
            addReplyError(c,"only (P)SUBSCRIBE / (P)UNSUBSCRIBE / PING / QUIT allowed in this context");
            return C_OK;
        }
    
        /* Only allow INFO and SLAVEOF when slave-serve-stale-data is no and
         * we are a slave with a broken link with master. */
        
        if (server.masterhost && server.repl_state != REPL_STATE_CONNECTED &&
            server.repl_serve_stale_data == 0 &&
            !(c->cmd->flags & CMD_STALE))
        {
            // // 如果本机是与master断开的slave时
            flagTransaction(c);
            addReply(c, shared.masterdownerr);
            return C_OK;
        }
    
        /* Loading DB? Return an error if the command has not the
         * CMD_LOADING flag. */
        if (server.loading && !(c->cmd->flags & CMD_LOADING)) {
            addReply(c, shared.loadingerr);
            return C_OK;
        }
    
        /* Lua script too slow? Only allow a limited number of commands. */
        // 当lua脚本很慢的时候，只允许部分操作
        if (server.lua_timedout &&
              c->cmd->proc != authCommand &&
              c->cmd->proc != replconfCommand &&
            !(c->cmd->proc == shutdownCommand &&
              c->argc == 2 &&
              tolower(((char*)c->argv[1]->ptr)[0]) == 'n') &&
            !(c->cmd->proc == scriptCommand &&
              c->argc == 2 &&
              tolower(((char*)c->argv[1]->ptr)[0]) == 'k'))
        {
            flagTransaction(c);
            addReply(c, shared.slowscripterr);
            return C_OK;
        }
    
        /* Exec the command */
        // 执行各个命令
        if (c->flags & CLIENT_MULTI &&
            c->cmd->proc != execCommand && c->cmd->proc != discardCommand &&
            c->cmd->proc != multiCommand && c->cmd->proc != watchCommand)
        {
            // 如果是client属于multi，且命令不是(exec，discard,multi,watch)，则将命令加入到队列中
            queueMultiCommand(c);
            addReply(c,shared.queued);
        } else {
            // 执行命令
            call(c,CMD_CALL_FULL);
            c->woff = server.master_repl_offset;
            if (listLength(server.ready_keys))
                handleClientsBlockedOnLists();
        }
        return C_OK;
    }

## `call()` ##

`call()`是Redis中执行命令的核心函数。

// server.c
    
    /* Call() is the core of Redis execution of a command.
     *
     * The following flags can be passed:
     * CMD_CALL_NONE        No flags.
     * CMD_CALL_SLOWLOG     Check command speed and log in the slow log if needed.
     * CMD_CALL_STATS       Populate command stats.
     * CMD_CALL_PROPAGATE_AOF   Append command to AOF if it modified the dataset
     *                          or if the client flags are forcing propagation.
     * CMD_CALL_PROPAGATE_REPL  Send command to salves if it modified the dataset
     *                          or if the client flags are forcing propagation.
     * CMD_CALL_PROPAGATE   Alias for PROPAGATE_AOF|PROPAGATE_REPL.
     * CMD_CALL_FULL        Alias for SLOWLOG|STATS|PROPAGATE.
     *
     * The exact propagation behavior depends on the client flags.
     * Specifically:
     *
     * 1. If the client flags CLIENT_FORCE_AOF or CLIENT_FORCE_REPL are set
     *    and assuming the corresponding CMD_CALL_PROPAGATE_AOF/REPL is set
     *    in the call flags, then the command is propagated even if the
     *    dataset was not affected by the command.
     * 2. If the client flags CLIENT_PREVENT_REPL_PROP or CLIENT_PREVENT_AOF_PROP
     *    are set, the propagation into AOF or to slaves is not performed even
     *    if the command modified the dataset.
     *
     * Note that regardless of the client flags, if CMD_CALL_PROPAGATE_AOF
     * or CMD_CALL_PROPAGATE_REPL are not set, then respectively AOF or
     * slaves propagation will never occur.
     *
     * Client flags are modified by the implementation of a given command
     * using the following API:
     *
     * forceCommandPropagation(client *c, int flags);
     * preventCommandPropagation(client *c);
     * preventCommandAOF(client *c);
     * preventCommandReplication(client *c);
     *
     */
    void call(client *c, int flags) {
        long long dirty, start, duration;
        int client_old_flags = c->flags;
    
        /* Sent the command to clients in MONITOR mode, only if the commands are
         * not generated from reading an AOF. */
        // 将命令发送到monitor的客户端（当server正在读AOF的数据或者客户端的命令设置了CMD_SKIP_MONITOR或CMD_ADMIN）
        // PS: MONITOR, 实时打印出 Redis 服务器接收到的命令，调试用
        if (listLength(server.monitors) &&
            !server.loading &&
            !(c->cmd->flags & (CMD_SKIP_MONITOR|CMD_ADMIN)))
        {
            replicationFeedMonitors(c,server.monitors,c->db->id,c->argv,c->argc);
        }
    
        /* Initialization: clear the flags that must be set by the command on
         * demand, and initialize the array for additional commands propagation. */
        c->flags &= ~(CLIENT_FORCE_AOF|CLIENT_FORCE_REPL|CLIENT_PREVENT_PROP);
        // 初始化also_propagate，部分命令会调用also_propagate()将一些AOF的传播函数添加进server.also_propagate中，
        // 然后在call()的末尾处调用
        redisOpArray prev_also_propagate = server.also_propagate;
        redisOpArrayInit(&server.also_propagate);
    
        /* Call the command. */
        dirty = server.dirty;
        start = ustime();
        // 执行命令
        c->cmd->proc(c);
        duration = ustime()-start; // 命令的执行时间
        dirty = server.dirty-dirty; // 用来记录DB是否被修改了
        if (dirty < 0) dirty = 0;
    
        /* When EVAL is called loading the AOF we don't want commands called
         * from Lua to go into the slowlog or to populate statistics. */
        // 当正在加载AOF，且是执行lua时
        // 不进入slow log 和 不统计数据
        if (server.loading && c->flags & CLIENT_LUA)
            flags &= ~(CMD_CALL_SLOWLOG | CMD_CALL_STATS);
    
        /* If the caller is Lua, we want to force the EVAL caller to propagate
         * the script if the command flag or client flag are forcing the
         * propagation. */
        // 如果是lua脚本，强制repl 和 aof
        if (c->flags & CLIENT_LUA && server.lua_caller) {
            if (c->flags & CLIENT_FORCE_REPL)
                server.lua_caller->flags |= CLIENT_FORCE_REPL;
            if (c->flags & CLIENT_FORCE_AOF)
                server.lua_caller->flags |= CLIENT_FORCE_AOF;
        }
    
        /* Log the command into the Slow log if needed, and populate the
         * per-command statistics that we show in INFO commandstats. */
        // 记录slow log
        if (flags & CMD_CALL_SLOWLOG && c->cmd->proc != execCommand) {
            char *latency_event = (c->cmd->flags & CMD_FAST) ?
                                  "fast-command" : "command";
            latencyAddSampleIfNeeded(latency_event,duration/1000);
            slowlogPushEntryIfNeeded(c,c->argv,c->argc,duration);
        }
        if (flags & CMD_CALL_STATS) {
            c->lastcmd->microseconds += duration;
            c->lastcmd->calls++;
        }
    
        /* Propagate the command into the AOF and replication link */
        // 传播数据库的变动到AOF或者主从复制中
        if (flags & CMD_CALL_PROPAGATE &&
            (c->flags & CLIENT_PREVENT_PROP) != CLIENT_PREVENT_PROP)
        {
            int propagate_flags = PROPAGATE_NONE;
    
            /* Check if the command operated changes in the data set. If so
             * set for replication / AOF propagation. */
             // 如果有数据库的变动，这设置传播AOF和主从
            if (dirty) propagate_flags |= (PROPAGATE_AOF|PROPAGATE_REPL);
    
            /* If the client forced AOF / replication of the command, set
             * the flags regardless of the command effects on the data set. */
            // 判断是否需要强制传播
            if (c->flags & CLIENT_FORCE_REPL) propagate_flags |= PROPAGATE_REPL;
            if (c->flags & CLIENT_FORCE_AOF) propagate_flags |= PROPAGATE_AOF;
    
            /* However prevent AOF / replication propagation if the command
             * implementatino called preventCommandPropagation() or similar,
             * or if we don't have the call() flags to do so. */
            // 判断client是否阻止AOF传播或者主从复制传播
            if (c->flags & CLIENT_PREVENT_REPL_PROP ||
                !(flags & CMD_CALL_PROPAGATE_REPL))
                    propagate_flags &= ~PROPAGATE_REPL;
            if (c->flags & CLIENT_PREVENT_AOF_PROP ||
                !(flags & CMD_CALL_PROPAGATE_AOF))
                    propagate_flags &= ~PROPAGATE_AOF;
    
            /* Call propagate() only if at least one of AOF / replication
             * propagation is needed. Note that modules commands handle replication
             * in an explicit way, so we never replicate them automatically. */
            if (propagate_flags != PROPAGATE_NONE && !(c->cmd->flags & CMD_MODULE))
                // 传播
                propagate(c->cmd,c->db->id,c->argv,c->argc,propagate_flags);
        }
    
        /* Restore the old replication flags, since call() can be executed
         * recursively. */
        c->flags &= ~(CLIENT_FORCE_AOF|CLIENT_FORCE_REPL|CLIENT_PREVENT_PROP);
        c->flags |= client_old_flags &
            (CLIENT_FORCE_AOF|CLIENT_FORCE_REPL|CLIENT_PREVENT_PROP);
    
        /* Handle the alsoPropagate() API to handle commands that want to propagate
         * multiple separated commands. Note that alsoPropagate() is not affected
         * by CLIENT_PREVENT_PROP flag. */
        // 调用使用alsoPropagate()添加的方法，alsoPropagate()会将方法添加到server.also_propagate中
        if (server.also_propagate.numops) {
            int j;
            redisOp *rop;
    
            if (flags & CMD_CALL_PROPAGATE) {
                for (j = 0; j < server.also_propagate.numops; j++) {
                    rop = &server.also_propagate.ops[j];
                    int target = rop->target;
                    /* Whatever the command wish is, we honor the call() flags. */
                    if (!(flags&CMD_CALL_PROPAGATE_AOF)) target &= ~PROPAGATE_AOF;
                    if (!(flags&CMD_CALL_PROPAGATE_REPL)) target &= ~PROPAGATE_REPL;
                    if (target)
                        propagate(rop->cmd,rop->dbid,rop->argv,rop->argc,target);
                }
            }
            redisOpArrayFree(&server.also_propagate);
        }
        server.also_propagate = prev_also_propagate;
        server.stat_numcommands++;
    }

转载于:https://my.oschina.net/jianming/blog/2998868

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20220114/3a162f9d82f843a7b832fe8216826e4d.png
[Redis_-]: https://my.oschina.net/jianming/blog/2991072