Version Redis2.2.2
Redis中可以支持主从结构,本文主要从master和slave的心跳机制出发(PING),分析redis的命令行交互。
在Redis中,server为每个连接建立一个redisClient数据对象,来描述对应的连接。其中,redisClient为命令交互设置了缓冲区。querybuf用于存储客户端送过来的命令,buf和reply是用于应答的缓冲。querybuf是在文件事件readQueryFromClient中被填充,每次填充的最大字节数默认为1024B。而应答缓冲区是由addReply()函数填充,并由文件事件sendReplyToClient中发送给客户端。具体数据流如图1所示。MasterPorcess与SlaveProcess进行命令交互。其中,蓝色矩形框代表函数,白色矩形框代表数据,曲线描述数据流,折线描述数据间的从属关系。
图1. Master&Slave交互的数据流(蓝色矩形框代表函数,白色矩形框代表数据,曲线描述数据流,折线描述数据间的从属关系)
typedef struct redisClient { int fd; //connect fd ... sds querybuf; //命令缓冲区,由readQueryFromClient()事件进行填充(sds equals to char*) int argc; //for command;记录参数个数 robj **argv; //for command;记录命令行参数 int reqtype; //命令解析协议:INLINE or MULTIBULK ... time_t lastinteraction; /* 最近交互时间 */ ... list *reply; //Replay object list /* Response buffer */ char buf[REDIS_REPLY_CHUNK_BYTES]; //Reply buffer,由addReply()函数进行填充 int bufpos; //记录buf已填充的长度 int sentlen; //Replay阶段,记录当前buf已发送了多少字节 } redisClient; struct redisServer { ... list *clients; dict *commands; /* Command table hahs table */ ... list *slaves, *monitors; //Master : slave链表 char neterr[ANET_ERR_LEN]; aeEventLoop *el; //Event list int cronloops; //ServerCorn 执行次数 ... redisClient *master; //Slave :记录 master 的连接信息的client int replstate; //Slave :当前的状态 ... }; struct redisCommand readonlyCommandTable[] = { ... {"sync",syncCommand,1,0,NULL,0,0,0}, ... {"ping",pingCommand,1,0,NULL,0,0,0}, ... }
从图1可以看出,命令交互数据query的读取是在文件事件readQueryFromClient中填充到c->querybuf中。之后,querybuf由函数processInputBuffer进行命令的解析。命令的解析过程如图2所示。在函数processInputBuffer中,将缓存与querybuf中的所有命令(命令间按\n\r分隔)进行解析。之后,查询命令hashtabe查找相关命令函数。最后调用相应命令hander执行命令。
图2.querybuf的解析
具体代码分析如下:
void readQueryFromClient(aeEventLoop *el, int fd, void *privdata, int mask) { redisClient *c = (redisClient*) privdata; char buf[REDIS_IOBUF_LEN]; int nread; REDIS_NOTUSED(el); REDIS_NOTUSED(mask); nread = read(fd, buf, REDIS_IOBUF_LEN); ...check... if (nread) { c->querybuf = sdscatlen(c->querybuf,buf,nread); c->lastinteraction = time(NULL);//更新时间戳 } else { return; } processInputBuffer(c);//处理client传输过来的数据 } void processInputBuffer(redisClient *c) { /* 执行querybub中的所有命令*/ while(sdslen(c->querybuf)) { ...check... /*判定命令的解析协议 */ if (!c->reqtype) { if (c->querybuf[0] == '*') { c->reqtype = REDIS_REQ_MULTIBULK; } else { c->reqtype = REDIS_REQ_INLINE;//按行解析 } } if (c->reqtype == REDIS_REQ_INLINE) { /*processInlineBuffer: 1. 取出c->querybuf起始端到\r\n位置的字符串,更新c->querybuf 2. 将取出的字符串按照“ ”空格进行分段解析,得到命令及其参数 格式为: argc,*argv[],其中argv[0]为命令,argv[1~argc-1]为参数*/ if (processInlineBuffer(c) != REDIS_OK) break; } else if (c->reqtype == REDIS_REQ_MULTIBULK) { ... } /* Multibulk processing could see a <= 0 length. */ if (c->argc == 0) { resetClient(c); } else { /* Only reset the client when the command was executed. */ if (processCommand(c) == REDIS_OK) //执行命令 resetClient(c); } } } /* If this function gets called we already read a whole * command, argments are in the client argv/argc fields. * processCommand() execute the command or prepare the * server for a bulk read from the client. */ int processCommand(redisClient *c) { struct redisCommand *cmd; ... /* Now lookup the command and check ASAP about trivial error conditions * such wrong arity, bad command name and so forth. */ cmd = lookupCommand(c->argv[0]->ptr); ...check... /* Exec the command */ if (c->flags & REDIS_MULTI && cmd->proc != execCommand && cmd->proc != discardCommand && cmd->proc != multiCommand && cmd->proc != watchCommand) { queueMultiCommand(c,cmd); addReply(c,shared.queued); } else { if (server.vm_enabled && server.vm_max_threads > 0 && blockClientOnSwappedKeys(c,cmd)) return REDIS_ERR; call(c,cmd); //执行命令 } return REDIS_OK; } /* Call() is the core of Redis execution of a command */ void call(redisClient *c, struct redisCommand *cmd) { long long dirty; dirty = server.dirty; cmd->proc(c); //执行命令 dirty = server.dirty-dirty; if (server.appendonly && dirty) feedAppendOnlyFile(cmd,c->db->id,c->argv,c->argc); if ((dirty || cmd->flags & REDIS_CMD_FORCE_REPLICATION) && listLength(server.slaves)) replicationFeedSlaves(server.slaves,c->db->id,c->argv,c->argc); if (listLength(server.monitors)) replicationFeedMonitors(server.monitors,c->db->id,c->argv,c->argc); server.stat_numcommands++; }
其中,addReply将相关命令执行结果放入client的reply缓冲区中。reply缓冲区的发送时机是在事件sendReplyToClient中进行。
#define REDIS_STRING 0 shared.pong = createObject(REDIS_STRING,sdsnew("+PONG\r\n")); //{"ping",pingCommand,1,0,NULL,0,0,0} void pingCommand(redisClient *c) { addReply(c,shared.pong); //ping的回复是pong,打乒乓,呵呵 } //将命令执行的返回结构写入c->buf 或者 c->reply void addReply(redisClient *c, robj *obj) { if (_installWriteEvent(c) != REDIS_OK) return;//创建event sendReplyToClient redisAssert(!server.vm_enabled || obj->storage == REDIS_VM_MEMORY); /* This is an important place where we can avoid copy-on-write * when there is a saving child running, avoiding touching the * refcount field of the object if it's not needed. * * If the encoding is RAW and there is room in the static buffer * we'll be able to send the object to the client without * messing with its page. */ if (obj->encoding == REDIS_ENCODING_RAW) { if (_addReplyToBuffer(c,obj->ptr,sdslen(obj->ptr)) != REDIS_OK) _addReplyObjectToList(c,obj); } else { /* FIXME: convert the long into string and use _addReplyToBuffer() * instead of calling getDecodedObject. As this place in the * code is too performance critical. */ obj = getDecodedObject(obj); if (_addReplyToBuffer(c,obj->ptr,sdslen(obj->ptr)) != REDIS_OK) _addReplyObjectToList(c,obj); decrRefCount(obj); } }
将c->buf 和 c->reply中的数据发送到客户端(slave or master)。在每次文件事件中发送所有的reply缓冲区中的数据。
void sendReplyToClient(aeEventLoop *el, int fd, void *privdata, int mask) { redisClient *c = privdata; int nwritten = 0, totwritten = 0, objlen; robj *o; REDIS_NOTUSED(el); REDIS_NOTUSED(mask); while(c->bufpos > 0 || listLength(c->reply)) { if (c->bufpos > 0) { //发送c->buf中的数据 if (c->flags & REDIS_MASTER) { /* Don't reply to a master */ nwritten = c->bufpos - c->sentlen; } else { nwritten = write(fd,c->buf+c->sentlen,c->bufpos-c->sentlen); if (nwritten <= 0) break; } c->sentlen += nwritten; totwritten += nwritten; /* If the buffer was sent, set bufpos to zero to continue with * the remainder of the reply. */ if (c->sentlen == c->bufpos) { c->bufpos = 0; c->sentlen = 0; } } else { //发送c->reply中的数据 o = listNodeValue(listFirst(c->reply)); objlen = sdslen(o->ptr); if (objlen == 0) { listDelNode(c->reply,listFirst(c->reply)); continue; } if (c->flags & REDIS_MASTER) { /* Don't reply to a master */ nwritten = objlen - c->sentlen; } else { nwritten = write(fd, ((char*)o->ptr)+c->sentlen,objlen-c->sentlen); if (nwritten <= 0) break; } c->sentlen += nwritten; totwritten += nwritten; /* If we fully sent the object on head go to the next one */ if (c->sentlen == objlen) { listDelNode(c->reply,listFirst(c->reply)); c->sentlen = 0; } } /* Note that we avoid to send more thank REDIS_MAX_WRITE_PER_EVENT * bytes, in a single threaded server it's a good idea to serve * other clients as well, even if a very large request comes from * super fast link that is always able to accept data (in real world * scenario think about 'KEYS *' against the loopback interfae) */ if (totwritten > REDIS_MAX_WRITE_PER_EVENT) break; } ...check... if (totwritten > 0) c->lastinteraction = time(NULL); /*reply数据全部发送完毕后,要关闭该文件的写事件。 该事件重新开启的时机为addReply()>>_installWriteEvent(c)(见3小节)*/ if (listLength(c->reply) == 0) { c->sentlen = 0; aeDeleteFileEvent(server.el,c->fd,AE_WRITABLE); /* Close connection after entire reply has been sent. */ if (c->flags & REDIS_CLOSE_AFTER_REPLY) freeClient(c); } }
命令行交互过程中,1.为每个连接有相应的数据进行描述(redisClient),这样便于连接的管理。2.命令行交互中,引入命令缓冲区querybuf,这样可以延时处理命令,这在事件轮询机制中,是至关重要的。
原文链接 http://blog.csdn.net/ordeder/article/details/16105345