Redis命令处理流程
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2022-05-23 12:53:41
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关键数据结构和方法 1) struct redisCommand redisCommandTable 位于redis.c:115 2) processCommand 位于redis.c:1653 redisCommand数据结构 struct redisCommand { char *name; redisCommandProc *proc; int arity; char *sflags; /* Flags as string rep
关键数据结构和方法
1) struct redisCommand redisCommandTable 位于redis.c:115 2) processCommand 位于redis.c:1653redisCommand数据结构
struct redisCommand { char *name; redisCommandProc *proc; int arity; char *sflags; /* Flags as string representation, one char per flag. */ int flags; /* The actual flags, obtained from the 'sflags' field. */ /* Use a function to determine keys arguments in a command line. */ redisGetKeysProc *getkeys_proc; /* What keys should be loaded in background when calling this command? */ int firstkey; /* The first argument that's a key (0 = no keys) */ int lastkey; /* The last argument that's a key */ int keystep; /* The step between first and last key */ long long microseconds, calls; };
对比某一个记录看一下字段的含义,也学习一下如何设计一个好的命令协议。 {"get",getCommand,2,"r",0,NULL,1,1,1,0,0},
{"set",setCommand,-3,"wm",0,noPreloadGetKeys,1,1,1,0,0},
最前面的name和proc是最容易也是最关键的,表示一个名字对应的处理函数。 arity表示参数的个数,如果是负数,则表示 最少n个参数,如果是正数字,则表示必选是n个参数; sflag表示该命令的属性,从populateCommandTable(redis.c:1445)中可以得出属性列表为:
* w: write command (may modify the key space). * r: read command (will never modify the key space). * m: may increase memory usage once called. Don't allow if out of memory. * a: admin command, like SAVE or SHUTDOWN. * p: Pub/Sub related command. * f: force replication of this command, regardless of server.dirty. * s: command not allowed in scripts. * R: random command. Command is not deterministic, that is, the same command * with the same arguments, with the same key space, may have different * results. For instance SPOP and RANDOMKEY are two random commands. * S: Sort command output array if called from script, so that the output * is deterministic. * l: Allow command while loading the database. * t: Allow command while a slave has stale data but is not allowed to * server this data. Normally no command is accepted in this condition * but just a few. * M: Do not automatically propagate the command on MONITOR.
redisGetKeysProc以及后续的参数是处理参数列表,从命令行中解析出那些是key那些是value。 firstkey ,lastkey ,keystep分别表示key是从哪个位置到哪个位置,间隔是多少。典型的比如 set name 'aa' ,则key是从1到1,间隔也是1。 sdiff key1 key2 ,则lastkey设置为-1表示,后面所有的都是key mset k1 'a' k2 'b' 则keysttep=2则表示,每隔一个参数为key
通过这三个参数可以表示出一些固定的,但是很难表示如下命令格式 COMMAND key value key value value key value value value 因为key没有规律。
设计一个自己的命令
在系统中,已经存在一个time命令,但是返回的是秒数和毫秒。假设我们希望返回服务端的易读懂的时间,并且根据传入的参数返回时间的格式。1) 在redisCommandTable中增加一条记录 {"utime",utimeCommand,-1,"r",0,NULL,0,0,0,0,0}
2)在redis.h增加函数声明: void utimeCommand(redisClient * c); 3)在redis.c增加实现函数:
void utimeCommand(redisClient *c) { char * fmt = c->argv[1]->ptr; char fmtResult[64]; memset(fmtResult,0,64); struct timeval tv; gettimeofday(&tv,NULL); struct tm *tm; tm = localtime(&tv.tv_sec); if(tm!=NULL){ strftime(fmtResult, sizeof fmtResult, fmt, tm); }else{ sprintf(fmtResult,"%s","error when retriving time"); } addReplyBulkCString(c,fmtResult); }