以下为个人笔记
/**
* process_command 在memcached中是用来处理用户发送的命令的，
* 包括get set，add，delete，replace，stats，flush_all等常用的和不常用的命令，全在这进行处理的。
* 一共有两个参数，conn *c 和字符串指针 char *command ；
* 关于conn结构体就先不说了，反正它是整个memcached中最重要的结构体就行了，等以后研究明白了再说，先从整体上领会精神吧。
* 这里我想说一下的是， memcached 和 redis 在处理命令上的想法还是有很大差别的，
* 在 redis 里面，你要是想看一下一共支持多少命令，每个命令对应的函数，很方便，都在一个名叫 redisCommandTable 的结构体数组里面，一目了然；
* 但是 memcached 却不是这样，我刚开始也是按照看 redis 源码的方式去找 memcached 中的，但是找了很久也没有发现，原因就是作者把支持的所有命令都散落在下面这个函数中了。
* 先说一下 memcached 是怎么从 command 字符串中分解出具体的命令和对应的参数的。
* 在函数中用到了一个结构体数组： tokens[MAX_TOKENS] ，它其实是用来存放分析完的 command 结果用的，分析工作在函数 tokenize_command 中进行。
* 如：有一个命令 "get aaaaaaaaaa" ，分析完以后存在tokens中的就是
* tokens[3] = {{value:"get",length:3},{value:"aaaaaaaaaa",length:10},{value:NULL,length:0}};
* 函数 tokenize_command 返回的是一个int型数据 ntokens，记录了 tokens 的大小，表示从 command 命令中分解出了几条数据，
* 当然 ntokens 的值会比实际中 command 中包含的数据多1，因为字符串结尾的'\0'也要占一样。
*
* 下面说说以 "get aaaaaaaaaa" 命令为例，具体的命令分析和函数调用过程：
* 当一条命令 "get aaaaaaaaaa" 传到 process_command 中之后，先调用负责解析命令的函数tokenize_command，
* 将解析后的命令存储在tokens数组中，结果如上面的tokens[3]，并返回ntokens，说明command中包含几个字段（这里得到的是3），
* 然后根据字段的数目进行判断应该到哪个条件语句去进行比对，当确认之后，就会跳到对应的条件语句中
* 所以这里应该到 tokenize_command 下面的第一个if语句中，然后使用tokens[0].value，也就是tokens数组中存储的get命令和字符串"get"进行比较，
* 匹配，则调用对应的函数，这里调用process_get_command(c, tokens, ntokens, false);
* 然后 process_command 的使命就结束了。
* 以下代码在memcached-1.4.22/memcached.c
*/
static void process_command(conn *c, char *command) { token_t tokens[MAX_TOKENS];
size_t ntokens;
int comm; assert(c != NULL); MEMCACHED_PROCESS_COMMAND_START(c->sfd, c->rcurr, c->rbytes); if (settings.verbose > )
fprintf(stderr, "<%d %s\n", c->sfd, command); /*
* for commands set/add/replace, we build an item and read the data
* directly into it, then continue in nread_complete().
*/ c->msgcurr = ;
c->msgused = ;
c->iovused = ;
if (add_msghdr(c) != ) {
out_of_memory(c, "SERVER_ERROR out of memory preparing response");
return;
} ntokens = tokenize_command(command, tokens, MAX_TOKENS);
if (ntokens >= &&
((strcmp(tokens[COMMAND_TOKEN].value, "get") == ) ||
(strcmp(tokens[COMMAND_TOKEN].value, "bget") == ))) { process_get_command(c, tokens, ntokens, false); } else if ((ntokens == || ntokens == ) &&
((strcmp(tokens[COMMAND_TOKEN].value, "add") == && (comm = NREAD_ADD)) ||
(strcmp(tokens[COMMAND_TOKEN].value, "set") == && (comm = NREAD_SET)) ||
(strcmp(tokens[COMMAND_TOKEN].value, "replace") == && (comm = NREAD_REPLACE)) ||
(strcmp(tokens[COMMAND_TOKEN].value, "prepend") == && (comm = NREAD_PREPEND)) ||
(strcmp(tokens[COMMAND_TOKEN].value, "append") == && (comm = NREAD_APPEND)) )) { process_update_command(c, tokens, ntokens, comm, false); } else if ((ntokens == || ntokens == ) && (strcmp(tokens[COMMAND_TOKEN].value, "cas") == && (comm = NREAD_CAS))) { process_update_command(c, tokens, ntokens, comm, true); } else if ((ntokens == || ntokens == ) && (strcmp(tokens[COMMAND_TOKEN].value, "incr") == )) { process_arithmetic_command(c, tokens, ntokens, ); } else if (ntokens >= && (strcmp(tokens[COMMAND_TOKEN].value, "gets") == )) { process_get_command(c, tokens, ntokens, true); } else if ((ntokens == || ntokens == ) && (strcmp(tokens[COMMAND_TOKEN].value, "decr") == )) { process_arithmetic_command(c, tokens, ntokens, ); } else if (ntokens >= && ntokens <= && (strcmp(tokens[COMMAND_TOKEN].value, "delete") == )) { process_delete_command(c, tokens, ntokens); } else if ((ntokens == || ntokens == ) && (strcmp(tokens[COMMAND_TOKEN].value, "touch") == )) { process_touch_command(c, tokens, ntokens); } else if (ntokens >= && (strcmp(tokens[COMMAND_TOKEN].value, "stats") == )) { process_stat(c, tokens, ntokens); } else if (ntokens >= && ntokens <= && (strcmp(tokens[COMMAND_TOKEN].value, "flush_all") == )) {
time_t exptime = ; set_noreply_maybe(c, tokens, ntokens); pthread_mutex_lock(&c->thread->stats.mutex);
c->thread->stats.flush_cmds++;
pthread_mutex_unlock(&c->thread->stats.mutex); if (!settings.flush_enabled) {
// flush_all is not allowed but we log it on stats
out_string(c, "CLIENT_ERROR flush_all not allowed");
return;
} if(ntokens == (c->noreply ? : )) {
settings.oldest_live = current_time - ;
item_flush_expired();
out_string(c, "OK");
return;
} exptime = strtol(tokens[].value, NULL, );
if(errno == ERANGE) {
out_string(c, "CLIENT_ERROR bad command line format");
return;
} /*
If exptime is zero realtime() would return zero too, and
realtime(exptime) - 1 would overflow to the max unsigned
value. So we process exptime == 0 the same way we do when
no delay is given at all.
*/
if (exptime > )
settings.oldest_live = realtime(exptime) - ;
else /* exptime == 0 */
settings.oldest_live = current_time - ;
item_flush_expired();
out_string(c, "OK");
return; } else if (ntokens == && (strcmp(tokens[COMMAND_TOKEN].value, "version") == )) { out_string(c, "VERSION " VERSION); } else if (ntokens == && (strcmp(tokens[COMMAND_TOKEN].value, "quit") == )) { conn_set_state(c, conn_closing); } else if (ntokens == && (strcmp(tokens[COMMAND_TOKEN].value, "shutdown") == )) { if (settings.shutdown_command) {
conn_set_state(c, conn_closing);
raise(SIGINT);
} else {
out_string(c, "ERROR: shutdown not enabled");
} } else if (ntokens > && strcmp(tokens[COMMAND_TOKEN].value, "slabs") == ) {
if (ntokens == && strcmp(tokens[COMMAND_TOKEN + ].value, "reassign") == ) {
int src, dst, rv; if (settings.slab_reassign == false) {
out_string(c, "CLIENT_ERROR slab reassignment disabled");
return;
} src = strtol(tokens[].value, NULL, );
dst = strtol(tokens[].value, NULL, ); if (errno == ERANGE) {
out_string(c, "CLIENT_ERROR bad command line format");
return;
} rv = slabs_reassign(src, dst);
switch (rv) {
case REASSIGN_OK:
out_string(c, "OK");
break;
case REASSIGN_RUNNING:
out_string(c, "BUSY currently processing reassign request");
break;
case REASSIGN_BADCLASS:
out_string(c, "BADCLASS invalid src or dst class id");
break;
case REASSIGN_NOSPARE:
out_string(c, "NOSPARE source class has no spare pages");
break;
case REASSIGN_SRC_DST_SAME:
out_string(c, "SAME src and dst class are identical");
break;
}
return;
} else if (ntokens == &&
(strcmp(tokens[COMMAND_TOKEN + ].value, "automove") == )) {
process_slabs_automove_command(c, tokens, ntokens);
} else {
out_string(c, "ERROR");
}
} else if (ntokens > && strcmp(tokens[COMMAND_TOKEN].value, "lru_crawler") == ) {
if (ntokens == && strcmp(tokens[COMMAND_TOKEN + ].value, "crawl") == ) {
int rv;
if (settings.lru_crawler == false) {
out_string(c, "CLIENT_ERROR lru crawler disabled");
return;
} rv = lru_crawler_crawl(tokens[].value);
switch(rv) {
case CRAWLER_OK:
out_string(c, "OK");
break;
case CRAWLER_RUNNING:
out_string(c, "BUSY currently processing crawler request");
break;
case CRAWLER_BADCLASS:
out_string(c, "BADCLASS invalid class id");
break;
}
return;
} else if (ntokens == && strcmp(tokens[COMMAND_TOKEN + ].value, "tocrawl") == ) {
uint32_t tocrawl;
if (!safe_strtoul(tokens[].value, &tocrawl)) {
out_string(c, "CLIENT_ERROR bad command line format");
return;
}
settings.lru_crawler_tocrawl = tocrawl;
out_string(c, "OK");
return;
} else if (ntokens == && strcmp(tokens[COMMAND_TOKEN + ].value, "sleep") == ) {
uint32_t tosleep;
if (!safe_strtoul(tokens[].value, &tosleep)) {
out_string(c, "CLIENT_ERROR bad command line format");
return;
}
if (tosleep > ) {
out_string(c, "CLIENT_ERROR sleep must be one second or less");
return;
}
settings.lru_crawler_sleep = tosleep;
out_string(c, "OK");
return;
} else if (ntokens == ) {
if ((strcmp(tokens[COMMAND_TOKEN + ].value, "enable") == )) {
if (start_item_crawler_thread() == ) {
out_string(c, "OK");
} else {
out_string(c, "ERROR failed to start lru crawler thread");
}
} else if ((strcmp(tokens[COMMAND_TOKEN + ].value, "disable") == )) {
if (stop_item_crawler_thread() == ) {
out_string(c, "OK");
} else {
out_string(c, "ERROR failed to stop lru crawler thread");
}
} else {
out_string(c, "ERROR");
}
return;
} else {
out_string(c, "ERROR");
}
} else if ((ntokens == || ntokens == ) && (strcmp(tokens[COMMAND_TOKEN].value, "verbosity") == )) {
process_verbosity_command(c, tokens, ntokens);
} else {
out_string(c, "ERROR");
}
return;
}
以上为个人笔记