整體概述
Redis 一個(gè)服務(wù)器可以和多個(gè)客戶端建立網(wǎng)絡(luò)連接，每個(gè)客戶端都可以向服務(wù)器發(fā)送命令請(qǐng)求，服務(wù)器接收客戶端的命令，處理后將結(jié)果返回給客戶端。
Redis 的文件事件處理器使用 I/O 多路復(fù)用，Redis 使用單線程單進(jìn)程處理命令請(qǐng)求，與多個(gè)客戶端進(jìn)行網(wǎng)絡(luò)通信。
image
每個(gè)連接了 Redis 服務(wù)器的客戶端，服務(wù)器都建立了一個(gè) redisClient 結(jié)構(gòu)的客戶端狀態(tài)，保存了客戶端當(dāng)前的狀態(tài)信息，以及執(zhí)行相關(guān)功能時(shí)用到的數(shù)據(jù)結(jié)構(gòu)。
Redis 服務(wù)器狀態(tài)結(jié)構(gòu)的 clients 屬性是一個(gè)鏈表，保存了所有與服務(wù)器連接的客戶端狀態(tài)。
struct redisServer {
……
// 保存了所有客戶端狀態(tài)的鏈表
list *clients;
……
};
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客戶端屬性
先貼一下 client 完整的數(shù)據(jù)結(jié)構(gòu)：
typedef struct client {
uint64_t id; /* Client incremental unique ID. */
connection *conn;
int resp; /* RESP protocol version. Can be 2 or 3. */
redisDb *db; /* Pointer to currently SELECTed DB. */
robj *name; /* As set by CLIENT SETNAME. */
sds querybuf; /* Buffer we use to accumulate client queries. */
size_t qb_pos; /* The position we have read in querybuf. */
sds pending_querybuf; /* If this client is flagged as master, this buffer
represents the yet not applied portion of the
replication stream that we are receiving from
the master. */
size_t querybuf_peak; /* Recent (100ms or more) peak of querybuf size. */
int argc; /* Num of arguments of current command. */
robj **argv; /* Arguments of current command. */
int original_argc; /* Num of arguments of original command if arguments were rewritten. */
robj **original_argv; /* Arguments of original command if arguments were rewritten. */
size_t argv_len_sum; /* Sum of lengths of objects in argv list. */
struct redisCommand *cmd, *lastcmd; /* Last command executed. */
user *user; /* User associated with this connection. If the
user is set to NULL the connection can do
anything (admin). */
int reqtype; /* Request protocol type: PROTO_REQ_* */
int multibulklen; /* Number of multi bulk arguments left to read. */
long bulklen; /* Length of bulk argument in multi bulk request. */
list *reply; /* List of reply objects to send to the client. */
unsigned long long reply_bytes; /* Tot bytes of objects in reply list. */
size_t sentlen; /* Amount of bytes already sent in the current
buffer or object being sent. */
time_t ctime; /* Client creation time. */
long duration; /* Current command duration. Used for measuring latency of blocking/non-blocking cmds */
time_t lastinteraction; /* Time of the last interaction, used for timeout */
time_t obuf_soft_limit_reached_time;
uint64_t flags; /* Client flags: CLIENT_* macros. */
int authenticated; /* Needed when the default user requires auth. */
int replstate; /* Replication state if this is a slave. */
int repl_put_online_on_ack; /* Install slave write handler on first ACK. */
int repldbfd; /* Replication DB file descriptor. */
off_t repldboff; /* Replication DB file offset. */
off_t repldbsize; /* Replication DB file size. */
sds replpreamble; /* Replication DB preamble. */
long long read_reploff; /* Read replication offset if this is a master. */
long long reploff; /* Applied replication offset if this is a master. */
long long repl_ack_off; /* Replication ack offset, if this is a slave. */
long long repl_ack_time;/* Replication ack time, if this is a slave. */
long long repl_last_partial_write; /* The last time the server did a partial write from the RDB child pipe to this replica */
long long psync_initial_offset; /* FULLRESYNC reply offset other slaves
copying this slave output buffer
should use. */
char replid[CONFIG_RUN_ID_SIZE+1]; /* Master replication ID (if master). */
int slave_listening_port; /* As configured with: REPLCONF listening-port */
char *slave_addr; /* Optionally given by REPLCONF ip-address */
int slave_capa; /* Slave capabilities: SLAVE_CAPA_* bitwise OR. */
multiState mstate; /* MULTI/EXEC state */
int btype; /* Type of blocking op if CLIENT_BLOCKED. */
blockingState bpop; /* blocking state */
long long woff; /* Last write global replication offset. */
list *watched_keys; /* Keys WATCHED for MULTI/EXEC CAS */
dict *pubsub_channels; /* channels a client is interested in (SUBSCRIBE) */
list *pubsub_patterns; /* patterns a client is interested in (SUBSCRIBE) */
sds peerid; /* Cached peer ID. */
sds sockname; /* Cached connection target address. */
listNode *client_list_node; /* list node in client list */
listNode *paused_list_node; /* list node within the pause list */
RedisModuleUserChangedFunc auth_callback; /* Module callback to execute
* when the authenticated user
* changes. */
void *auth_callback_privdata; /* Private data that is passed when the auth
* changed callback is executed. Opaque for
* Redis Core. */
void *auth_module; /* The module that owns the callback, which is used
* to disconnect the client if the module is
* unloaded for cleanup. Opaque for Redis Core.*/
/* If this client is in tracking mode and this field is non zero,
* invalidation messages for keys fetched by this client will be send to
* the specified client ID. */
uint64_t client_tracking_redirection;
rax *client_tracking_prefixes; /* A dictionary of prefixes we are already
subscribed to in BCAST mode, in the
context of client side caching. */
/* In clientsCronTrackClientsMemUsage() we track the memory usage of
* each client and add it to the sum of all the clients of a given type,
* however we need to remember what was the old contribution of each
* client, and in which categoty the client was, in order to remove it
* before adding it the new value. */
uint64_t client_cron_last_memory_usage;
int client_cron_last_memory_type;
/* Response buffer */
int bufpos;
char buf[PROTO_REPLY_CHUNK_BYTES];
} client;
套接字描述符
typedef struct client {
……
// 記錄客戶端正在使用的套接字描述符
int fd;
……
}
image
標(biāo)志
客戶端的標(biāo)志屬性 flags 記錄了客戶端的角色（role），以及客戶端目前所處的狀態(tài)：
typedef struct redisClient {
// ...
int flags;
// ...
} redisClient;
具體值可參考：《Redis 設(shè)計(jì)與實(shí)現(xiàn)-客戶端屬性》，flag 例子：
# 客戶端是一個(gè)主服務(wù)器
REDIS_MASTER
# 客戶端正在被列表命令阻塞
REDIS_BLOCKED
# 客戶端正在執(zhí)行事務(wù)，但事務(wù)的安全性已被破壞
REDIS_MULTI | REDIS_DIRTY_CAS
# 客戶端是一個(gè)從服務(wù)器，并且版本低于 Redis 2.8
REDIS_SLAVE | REDIS_PRE_PSYNC
# 這是專門用于執(zhí)行 Lua 腳本包含的 Redis 命令的偽客戶端
# 它強(qiáng)制服務(wù)器將當(dāng)前執(zhí)行的命令寫入 AOF 文件，并復(fù)制給從服務(wù)器
REDIS_LUA_CLIENT | REDIS_FORCE_AOF | REDIS_FORCE_REPL
輸入緩沖區(qū)
客戶端狀態(tài)的輸入緩沖區(qū)用于保存客戶端發(fā)送的命令請(qǐng)求：
typedef struct redisClient {
// ...
sds querybuf;
// ...
} redisClient;
如果客戶端向服務(wù)器發(fā)送了以下命令請(qǐng)求：
SET key value
客戶端狀態(tài)的 querybuf 屬性將是一個(gè)包含以下內(nèi)容的 SDS 值：
*3\r\n$3\r\nSET\r\n$3\r\nkey\r\n$5\r\nvalue\r\n
展示了這個(gè) SDS 值以及 querybuf 屬性的樣子：
image
命名及命令參數(shù)
在服務(wù)器將客戶端發(fā)送的命令請(qǐng)求保存到客戶端狀態(tài)的 querybuf 后，服務(wù)器會(huì)分析該命令，將得到的命令參數(shù)、命令參數(shù)的個(gè)數(shù)分別保存到客戶端狀態(tài)的 argv 屬性和 argc 屬性中：
typedef struct redisClient {
// ...
robj **argv;
int argc;
// ...
} redisClient;
image
命令的實(shí)現(xiàn)函數(shù)
當(dāng)服務(wù)器從協(xié)議內(nèi)容中分析并得出 argv 屬性和 argc 屬性的值之后， 服務(wù)器將根據(jù)項(xiàng) argv[0] 的值，在命令表中查找命令所對(duì)應(yīng)的命令實(shí)現(xiàn)函數(shù)。
當(dāng)程序在命令表中成功找到 argv[0] 所對(duì)應(yīng)的 redisCommand 結(jié)構(gòu)時(shí)， 它會(huì)將客戶端狀態(tài)的 cmd 指針指向這個(gè)結(jié)構(gòu)：
typedef struct redisClient {
// ...
struct redisCommand *cmd;
// ...
} redisClient;
struct redisCommand {
char *name;
redisCommandProc *proc;
int arity;
char *sflags; /* Flags as string representation, one char per flag. */
uint64_t flags; /* The actual flags, obtained from the 'sflags' field. */
/* Use a function to determine keys arguments in a command line.
* Used for Redis Cluster redirect. */
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, rejected_calls, failed_calls;
int id; /* Command ID. This is a progressive ID starting from 0 that
is assigned at runtime, and is used in order to check
ACLs. A connection is able to execute a given command if
the user associated to the connection has this command
bit set in the bitmap of allowed commands. */
};
每個(gè)命令所對(duì)應(yīng)的處理函數(shù)在是下面的 table：
struct redisCommand redisCommandTable[] = {
{"module",moduleCommand,-2,
"admin no-script",
0,NULL,0,0,0,0,0,0},
{"get",getCommand,2,
"read-only fast @string",
0,NULL,1,1,1,0,0,0},
{"getex",getexCommand,-2,
"write fast @string",
0,NULL,1,1,1,0,0,0},
……
}
輸出緩沖區(qū)
保存執(zhí)行命令所得的命令回復(fù)。
image
客戶端的固定大小緩沖區(qū)由 buf 和 bufpos 兩個(gè)屬性組成：
typedef struct redisClient {
// ...
char buf[REDIS_REPLY_CHUNK_BYTES];
// 記錄了 buf 數(shù)組目前已使用的字節(jié)數(shù)量
int bufpos;
// ...
} redisClient;
可變大小緩沖區(qū)由 reply 鏈表和一個(gè)或多個(gè)字符串對(duì)象組成：
typedef struct redisClient {
// ...
list *reply;
// ...
} redisClient;
通過(guò)使用鏈表來(lái)連接多個(gè)字符串對(duì)象， 服務(wù)器可以為客戶端保存一個(gè)非常長(zhǎng)的命令回復(fù)， 而不必受到固定大小緩沖區(qū) 16 KB 大小的限制。展示了一個(gè)包含三個(gè)字符串對(duì)象的 reply 鏈表。
image
客戶端的創(chuàng)建與關(guān)閉
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創(chuàng)建普通客戶端
使用 connect 函數(shù)連接到服務(wù)器，服務(wù)器調(diào)用連接事件處理器，為客戶端創(chuàng)建對(duì)應(yīng)的客戶端狀態(tài)，并將其添加到服務(wù)器狀態(tài)結(jié)構(gòu) clients 鏈表的末尾。
image
關(guān)閉普通客戶端
關(guān)閉普通客戶端的原因：
- 客戶端進(jìn)程退出或被殺死，客戶端與服務(wù)端的網(wǎng)絡(luò)連接被關(guān)閉
- 客戶端向服務(wù)端發(fā)送了不符合協(xié)議格式的命令請(qǐng)求
- 客戶端成為了 CLIENT KILL 命令的目標(biāo)
- 客戶端的空轉(zhuǎn)時(shí)間超過(guò) timeout 配置選項(xiàng)的值
- 客戶端發(fā)送的命令請(qǐng)求大小，超過(guò)了深入緩沖區(qū)的限制大?。J(rèn)為 1GB）
- 服務(wù)端返回給客戶端的數(shù)據(jù)超過(guò)了輸出緩沖區(qū)的限制大小
參考鏈接
Redis 源碼簡(jiǎn)潔剖析系列
Java 編程思想-最全思維導(dǎo)圖-GitHub 下載鏈接，需要的小伙伴可以自取~
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