之前读了一下redis事件处理器的代码点我，今天无所事事，看了下redis对输入缓冲区(querybuf)和输出缓冲区(buf/replylist)的代码，记录一下学习过程。
1. 读缓冲区处理
读取fd数据,然后放入client的输入缓冲区(querybuf)的整个调用栈如下：
1211 int processMultibulkBuffer(client *c) {
(gdb) bt
#0 processMultibulkBuffer (c=c@entry=0x7ffff6f15e00) at networking.c:1211
#1 0x000000000043c736 in processInputBuffer (c=0x7ffff6f15e00)
at networking.c:1408
#2 0x00000000004262de in aeProcessEvents (
eventLoop=eventLoop@entry=0x7ffff6e340a0, flags=flags@entry=11) at ae.c:452
#3 0x000000000042670b in aeMain (eventLoop=0x7ffff6e340a0) at ae.c:495
#4 0x00000000004232d6 in main (argc=<optimized out>, argv=0x7fffffffe3e8)
at server.c:38971.1 读事件注册
- 在redis代码src/server.c文件中void initServer(void)函数首先完成了socket创建，bind, listen操作，然后在事件处理器上注册了accept处理的handler(function: acceptTcpHandler)
/* Create an event handler for accepting new connections in TCP and Unix
* domain sockets. */
//fd事件
//在事件处理器上注册handler, 处理listen fd上的可读事件(表示有新的连接到来)
for (j = 0; j < server.ipfd_count; j++) {
//在每个listfd上创建event
//aeCreateFileEvent means epoll_ctl
if (aeCreateFileEvent(server.el, server.ipfd[j], AE_READABLE,
acceptTcpHandler,NULL) == AE_ERR)
{
serverPanic(
"Unrecoverable error creating server.ipfd file event.");
}
}- 其中acceptTcpHandler的实现如下:
acceptCommonHandler函数为cfd（新连接fd）创建对应的client结构体，并且为cfd注册读事件
void acceptTcpHandler(aeEventLoop *el, int fd, void *privdata, int mask) {
int cport, cfd, max = MAX_ACCEPTS_PER_CALL;
char cip[NET_IP_STR_LEN];
UNUSED(el);
UNUSED(mask);
UNUSED(privdata);
//max表示每次listenfd可读的时候，accept获取连接的最大执行次数
while(max--) {
//accept封装
//cip为客户端的ip地址，cport为客户端的端口
cfd = anetTcpAccept(server.neterr, fd, cip, sizeof(cip), &cport);
if (cfd == ANET_ERR) {
if (errno != EWOULDBLOCK)
serverLog(LL_WARNING,
"Accepting client connection: %s", server.neterr);
return;
}
serverLog(LL_VERBOSE,"Accepted %s:%d", cip, cport);
//给accept fd创建client结构体
acceptCommonHandler(cfd,0,cip);
}
}- acceptCommonHandler函数中调用createClient函数创建客户端对应的结构体对象:
//创建客户端对应的数结构体
if ((c = createClient(fd)) == NULL) {
serverLog(LL_WARNING,
"Error registering fd event for the new client: %s (fd=%d)",
strerror(errno),fd);
close(fd); /* May be already closed, just ignore errors */
return;
}- 其中createClient函数调用aeCreateFileEvent在事件处理器上注册该fd的读事件（function:readQueryFromClient）：
/* passing -1 as fd it is possible to create a non connected client.
* This is useful since all the commands needs to be executed
* in the context of a client. When commands are executed in other
* contexts (for instance a Lua script) we need a non connected client. */
//fd =-1表示伪客户端
if (fd != -1) {
//设置为非阻塞模式
anetNonBlock(NULL,fd);
anetEnableTcpNoDelay(NULL,fd);
if (server.tcpkeepalive)
anetKeepAlive(NULL,fd,server.tcpkeepalive);
//读取客户端发送的消息
//注册fd读回调函数
if (aeCreateFileEvent(server.el,fd,AE_READABLE,
readQueryFromClient, c) == AE_ERR)
{
close(fd);
//释放c
zfree(c);
return NULL;
}
}- readQueryFromClient函数实现如下：
//当fd可读的时候，回调函数
void readQueryFromClient(aeEventLoop *el, int fd, void *privdata, int mask) {
//每个连接的client结构体的privdata为对应client指针，即c
client *c = (client*) privdata;
int nread, readlen;
size_t qblen;
UNUSED(el);
UNUSED(mask);
//IO buffer 16K
readlen = PROTO_IOBUF_LEN;
/* If this is a multi bulk request, and we are processing a bulk reply
* that is large enough, try to maximize the probability that the query
* buffer contains exactly the SDS string representing the object, even
* at the risk of requiring more read(2) calls. This way the function
* processMultiBulkBuffer() can avoid copying buffers to create the
* Redis Object representing the argument. */
//multibulklen表示待从读取的参数的个数
//bulklen表示当前参数的长度
//客户端为redis-cli
//如果还有待读取的bulk（参数）,并且上次读取的最后一个参数的数据不完整，
//并且上次读取的最后一个参数大于等于PROTO_MUBULK_BIG_ARG
if (c->reqtype == PROTO_REQ_MULTIBULK && c->multibulklen && c->bulklen != -1
&& c->bulklen >= PROTO_MBULK_BIG_ARG)
{
//待读取的数据长度
int remaining = (unsigned)(c->bulklen+2)-sdslen(c->querybuf);
//确定该次读取的数据长度
//如果大于PROTO_IOBUF_LEN,则读取PROTO_IOBUF_LEN
//否则读取全部剩余的数据
if (remaining < readlen) readlen = remaining;
}
//qlen表示当前buf中的数据量
qblen = sdslen(c->querybuf);
//peak of querybuff size
//判断是否更新峰值
if (c->querybuf_peak < qblen) c->querybuf_peak = qblen;
//makeroom for readlen
c->querybuf = sdsMakeRoomFor(c->querybuf, readlen);
//读取客户端请求到querybuf缓冲区
nread = read(fd, c->querybuf+qblen, readlen);
if (nread == -1) {
//表示读取缓冲区为空
if (errno == EAGAIN) {
return;
} else {
serverLog(LL_VERBOSE, "Reading from client: %s",strerror(errno));
//释放客户端
freeClient(c);
return;
}
serverLog(LL_VERBOSE, "Client closed connection");
freeClient(c);
return;
} else if (c->flags & CLIENT_MASTER) {
/* Append the query buffer to the pending (not applied) buffer
* of the master. We'll use this buffer later in order to have a
* copy of the string applied by the last command executed. */
//将读取的数据追加到pending_querbuf末尾
c->pending_querybuf = sdscatlen(c->pending_querybuf,
c->querybuf+qblen,nread);
}
//增加querbuf的长度
sdsIncrLen(c->querybuf,nread);
//更新server与客户端最新的交互时间
c->lastinteraction = server.unixtime;
if (c->flags & CLIENT_MASTER) c->read_reploff += nread;
server.stat_net_input_bytes += nread;
//如果querybuf缓冲区长度大于client_max_querybuf_len
if (sdslen(c->querybuf) > server.client_max_querybuf_len) {
sds ci = catClientInfoString(sdsempty(),c), bytes = sdsempty();
bytes = sdscatrepr(bytes,c->querybuf,64);
serverLog(LL_WARNING,"Closing client that reached max query buffer length: %s (qbuf initial bytes: %s)", ci, bytes);
sdsfree(ci);
sdsfree(bytes);
freeClient(c);
return;
}
/* Time to process the buffer. If the client is a master we need to
* compute the difference between the applied offset before and after
* processing the buffer, to understand how much of the replication stream
* was actually applied to the master state: this quantity, and its
* corresponding part of the replication stream, will be propagated to
* the sub-slaves and to the replication backlog. */
if (!(c->flags & CLIENT_MASTER)) {
//处理客户端输入缓冲区
processInputBuffer(c);
} else {
size_t prev_offset = c->reploff;
processInputBuffer(c);
size_t applied = c->reploff - prev_offset;
if (applied) {
replicationFeedSlavesFromMasterStream(server.slaves,
c->pending_querybuf, applied);
sdsrange(c->pending_querybuf,applied,-1);
}
}
}
- 其中processInputBuffer函数的源码如下：
/* This function is called every time, in the client structure 'c', there is
* more query buffer to process, because we read more data from the socket
* or because a client was blocked and later reactivated, so there could be
* pending query buffer, already representing a full command, to process. */
void processInputBuffer(client *c) {
server.current_client = c;
/* Keep processing while there is something in the input buffer */
while(sdslen(c->querybuf)) {
/* Return if clients are paused. */
if (!(c->flags & CLIENT_SLAVE) && clientsArePaused()) break;
/* Immediately abort if the client is in the middle of something. */
if (c->flags & CLIENT_BLOCKED) break;
/* CLIENT_CLOSE_AFTER_REPLY closes the connection once the reply is
* written to the client. Make sure to not let the reply grow after
* this flag has been set (i.e. don't process more commands).
*
* The same applies for clients we want to terminate ASAP. */
if (c->flags & (CLIENT_CLOSE_AFTER_REPLY|CLIENT_CLOSE_ASAP)) break;
/* Determine request type when unknown. */
if (!c->reqtype) {
//redis-cli客户端
if (c->querybuf[0] == '*') {
c->reqtype = PROTO_REQ_MULTIBULK;
} else {
c->reqtype = PROTO_REQ_INLINE;
}
}
if (c->reqtype == PROTO_REQ_INLINE) {
if (processInlineBuffer(c) != C_OK) break;
} else if (c->reqtype == PROTO_REQ_MULTIBULK) {
//如果返回C_OK，表示从querybuf中解析出一个完成的命令
if (processMultibulkBuffer(c) != C_OK) break;
} else {
serverPanic("Unknown request type");
}
/* Multibulk processing could see a <= 0 length. */
if (c->argc == 0) {
resetClient(c);
} else {
/* Only reset the client when the command was executed. */
//执行从querybuf解析出来的命令
if (processCommand(c) == C_OK) {
if (c->flags & CLIENT_MASTER && !(c->flags & CLIENT_MULTI)) {
/* Update the applied replication offset of our master. */
c->reploff = c->read_reploff - sdslen(c->querybuf);
}
/* Don't reset the client structure for clients blocked in a
* module blocking command, so that the reply callback will
* still be able to access the client argv and argc field.
* The client will be reset in unblockClientFromModule(). */
if (!(c->flags & CLIENT_BLOCKED) || c->btype != BLOCKED_MODULE)
resetClient(c);
}
/* 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) break;
}
}
server.current_client = NULL;
}
- 其中processMultibulkBuffer函数的源码如下：
/* Process the query buffer for client 'c', setting up the client argument
* vector for command execution. Returns C_OK if after running the function
* the client has a well-formed ready to be processed command, otherwise
* 如果read buffer中不是一个完整的命令，则返回C_ERR
* C_ERR if there is still to read more buffer to get the full command.
* The function also returns C_ERR when there is a protocol error: in such a
* case the client structure is setup to reply with the error and close
* the connection.
*
* This function is called if processInputBuffer() detects that the next
* command is in RESP format, so the first byte in the command is found
* to be '*'. Otherwise for inline commands processInlineBuffer() is called. */
int processMultibulkBuffer(client *c) {
char *newline = NULL;
int pos = 0, ok;
long long ll;
//multibulklen=0表示现在buffer中是一个新的命令
//此时，首先获取*num中的num字段
if (c->multibulklen == 0) {
/* The client should have been reset */
serverAssertWithInfo(c,NULL,c->argc == 0);
/* Multi bulk length cannot be read without a \r\n */
//'\r'字符首次在querbuf出现的位置
newline = strchr(c->querybuf,'\r');
//如果querybuf中没有'\r'字符
//表示不是一个完整的参数
if (newline == NULL) {
if (sdslen(c->querybuf) > PROTO_INLINE_MAX_SIZE) {
addReplyError(c,"Protocol error: too big mbulk count string");
setProtocolError("too big mbulk count string",c,0);
}
return C_ERR;
}
/* Buffer should also contain \n */
if (newline-(c->querybuf) > ((signed)sdslen(c->querybuf)-2))
return C_ERR;
/* We know for sure there is a whole line since newline != NULL,
* so go ahead and find out the multi bulk length. */
serverAssertWithInfo(c,NULL,c->querybuf[0] == '*');
//*num 获取num字段
ok = string2ll(c->querybuf+1,newline-(c->querybuf+1),&ll);
if (!ok || ll > 1024*1024) {
addReplyError(c,"Protocol error: invalid multibulk length");
setProtocolError("invalid mbulk count",c,pos);
return C_ERR;
}
//*num\r\n
//pos指向num之后下一个字段,即：第一个参数的字符长度字段的首地址($len)
pos = (newline-c->querybuf)+2;
if (ll <= 0) {
sdsrange(c->querybuf,pos,-1);
return C_OK;
}
//表示该cmd的待读取的参数个数
c->multibulklen = ll;
/* Setup argv array on client structure */
if (c->argv) zfree(c->argv);
//创建multibulklen参数对应的multibulklen个robj
c->argv = zmalloc(sizeof(robj*)*c->multibulklen);
}
serverAssertWithInfo(c,NULL,c->multibulklen > 0);
//mutibulklen表示命令中参数的个数，
//根据此变量才从buffer中解析每个参数(bulk)
while(c->multibulklen) {
/* Read bulk length if unknown */
//如果bulklen为-1，表示开始一个新的bulk读取
if (c->bulklen == -1) {
newline = strchr(c->querybuf+pos,'\r');
if (newline == NULL) {
if (sdslen(c->querybuf) > PROTO_INLINE_MAX_SIZE) {
addReplyError(c,
"Protocol error: too big bulk count string");
setProtocolError("too big bulk count string",c,0);
return C_ERR;
}
break;
}
/* Buffer should also contain \n */
if (newline-(c->querybuf) > ((signed)sdslen(c->querybuf)-2))
break;
if (c->querybuf[pos] != '$') {
addReplyErrorFormat(c,
"Protocol error: expected '$', got '%c'",
c->querybuf[pos]);
setProtocolError("expected $ but got something else",c,pos);
return C_ERR;
}
//获取$len中的len字段
ok = string2ll(c->querybuf+pos+1,newline-(c->querybuf+pos+1),&ll);
if (!ok || ll < 0 || ll > 512*1024*1024) {
addReplyError(c,"Protocol error: invalid bulk length");
setProtocolError("invalid bulk length",c,pos);
return C_ERR;
}
//指向长度为len的字符串的首地址
pos += newline-(c->querybuf+pos)+2;
if (ll >= PROTO_MBULK_BIG_ARG) {
size_t qblen;
/* If we are going to read a large object from network
* try to make it likely that it will start at c->querybuf
* boundary so that we can optimize object creation
* avoiding a large copy of data. */
sdsrange(c->querybuf,pos,-1);
pos = 0;
qblen = sdslen(c->querybuf);
/* Hint the sds library about the amount of bytes this string is
* going to contain. */
if (qblen < (size_t)ll+2)
c->querybuf = sdsMakeRoomFor(c->querybuf,ll+2-qblen);
}
//当前参数（bulk）的长度
c->bulklen = ll;
}
/* Read bulk argument */
if (sdslen(c->querybuf)-pos < (unsigned)(c->bulklen+2)) {
/* Not enough data (+2 == trailing \r\n) */
break;
} else {
/* Optimization: if the buffer contains JUST our bulk element
* instead of creating a new object by *copying* the sds we
* just use the current sds string. */
//如果buffer中仅含有一个参数(bulk)
if (pos == 0 &&
c->bulklen >= PROTO_MBULK_BIG_ARG &&
(signed) sdslen(c->querybuf) == c->bulklen+2)
{
c->argv[c->argc++] = createObject(OBJ_STRING,c->querybuf);
sdsIncrLen(c->querybuf,-2); /* remove CRLF */
/* Assume that if we saw a fat argument we'll see another one
* likely... */
//重新创建一个querybuf
c->querybuf = sdsnewlen(NULL,c->bulklen+2);
sdsclear(c->querybuf);
pos = 0;
} else {
//创建String robj
c->argv[c->argc++] =
createStringObject(c->querybuf+pos,c->bulklen);
pos += c->bulklen+2;
}
//表示读取了一个完整的bulk（参数）
c->bulklen = -1;
//待读取的bulk（参数）数量
c->multibulklen--;
}
}
/* Trim to pos */
//将最后一个’\r‘字符的地址偏移量pos到querbuf结尾的字段截取出来，保存到querbuf
if (pos) sdsrange(c->querybuf,pos,-1);
/* We're done when c->multibulk == 0 */
//表示从querbuf中读取了一个完整命令
if (c->multibulklen == 0) return C_OK;
/* Still not ready to process the command */
return C_ERR;
}2. 写缓冲区处理
redis写缓冲区的处理过程如下：在进入epoll_wait或者select阻塞之前，会执行beforeSleep函数，该函数会调用handleClientsWithPendingWrites函数处理fd中的写缓冲区，进行循环写，如果返回-1，并且此时缓冲区中还有数据，则在该fd注册写事件;如果循环写将输出缓冲区中的数据写完，则此时删除该fd上的写事件.
- 函数调用栈如下
Thread 1 "redis-server" hit Breakpoint 1, writeToClient (fd=8,
c=c@entry=0x7ffff6f15e00, handler_installed=handler_installed@entry=0)
at networking.c:935
935 int writeToClient(int fd, client *c, int handler_installed) {
(gdb) bt
#0 writeToClient (fd=8, c=c@entry=0x7ffff6f15e00,
handler_installed=handler_installed@entry=0) at networking.c:935
#1 0x00000000004391cb in handleClientsWithPendingWrites ()
at networking.c:1060
#2 0x0000000000429b61 in beforeSleep (eventLoop=<optimized out>)
at server.c:1234
#3 0x00000000004266fe in aeMain (eventLoop=0x7ffff6e340a0) at ae.c:494
#4 0x00000000004232d6 in main (argc=<optimized out>, argv=0x7fffffffe3e8)
at server.c:3897
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