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关于MYSQL 5.7 新连接建立流程源码接口(和5.6不同)

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今天在看运维内参第三章源码的时候，发现书上很多代码入口函数和我用的5.7.14的源码对不上，然后再看了一下5.6的源码，
书上写的基本都是5.6的源码(书是2015年开始写的)5.7.14在连接这一块做了相当大的改动，加了很多抽象类，变得更加复杂了。
当然这也是软件模块划分的更加清晰的必然的结果，顺便说一下MYSQL在UNIX上使用的select/poll 这种多路I/O转接模型来监听
客户端的连接,监听的只是读操作，当客户端发起连接的时候select/poll通过监听LISTEN scoket上的是否有读取信息来判断，是否
有新的连接到来,然后调用线程回调函数建立新的线程来处理这个新的accpet的socket通道(还会判断是否有空闲的线程队列而不需要
新建立新的线程来处理)，线程的建立我们说是比进程代价小很多，他没有独立的内存三区(共享区,代码段和堆内存)，但是他也有PCB
有独立的栈空间所以能节约一点是一点吧。
关于MYSQL的源码各种多态太多了，真是眼花缭乱

下面是我使用到一些断点。

(gdb) info b
Num Type Disp Enb Address What
1 breakpoint keep y 0x0000000000ebd333 in main(int, char**) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/main.cc:25
breakpoint already hit 1 time
2 breakpoint keep y 0x00000000016e350d in inline_mysql_socket_accept(char const*, uint, PSI_socket_key, MYSQL_SOCKET, sockaddr*, socklen_t*) at /root/mysql5.7.14/percona-server-5.7.14-7/include/mysql/psi/mysql_socket.h:1110
breakpoint already hit 18 times
6 breakpoint keep y 0x0000000000f1b8d9 in Connection_handler_manager::process_new_connection(Channel_info*) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_manager.cc:289
breakpoint already hit 15 times
8 breakpoint keep y 0x00000000016e197f in handle_connection(void*) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_per_thread.cc:239
breakpoint already hit 6 times
9 breakpoint keep y 0x0000000000f1b1d5 in Connection_handler_manager::check_and_incr_conn_count(bool) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_manager.cc:105
breakpoint already hit 1 time
12 breakpoint keep y 0x00000000016e1f41 in Per_thread_connection_handler::add_connection(Channel_info*) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_per_thread.cc:399

下面按照调用流程解释一下这几个函数作用，希望帮到在5.7.14下使用GDB调试MYSQL连接的同学一点帮助
1、不解释主函数main

2、 inline_mysql_socket_accept
当然也就是sokcet accept返回新的socket文件描述符的函数，因为找不到多路I/O转接 select和poll的入口用了这招去找
找到多路I/O转接接口变为了Channel_info* Mysqld_socket_listener::listen_for_connection_event()
Channel_info就是一个抽象类，这个函数会返回连接socket的相关信息给 Channel_info这个基类指针。
又有多太发生了擦。

这里贴出一点和运维内参同样的代码，但是入口函数全部变了，而且除了逻辑相似，很多实现都变了
大量的用多态

点击(此处)折叠或打开

#ifdef HAVE_POLL //多路I/O转接判断是否有写连接到来
int retval= poll(&m_poll_info.m_fds[0], m_socket_map.size(), -1);
#else
m_select_info.m_read_fds= m_select_info.m_client_fds;
int retval= select((int) m_select_info.m_max_used_connection,
&m_select_info.m_read_fds, 0, 0, 0);
#endif

点击(此处)折叠或打开

#ifdef HAVE_POLL //多路I/O转接判断是否有写连接到来
int retval= poll(&m_poll_info.m_fds[0], m_socket_map.size(), -1);
#else
m_select_info.m_read_fds= m_select_info.m_client_fds;
int retval= select((int) m_select_info.m_max_used_connection,
&m_select_info.m_read_fds, 0, 0, 0);
#endif

点击(此处)折叠或打开

for (uint retry= 0; retry < MAX_ACCEPT_RETRY; retry++) //重试次数MAX_ACCEPT_RETRY好像是10
{
socket_len_t length= sizeof(struct sockaddr_storage);
connect_sock= mysql_socket_accept(key_socket_client_connection, listen_sock,
(struct sockaddr *)(&cAddr), &length);//这里没什么好说的返回新的sokcet文件描述符了
if (mysql_socket_getfd(connect_sock) != INVALID_SOCKET ||//返回的新的socket文件描述符无效(-1)
(socket_errno != SOCKET_EINTR && socket_errno != SOCKET_EAGAIN)) //如果是信号中断或者eagain重试没关系再来
break;
}

点击(此处)折叠或打开

Channel_info* channel_info= NULL;
//注意下面有多态发生这里和5.6很多不同了
if (is_unix_socket) //是否是本地UNIX_DOMAIN SOCKET
channel_info= new (std::nothrow) Channel_info_local_socket(connect_sock);
else//不是就是远程TCP/IP SCOKET
channel_info= new (std::nothrow)
Channel_info_tcpip_socket(connect_sock,
(mysql_socket_getfd(listen_sock)
== m_extra_tcp_port_fd)); //根据connect_scok 建立channel_info
if (channel_info == NULL) //分配内存是否正常不正常搞下面的。
{
(void) mysql_socket_shutdown(connect_sock, SHUT_RDWR);
(void) mysql_socket_close(connect_sock);
connection_errors_internal++;
return NULL;
}
return channel_info;

栈帧
#0 inline_mysql_socket_accept (src_file=0x21c5f30 "/root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/socket_connection.cc", src_line=928, key=3, socket_listen=..., addr=0x7fffffffdc50, addr_len=0x7fffffffdcdc)
at /root/mysql5.7.14/percona-server-5.7.14-7/include/mysql/psi/mysql_socket.h:1110
#1 0x00000000016e4981 in Mysqld_socket_listener::listen_for_connection_event (this=0x2fca760) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/socket_connection.cc:928
#2 0x0000000000ecf016 in Connection_acceptor::connection_event_loop (this=0x2fc9b30) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_acceptor.h:66
#3 0x0000000000ec6a06 in mysqld_main (argc=52, argv=0x2e97438) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/mysqld.cc:5287
#4 0x0000000000ebd344 in main (argc=9, argv=0x7fffffffe418) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/main.cc:25

6、Connection_handler_manager::process_new_connection，通过Channel_info指针指向的SCOKET信息建立新线程

栈帧
#1 0x0000000000f1b9c6 in Connection_handler_manager::process_new_connection (this=0x2e98fc0, channel_info=0x34c4a30) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_manager.cc:301
#2 0x0000000000ecf034 in Connection_acceptor::connection_event_loop (this=0x2fc9b30) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_acceptor.h:68
#3 0x0000000000ec6a06 in mysqld_main (argc=52, argv=0x2e97438) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/mysqld.cc:5287
#4 0x0000000000ebd344 in main (argc=9, argv=0x7fffffffe418) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/main.cc:25

9、 Connection_handler_manager::check_and_incr_conn_count(bool)
这里判断MAX_CONNECTIONS是否合适这里也和运维内参说的5.6的代码有了
很大的不同，但是逻辑一样如下：

点击(此处)折叠或打开

if (extra_port_connection)
{
if (extra_connection_count > extra_max_connections)
{
connection_accepted= false;
m_connection_errors_max_connection++;
}
else
{
++extra_connection_count;
}
}
else if (connection_count > max_connections)
{
connection_accepted= false;
m_connection_errors_max_connection++;
}

GDB如下：

(gdb) n
106 mysql_mutex_lock(&LOCK_connection_count);
(gdb) n
115 if (extra_port_connection)
(gdb) n
127 else if (connection_count > max_connections)
(gdb) P max_connections
$4 = 6
(gdb) p connection_count
$5 = 7
(gdb) n
129 connection_accepted= false;
(gdb) n
130 m_connection_errors_max_connection++;
(gdb) n
141 mysql_mutex_unlock(&LOCK_connection_count);
(gdb) n
142 return connection_accepted;

栈帧
#0 Connection_handler_manager::check_and_incr_conn_count (this=0x2e98fc0, extra_port_connection=false) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_manager.cc:105
#1 0x0000000000f1b904 in Connection_handler_manager::process_new_connection (this=0x2e98fc0, channel_info=0x34c4a30) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_manager.cc:289
#2 0x0000000000ecf034 in Connection_acceptor::connection_event_loop (this=0x2fc9b30) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_acceptor.h:68
#3 0x0000000000ec6a06 in mysqld_main (argc=52, argv=0x2e97438) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/mysqld.cc:5287
#4 0x0000000000ebd344 in main (argc=9, argv=0x7fffffffe418) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/main.cc:25

12、 Per_thread_connection_handler::add_connection(Channel_info*) 这个函数会判断连接队列是否有空闲的，如果没有调用mysql_thread_create建立新的线程
截取如下：

点击(此处)折叠或打开

if (!check_idle_thread_and_enqueue_connection(channel_info)) //判断是否有空闲的连接队里
DBUG_RETURN(false);
/*
There are no idle threads avaliable to take up the new
connection. Create a new thread to handle the connection
*/
error= mysql_thread_create(key_thread_one_connection, &id, //建立新的线程对接
&connection_attrib,
handle_connection,
(void*) channel_info);

栈帧
#0 Per_thread_connection_handler::add_connection (this=0x2f67b10, channel_info=0x34c4a30) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_per_thread.cc:399
#1 0x0000000000f1b9c6 in Connection_handler_manager::process_new_connection (this=0x2e98fc0, channel_info=0x34c4a30) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_manager.cc:301
#2 0x0000000000ecf034 in Connection_acceptor::connection_event_loop (this=0x2fc9b30) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_acceptor.h:68
#3 0x0000000000ec6a06 in mysqld_main (argc=52, argv=0x2e97438) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/mysqld.cc:5287
#4 0x0000000000ebd344 in main (argc=9, argv=0x7fffffffe418) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/main.cc:25

8、 handle_connection(void*) 这里就是5.7.16真正的回调函数用于建立线程，这里就不解释了，因为这里只是分析流程，以后在详细研究

这里终于找到了建立线程的回调函数，调试有时候不知道入口函数名字也是一种悲剧

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关于MYSQL 5.7 新连接建立流程源码接口(和5.6不同)