关于MYSQL 5.7 新连接建立流程源码接口(和5.6不同)

原创 水平有限

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






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：


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：

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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