码版本：5.7.29 简单记录信号如何生效的。poll收到信号后如何中断后如何处理的，需要确认。 --- 公众号 MySQL学习 ###一 初始化信号处理方式，设置信号的处理的处理方式，屏蔽某些信号，并且继承到子线程(pthread_sigmask)，主要屏蔽的为SIGTERM、SIGQUIT、SIGHUP、SIGTSTP四个。其他信号按照默认处理方式，但是处理前打印crash栈，handle_fatal_signal 对于siguser1 进行捕获，处理函数为空empty_signal_handler ``` #0 my_init_signals () at /home/mysql/soft/percona-server-5.7.29-32/sql/mysqld.cc:2225 #1 0x00000000015fefc9 in mysqld_main (argc=79, argv=0x2e22368) at /home/mysql/soft/percona-server-5.7.29-32/sql/mysqld.cc:4846 #2 0x0000000000e8795d in main (argc=4, argv=0x7fffffffe538) at /home/mysql/soft/percona-server-5.7.29-32/sql/main.cc:32 ``` ###二 启动信号处理线程start_signal_handler线程调用函数为 signal_hand, 使用sigwait获取未决信号集合，如果为SIGTERM和SIGQUIT，设置abort_loop= true; 并且发送sigusr1个主线程，准备正常退出pthread_kill(main_thread_id, SIGUSR1)) //给主线程发送sigusr1信号 如果为SIGHUP则重载一下reload_acl_and_cache相关缓存。 start_signal_handler线程调用函数为 signal_hand ``` #0 start_signal_handler () at /home/mysql/soft/percona-server-5.7.29-32/sql/mysqld.cc:2301 #1 0x00000000015fff70 in mysqld_main (argc=79, argv=0x2e22368) at /home/mysql/soft/percona-server-5.7.29-32/sql/mysqld.cc:5407 #2 0x0000000000e8795d in main (argc=4, argv=0x7fffffffe538) at /home/mysql/soft/percona-server-5.7.29-32/sql/main.cc:32 ``` ###三、 如果为SIGTERM和SIGQUIT，主线程（main）正在poll接受连接，收到了sigusr1 信号后进行中断处理，接下来进行判断 全局变量abort_loop，然后进入正常退出流程。 ``` #0 empty_signal_handler (sig=32767) at /home/mysql/soft/percona-server-5.7.29-32/sql/mysqld.cc:2219 #1 <signal handler called> #2 0x00007ffff5f20c3d in poll () from /lib64/libc.so.6 #3 0x00000000015ec077 in Mysqld_socket_listener::listen_for_connection_event (this=0x35a76f0) at /home/mysql/soft/percona-server-5.7.29-32/sql/conn_handler/socket_connection.cc:883 #4 0x0000000001607542 in Connection_acceptor<Mysqld_socket_listener>::connection_event_loop (this=0x35a70e0) at /home/mysql/soft/percona-server-5.7.29-32/sql/conn_handler/connection_acceptor.h:73 #5 0x00000000016001f2 in mysqld_main (argc=79, argv=0x2e22368) at /home/mysql/soft/percona-server-5.7.29-32/sql/mysqld.cc:5513 #6 0x0000000000e8795d in main (argc=4, argv=0x7fffffffe538) at /home/mysql/soft/percona-server-5.7.29-32/sql/main.cc:32 ``` main thread ``` mysqld_socket_acceptor->connection_event_loop(); //监听3306 端口 #endif /* _WIN32 */ server_operational_state= SERVER_SHUTTING_DOWN; //这里开始进行关闭处理 DBUG_PRINT("info", ("No longer listening for incoming connections")); mysql_audit_notify(MYSQL_AUDIT_SERVER_SHUTDOWN_SHUTDOWN, Mysqld_socket_listener::listen_for_connection_event MYSQL_AUDIT_SERVER_SHUTDOWN_REASON_SHUTDOWN, MYSQLD_SUCCESS_EXIT); terminate_compress_gtid_table_thread(); ```