handle_slave_io函数调用read_event函数：
read_event函数从连接中读取事件，如果没有事件将会阻塞在这里等待master发送事件。
#0 0x00898402 in __kernel_vsyscall () #1 0x00c28133 in poll () from /lib/libc.so.6 #2 0x08a90315 in vio_io_wait (vio=0xa82faa8, event=VIO_IO_EVENT_READ, timeout=3600000) at /home/mysql26/mysql-5.6.26/vio/viosocket.c:771 #3 0x08a8eb78 in vio_socket_io_wait (vio=0xa82faa8, event=VIO_IO_EVENT_READ) at /home/mysql26/mysql-5.6.26/vio/viosocket.c:68 #4 0x08a8ec6a in vio_read (vio=0xa82faa8, buf=0xa882c90 "P", size=16384) at /home/mysql26/mysql-5.6.26/vio/viosocket.c:123 #5 0x08a8ef05 in vio_read_buff (vio=0xa82faa8, buf=0xa89a530 "\031", size=4) at /home/mysql26/mysql-5.6.26/vio/viosocket.c:157 #6 0x0830e010 in net_read_raw_loop (net=0xa7591b8, count=4) at /home/mysql26/mysql-5.6.26/sql/net_serv.cc:669 #7 0x0830e1f2 in net_read_packet_header (net=0xa7591b8) at /home/mysql26/mysql-5.6.26/sql/net_serv.cc:757 #8 0x0830ef83 in net_read_packet (net=0xa7591b8, complen=0xa34fc168) at /home/mysql26/mysql-5.6.26/sql/net_serv.cc:816 #9 0x0830f0ea in my_net_read (net=0xa7591b8) at /home/mysql26/mysql-5.6.26/sql/net_serv.cc:894 #10 0x084af8a0 in cli_safe_read (mysql=0xa7591b8) at /home/mysql26/mysql-5.6.26/sql-common/client.c:620 #11 0x0866f2da in read_event (mysql=0xa7591b8, mi=0xa709368, suppress_warnings=0xa34fc31b) at /home/mysql26/mysql-5.6.26/sql/rpl_slave.cc:3533 #12 0x086799f6 in handle_slave_io (arg=0xa709368) at /home/mysql26/mysql-5.6.26/sql/rpl_slave.cc:4730 #13 0x089b3141 in pfs_spawn_thread (arg=0xa8302b0) at /home/mysql26/mysql-5.6.26/storage/perfschema/pfs.cc:1860 #14 0x00cdc832 in start_thread () from /lib/libpthread.so.0 #15 0x00c31e0e in clone () from /lib/libc.so.6
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MySQL半同步复制--handle_slave_io等待master发送event
原文地址：http://yanzongshuai.blog.51cto.com/3057928/1971535
