slave IO流程之一：mysql登陆过程（mysql_real_connect）

  1 for (t_res= res_lst; t_res; t_res= t_res->ai_next)
  2     {
  3       DBUG_PRINT("info", ("Create socket, family: %d  type: %d  proto: %d",
  4                           t_res->ai_family, t_res->ai_socktype,
  5                           t_res->ai_protocol));
  6 
  7       sock= socket(t_res->ai_family, t_res->ai_socktype, t_res->ai_protocol);
  8       if (sock == SOCKET_ERROR)
  9       {
 10         DBUG_PRINT("info", ("Socket created was invalid"));
 11         /* Try next address if there is one */
 12         saved_error= socket_errno;
 13         continue;
 14       }
 15 
 16       if (client_bind_ai_lst)
 17       {
 18         struct addrinfo* curr_bind_ai= NULL;
 19         DBUG_PRINT("info", ("Attempting to bind socket to bind address(es)"));
 20 
 21         /*
 22            We'll attempt to bind to each of the addresses returned, until
 23            we find one that works.
 24            If none works, we'll try the next destination host address
 25            (if any)
 26         */
 27         curr_bind_ai= client_bind_ai_lst;
 28 
 29         while (curr_bind_ai != NULL)
 30         {
 31           /* Attempt to bind the socket to the given address */
 32           bind_result= bind(sock,
 33                             curr_bind_ai->ai_addr,
 34                             curr_bind_ai->ai_addrlen);
 35           if (!bind_result)
 36             break;   /* Success */
 37 
 38           DBUG_PRINT("info", ("bind failed, attempting another bind address"));
 39           /* Problem with the bind, move to next address if present */
 40           curr_bind_ai= curr_bind_ai->ai_next;
 41         }
 42 
 43         if (bind_result)
 44         {
 45           /*
 46             Could not bind to any client-side address with this destination
 47              Try the next destination address (if any)
 48           */
 49           DBUG_PRINT("info", ("All bind attempts with this address failed"));
 50           saved_error= socket_errno;
 51           closesocket(sock);
 52           continue;
 53         }
 54         DBUG_PRINT("info", ("Successfully bound client side of socket"));
 55       }
 56 
 57       /* Create a new Vio object to abstract the socket. */
 58       if (!net->vio)
 59       {
 60         if (!(net->vio= vio_new(sock, VIO_TYPE_TCPIP, flags)))
 61         {
 62           set_mysql_error(mysql, CR_OUT_OF_MEMORY, unknown_sqlstate);
 63           closesocket(sock);
 64           freeaddrinfo(res_lst);
 65           if (client_bind_ai_lst)
 66             freeaddrinfo(client_bind_ai_lst);
 67           goto error;
 68         }
 69       }
 70       /* Just reinitialize if one is already allocated. */
 71       else if (vio_reset(net->vio, VIO_TYPE_TCPIP, sock, NULL, flags))
 72       {
 73         set_mysql_error(mysql, CR_UNKNOWN_ERROR, unknown_sqlstate);
 74         closesocket(sock);
 75         freeaddrinfo(res_lst);
 76         if (client_bind_ai_lst)
 77           freeaddrinfo(client_bind_ai_lst);
 78         goto error;
 79       }
 80 
 81       DBUG_PRINT("info", ("Connect socket"));
 82       status= vio_socket_connect(net->vio, t_res->ai_addr,
 83                                  (socklen_t)t_res->ai_addrlen,
 84                                  get_vio_connect_timeout(mysql));
 85       /*
 86         Here we rely on vio_socket_connect() to return success only if
 87         the connect attempt was really successful. Otherwise we would
 88         stop trying another address, believing we were successful.
 89       */
 90       if (!status)
 91         break;
 92 
 93       /*
 94         Save either the socket error status or the error code of
 95         the failed vio_connection operation. It is necessary to
 96         avoid having it overwritten by later operations.
 97       */
 98       saved_error= socket_errno;
 99 
100       DBUG_PRINT("info", ("No success, try next address."));
101     }