昨天聽zhuzhaoyuan說的一個connect細節. 通常我們connect的時候都是非阻塞的, 在connect呼叫後把控制代碼掛到poll去, 等poll通知可寫的時候, 我們就認為connect成功了. 但是在linux平臺下實際上不一定成功, 具體的要用socket get_opt來檢查下出錯碼來決定.

以下是從man 2 connnect摘抄的:

EINPROGRESS
The socket(2,7,n) is non-blocking and the connection cannot be com-
pleted immediately. It is possible to select(2,7,2 select_tut)(2) or poll(2) for
completion by selecting the socket(2,7,n) for writing. After select(2,7,2 select_tut)
indicates writability, use getsockopt(2) to read(2,n,1 builtins) the SO_ERROR
option at level SOL_SOCKET to determine whether connect com-
pleted successfully (SO_ERROR is zero) or unsuccessfully
(SO_ERROR is one of the usual error(8,n) codes listed here, explain-
ing the reason for the failure).

我們看下erlang的inet_drv是如何處理的.
./erts/emulator/drivers/common/inet_drv.c:

        {
            int error = 0;      /* Has to be initiated, we check it */
            unsigned int sz = sizeof(error); /* even if we get -1 */
            int code = sock_getopt(desc->inet.s, SOL_SOCKET, SO_ERROR,
                                   (void *)&error, &sz);

            if ((code < 0) || error) {
                desc->inet.state = TCP_STATE_BOUND;  /* restore state */
                ret = async_error(INETP(desc), error);
                goto done;
            }
        }

結論: 細節決定品質.

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