Re: [問題] select read & write同一fd

看板C_and_CPP (C/C++)作者StubbornLin (Victor)時間16年前 (2009/07/31 12:52)推噓4(4推 0噓 11→)

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※ 引述《godman362 (青)》之銘言： : 我想問一下，上述的寫法會不會有問題？ : 因為我不懂select是用什麼去判別資料是否準備好 : 還請各位先進指點一番，謝謝給你看我很久以前寫的 /** @brief 更新socket的狀態 @return 是否成功 **/ virtual bool Update(){ fd_set Read; fd_set Write; fd_set Except; FD_ZERO(&Read); FD_ZERO(&Write); FD_ZERO(&Except); FD_SET(m_Socket.getSocket(),&Read); FD_SET(m_Socket.getSocket(),&Write); FD_SET(m_Socket.getSocket(),&Except); timeval TimeOut; TimeOut.tv_sec = 0; TimeOut.tv_usec = 0; int Result; Result = select(0,&Read,&Write,&Except,&TimeOut); if(Result == SOCKET_ERROR){ setLastErrorDescription("select failed at Update"); return false; } // normal state if(m_IsListening==false && m_IsConnecting==false){ if(FD_ISSET(m_Socket.getSocket(),&Read)){ int Length = 0; Result = ioctlsocket(m_Socket.getSocket(),FIONREAD,(unsigned long *)&Length); // connection gracefully closed if(Length == 0){ Close(); m_EventInterface.OnClose(true); // connection is not be gracefully closeed }else if(recv(m_Socket.getSocket(),0,0,0) == SOCKET_ERROR){ Close(); m_EventInterface.OnClose(false); }else{ m_EventInterface.OnReadable(Length); } } // dada can be sent if(FD_ISSET(m_Socket.getSocket(),&Write)){ m_EventInterface.OnSendable(); } // error occur if(FD_ISSET(m_Socket.getSocket(),&Except)){ m_EventInterface.OnExcept(); } // listening for connection }else if(m_IsListening){ // there is a new connection if(FD_ISSET(m_Socket.getSocket(),&Read)){ m_EventInterface.OnAcceptable(m_Socket); } // wait for connecting result }else if(m_IsConnecting){ // successfully connected if( FD_ISSET( (m_Socket.getSocket()) , (&Write) ) ){ sockaddr_in Address; memset(&Address,0,sizeof(Address)); int Length = sizeof(SOCKADDR); Result = getsockname(m_Socket.getSocket(),(LPSOCKADDR)&Address,&Length); if(Result == SOCKET_ERROR){ setLastErrorDescription("getsockname failed at Connect"); return false; } m_LocalAddress = inet_ntoa(Address.sin_addr); m_LocalPort = ntohs(Address.sin_port); m_EventInterface.OnConnect(); m_IsConnecting = false; } // connect failed if(FD_ISSET(m_Socket.getSocket(),&Except)){ m_EventInterface.OnConnectFailed(); m_IsConnecting = false; } } return true; } 其實select用來判斷socket的事件很簡單他的概念是這樣，在不同情況下，read、write等等事件各代表不同意思至於代表什麼意思這點就需要看文件怎麼寫像listening時，read事件發生是表示有連線進來了而像你說的連線時的write，那是表示可以寫資料了為什麼需要有那個事件，因為socket有輸出用的buffer 你寫資料其實是先放進去，接著socket幫你打包丟出去而當buffer滿了，他當然不讓你丟所以連線中的write event是告訴你，outgoing buffer有位置了可以丟資料了大至上像這樣，更細節的部份 MSDN裡都有寫得很清楚什麼時候的event代表什麼意思該做什麼事 -- 哇咧咧創意投票系統 http://walele.com 易記學程式設計教學 http://ez2learn.com/ 易記學程式設計討論區 http://forum.ez2learn.com VICTOR's 個人Blog http://blog.ez2learn.com/ 財報分析王 http://victorlin.serveftp.org/stock/ -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 118.170.171.45