Question

试图了解阻塞套接字recv（）。阻止在客户端应用程序中实现的套接字并连接到服务器。服务器应用程序中实现的IOCP非阻塞套接字。客户端应用程序发送一些请求，服务器响应肯定或否定回复。有时服务器中的处理时间在同一毫秒内。一旦收到请求服务器应用程序立即响应。处理大约400个请求/响应时，服务器应用程序以相同的毫秒响应，但客户端应用程序在5秒后收到。时间延迟。

我们尝试使用wireshark来分析延迟和观察的位置：

wireshark时间戳和客户端app log timestamp.i.e之间存在5秒的时差。客户端应用程序日志比wireshark时间戳晚5秒。
我们发现recv（）从套接字缓冲区读取数据的平均时间为15毫秒。

问题是由于阻塞套接字？这是代码;

int classA::ReceiveFullMessage(int sock)
{
    int i=0, nRet;
    unsigned short *tmplen, pktlen;
    struct timeval tv;
    int g_RcvLen = 0;   
    bool bIsTimeOut = false;
    //HRESULT hr;
    char *hbInvokeId;
    char strMsg[2048];

    memset(g_RcvBuf,0,MAXMESSAGEPACKET);
    while (1)
    {
        // ***
        tv.tv_sec = bIsTimeOut ? 5 : 60; // Wait for 1 minute in normal case, if time out happens
        tv.tv_usec = 0;                  // Send heartbeat pkt and wait for 5 seconds for response
        FD_ZERO(&rdfs);
        FD_SET(sock,&rdfs);

        nRet = select(sock+1, &rdfs, (fd_set *)0, (fd_set *)0, (struct timeval *)&tv);

        //log mesg --returnValue[%d] receivedLength[%d], nRet, g_RcvLen

        if (nRet < 0)       {   
            //log mesgreturnValue = -1
            return -1;
        }
        else if(nRet == 0)
        {
            if(!bIsTimeOut)
            {
                //Timeout happened, send heart beat
                bIsTimeOut = true;
                if (strlen(szServerIp) > 0) {
                    // send heart beat packet
                    hbInvokeId = SendRequest(szBuf, NULL);
                }
                else
                    hbInvokeId = SendRequest("<Echo>APIXport HB</Echo>", NULL);
            }
            else    {
                //Timeout happened, No response for heart beat                      
                m_packet[atoi(hbInvokeId)].inUse = false;
                return -1;
            }
        }
        else if (nRet > 0)
        {
            bIsTimeOut = false; //***
            if(FD_ISSET(sock,&rdfs))
            {
                if (g_RcvLen < 2)
                {
                    //log mesg receivedLength[%d] < 2, g_RcvLen

                    // read header
                    nRet = recv(sock,&g_RcvBuf[g_RcvLen], 1, 0);

                    if (nRet <= 0)
                    {
                        // log mesg --Recvd Improper Header
                        return -1;
                    }

                    // receive two successive zeros..frame header
                    if (g_RcvBuf[g_RcvLen] == 0) g_RcvLen++;
                    else g_RcvLen = 0;

                    //log mesg receivedLength[%d] < 2 at --end returnValue[%d], g_RcvLen, nRet

                }
                else if (g_RcvLen < 4)
                {
                    // log mesg --receivedLength[%d] < 4, g_RcvLen

                    // read length
                    nRet = recv(sock, &g_RcvBuf[g_RcvLen], 1, 0);

                    if (nRet <= 0)  {
                        //Recvd Improper Length
                        return -1;
                    }
                    g_RcvLen++;

                    //log mesg --receivedLength[%d] < 4 --end returnValue[%d]", g_RcvLen, nRet
                    logMsg(strMsg, VERBOSE);
                }
                else if (g_RcvLen >= 4)
                {
                    // try to receive full packet
                    tmplen= (unsigned short*)&g_RcvBuf[2];
                    pktlen = ntohs(*tmplen);

                    nRet = recv(sock, &g_RcvBuf[g_RcvLen], pktlen-g_RcvLen, 0);
                    if (nRet <= 0)  {
                        //log -- Recvd Invalid Packet
                        return -1;
                    }

                    g_RcvLen += nRet;  // add only received number of bytes

                    //log mesg --receivedLngth[%d] >= 4 --end returnValue[%d], g_RcvLen, nRet

                    if (g_RcvLen == pktlen)
                    {
                        // full packet received
                        return (g_RcvLen); // exit with length
                    }
                }
            }
        }
    }
    return g_RcvLen;
}

套接字缓冲区 - recv（）

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