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Tcp connection accidentally occurs at high load

Our application uses the use of a non-blocking socket when connecting and selecting operations (c-code). The pusedo code is as follows:

unsigned int ConnectToServer(struct sockaddr_in *pSelfAddr,struct sockaddr_in *pDestAddr)
    {
         int sktConnect = -1;
         sktConnect = socket(AF_INET,SOCK_STREAM,0);
         if(sktConnect == INVALID_SOCKET)
             return -1;
         fcntl(sktConnect,F_SETFL,fcntl(sktConnect,F_GETFL) | O_NONBLOCK);
         if(pSelfAddr != 0)
         {
             if(bind(sktConnect,(const struct sockaddr*)(void *)pSelfAddr,sizeof(*pSelfAddr)) != 0)
             {
                 closesocket(sktConnect);
                 return -1;
             }
         }
         errno = 0;
         int nRc = connect(sktConnect,(const struct sockaddr*)(void *)pDestAddr, sizeof(*pDestAddr));
         if(nrC != -1)
         {
             return sktConnect;
         }
         if(errno != EINPROGRESS)
         {
             int savedError = errno;
             closesocket(sktConnect);
             return -1;
         }
         fd_set scanSet;
         FD_ZERO(&scanSet);
         FD_SET(sktConnect,&scanSet);
         struct timeval waitTime;
         waitTime.tv_sec = 2;
         waitTime.tv_usec = 0;
         int tmp;
         tmp = select(sktConnect +1, (fd_set*)0, &scanSet, (fd_set*)0,&waitTime);
         if(tmp == -1 || !FD_ISSET(sktConnect,&scanSet))
         {
             int savedErrorNo = errno;
             writeLog("Connect %s failed after select, cause %d, error %s",inet_ntoa(pDestAddr->sin_addr),savedErrorNo,strerror(savedErrorNo));
             closesocket(sktConnect);
             return -1;
         } 
    .        .        .     .     .}

There are 80 such nodes, and the application connects to all its partner in a circular way. At this point, some of the nodes cannot connect (api - connect + select) with error number 115.

In the logs below (from tcpdump output) for the success scenario, we can see (SYN, SYN + ACK, ACK), but there is not even a SYN entry for failed nodes in tcpdump logs.

Tcpdump logs:

387937 2012-07-05 07:45:30.646514 10.18.92.173          10.137.165.136        TCP      33728 > 8441 [SYN] Seq=0 Ack=0 Win=5792 Len=0 MSS=1460 TSV=1414450402 TSER=912308224 WS=8 
387947 2012-07-05 07:45:30.780762 10.137.165.136        10.18.92.173          TCP      8441 > 33728 [SYN, ACK] Seq=0 Ack=1 Win=5792 Len=0 MSS=1460 TSV=912309754 TSER=1414450402 WS=8 
387948 2012-07-05 07:45:30.780773 10.18.92.173          10.137.165.136        TCP      33728 > 8441 [ACK] Seq=1 Ack=1 Win=5888 Len=0 TSV=1414450435 TSER=912309754 
All the above three events indicate the success information.
387949 2012-07-05 07:45:30.782652 10.18.92.173          10.137.165.136        TCP      33728 > 8441 [PSH, ACK] Seq=1 Ack=1 Win=5888 Len=320 TSV=1414450436 TSER=912309754 
387967 2012-07-05 07:45:30.915615 10.137.165.136        10.18.92.173          TCP      8441 > 33728 [ACK] Seq=1 Ack=321 Win=6912 Len=0 TSV=912309788 TSER=1414450436 
388011 2012-07-05 07:45:31.362712 10.18.92.173          10.137.165.136        TCP      33728 > 8441 [PSH, ACK] Seq=321 Ack=1 Win=5888 Len=320 TSV=1414450581 TSER=912309788 
388055 2012-07-05 07:45:31.495558 10.137.165.136        10.18.92.173          TCP      8441 > 33728 [ACK] Seq=1 Ack=641 Win=7936 Len=0 TSV=912309933 TSER=1414450581 
388080 2012-07-05 07:45:31.702336 10.137.165.136        10.18.92.173          TCP      8441 > 33728 [PSH, ACK] Seq=1 Ack=641 Win=7936 Len=712 TSV=912309985 TSER=1414450581 
388081 2012-07-05 07:45:31.702350 10.18.92.173          10.137.165.136        TCP      33728 > 8441 [ACK] Seq=641 Ack=713 Win=7424 Len=0 TSV=1414450666 TSER=912309985 
388142 2012-07-05 07:45:32.185612 10.137.165.136        10.18.92.173          TCP      8441 > 33728 [PSH, ACK] Seq=713 Ack=641 Win=7936 Len=320 TSV=912310106 TSER=1414450666 
388143 2012-07-05 07:45:32.185629 10.18.92.173          10.137.165.136        TCP      33728 > 8441 [ACK] Seq=641 Ack=1033 Win=8704 Len=0 TSV=1414450786 TSER=912310106 
388169 2012-07-05 07:45:32.362622 10.18.92.173          10.137.165.136        TCP      33728 > 8441 [PSH, ACK] Seq=641 Ack=1033 Win=8704 Len=320 TSV=1414450831 TSER=912310106 
388212 2012-07-05 07:45:32.494833 10.137.165.136        10.18.92.173          TCP      8441 > 33728 [ACK] Seq=1033 Ack=961 Win=9216 Len=0 TSV=912310183 TSER=1414450831 
388219 2012-07-05 07:45:32.501613 10.137.165.136        10.18.92.173          TCP      8441 > 33728 [PSH, ACK] Seq=1033 Ack=961 Win=9216 Len=356 TSV=912310185 TSER=1414450831 
388220 2012-07-05 07:45:32.501624 10.18.92.173          10.137.165.136        TCP      33728 > 8441 [ACK] Seq=961 Ack=1389 Win=10240 Len=0 TSV=1414450865 TSER=912310185

Application logs reporting a connection error (i.e. api - connect + select)

[5258: 2012-07-05 07:45:30]Connect [10.137.165.136 <- 10.18.92.173] success. 
[5258: 2012-07-05 07:45:32]Connect 10.137.165.137 fail after select, cause:115, error Operation now in progress. Check whether remote machine exist and the network is normal or not. 
[5258: 2012-07-05 07:45:32]Connect to server([10.137.165.137 <- 10.18.92.173], port=8441) Failed!

Success logs corresponding to the first three tcpdump inputs. And a crash log where there are no events in tcpdump

: "connect" api , - tcpdump ( SYN). .

+5
2

EINPROGRESS. connect man:

, . (2) (2), . , select (2) , getsockopt (2), SO_ERROR SOL_SOCKET, , () (SO_ERROR ) (SO_ERROR , , ).

, EINPROGRESS , ​​ , . , , "ESTABLISHED". select, getsockopt, , connect.

, SYN_SENT , .

+2

select() - errno ( connect()). , select() .

getsockopt(sktConnect, SOL_SOCKET, SO_ERROR, &err, ...), select().

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