连接linux tcp连接失败,linux – tcp连接在高负载下随机失败

川长思鸟来 2022-10-20 12:30 211阅读 0赞

我们的应用程序使用非阻塞套接字使用连接和选择操作(c代码). pusedo代码如下：

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;

. . . . .\}

有80个这样的节点,应用程序以循环方式连接到所有对等节点.

在此阶段,某些节点无法连接(api – connect select),错误号为115.

In the below logs (of tcpdump output) for success scenario, we can

see (SYN, SYN+ACK, ACK) but no entry of even SYN is present for failed

node in tcpdump logs.

tcpdump日志是：

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

应用程序日志通知连接错误(即api – connect select)

\[5258: 2012-07-05 07:45:30\]Connect \[10.137.165.136

\[5258: 2012-07-05 07:45:32\]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

成功日志对应tcpdump的前3个条目.并且在tcpdump中没有事件的故障日志

My question is : When client initiates “connect” api for failed case,

i am not able to see any event in the tcpdump at client side (even

initial SYN). What can be the reason of this randomness.