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社区首页 >问答首页 >TCP，recv函数不顾KEEPALIVE而挂起

问TCP，recv函数不顾KEEPALIVE而挂起
EN

Stack Overflow用户
提问于 2015-06-26 15:21:13
回答 2查看 1.9K关注 0票数 5

在服务器死后，TCP是否保持活动(有少量超时)，以防止客户端挂在recv上？

设想情况：

服务器和客户端在单独的机器上运行：

  1. 客户端通过带有KEEPALIVE选项的TCP连接到服务器
  2. 客户端发送"Hello server“并等待响应。
  3. 服务器接收"Hello server“并响应"Hello client”。
  4. 客户端接收响应，休眠10s，重复步骤2-4 (步骤1现在被跳过-连接被保留)

在客户端睡眠期间，服务器被插入，现在：

  1. 客户醒过来
  2. 发送"Hello server“并等待响应
  3. 在20分钟后，recv放弃了--我原以为KEEPALIVE会在45秒之后中断recv功能

设置KEEPALIVE选项：

代码语言：javascript
复制
void TCPclient::setkeepalive()
{
   int optval;
   socklen_t optlen = sizeof(optval);

   /* Check the status for the keepalive option */
   if(getsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &optval, &optlen) < 0) {
        throw std::string("getsockopt");
   }

   optval = 1;
   optlen = sizeof(optval);
   if(setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0) {
      close(s);
      exit(EXIT_FAILURE);
   }

    optval = 2;
    if (setsockopt(sock, SOL_TCP, TCP_KEEPCNT, &optval, optlen) < 0) {
        throw std::string("setsockopt");
    }

    optval = 15;
    if (setsockopt(sock, SOL_TCP, TCP_KEEPIDLE, &optval, optlen) < 0) {
        throw std::string("setsockopt");
    }

    optval = 15;
    if (setsockopt(sock, SOL_TCP, TCP_KEEPINTVL, &optval, optlen) < 0) {
        throw std::string("setsockopt");
    }   
}

Linux3.2.084-通用

c++
linux
sockets
tcp
network-programming
EN

回答 2

Stack Overflow用户

发布于 2015-06-26 15:57:47

当线路闲置15秒时，保持活动状态。在您的示例中，Keepalive启动超时为15秒，睡眠为10秒，这意味着"Hello server“将是服务器被杀死后发送的下一个命令。

您的Linux将尝试多次重传此消息。保护仍然不会被触发。到达重试限制后，连接将中断--这将需要10-30分钟。

票数 6
EN

Stack Overflow用户

发布于 2015-06-29 05:38:57

@MMA的回答是正确的。我写了一个类似的客户在写之前等了20秒。一旦客户端唤醒并发送消息，由“保持活动”发送的ACK消息将不再发送(连接不再空闲)。

在15次重试(在/proc/sys/net/ipv4 4中配置了tcp_retries2 )之后，发送tcp段，其中超时呈指数增长，直到达到2分钟(在我的例子中)，连接被设置为错误，并使用ETIMEDOUT (errno 110)挂起读取或recv返回。在我看来，大约花了15分钟。这一次取决于RTO。查看TCPDUMP，有两个ack在三路握手之后(我不知道为什么第一个是2ack)，然后是15条带有数据和推送标志集的消息。

代码语言：javascript
复制
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on p2p1, link-type EN10MB (Ethernet), capture size 65535 bytes
01:16:45.296179 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [S], seq 515423022, win 14600, options [mss 1460,sackOK,TS val 19212623 ecr 0,nop,wscale 7], length 0
E..<.a@.@......d4.....'...........9............
.%)O........
01:16:45.477983 IP ec2-52-7-150-140.compute-1.amazonaws.com.10221 > 192.168.2.100.60895: Flags [S.], seq 3672727778, ack 515423023, win 26847, options [mss 1436,sackOK,TS val 114765522 ecr 19212623,nop,wscale 7], length 0
E..<..@.-...4......d'.....`..../..h............
.....%)O....
01:16:45.478046 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [.], ack 1, win 115, options [nop,nop,TS val 19212805 ecr 114765522], length 0
E..4.b@.@......d4.....'..../..`....s.......
.%*.....
01:17:00.512812 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [.], ack 1, win 115, options [nop,nop,TS val 19227840 ecr 114765522], length 0
E..4.c@.@......d4.....'.......`....s.......
.%d.....
01:17:00.731160 IP ec2-52-7-150-140.compute-1.amazonaws.com.10221 > 192.168.2.100.60895: Flags [.], ack 1, win 210, options [nop,nop,TS val 114769336 ecr 19212805], length 0
E..4N.@.-.r.4......d'.....`..../....M......
..=..%*.
01:17:05.478933 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 19232806 ecr 114769336], length 14
E..B.d@.@......d4.....'..../..`....s.......
.%x&..=.Hello Word :).
01:17:06.027768 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 19233354 ecr 114769336], length 14
E..B.e@.@......d4.....'..../..`....s.......
.%zJ..=.Hello Word :).
01:17:07.120879 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 19234448 ecr 114769336], length 14
E..B.f@.@......d4.....'..../..`....s.......
.%~...=.Hello Word :).
01:17:09.312833 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 19236640 ecr 114769336], length 14
E..B.g@.@......d4.....'..../..`....s.......
.%. ..=.Hello Word :).
01:17:13.697663 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 19241024 ecr 114769336], length 14
E..B.h@.@......d4.....'..../..`....s.......
.%.@..=.Hello Word :).
01:17:22.466187 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 19249793 ecr 114769336], length 14
E..B.i@.@......d4.....'..../..`....s.......
.%....=.Hello Word :).
01:17:40.001653 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 19267328 ecr 114769336], length 14
E..B.j@.@......d4.....'..../..`....s.......
.%....=.Hello Word :).
01:18:15.074493 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 19302401 ecr 114769336], length 14
E..B.k@.@......d4.....'..../..`....s.......
.&....=.Hello Word :).
01:19:25.217799 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 19372545 ecr 114769336], length 14
E..B.l@.@......d4.....'..../..`....s.......
.'....=.Hello Word :).
01:21:25.537775 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 19492864 ecr 114769336], length 14
E..B.m@.@......d4.....'..../..`....s.......
.)p...=.Hello Word :).
01:23:25.856854 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, 69336], length 14
E..B.n@.@......d4.....'..../..`....s.......
.+F...=.Hello Word :).
01:25:26.176894 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, 69336], length 14
E..B.o@.@......d4.....'..../..`....s.......
.-....=.Hello Word :).
01:27:26.497691 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, 69336], length 14
E..B.p@.@......d4.....'..../..`....s.......
......=.Hello Word :).
01:29:26.816905 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, 69336], length 14
E..B.q@.@......d4.....'..../..`....s.......
.0....=.Hello Word :).
01:31:27.137013 IP 192.168.2.100.60895 > ec2-52-7-150-140.compute-1.amazonaws.com.10221: Flags [P.], seq 1:15, ack 1, win 115, options [nop,nop,TS val 20094464 ecr 114769336], length 14
E..B.r@.@......d4.....'..../..`....s.......
.2....=.Hello Word :).

我使用的客户端代码：

代码语言：javascript
复制
#include <sys/types.h>
#include <sys/socket.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <netinet/in.h>
#include <net/if.h>
#include <arpa/inet.h>
#include <stdio.h>


#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/tcp.h>


#define DEST_PORT 10221
#define ADDRLEN INET_ADDRSTRLEN


int main(int argc, char** argv)
{
    int sock;
    int bytesWritten;
    struct sockaddr_in their_addr;
    char buffer[] = "Hello Word :)";
    char addrstr[ADDRLEN + 1];

    if (argc != 2)
    {
       printf("ERROR - Number of args\n");
       return 10;
    }

    strncpy(addrstr, argv[1], ADDRLEN);

    bzero(&their_addr, sizeof(their_addr));
    their_addr.sin_family = AF_INET;
    their_addr.sin_port = htons(DEST_PORT);

    if (inet_pton(AF_INET, addrstr,(void *)&their_addr.sin_addr) != 1)
    {
        printf("ERROR - Converting Address: %d\n", errno);
        return 2;
    }

    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        printf("ERROR - Socket could not be open: %d\n", errno);
        return 1;
    }

//// Copied option setting
   int optval;
   socklen_t optlen = sizeof(optval);

   /* Check the status for the keepalive option */
   if(getsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &optval, &optlen) < 0) {
        printf("ERROR - SOL_SOCKET: %d\n", errno);
        return 19;
   }

   optval = 1;
   optlen = sizeof(optval);
   if(setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0) {
        printf("ERROR - SOL_SOCKET-2: %d\n", errno);
        return 20;
   }

    optval = 2;
    if (setsockopt(sock, SOL_TCP, TCP_KEEPCNT, &optval, optlen) < 0) {
        printf("ERROR - SOL_TCP: %d\n", errno);
        return 21;
    }

    optval = 15;
    if (setsockopt(sock, SOL_TCP, TCP_KEEPIDLE, &optval, optlen) < 0) {
        printf("ERROR - SOL_TCP-2: %d\n", errno);
        return 22;
    }

    optval = 15;
    if (setsockopt(sock, SOL_TCP, TCP_KEEPINTVL, &optval, optlen) < 0) {
        printf("ERROR - SOL_TCP-3: %d\n", errno);
        return 23;
    }   
/////
    if (connect(sock, (const struct sockaddr *)&their_addr, 
                (socklen_t)sizeof(their_addr)) == -1)
    {
        printf("ERROR - Could not connect to destination: %d\n", errno);
        return 3;
    }

/// Sleep 20 seconds    
    sleep(20);
    printf("About to write\n");

    if ((bytesWritten = write(sock, (const void *)buffer, sizeof(buffer))) == -1)
    {
        printf("ERROR - Sending message: %d\n", errno);
        return 4;
    }

    printf("Message Sent to Address %s, Port: %d\n\n", addrstr, DEST_PORT);

    int bytesRead;

    if ((bytesRead = read(sock, buffer, sizeof(buffer))) == -1)
    {
        printf("ERROR - Sending message: %d\n", errno);
        return 4;
    }

    close(sock);

    return 0;
}

我在AWS中托管的服务器上运行这个测试。模拟删除服务器而没有注意到客户端的方法是:我有一个与服务器相关联的公共(弹性) IP，在三次握手之后，我立即将Elastic从服务器上断开。我不能粘贴服务器代码，但在这里不相关。

请不要因为发送消息而停止在本例中保持活动。

票数 0
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/31076858

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