UNIX网络编程：套接字选项（心跳检测、绑定地址复用）

01./* 设置套接字选项周期性消息检测连通性 心跳包、 心博。主要用于长连接。

02. * 参数：套接字， 1或0开启, 首次间隔时间, 两次间隔时间, 断开次数

03. */

04.void setKeepAlive( int iSockfd , int iSockAttrOn, socklen_t iIdleTime , socklen_t iInterval , socklen_t iCount ){

05. setsockopt( iSockfd , SOL_SOCKET , SO_KEEPALIVE , (const char*)&iSockAttrOn , sizeof(iSockAttrOn) );

06. setsockopt( iSockfd , SOL_TCP , TCP_KEEPIDLE , (const char*)&iIdleTime , sizeof(iIdleTime) );

07. setsockopt( iSockfd , SOL_TCP , TCP_KEEPINTVL , (const char*)&iInterval,sizeof(iInterval) );

08. setsockopt( iSockfd , SOL_TCP , TCP_KEEPCNT , (const char*)&iCount,sizeof(iCount) );

09.}

10./* 绑定地址复用. 主要用于TCP Server端 */

11.setsockopt(iSockfd, SOL_SOCKET, SO_REUSEADDR, &iSockAttrOn,sizeof(iSockAttrOn) );

/* 设置套接字选项周期性消息检测连通性 心跳包、 心博。主要用于长连接。

* 参数：套接字， 1或0开启, 首次间隔时间, 两次间隔时间, 断开次数

*/

void setKeepAlive( int iSockfd , int iSockAttrOn, socklen_t iIdleTime , socklen_t iInterval , socklen_t iCount ){

setsockopt( iSockfd , SOL_SOCKET , SO_KEEPALIVE , (const char*)&iSockAttrOn , sizeof(iSockAttrOn) );

setsockopt( iSockfd , SOL_TCP , TCP_KEEPIDLE , (const char*)&iIdleTime , sizeof(iIdleTime) );

setsockopt( iSockfd , SOL_TCP , TCP_KEEPINTVL , (const char*)&iInterval,sizeof(iInterval) );

setsockopt( iSockfd , SOL_TCP , TCP_KEEPCNT , (const char*)&iCount,sizeof(iCount) );

}

/* 绑定地址复用. 主要用于TCP Server端 */

setsockopt(iSockfd, SOL_SOCKET, SO_REUSEADDR, &iSockAttrOn,sizeof(iSockAttrOn) );

SO_KEEPALIVE 保持连接检测对方主机是否崩溃，避免（服务器）永远阻塞于TCP连接的输入。设置该选项后，如果2小时内在此套接口的任一方向都没有数据交换，TCP就自 动给对方 发一个保持存活探测分节(keepalive probe)。这是一个对方必须响应的TCP分节.它会导致以下三种情况：对方接收一切正常：以期望的ACK响应。2小时后，TCP将发出另一个探测分节。对方已崩溃且已重新启动：以RST响应。套接口的待处理错误被置为ECONNRESET，套接 口本身则被关闭。对方无任何响应：源自berkeley的TCP发送另外8个探测分节，相隔75秒一个，试图得到一个响应。在发出第一个探测分节11分钟 15秒后若仍无响应就放弃。套接口的待处理错误被置为ETIMEOUT，套接口本身则被关闭。如ICMP错误是“host unreachable(主机不可达)”，说明对方主机并没有崩溃，但是不可达，这种情况下待处理错误被置为 EHOSTUNREACH。

如果我们不能接受如此之长的等待时间，从TCP-Keepalive-HOWTO上可以知道一共有两种方式可以设置，一种是修改内核关于网络方面的 配置参数，另外一种就是SOL_TCP字段的TCP_KEEPIDLE， TCP_KEEPINTVL， TCP_KEEPCNT三个选项。

1) The tcp_keepidle parameter specifies the interval of inactivity that causes TCP to generate a KEEPALIVE transmission for an application that requests them. tcp_keepidle defaults to 14400 (two hours).

/*开始首次KeepAlive探测前的TCP空闭时间 */

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2) The tcp_keepintvl parameter specifies the interval between the nine retries that are attempted if a KEEPALIVE transmission is not acknowledged. tcp_keepintvl defaults to 150 (75 seconds).

/* 两次KeepAlive探测间的时间间隔 */

3) The tcp_keepcnt option specifies the maximum number of keepalive probes to be sent. The value of TCP_KEEPCNT is an integer value between 1 and n, where n is the value of the systemwide tcp_keepcnt parameter.

/* 判定断开前的KeepAlive探测次数

[cpp] view plaincopyprint?

01.int keepIdle = 1000;

02.int keepInterval = 10;

03.int keepCount = 10;

04.Setsockopt(listenfd, SOL_TCP, TCP_KEEPIDLE, (void *)&keepIdle, sizeof(keepIdle));

05.Setsockopt(listenfd, SOL_TCP,TCP_KEEPINTVL, (void *)&keepInterval, sizeof(keepInterval));

06.Setsockopt(listenfd,SOL_TCP, TCP_KEEPCNT, (void *)&keepCount, sizeof(keepCount));

int keepIdle = 1000;

int keepInterval = 10;

int keepCount = 10;

Setsockopt(listenfd, SOL_TCP, TCP_KEEPIDLE, (void *)&keepIdle, sizeof(keepIdle));

Setsockopt(listenfd, SOL_TCP,TCP_KEEPINTVL, (void *)&keepInterval, sizeof(keepInterval));

Setsockopt(listenfd,SOL_TCP, TCP_KEEPCNT, (void *)&keepCount, sizeof(keepCount));

Remember that keepalive is not program?related, but socket?related, so if you have multiple sockets, you can handle keepalive for each of them separately.

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