祁东网站开发,大濮网最新濮阳消息,网站建设技术标准,洛阳外贸网站推广对于面向连接的TCP socket,在实际应用中通常都要检测对端是否处于连接中,连接端口分两种情况: 1、连接正常关闭,调用close() shutdown()连接优雅关闭,send与recv立马返回错误,select返回SOCK_ERR; 2、连接的对端异常关闭,比如网络断掉,突然断电. 对于第二种情况,判断连接是否断…对于面向连接的TCP socket,在实际应用中通常都要检测对端是否处于连接中,连接端口分两种情况: 1、连接正常关闭,调用close() shutdown()连接优雅关闭,send与recv立马返回错误,select返回SOCK_ERR; 2、连接的对端异常关闭,比如网络断掉,突然断电. 对于第二种情况,判断连接是否断开的方法有一下几种: 1、自己编写心跳包程序,简单的说就是自己的程序加入一条线程,定时向对端发送数据包,查看是否有ACK,根据ACK的返回情况来管理连接。此方法比较通用,一般使用业务层心跳处理,灵活可控,但改变了现有的协议; 2、使用TCP的keepalive机制,UNIX网络编程不推荐使用SO_KEEPALIVE来做心跳检测(为什么??)。 keepalive原理:TCP内嵌有心跳包,以服务端为例,当server检测到超过一定时间(/proc/sys/net/ipv4/tcp_keepalive_time 7200 即2小时)没有数据传输,那么会向client端发送一个keepalive packet,此时client端有三种反应: 1、client端连接正常,返回一个ACK.server端收到ACK后重置计时器,在2小时后在发送探测.如果2小时内连接上有数据传输,那么在该时间的基础上向后推延2小时发送探测包; 2、客户端异常关闭,或网络断开。client无响应,server收不到ACK,在一定时间(/proc/sys/net/ipv4/tcp_keepalive_intvl 75 即75秒)后重发keepalive packet, 并且重发一定次数(/proc/sys/net/ipv4/tcp_keepalive_probes 9 即9次); 3、客户端曾经崩溃,但已经重启.server收到的探测响应是一个复位,server端终止连接。
修改三个参数的系统默认值 临时方法:向三个文件中直接写入参数,系统重启需要重新设置; 临时方法:sysctl -w net.ipv4.tcp_keepalive_intvl20 全局设置:可更改/etc/sysctl.conf,加上: net.ipv4.tcp_keepalive_intvl 20 net.ipv4.tcp_keepalive_probes 3 net.ipv4.tcp_keepalive_time 60 /* Set TCP keep alive option to detect dead peers. The interval option* is only used for Linux as we are using Linux-specific APIs to set* the probe send time, interval, and count. */
int anetKeepAlive(char *err, int fd, int interval)
{int val 1;//开启keepalive机制if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, val, sizeof(val)) -1){anetSetError(err, setsockopt SO_KEEPALIVE: %s, strerror(errno));return ANET_ERR;}#ifdef __linux__/* Default settings are more or less garbage, with the keepalive time* set to 7200 by default on Linux. Modify settings to make the feature* actually useful. *//* Send first probe after interval. */val interval;if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPIDLE, val, sizeof(val)) 0) {anetSetError(err, setsockopt TCP_KEEPIDLE: %s\n, strerror(errno));return ANET_ERR;}/* Send next probes after the specified interval. Note that we set the* delay as interval / 3, as we send three probes before detecting* an error (see the next setsockopt call). */val interval/3;if (val 0) val 1;if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPINTVL, val, sizeof(val)) 0) {anetSetError(err, setsockopt TCP_KEEPINTVL: %s\n, strerror(errno));return ANET_ERR;}/* Consider the socket in error state after three we send three ACK* probes without getting a reply. */val 3;if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPCNT, val, sizeof(val)) 0) {anetSetError(err, setsockopt TCP_KEEPCNT: %s\n, strerror(errno));return ANET_ERR;}
#endifreturn ANET_OK;
}
