怎样及时检测出非正常断开的TCP连接

此处的”非正常断开”指TCP连接不是以优雅的方式断开,如网线故障等物理链路的原因,还有突然主机断电等原因
        有两种方法可以检测:1.TCP连接双方定时发握手消息 2.利用TCP协议栈中的KeepAlive探测
        第二种方法简单可靠,只需对TCP连接两个Socket设定KeepAlive探测,所以本文只讲第二种方法在Linux,Window2000下的实现(在其它的平台上没有作进一步的测试)
        Windows 2000平台下
//定义结构及宏
struct TCP_KEEPALIVE {
    u_long  onoff;
    u_long  keepalivetime;
    u_long  keepaliveinterval;
} ;

#define SIO_KEEPALIVE_VALS   _WSAIOW(IOC_VENDOR,4)

//KeepAlive实现
TCP_KEEPALIVE inKeepAlive = {0}; //输入参数
        unsigned long ulInLen = sizeof(TCP_KEEPALIVE); 

        TCP_KEEPALIVE outKeepAlive = {0}; //输出参数
        unsigned long ulOutLen = sizeof(TCP_KEEPALIVE); 
        
        unsigned long ulBytesReturn = 0; 

        //设置socket的keep alive为5秒，并且发送次数为3次  
        inKeepAlive.onoff = 1; 
        inKeepAlive.keepaliveinterval = 5000; //两次KeepAlive探测间的时间间隔
        inKeepAlive.keepalivetime = 5000; //开始首次KeepAlive探测前的TCP空闭时间
       
        if (WSAIoctl((unsigned int)s, SIO_KEEPALIVE_VALS,  
        (LPVOID)&inKeepAlive, ulInLen,  
        (LPVOID)&outKeepAlive, ulOutLen,  
        &ulBytesReturn, NULL, NULL) == SOCKET_ERROR) 
        {         
                ACE_DEBUG ((LM_INFO,
                        ACE_TEXT ("(%P|%t)        /WSAIoctl failed. error code(%d)!/n"),WSAGetLastError()));
        }

        Linux平台下
        #include <netinet/tcp.h>
……
        ////KeepAlive实现
//下面代码要求有ACE,如果没有包含ACE,则请把用到的ACE函数改成linux相应的接口
int keepAlive = 1;//设定KeepAlive
        int keepIdle = 5;//开始首次KeepAlive探测前的TCP空闭时间
        int keepInterval = 5;//两次KeepAlive探测间的时间间隔
        int keepCount = 3;//判定断开前的KeepAlive探测次数
        
        if(setsockopt(s,SOL_SOCKET,SO_KEEPALIVE,(void*)&keepAlive,sizeof(keepAlive)) == -1)
        {
                ACE_DEBUG ((LM_INFO,
                        ACE_TEXT ("(%P|%t)        setsockopt SO_KEEPALIVE error!/n")));
        
        }
        
        if(setsockopt(s,SOL_TCP,TCP_KEEPIDLE,(void *)&keepIdle,sizeof(keepIdle)) == -1)
        {
                ACE_DEBUG ((LM_INFO,
                        ACE_TEXT ("(%P|%t)        setsockopt TCP_KEEPIDLE error!/n")));
        }

        if(setsockopt(s,SOL_TCP,TCP_KEEPINTVL,(void *)&keepInterval,sizeof(keepInterval)) == -1)
        {
                ACE_DEBUG ((LM_INFO,
                        ACE_TEXT ("(%P|%t)        setsockopt TCP_KEEPINTVL error!/n")));
        }
        
        if(setsockopt(s,SOL_TCP,TCP_KEEPCNT,(void *)&keepCount,sizeof(keepCount)) == -1)
        {
                ACE_DEBUG ((LM_INFO,
                        ACE_TEXT ("(%P|%t)  setsockopt TCP_KEEPCNT error!/n")));
        }

测试中表明,当Linux服务器设定了KeepAlive,Windows客户端可以不设KeepAlive

                                                                        引用请注明作者:在水一鱼