01./* 設置套接字選項周期性消息檢測連通性 心跳包、 心博。主要用於長連接。
02. * 參數：套接字， 1或0開啟, 首次間隔時間, 兩次間隔時間, 斷開次數
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./* 綁定地址復用. 主要用於TCP Server端 */
11.setsockopt(iSockfd, SOL_SOCKET, SO_REUSEADDR, &iSockAttrOn,sizeof(iSockAttrOn) );
/* 設置套接字選項周期性消息檢測連通性 心跳包、 心博。主要用於長連接。
* 參數：套接字， 1或0開啟, 首次間隔時間, 兩次間隔時間, 斷開次數
*/
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) );
}
/* 綁定地址復用. 主要用於TCP Server端 */
setsockopt(iSockfd, SOL_SOCKET, SO_REUSEADDR, &iSockAttrOn,sizeof(iSockAttrOn) );
SO_KEEPALIVE 保持連接檢測對方主機是否崩潰，避免（服務器）永遠阻塞於TCP連接的輸入。設置該選項後，如果2小時內在此套接口的任一方向都沒有數據交換，TCP就自 動給對方 發一個保持存活探測分節(keepalive probe)。這是一個對方必須響應的TCP分節.它會導致以下三種情況：對方接收一切正常：以期望的ACK響應。2小時後，TCP將發出另一個探測分節。對方已崩潰且已重新啟動：以RST響應。套接口的待處理錯誤被置為ECONNRESET，套接 口本身則被關閉。對方無任何響應：源自berkeley的TCP發送另外8個探測分節，相隔75秒一個，試圖得到一個響應。在發出第一個探測分節11分鐘 15秒後若仍無響應就放棄。套接口的待處理錯誤被置為ETIMEOUT，套接口本身則被關閉。如ICMP錯誤是“host unreachable(主機不可達)”，說明對方主機並沒有崩潰，但是不可達，這種情況下待處理錯誤被置為 EHOSTUNREACH。
如果我們不能接受如此之長的等待時間，從TCP-Keepalive-HOWTO上可以知道一共有兩種方式可以設置，一種是修改內核關於網絡方面的 配置參數，另外一種就是SOL_TCP字段的TCP_KEEPIDLE， TCP_KEEPINTVL， TCP_KEEPCNT三個選項。
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).
/*開始首次KeepAlive探測前的TCP空閉時間 */
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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).
/* 兩次KeepAlive探測間的時間間隔 */
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.
/* 判定斷開前的KeepAlive探測次數
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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.