指数退避算法

Exponential backoff （指数退避）
在Socket连接中用到该算法的代码片段：

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>

#define MAXSLEEP 128

int connect_retry(int domain,int type,int protocol,const struct sockaddr *addr,socklen_t alen){
    int numsec,fd;
    /* Try to connect with exponential backoff */
    for(numsec=1; numsec <= MAXSLEEP; numsec <<= 1){
        if((fd = socket(domain, type, protocol)) < 0 )
            return(-1);
        if(connect(fd, addr, alen) == 0){
            /* Connection accepted. */
            return(fd);
        }
        close(fd);
        /* Delay before trying again */
        if(numsec <= MAXSLEEP/2)
            sleep(numsec);
    }
    return(-1);
}