使用select io复用实现超时设置

在linux的socket编程中，经常会遇到超时设置的问题，例如请求方如果在Ks内不发送数据则服务器要断开连接停止服务。这里我使用select的io复用实现超时5s设置，具体代码片段如下：

fd_set fs;
timeval tv;
tv.tv_sec = 5;
tv.tv_usec = 0;
FD_ZERO(&fs);
FD_SET(socket_fd,&fs);
int ret = select(socket_fd+1,&fs,NULL,NULL,&tv);
if(ret == -1){
  fprintf(stderr, "socket_job:run:error.\n");
}else if(ret == 0){
 fprintf(stderr, "socket_job:run:time out.\n");
}else{
  if(FD_ISSET(socket_fd,&fs)){
  int length = 1024*1024;
  char* buffer = new char[length];
  memset(buffer,0,sizeof(char)*length);
  int n = recv(socket_fd,buffer,sizeof(char)*length,0);
  if(n > 0){
    //deal msg
    buffer[length] = '\0';
    search_collector* searcher = new search_collector();
    string result("");
    searcher->search(buffer,10,result);
    //send result,result must be end with \n
    int result_length = strlen(result.c_str());
    ret = send(socket_fd,result.c_str(),result_length,0);
    int all_send = 0;
    while(ret > 0 && ret < result_length){
       result_length -= ret;
       all_send += ret;
       ret = send(socket_fd,result.c_str()+all_send,result_length,0);
    }
 }
 delete[] buffer;
} }