Using file attributes combined with Session to implement online people counting_PHP tutorial

ob_start();
session_start();
$num=0;
$dirpt    =    "online";
$reftime    =    1;

if (is_dir($dirpt) && $dir = opendir($dirpt)) {
  while (($file = readdir($dir)) !== false) {
    if(strcmp($file,"..")==0 || strcmp($file,".")==0){
        continue;
    }
    $D_[date("Y-m-d H:i:s",filemtime($dirpt."/".$file))]=$file;
    $num++;
    unset($cum);
  }  
  closedir($dir);
  $filename    =    session_id();
  $fp        =    fopen($dirpt."/".$filename,"w");
  fputs($fp,"");
  fclose($fp);

  $ntime    =    date("Y-m-d H:i:s",mktime(date("H"),date("i")-1,0,date("m"),date("d"),date("Y")));
  $D_[$ntime]="-";
  krsort($D_);
  $onlinenumber=0;
  while(1){
    $vkey=key($D_);
    $onlinenumber++;
    if(strcmp($ntime,$vkey)==0){
        break;
    }else{
        array_shift($D_);
    }
  }
  array_shift($D_);
  reset($D_);
  while(count($D_)>0){
    $ckey=key($D_);
    unlink($dirpt."/".$D_[$ckey]);
    if(!next($D_)){
        break;
    }
  }

}else{
    @chmod("..",0777);
    @mkdir($dirpt,0777);

}
$online=$onlinenumber-1;
$retime=60*$reftime;
echo "当前在线$online人";
ob_end_flush();
?>