class cache2{
  var $path = "/srv/so23_html/cache/";
  var $data;
  var $file;
  var $key;
  //
  function __construct(array &$data=null){
    if($data)
      $this->data = &$data;
    
    if(isset($_COOKIE['cache'])){
      $this->key = $_COOKIE['cache'];
      $this->path = $this->path.$this->key;
    } else {
      $this->generateKey();
    }  
    $this->open();
  }

  function printCache(){
    echo "<pre>";
    print_r($this->data);
    echo "</pre>";
  }
  //Сохранить
  function save(){
    file_put_contents($this->path,"");
    $data = json_encode($this->data);
    fwrite($this->file, $data);
  }
  //Прочитать данные
  function read(){
    if($size=fileSize($this->path)){
      $data = fread($this->file, $size);
      $data = json_decode($data, true);
      return $data;
    }
  }
  
  function delete(){}
  
  //Сгенерировать имя файла
  function generateKey(){
    $time = time();
    $key = $time.$_SERVER['REMOTE_ADDR'];
    $this->key = $time."_".md5($key).".cache";
    setcookie("cache", $this->key, $time+3600*24*365, $_SERVER['REQUEST_URI'], $_SERVER['HTTP_HOST']);
    return $this->path = $this->path.$this->key;
  }
  
  //Создать файл
  function createCacheFile(){
   $this->file = fopen($this->path, "w+");
   chmod($this->path, 0755);
  }
  
  //Открыть файл
  function open(){
    if(is_file($this->path))
      $this->file = fopen($this->path, "r+");
    else
      $this->createCacheFile();
  }
  
  function __destruct(){
    clearstatcache();
  }

}

$data = array(1,2,3,4,5,6,7, "test"=>3);
$cache = new cache2($data);

$cache->save();
 
$data = array('test'=>1,'test1'=>2);
 
$cache->save();
$cache->save();
$cache->save();
$cache->save();

print_r($cache->read());

file_put_contents()

ftruncate()

  function save(){
    file_put_contents($this->path,"");
    $data = json_encode($this->data);
    fwrite($this->file, $data);
  }

function save(){
    ftruncate($this->file, 0);
    $data = json_encode($this->data);
    fwrite($this->file, $data);
  }

$this->file = fopen($this->path, "r+");

$this->file = fopen($this->path, "a+");