Upload big file in chunk with ajax

Big file upload php in chunk in ajax

 if (isset($_FILES['upload'])) {
            $target_path = __DIR__.'/upload/';

            $tmp_name    = $_FILES['upload']['tmp_name'];
            $filename    = $_FILES['upload']['name'];
            $size        = $_FILES['upload']['size'];
            $target_file = $target_path.$filename;
            //$num = isset($_POST['num'])?$_POST['num']:1;
            $num = $_POST['num'];
            uploadBigFile( $tmp_name, $num, $target_file, $_POST['size']);
        }
            /**
             * @param     $tmp_file  temporary file //tmp_name
             * @param int $current_file_size  // how much bite uploaded till now
             * @param     $target_file_path  // where to save the file
             * @param     $file_size // file actual size 
             */

        function uploadBigFile($tmp_file,$current_file_size=0,$target_file_path,$file_size){

                header('content-type:application/json');

                if (!is_dir('upload')) {
                    mkdir('upload');
                }


                $count    = 0;
                while ($current_file_size != 0 && !file_exists($target_file_path)) {
                    $count++;
                    if ($count > 20) {
                        // after 1 seconds
                        echo json_encode(array('status' => false));
                        exit;
                    }
                    usleep(50000);

                }
                if ($current_file_size == 0) {
                    $desc = fopen($target_file_path, 'c');
                    // you may decide the max size
                    ftruncate($desc, $file_size);
                } else {

                    for ($count = 0;; $count++) {
                        if (filesize($target_file_path) == 0) {
                            if ($count > 20) {
                                // after 1 seconds
                                echo json_encode(array('status' => false));
                                exit;
                            }
                            usleep(50000);
                            clearstatcache(false, $target_file_path);
                        } else {
                            $desc = fopen($target_file_path, 'r+');
                            break;
                        }
                    }
                }
                fseek($desc, $current_file_size);
                $src = fopen($tmp_file, 'r');
                while (!feof($src)) {
                    $buf = fread($src, 2097152); //4M
                    fwrite($desc, $buf);
                }

                fclose($src);
                fclose($desc);
                //echo json_encode(array('status' => true, 'block' => $_POST['block']));
                die();


        }