会话中的jQuery ajax发布

I have a problem with jquery ajax's post method.

What trying to doing , When user upload multiple file on sucess upload it to session and save to database , but if im using alert it's correctly working ,

 $('#uploader_div').ajaxupload({
                                    url: '<?php echo base_url(); ?>product/multifile',
                                    editFilename: true,
                                    form: '#create',
                                    //autoStart: true,
                                    remotePath: 'product/<?php echo $id; ?>',
                                    thumbHeight: 300,
                                    finish: function(files_array) {
                                        $.post("<?php echo base_url(); ?>product/file_upload", {files: files_array});
                                        //alert ("Workin");


                                    },
                                    //max number of files can be selected

                                });

Im working on Real ajax uploder in codeigniter

Here is my other part of code

public function multifile() {
    $this->load->helper('upload_helper');
}

public function file_upload() {
    $data = array();
    $id = $this->session->userdata('id');
    $files = $this->input->post('files', true);


    $i = 1;
    foreach ($files as $files) {
        $images = "img_" . $i;
        $data [$images] = base_url() . "product/" . $id . "/". $files;
       $this->session->set_userdata($data);
        $i++;
    }
}

In view : $this->session->unset_userdata('img_1'); flow of function upload->set session->data save to db -> onsucess removed from session But if i removed the alert the image not comes up it set 0 value , actually my $.post images array not working hope understandable now !