What is the correct way to use flush(); and Sleep(); in a foreach?

Question

I made a page in php to generate a sales report in the format . csv through Woocommerce on the Wordpress system.

<?php 
//incluir as funções principais do WordPress
require("/home/site/public_html/wp-blog-header.php");
require_once("/home/site/public_html/wp-config.php");
require_once("/home/site/public_html/wp-includes/wp-db.php");
?>

<?php
$order_statuses = array( 'wc-completed');

$customer_orders = wc_get_orders( array (
    'date_completed' => '2020-09-14...2020-09-15',
    'meta_key' => '_customer_user',
    'post_status' => $order_statuses,
    'orderby' => 'date',
    'order' => 'ASC',
    'numberposts' => -1,
) );
$myfile1 = fopen("/home/site/public_html/shop/report/2020.csv", "w") or die("Erro ao abrir relatório!<br>");
fwrite($myfile1, "\"Data\",\"Pedido\",\"Item\",\"Categoria\",\"Quant.\",\"Valor\",\"Pagamento\",\"Usuário\"\r");
echo '<table><tbody>
        <tr>
            <th><strong>Data</strong></th>
            <th><strong>Pedido</strong></th>
            <th><strong>Item</strong></th>
            <th><strong>Categoria</strong></th>
            <th><strong>Quant.</strong></th>
            <th><strong>Valor</strong></th>
            <th><strong>Pagamento</strong></th>
            <th><strong>Usuário</strong></th>
            </tr>';

foreach($customer_orders as $order ){

    $order_id = method_exists( $order, 'get_id' ) ? $order->get_id() : $order->id;

    foreach($order->get_items() as $item_id => $item){

    $product_id = method_exists( $item, 'get_product_id' ) ? $item->get_product_id() : $item['product_id'];

    if( method_exists( $item, 'get_data' ) ) {
         $item_data = $item->get_data();
         $pedido = $item_data['order_id'];
         $item_name = $item->get_name();
         $produto = $item_data['product_id'];
         $quantity = $item_data['quantity'];
         $total = $item_data['total'];
         $total=str_replace(".", ",", $total);
         $pgto=$order->payment_method_title;
         $order_date_modified=$order->date_completed;
         $data=date_format($order_date_modified, "d/m/Y H:i:s");
         $userid=$order->customer_user;
         $user_info = get_userdata($order->user_id);
         $usuario = $user_info->user_login;
         //$email=$order->billing_email;
    } else {
         $total = wc_get_order_item_meta( $item_id, '_line_total', true );
    }

        foreach( wp_get_post_terms( $produto, 'product_cat' ) as $term ){
            if( $term ){
                $categoria = $term->name;
            }
        }
        
        echo '<tr><td>'.$data.'</td>';
        echo '<td>#'.$pedido.'</td>';
        echo '<td>'.$item_name.'</td>';
        echo '<td>'.$categoria.'</td>';
        echo '<td>'.$quantity.'</td>';
        echo '<td>'.$total.'</td>';
        echo '<td>'.$pgto.'</td>';
        echo '<td>'.$usuario.'</td>';
        
        fwrite($myfile1,"\"$data\",\"$pedido\",\"$item_name\",\"$categoria\",\"$quantity\",\"$total\",\"$pgto\",\"$usuario\"\r");
        
        flush();
        sleep(1);
    
    }
}

fclose($myfile1);
echo '</tbody></table>';
?>

I added the flush(); and Sleep(1); after recording each line in the . csv file, as I want the table to be created in the browser page, as in the example below. where a line appears every second:

<?php

    for($i=1;$i<=10;$i++){
        echo 'processing...<br>';
        flush();
        sleep(1);
    }
?>

But the page I created processes all the information at once and not slowly as expected.

I am looking for alternatives to record data without receiving an error from timeout, because when we run the script to pull all requests this year the process is simply stopped, sometimes it shows a timeout message in the browser, but does not generate any error log.

Answer 1

In theory your script could work, but in the php manual it explains that many servers do not send the page until all the script has been completed, even if you buffer part of the code.

The explanation is on this link: manual flush

One solution for this would be to use ajax to load parts of the screen every second, or to load the entire screen with mostly hidden and go displaying with javascript (display:None => display:block) gradually. Particularly I would choose the second option.