Somewhere in the code below seems to be a memory leak. A couple of users were exceeding 512Mb and I'm not sure how.

Adapted the following SO code to try and test memory usage of each function on the (OpenCart extension) page:

public function mem_test($func_name){
     declare(ticks=1);
    $handle = fopen("/Users/mikekilmer/Sites/mzoo/dev/php/open_cart_memory.txt", "a+");
    $mem = memory_get_usage();
    $bt = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 2);
    fwrite($handle, $bt[0]["file"]."\t: ".$func_name." :".$bt[0]["line"]."\t".$mem."\n");
    $vars = get_defined_vars();
    foreach($vars as $var){
        if(is_array($var)){
                foreach($var as $v){
                    fwrite($handle, implode(", ", $v)." (in array) \n");
                    }
                }else{
                fwrite($handle, $var."\n");
                }
            }
}

All of which are returning less than 1MB (around 700000 - 900000). Added the get_defined_vars() to see if there were some large variables being toted around, which returns four small variables.

Below is the offending code:

  public function alert_stock($pid, $qtd) {
        $this->mem_test("alert_stock");
        $qry = $this->db->query("SELECT quantity, model FROM " . DB_PREFIX . "product WHERE product_id = '" . $pid . "'");
        if ($qry->row['quantity'] < 5) {
            $mail = new Mail($this->config->get('config_mail_protocol'), $this->config->get('config_smtp_host'), $this->config->get('config_smtp_username'), html_entity_decode($this->config->get('config_smtp_password'), ENT_QUOTES, 'UTF-8'), $this->config->get('config_smtp_port'), $this->config->get('config_smtp_timeout'));                   
            $mail->setTo($this->config->get('config_email'));
            $mail->setFrom($this->config->get('config_email'));
            $mail->setSender($this->config->get('config_email'));
            $mail->setSubject('Low Stock on: ' . $qry->row['model']);
            $mail->setText('Low Stock on: ' . $qry->row['model'] . "\n" . $qry->row['quantity'] . " remaining.\nThank you for your great work and have a wonderful day.");
            $mail->send();
        }
    }

    public function sub_stock($pid, $qtd, $chave) {
        $this->mem_test("sub_stock");
    
        $this->db->query("UPDATE " . DB_PREFIX . "product_option_value SET quantity = (quantity - " . (int)$qtd . ") WHERE product_option_value_id = '" . (int)$chave . "' AND subtract = '1'");        
        $this->db->query("UPDATE " . DB_PREFIX . "product SET quantity = (quantity - " . (int) $qtd . ") WHERE product_id = '" . (int) $pid . "' AND subtract = '1'");
    }

    public function upd_stock($key,$qty) {
        $this->mem_test("upd_stock");
        $products = $this->getProducts();
        $pid = $products[$key]['product_id'];
        $qtd = $products[$key]['quantity'];
        if ((int) $qty != (int) $qtd) {
            if ($products[$key]['option']) {
                $opt_id = $products[$key]['option'][0]['product_option_value_id'];
                if ($qty > $qtd) {
                    $qtx = (int) $qty - (int) $qtd;
                    $this->db->query("UPDATE " . DB_PREFIX . "product_option_value SET quantity = (quantity - " . (int) $qtx . ") WHERE product_option_value_id = '" . (int) $opt_id . "' AND subtract = '1'");
                } else {
                    $qtx = (int) $qtd - (int) $qty;
                    $this->db->query("UPDATE " . DB_PREFIX . "product_option_value SET quantity = (quantity + " . (int) $qtx . ") WHERE product_option_value_id = '" . (int) $opt_id . "' AND subtract = '1'");
                }
            }
            if ($qty > $qtd) {
                $qtx = (int) $qty - (int) $qtd;
                $this->db->query("UPDATE " . DB_PREFIX . "product SET quantity = (quantity - " . (int) $qtx . ") WHERE product_id = '" . (int) $pid . "' AND subtract = '1'");
            } else {
                $qtx = (int) $qtd - (int) $qty;
                $this->db->query("UPDATE " . DB_PREFIX . "product SET quantity = (quantity + " . (int) $qtx . ") WHERE product_id = '" . (int) $pid . "' AND subtract = '1'");
            }
        }
    
    }

    public function add_stock($key) {
        $this->mem_test("add_stock");
    
        $products = $this->getProducts();
        print_r($products);
        die();
        $pid = $products[$key]['product_id'];
        $qtd = $products[$key]['quantity'];
        if ($products[$key]['option']) {
            $opt_id = $products[$key]['option'][0]['product_option_value_id'];
            $this->db->query("UPDATE " . DB_PREFIX . "product_option_value SET quantity = (quantity + " . (int) $qtd . ") WHERE product_option_value_id = '" . (int) $opt_id . "' AND subtract = '1'");
        }
        $this->db->query("UPDATE " . DB_PREFIX . "product SET quantity = (quantity + " . (int) $qtd . ") WHERE product_id = '" . (int) $pid . "' AND subtract = '1'");
    }

Does anyone see anything in the code that might be causing a memory leak, or can offer suggestions for further testing/investigating.