What is the life span of a helper in Magento 1?

Question

As I understand, helpers are singletons in Magento. I was wondering what the life span of the singleton is in Magento. Is only 1 instantiated for the life of the app (web server process start to finish) or is it per request? Or is it something else?

I have a helper that memoizes some data, and I was wondering how long it would hold on to it. I figured it would be for the life span of the helper.

Answer 1

Most variables in PHP last as long as the page request or an execution lasts. So, if you instantiate a helper object for a certain page request or a script execution in command line, the helper will retain the cached $this->_variable variable for that request only. When you refresh the page or run the script again, it will re-create itself. Consider the following dummy helper.

class My_Extension_Helper_Data extends Mage_Core_Helper_Data
{
    protected $_temp = null;

    public function getTemp()
    {
        if (!isset($this->_temp)) {
            $this->_temp = rand(0,10);
        }

        return $this->_temp;
    }
}    

Call $helper->getTemp() and see what variable it returns. You'll see that it changes on every single run or page request.

Answer 2

As you can see below, the helper is set in registry:

/**
 * Retrieve helper object
 *
 * @param string $name the helper name
 * @return Mage_Core_Helper_Abstract
 */
public static function helper($name)
{
    $registryKey = '_helper/' . $name;
    if (!self::registry($registryKey)) {
        $helperClass = self::getConfig()->getHelperClassName($name);
        self::register($registryKey, new $helperClass);
    }
    return self::registry($registryKey);
}

which basically sets a static var. That being said and more simply put, the helper will only be instantiated and initialised for the life of the app. Once the helper is called in a new process, the data previously set will be lost.

If you are looking to store data to be reused later on, you could use core/sessions else implement a session class of your own.