Dispatcher::forward() behavior

Everything starts in the router:

The router parses the URI according to the one passed to it, ($_GET['_url'], $_SERVER['REQUEST_URI'], others) After this handling the router pass the processed module/namespace/controller/action to the dispatcher:

$dispatcher->setControllerName($router->getControllerName());
$dispatcher->setActionName($router->getActionName());
$dispatcher->setParams($router->getParams());

When $dispatcher->dispatch() is executed, this starts a dispatch loop which basically uses a flag variable ($finished) in the dispatcher to know if there are remaining actions to dispatch:

$this->_finished = false;
while (!$this->_finished) {

   //execute actions

   $this->_finished = true;
}

The dispatch loop allows the developer to perform additional forwards, this means that $this->_finished is reset to false making the dispatcher loop again and execute the forwarded action.

$eventsManager->fire('dispatch:beforeDispatchLoop');

$this->_finished = false;
while (!$this->_finished) {

    $eventsManager->fire('dispatch:beforeDispatch');
    if ($this->_finished==false) {
        continue;
    }   

    $controllerName = $this->_controllerName;
    $actionName = $this->_actionName;
    $params = $this->_params;

    /**
     * Controllers are instantiated via the DI
     * This ensures that only one instance will be created
     * in the application;
     */
    $controller = $di->getShared($controllerName . 'Controller');

    if (!method_exists($controller, $action . 'Action')) {
        throw new Exception('404 not found');
    }

    $eventsManager->fire('dispatch:beforeExecuteAction');   
    if ($this->_finished==false) {
        continue;
    }   

    $controller->$action($params);

    $eventsManager->fire('dispatch:afterExecuteAction');
    if ($this->_finished==false) {
        continue;
    }   

    $eventsManager->fire('dispatch:afterDispatchLoop');
    if ($this->_finished==false) {
        continue;
    }   

    $this->_finished = true;
}

When you make a forward the internal $this->_finished is changed to false, this is detected and the dispatch loop iterates again:

public function forward($forward)
{
    if (isset($forward['controller']))  {
        $this->_controllerName = $forward['controller'];
    }
    if (isset($forward['action']))  {
        $this->_actionName = $forward['action'];
    }
    $this->_finished = false;
}