Classes/Console/Install/Upgrade/UpgradeHandling.php
public function executeInSubProcess($command, array $arguments = [], array &$messages = [])
    {
        $messages = $this->ensureUpgradeIsPossible();

        return @unserialize($this->commandDispatcher->executeCommand('upgrade:subprocess', [$command, serialize($arguments)]));
    }
public function executeInSubProcess($command, array $arguments = [], array &$messages = [])
    {
        $messages = $this->ensureUpgradeIsPossible();

        return @unserialize($this->commandDispatcher->executeCommand('upgrade:subprocess', [$command, serialize($arguments)]));
    }
Execute the command in a sub process,
but execute some automated migration steps beforehand

@param string $command
@param array $arguments
@param array &$messages
@throws FailedSubProcessCommandException
@throws \UnexpectedValueException
@throws \RuntimeException
@return mixed