This can cause a memory leak if the process is being retried using STRATEGY_RETRY.

Example below:
```php
        $manager = new ProcessManager();
        $manager->setTimeoutStrategy(ProcessManager::STRATEGY_RETRY);

        for ($i = 0; $i < 10; $i++) {
            $p = new Process("while true; do date > /dev/null; done;");
            $p->setTimeout(1);
            $manager->add($p);
        }

        $manager->start();

        while ($manager->isRunning()) {
            $output->writeln(sprintf('Memory usage: <info>%dKB</info>/ <comment>%dKB</comment>', round(memory_get_usage(true) / 1024), memory_get_peak_usage(true) / 1024));
        }
```