As the title says, When using Process::getIterator execution hangs regardless of the timeout value. This doesn't happen when using a callback supplied to Process::wait.

Shouldn't the getIterator method internally call checkTimeout?

A workaround is to call getIterator with the ITER_NON_BLOCKING flag, and manually call checkTimeout.

foreach ($process->getIterator(Process::ITER_NON_BLOCKING) as $type => $data) {
    try {
        $process->checkTimeout();
    } catch (\Exception $err) {
        break;
    }
    if (empty($data)) {
        usleep(100);
        continue;
    }
    // Handle data as usual
}