code: private function safeSendSignal($process, string $signal, int $mappedSignal): void
      {
          if (true !== proc_terminate($process, $mappedSignal)) {
              throw new CommandExecutionException(
                  'Call to proc_terminate with signal "' . $signal . '" failed for unknown reason.'
              );
          }
      }
docs: 'Safe' send signal method; throws an exception if the signal send fails for any reason.
  
  @throws CommandExecutionException on error.