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

@throws CommandExecutionException on error.