private function close(): int
    {
        $this->processPipes->close();
        if (\is_resource($this->process)) {
            proc_close($this->process);
        }
        $this->exitcode = $this->processInformation['exitcode'];
        $this->status = self::STATUS_TERMINATED;

        if (-1 === $this->exitcode) {
            if ($this->processInformation['signaled'] && 0 < $this->processInformation['termsig']) {
                // if process has been signaled, no exitcode but a valid termsig, apply Unix convention
                $this->exitcode = 128 + $this->processInformation['termsig'];
            } elseif ($this->isSigchildEnabled()) {
                $this->processInformation['signaled'] = true;
                $this->processInformation['termsig'] = -1;
            }
        }

        // Free memory from self-reference callback created by buildCallback
        // Doing so in other contexts like __destruct or by garbage collector is ineffective
        // Now pipes are closed, so the callback is no longer necessary
        $this->callback = null;

        return $this->exitcode;
    }