think\Process::start PHP Method

    public function start($callback = null)
    {
        if ($this->isRunning()) {
            throw new \RuntimeException('Process is already running');
        }
        if ($this->outputDisabled && null !== $callback) {
            throw new \LogicException('Output has been disabled, enable it to allow the use of a callback.');
        }
        $this->resetProcessData();
        $this->starttime = $this->lastOutputTime = microtime(true);
        $this->callback = $this->buildCallback($callback);
        $descriptors = $this->getDescriptors();
        $commandline = $this->commandline;
        if ('\\' === DS && $this->enhanceWindowsCompatibility) {
            $commandline = 'cmd /V:ON /E:ON /C "(' . $commandline . ')';
            foreach ($this->processPipes->getFiles() as $offset => $filename) {
                $commandline .= ' ' . $offset . '>' . Utils::escapeArgument($filename);
            }
            $commandline .= '"';
            if (!isset($this->options['bypass_shell'])) {
                $this->options['bypass_shell'] = true;
            }
        }
        $this->process = proc_open($commandline, $descriptors, $this->processPipes->pipes, $this->cwd, $this->env, $this->options);
        if (!is_resource($this->process)) {
            throw new \RuntimeException('Unable to launch a new process.');
        }
        $this->status = self::STATUS_STARTED;
        if ($this->tty) {
            return;
        }
        $this->updateStatus(false);
        $this->checkTimeout();
    }