Is swoole multi-threaded?

<?php
/**
 * 创建多进程
 */
$worker_num         = 6;        // 默认进程数
$workers             = [];        // 进程保存
$redirect_stdout    = false;    // 重定向输出  ; 这个参数用途等会我们看效果
for($i = 0; $i < $worker_num; $i++){
    $process = new swoole_process(&#39;callback_function&#39;, $redirect_stdout);
 
    // 启用消息队列 int $msgkey = 0, int $mode = 2
    $process->useQueue(0, 2);
    $pid = $process->start();
 
    // 管道写入内容
    $process->write(&#39;index:&#39;.$i);
 
    $process->push(&#39;进程的消息队列内容&#39;);
    // 将每一个进程的句柄存起来
    $workers[$pid] = $process;
}
 
 
/**
 * 子进程回调
 * @param  swoole_process $worker [description]
 * @return [type]                 [description]
 */
function callback_function(swoole_process $worker)
{
    $recv = $worker->pop();
    echo "子输出主内容: {$recv}".PHP_EOL;
    //get guandao content
    $recv = $worker->read();
    $result = doTask();
    
    echo PHP_EOL.$result.&#39;===&#39;.$worker->pid.&#39;===&#39;.$recv;
 
    $worker->exit(0);
}
 
 
/**
 * 监控/回收子进程
 */
while(1){
    $ret = swoole_process::wait();
    if ($ret){// $ret 是个数组 code是进程退出状态码，
        $pid = $ret[&#39;pid&#39;];
        echo PHP_EOL."Worker Exit, PID=" . $pid . PHP_EOL;
    }else{
        break;
    }
}
 
 
/**
 * doTask
 * @return [type] [description]
 */
function doTask()
{
    sleep(2);
    return true;
}