swoole_process::signal(SIGALRM, function () {
    static $i = 0;
    echo "#{$i}\t alarm\n";
    $i++;
    if ($i > 20) {
        swoole_process::alarm(-1);// 清除定时器
    }
});

//100ms
swoole_process::alarm(100 * 1000);// 定时器，类似于定时触发，类似js 里面的setinterval()