为何最大TCP连接数为 254

require_once 'workrtman/Autoloader.php';
use Workerman\Worker;
use workerman\Connection\AsyncTcpConnection;
use \Workerman\Lib\Timer;

$_SESSION==0;

$http_worker= new Worker('tcp://10.163.58.200:1234');

// 启动4个进程对外提供服务
$http_worker->count = 4;

// 接收到浏览器发送的数据时回复hello world给浏览器
$http_worker->onMessage = function($connection, $data)
{

    if($data=='yes')
    {
        echo @$_SESSION+=1;
        echo "\n";
        }

    // 向浏览器发送hello world
    $connection->send('hello world');
};

// 运行worker
Worker::runAll()