PHPSocketIO里面的心跳疑问

<?php
use Workerman\Worker;
use PHPSocketIO\SocketIO;

require_once './vendor/autoload.php';
$debug = true;
$io = new SocketIO(2020);

$io->on('connection', function() use ($socket) {

    $socket->on('disconnect', function () {
        echo "disconnect called" . PHP_EOL;
    });

    $socket->on('close', function () use ($socket) {
        echo "has ok closed!" . PHP_EOL;
    });
});