From the docs:
http://guzzle3.readthedocs.org/http-client/client.html#sending-requests-in-parallel
For an easy to use solution that returns a hash of request objects mapping to a response or error, see http://guzzle3.readthedocs.org/batching/batching.html#batching
Short example:
<?php
$client->send(array(
$client->get('http://www.example.com/foo'),
$client->get('http://www.example.com/baz'),
$client->get('http://www.example.com/bar')
));