Is making asynchronous HTTP requests possible with PHP?

Solution 1:

Check out curl-easy. It supports both blocking and not-blocking requests in parallel or single request at once. Also, it is unit-tested, unlike many simple or buggy libraries.

Disclosure: I am the author of this library. The library has it's own test suite so I'm pretty confident it is robust.

Also, check out example of use below:

<?php
// We will download info about 2 YouTube videos:
// http://youtu.be/XmSdTa9kaiQ and
// http://youtu.be/6dC-sm5SWiU

// Init queue of requests
$queue = new cURL\RequestsQueue;
// Set default options for all requests in queue
$queue->getDefaultOptions()
    ->set(CURLOPT_TIMEOUT, 5)
    ->set(CURLOPT_RETURNTRANSFER, true);
// Set callback function to be executed when request will be completed
$queue->addListener('complete', function (cURL\Event $event) {
    $response = $event->response;
    $json = $response->getContent(); // Returns content of response
    $feed = json_decode($json, true);
    echo $feed['entry']['title']['$t'] . "\n";
});

$request = new cURL\Request('http://gdata.youtube.com/feeds/api/videos/XmSdTa9kaiQ?v=2&alt=json');
$queue->attach($request);

$request = new cURL\Request('http://gdata.youtube.com/feeds/api/videos/6dC-sm5SWiU?v=2&alt=json');
$queue->attach($request);

// Execute queue
$queue->send();

Solution 2:

Yes.

There is the multirequest PHP library (or see: archived Google Code project). It's a multi-threaded CURL library.

As another solution, you could write a script that does that in a language that supports threading, like Ruby or Python. Then, just call the script with PHP. Seems rather simple.

Solution 3:

For PHP5.5+, mpyw/co is the ultimate solution. It works as if it is tj/co in JavaScript.

Example

Assume that you want to download specified multiple GitHub users' avatars. The following steps are required for each user.

1. Get content of http://github.com/mpyw (GET HTML)
2. Find <img class="avatar" src="..."> and request it (GET IMAGE)

---: Waiting my response
...: Waiting other response in parallel flows

Many famous curl_multi based scripts already provide us the following flows.

        /-----------GET HTML\  /--GET IMAGE.........\
       /                     \/                      \ 
[Start] GET HTML..............----------------GET IMAGE [Finish]
       \                     /\                      /
        \-----GET HTML....../  \-----GET IMAGE....../

However, this is not efficient enough. Do you want to reduce worthless waiting times ...?

        /-----------GET HTML--GET IMAGE\
       /                                \            
[Start] GET HTML----------------GET IMAGE [Finish]
       \                                /
        \-----GET HTML-----GET IMAGE.../

Yes, it's very easy with mpyw/co. For more details, visit the repository page.