Asynchronous curl request in PHP

Executing multiple curl requests simultaneously can be a challenge in PHP. In this article, we'll explore different approaches to achieve asynchronous execution using built-in functions and external libraries.

cURL multi-threading

PHP's curl_multi_* functions allow for asynchronous execution of multiple cURL requests. Here's an example:

curl_multi_init();
$mh = curl_multi_init();

$ch1 = curl_init();
curl_setopt($ch1, CURLOPT_URL, 'http://example.com/endpoint');
curl_multi_add_handle($mh, $ch1);

$ch2 = curl_init();
curl_setopt($ch2, CURLOPT_URL, 'http://example.com/endpoint2');
curl_multi_add_handle($mh, $ch2);

$active = null;
do {
    $mrc = curl_multi_exec($mh, $active);
} while ($mrc == CURLM_CALL_MULTI_PERFORM);

while ($active && $mrc == CURLM_OK) {
    if (curl_multi_select($mh) != -1) {
        do {
            $mrc = curl_multi_exec($mh, $active);
        } while ($mrc == CURLM_CALL_MULTI_PERFORM);
    }
}

curl_multi_remove_handle($mh, $ch1);
curl_multi_remove_handle($mh, $ch2);
curl_multi_close($mh);

pthreads

The pthreads library allows for multi-threaded programming in PHP. Using pthreads, asynchronous curl requests can be achieved like this:

class RequestThread extends Thread {
    public function run() {
        $ch = curl_init();
        // ... set cURL options here

        curl_exec($ch);
        curl_close($ch);
    }
}

$thread = new RequestThread();
$thread->start();

Parallel execution using library

There are also libraries specifically designed for parallel execution in PHP, such as parallel-functions and parallel-request. Here's an example using the parallel-request library:

use Parallel\{Task, Runtime};

$runtime = new Runtime;

$tasks = [
    new Task(function () {
        // ... cURL request 1
    }),
    new Task(function () {
        // ... cURL request 2
    }),
];

$runtime->run($tasks);

Considerations

When executing asynchronous requests, it's important to consider the server's resource limits and potential bottlenecks. It's also crucial to handle errors and exceptions that may occur during execution.