Using curl_multi_add_handle() to Manage Multiple cURL Handles in PHP

The PHP curl library is a widely used tool for making HTTP requests such as GET and POST, setting headers, and handling cookies. When many requests need to be sent simultaneously, creating a separate cURL handle for each can waste resources.

PHP offers the curl_multi_add_handle() function to add multiple cURL handles to a single multi‑handle session, allowing efficient management of concurrent requests.

The syntax of curl_multi_add_handle() is:

resource curl_multi_add_handle ( resource $mh , resource $ch )

Parameters:

$mh – an initialized cURL multi‑handle session.

$ch – the cURL handle to be added to the multi‑handle.

Below is a complete example that demonstrates how to use the function:

<?php
$mh = curl_multi_init();  // initialize multi‑handle

$ch1 = curl_init();
curl_setopt($ch1, CURLOPT_URL, "https://www.example.com/api1");
curl_setopt($ch1, CURLOPT_RETURNTRANSFER, true);
curl_multi_add_handle($mh, $ch1);  // add first handle

$ch2 = curl_init();
curl_setopt($ch2, CURLOPT_URL, "https://www.example.com/api2");
curl_setopt($ch2, CURLOPT_RETURNTRANSFER, true);
curl_multi_add_handle($mh, $ch2);  // add second handle

// Execute until all requests are complete
do {
    $status = curl_multi_exec($mh, $running);
} while ($status === CURLM_CALL_MULTI_PERFORM || $running);

// Retrieve results
$response1 = curl_multi_getcontent($ch1);
echo "Response 1: " . $response1 . "\n";
$response2 = curl_multi_getcontent($ch2);
echo "Response 2: " . $response2 . "\n";

// Clean up
curl_multi_remove_handle($mh, $ch1);
curl_multi_remove_handle($mh, $ch2);
curl_multi_close($mh);
?>

The script initializes a multi‑handle, creates two independent cURL handles, sets their URLs and options, adds them to the multi‑handle, and then loops with curl_multi_exec() until both requests finish. After execution, curl_multi_getcontent() fetches each response, which is then printed.

Using curl_multi_add_handle() improves network request efficiency and code maintainability by managing multiple handles within a single session. In practice, it can be combined with curl_multi_remove_handle() and curl_multi_close() for more complex request workflows.

In summary, the curl_multi_add_handle() function is a powerful tool for adding several cURL handles to one session, enabling concurrent requests, reducing resource consumption, and simplifying backend HTTP communication in PHP applications.