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When using the cURL share handle feature (curl_share_init()) in PHP, failing to properly release shared resources can easily cause resource leaks, which may negatively impact server performance and even stability. This article will explain the correct usage of curl_share_init() and curl_share_close() to help developers avoid potential issues.
curl_share_init() is a function provided by PHP to initialize a cURL share handle. This handle allows multiple cURL sessions to share information such as DNS cache and cookies, improving performance and resource reuse.
A typical usage flow of the share handle is as follows:
$sh = curl_share_init();
curl_share_setopt($sh, CURLSHOPT_SHARE, CURL_LOCK_DATA_COOKIE);
This share handle can then be associated with multiple cURL requests via curl_setopt():
$ch = curl_init('https://www.m66.net/api/data');
curl_setopt($ch, CURLOPT_SHARE, $sh);
curl_exec($ch);
curl_close($ch);
The problem is that many developers forget to call curl_share_close() to release resources after finishing with the share handle.
// Incorrect example: share handle not closed
$sh = curl_share_init();
// ... a series of operations
// forgot to call curl_share_close($sh);
This negligence causes internal server resources (such as memory and DNS cache) to remain occupied, which may eventually trigger "memory leak" warnings, degrade performance, or even cause PHP-FPM workers to be forcibly terminated by the operating system.
You should always call curl_share_close() to release resources once the share handle is no longer needed:
$sh = curl_share_init();
curl_share_setopt($sh, CURLSHOPT_SHARE, CURL_LOCK_DATA_COOKIE);
<p>// Execute multiple requests<br>
foreach ($urls as $url) {<br>
$ch = curl_init($url);<br>
curl_setopt($ch, CURLOPT_SHARE, $sh);<br>
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);<br>
$response = curl_exec($ch);<br>
curl_close($ch);<br>
}</p>
<p>curl_share_close($sh); // release shared resources<br>
This is similar to the regular curl_close(), and the key is that developers must not omit the release of the share handle.
cURL share handles are designed for a single process and cannot be shared across multiple threads or processes. This means that in PHP-FPM’s multi-process model, each child process must manage its own share handle.
Once a share handle is associated with a cURL request, its share options cannot be changed again, or internal state errors may occur. For example:
$sh = curl_share_init();
curl_share_setopt($sh, CURLSHOPT_SHARE, CURL_LOCK_DATA_DNS);
// Setting before association is correct, do not modify afterwards
Using shared DNS cache may cause stale resolution results. Set an appropriate TTL based on your needs, and periodically clear the cache or reinitialize the share handle.
When encapsulating HTTP request classes, introduce a share handle pool and release it uniformly in the class destructor or shutdown function;
Use register_shutdown_function() to register cleanup logic;
Add logging or debugging information before and after using shared handles to ensure no lingering unreleased resources;
In high concurrency environments, evaluate whether sharing significantly improves performance; otherwise, using default handles is simpler and safer.
curl_share_init() is a valuable tool to enhance cURL performance, but it comes with the responsibility of resource management. Developers should always call curl_share_close() to release resources after use and ensure the share handle’s lifecycle is clear and controlled. Only then can the performance benefits of sharing be enjoyed without unnecessary resource waste or risks.
