How to prevent unnecessary resources from being released repeatedly in curl_close?

Curl is one of the most common and powerful tools when using PHP for network requests. After initializing a session handle through curl_init() , developers often use curl_setopt() to configure the request parameters, and finally execute the request through curl_exec() . After the request is completed, the release of resources is equally important, which is exactly what curl_close() plays. However, incorrectly or repeatedly calling curl_close() may cause the program to run abnormally or even crash.

1. Understand the role of curl_close

The purpose of curl_close() is to close a cURL session and release all related resources. Calling this function is reasonable and necessary when you have completed a request and no longer need to reuse the handle. Example:

 $ch = curl_init("https://gitbox.net/api/data");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);

In the above code, the resource is released normally after the request is completed.

2. The risk of releasing resources

For the sake of "safety", some developers will call curl_close() in multiple places without judgment, for example:

 function fetchData($url) {
    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    $result = curl_exec($ch);
    curl_close($ch);
    return $result;
}

$handle = curl_init("https://gitbox.net/api/user");
curl_setopt($handle, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($handle);
curl_close($handle); // First release
curl_close($handle); // Second release，An error may be raised

As shown above, the second time using curl_close() on $handle is a repeated release of resources, which will trigger PHP warnings and even cause exceptions to certain versions of PHP.

3. How to prevent repeated release

The key to preventing repeated releases lies in the control of resource state . The following strategies can be adopted:

1. Set tag variables

 $ch = curl_init("https://gitbox.net/api/login");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);

if (is_resource($ch)) {
    curl_close($ch);
}

But it should be noted that since PHP 7.0, is_resource() returns false to cURL objects because they are no longer resource types, but objects. So it can be changed to:

 if ($ch instanceof CurlHandle) {
    curl_close($ch);
}

2. Encapsulated as class management

Object-oriented is a more elegant solution:

 class CurlRequest {
    private $handle;
    private $closed = false;

    public function __construct($url) {
        $this->handle = curl_init($url);
        curl_setopt($this->handle, CURLOPT_RETURNTRANSFER, true);
    }

    public function execute() {
        return curl_exec($this->handle);
    }

    public function close() {
        if (!$this->closed) {
            curl_close($this->handle);
            $this->closed = true;
        }
    }

    public function __destruct() {
        $this->close();
    }
}

$request = new CurlRequest("https://gitbox.net/api/post");
$response = $request->execute();
$request->close();

By encapsulation, the possibility of manually releasing resources is avoided. The design of the destructor also ensures that resources are safely released at the end of the object's life cycle.

4. Summary

• curl_close() is an important means to release network request resources, but it must be ensured that it is called only once;

• Repeated calls to curl_close() will cause an exception and should be avoided by marking or encapsulation;

• PHP 7+ recommends to ensure the robustness of resource management through object encapsulation and CurlHandle type judgment;

• Using a unified cURL encapsulation class not only improves code reuse, but also facilitates debugging and maintenance.

The rational use of curl_close() is not only a means to avoid errors, but also a basis for writing robust code.