How to reasonably release resources through curl_close in a multi-threaded environment?

cURL is a tool used to send HTTP requests, through which you can easily interact with other web services. When you execute HTTP requests through cURL, it will allocate some memory to save the requested configuration, execution status and other information. If these resources are not released at the right time, it may lead to memory leaks.

In a multithreaded environment (for example, performing concurrent requests through the curl_multi_* function group), multiple threads may execute multiple cURL requests simultaneously. If these cURL resources are not closed correctly, memory leaks will become more severe, affecting the performance and stability of the system.

2. Use curl_multi to perform concurrent requests

In PHP, the curl_multi_* series of functions allow you to process multiple cURL requests at the same time, thereby improving the efficiency of your program. Typically, the following code is used to initiate multiple requests at the same time:

 // Create multiplecURLHandle
$multiCurl = curl_multi_init();
$curlHandles = [];

// Initialize multiplecURLSession
for ($i = 0; $i < 5; $i++) {
    $curlHandles[$i] = curl_init();
    curl_setopt($curlHandles[$i], CURLOPT_URL, "http://gitbox.net/api/data?id=$i");
    curl_setopt($curlHandles[$i], CURLOPT_RETURNTRANSFER, 1);
    curl_multi_add_handle($multiCurl, $curlHandles[$i]);
}

// Perform concurrent requests
$running = null;
do {
    curl_multi_exec($multiCurl, $running);
} while ($running > 0);

// closurecURLSession
foreach ($curlHandles as $handle) {
    curl_multi_remove_handle($multiCurl, $handle);
    curl_close($handle);  // 正确closure资源
}

// closure多路复用Handle
curl_multi_close($multiCurl);

In the above code, we use curl_multi_init() to create a multiplexed handle, then add multiple cURL handles to the multiplex via curl_multi_add_handle() and finally execute all requests. Each cURL handle is closed via curl_close() to free up memory.

3. Why do you need to use curl_close() to correctly release resources

In a multi-threaded environment, each cURL request involves the allocation of memory resources, especially when there are many requests, the memory usage will be large. If you forget to close a cURL handle, the PHP process will not be able to free these resources, which will eventually lead to a memory leak.

In the example above, after each cURL request is completed, we explicitly release the resources through curl_close($handle) to ensure that the memory is not continuously occupied and avoid potential memory leaks.

4. How to ensure that resources can be released in error situations

In a multi-threaded environment, some unexpected errors may occur, such as network request failure, cURL configuration errors, etc. In this case, it is particularly important to release resources in a timely manner. To ensure that the resource is released, you can use the try-catch statement or finally statement to ensure that the resource will be released correctly regardless of whether an exception occurs.

 try {
    // Initiate a concurrent request
    $multiCurl = curl_multi_init();
    $curlHandles = [];
    for ($i = 0; $i < 5; $i++) {
        $curlHandles[$i] = curl_init();
        curl_setopt($curlHandles[$i], CURLOPT_URL, "http://gitbox.net/api/data?id=$i");
        curl_setopt($curlHandles[$i], CURLOPT_RETURNTRANSFER, 1);
        curl_multi_add_handle($multiCurl, $curlHandles[$i]);
    }

    $running = null;
    do {
        curl_multi_exec($multiCurl, $running);
    } while ($running > 0);

    // 处理响应并closureHandle
    // Here you can process the returned results

} catch (Exception $e) {
    // Handle exceptions
    echo "Error occurred: " . $e->getMessage();
} finally {
    // Ensure resources are released
    foreach ($curlHandles as $handle) {
        curl_multi_remove_handle($multiCurl, $handle);
        curl_close($handle);
    }
    curl_multi_close($multiCurl);
}

Ensure that the cURL handle is closed regardless of whether an exception occurs, thereby avoiding memory leaks.

5. Summary

In a multithreaded environment, it is crucial to use the curl_close() function correctly to free resources, especially when handling multiple concurrent requests. By ensuring that curl_close() is called after each cURL request and the resource release can be guaranteed when an exception occurs, the memory leak problem can be effectively avoided, thereby improving the stability and performance of the program.

In actual development, we should always pay attention to memory management, especially when handling a large number of concurrent requests. I hope this article will be helpful to your resource management using cURL in a multi-threaded environment.