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Error log of curl_multi_close function: How to troubleshoot unclosed CURL handles

gitbox 2025-05-12

In PHP, curl_multi_close is a function used to close multithreaded cURL handles. It is usually used with functions such as curl_multi_init and curl_multi_exec to handle concurrent HTTP requests. Although this function is very useful, if the CURL handle is not closed correctly, it may cause resource leakage, request failure to execute successfully, etc. This article will explain how to troubleshoot the error log of the curl_multi_close function, as well as common problems and solutions when the CURL handle is not properly closed.

1. What is the curl_multi_close function?

The curl_multi_close function is used to close a multithreaded cURL handle created by curl_multi_init() . Its role is to release resources and ensure that all cURL handles are properly cleaned. If this function is not called, it may result in memory leaks and unclosed connections, ultimately affecting the performance and stability of the application.

2. Common error: Unclosed CURL handle

When using curl_multi_exec to perform multiple requests, if you forget to call curl_multi_close in your program, or use it incorrectly, it may cause some difficult to troubleshoot errors. Common errors include:

  • The request is not completed or stuck, causing a dead loop in the program.

  • Memory leaks, especially when multiple requests need to be made simultaneously, unfree cURL handles can take up system resources.

  • The requested result does not meet expectations, or the cURL request timed out.

3. Troubleshooting error logs

3.1 View error output

First, check whether there is any related error log output. Before calling curl_multi_close , it is best to make sure that each cURL handle has been executed successfully and no errors have occurred. You can use curl_error and curl_getinfo functions to get more information.

Sample code:

 // Initialize multithreading cURL
$multiHandle = curl_multi_init();
$handles = array();

// Add multiple cURL ask
foreach ($urls as $url) {
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, "https://gitbox.net/".$url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_multi_add_handle($multiHandle, $ch);
    $handles[] = $ch;
}

// 执行多线程ask
do {
    curl_multi_exec($multiHandle, $active);
} while ($active > 0);

// Check for errors in each handle
foreach ($handles as $ch) {
    $error = curl_error($ch);
    if ($error) {
        echo "Error: " . $error . "\n";
    } else {
        echo "Request successful\n";
    }
}

// Close multi-threaded handle
curl_multi_close($multiHandle);

In this code, we check the error information for each cURL handle by curl_error() . If there is an error, you can use this method to locate the problem.

3.2 Debugging cURL return information

Another way to troubleshoot problems is to use curl_getinfo() to get detailed information of each request, such as HTTP status code, response time, etc. This information can help you further locate the problem, whether the request failed, whether a 404 or 500 error was returned, etc.

Sample code:

 // Call curl_getinfo 获取ask的详细信息
foreach ($handles as $ch) {
    $info = curl_getinfo($ch);
    echo "URL: " . $info['url'] . "\n";
    echo "HTTP Code: " . $info['http_code'] . "\n";
    echo "Total Time: " . $info['total_time'] . " seconds\n";
}

// Close multi-threaded handle
curl_multi_close($multiHandle);

4. Why make sure to close the cURL handle?

Failure to close the cURL handle correctly can cause multiple problems:

  • Resource Leak : If the cURL handle is not closed, the system consumes additional memory and network connection resources.

  • Performance issues : In high concurrency scenarios, an unclosed cURL handle will cause the application to respond slowly, and may even cause the request to time out or fail.

  • Potential BUG : When unclosed handles accumulate to a certain level, other unknown errors may be triggered, resulting in system instability.

5. Solution

To avoid the problems caused by not closing the cURL handle, you can follow these steps:

  • Make sure curl_multi_close is called after each request is executed.

  • Use curl_multi_remove_handle to remove requests from multithreaded handles and then close each individual cURL handle.

  • Use curl_error() and curl_getinfo() to debug each request to ensure they execute successfully.

The correct way to deal with it is as follows:

 foreach ($handles as $ch) {
    curl_multi_remove_handle($multiHandle, $ch); // Remove the handle
    curl_close($ch); // Close a single handle
}

// 最后Close multi-threaded handle
curl_multi_close($multiHandle);

6. Summary

The function of the curl_multi_close function is to close all cURL handles in multiple concurrent requests to ensure that system resources are freed. When using multithreaded cURL requests, be sure to check that all handles are closed correctly. By debugging and troubleshooting error logs, you can effectively resolve issues caused by not closing the CURL handle. Release resources in a timely manner not only improves the performance of the application, but also avoids potential problems in the system operation.

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