[php-src] Issue #12656: fclose() does not set file ressource to NULL causing error 500 on Siteground host. Combination of possible bug and hitting
ressource limits.

Issue: https://github.com/php/php-src/issues/12656 Author: rene-hermenau ### Description Found a possible bug in fclose() that appears when hitting some ressource limits like having open too many file ressources. The issue currently appears only the Siteground hosting provider when opening and closing a few thousand files, quickly one after another. (Not opening them concurrently!) Due to the nature of the issue I am not able to provide you code that makes it fully reproduceable but I will provide the code that fails and the solution that works for us: I've simplified the code but essentially these basic functions fail when opening and closing many files quickly: ```` for ($i = 0; $i < 40000; $i++) { $destFile = $dirname . '/test' . $i . '.text'; $fp = fopen($destFile, 'ab'); fwrite($fp, 'test'); fclose($fp); } ```` You can also use file_put_contents() instead of fopen, fwrite and fcose and the result will be the same, a fatal error without any error message during execution! Setting the file ressource to null after closing it will make it pass. So this code works: ```` for ($i = 0; $i < 40000; $i++) { $destFile = $dirname . '/test' . $i . '.text'; $fp = fopen($destFile, 'ab'); fwrite($fp, 'test'); fclose($fp); $fp = null; // the only difference } ```` Unfortunately the failed system throws a fatal error 500 without actual throwing an error message so we can not provide exact reason why it fails but it looks like a ressource problem in combination with a bug . A little bit more about the application where this code is used and to proof that we have no fundamental flaw in the rest of our code base: We use that code for a heavily unit tested backup application that works on more than 150.000 active websites with all types of php versions higher than 7.0 up to 8.3 and all types of different hosting providers without any issues. The specific problem happens only one one of these clients and currently only on the siteground hosting platform and with a larger backup file that has multiple GB's, so we think its pure coincidence we found that problem. I think it is both (a bug and a resource problem). Because freeing the resource on fclose() immediately may not be required but on a single function like file_put_contents and file_get_contents which doesn't provide access to internal resource it should be freed automatically immediately. I digged a little bit into the php source and found many occurances of: ```` php_stream_close(stream); stream = NULL; ```` while many other usages only call ```` php_stream_close(stream); ````` without setting stream to null. I am not sure if this inconsistency is intended or is there a reason to not always set stream to null **after** closing it? I am curious if you have an idea what goes wrong here. ### PHP Version php 8.1.25 ### Operating System ubuntu 20.04