Bug #78485 [Com]: Random "couldn't resolve host" failures in curl_multi

Edit report at https://bugs.php.net/bug.php?id=78485&edit=1 ID: 78485 Comment by: sinus at sinpi dot net Reported by: sinus at sinpi dot net Summary: Random "couldn't resolve host" failures in curl_multi Status: Open Type: Bug Package: HTTP related Operating System: CloudLinux PHP Version: 7.2.22 Block user comment: N Private report: N New Comment: To try and work around the issue, I wrote a retry mechanism - if a CURLE_COULDNT_RESOLVE_HOST message is detected, I curl_multi_remove_handle the handle, curl_close it, make a new curl_init and curl_multi_add_handle again, and return to calling curl_multi_exec. The docs don't state whether adding or removing handles during a multi session is permitted, so why not give it a try. The result, however, was exactly the same. All of the newly re-added child handles immediately got CURLE_COULDNT_RESOLVE_HOST results. Previous Comments: ------------------------------------------------------------------------ [2019-09-02 17:02:32] sinus at sinpi dot net Description: ------------ I'm experiencing a pretty random failure of curl_multi to grab some of the handles added to it. I've already reported it to devs of libcurl, but they told me to toss this hot potato back here, as apparently curl_multi_exec is php7-curl's wrapper around libcurl's curl_multi_perform and any faults must lie in there. So, the matter at hand. I create 12 handles for http:// URLs, all using the same target machine, just different files. I add them to curl_multi. And as soon as I curl_multi_exec, randomly sometimes they all work, and sometimes only exactly first 8 get fetched, others immediately get a 6=="couldn't resolve host name" message queued in curl_multi_info_read. It's always the first handles that succeed, and the final handles that fail - n first handles work, n+1 till the end fail to resolve, with n sometimes being all 12, sometimes 8, a few times 4, but I also caught it on 11. This is in cURL 7.62 under PHP 7.2.21. Test script: --------------- $cm = curl_multi_init(); for ($i=1;i<=12;i++) { $handles[$i] = curl_init ("http://the.same.host.com/file" . $i); curl_multi_add_handle ( $cm, $handles[$i]); } $status = curl_multi_exec ($cm, $still_running); // $status gets 0, $still_running gets 8. $info = curl_multi_info_read ($cm, $queue); // $info['result']==6 "couldn't resolve host" for handle 9, $queue==3 as there are also failures queued for handles 10, 11 and 12 Expected result: ---------------- All 12 URLs retrieved, naturally. Actual result: -------------- Usually only 8 retrieved, or 12 as intended, or 4, or other numbers. It's always the last handles that fail. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=78485&edit=1