Doc #63842 [Com]: Infinite loop in example code

Edit report at https://bugs.php.net/bug.php?id=63842&edit=1 ID: 63842 Comment by: karl at silverglassworks dot com Reported by: dean at ovts dot com dot au Summary: Infinite loop in example code Status: Not a bug Type: Documentation Problem Package: Documentation problem PHP Version: Irrelevant Block user comment: N Private report: N New Comment: The current example is definitely an incorrect way of doing things, and was causing an infinite loop for me today. From the cURL documentation (http://curl.haxx.se/libcurl/c/curl_multi_fdset.html): ****************************************************************************** When libcurl returns -1 in max_fd, it is because libcurl currently does something that isn't possible for your application to monitor with a socket and unfortunately you can then not know exactly when the current action is completed using select(). When max_fd returns with -1, you need to wait a while and then proceed and call curl_multi_perform anyway. How long to wait? I would suggest 100 milliseconds at least, but you may want to test it out in your own particular conditions to find a suitable value. ****************************************************************************** So in the situation where libcurl can't use select(), it will always return -1, and thus the example will be an infinite loop, as I have been experiencing. I changed my code to the following, and it now works: while ($active && $mrc == CURLM_OK) { if (curl_multi_select($mh) === -1) { usleep(100); } do { $mrc = curl_multi_exec($mh, $active); } while ($mrc == CURLM_CALL_MULTI_PERFORM); } Previous Comments: ------------------------------------------------------------------------ [2013-01-16 19:21:35] dean at ovts dot com dot au Googleguy, under bug #61141, several people report that they do indeed get an infinite loop because curl_multi_select returns -1 indefinitely... ------------------------------------------------------------------------ [2013-01-16 19:14:19] dean at ovts dot com dot au If the loop is entered and curl_multi_select then returns -1, the variables determining the loop condition remain unchanged, so curl_multi_select is simply called repeatedly until such time as it returns something other than -1. Googleguy, I don't quite understand what you were saying: Is it that eventually curl_multi_select is *GUARANTEED* to return something other than -1? *IF* that's true then there's no infinite loop. However, it's still very unclear exectly how/why this code is supposed to work. I'd like to see an explanation/clarification in the docs of the return values from curl_multi_exec and curl_multi_select, and of the $active flag. What exactly does a -1 returned from curl_multi_select imply? And (again) what would it mean if $active were true, but the return value from curl_multi_exec wasn't CURLM_OK? At the moment, without any such explanation in the docs, the example code is like an opaque magic formula for how curl_multi_exec should be used. It's difficult to trust it, when there are many "alternative versions" posted on the internet, and some on other php docs pages too! ------------------------------------------------------------------------ [2013-01-16 18:31:56] googleguy@php.net *Correction to my last comment "This is not a bug, because the condition of the loop is NOT dependent upon curl_multi_select." ------------------------------------------------------------------------ [2013-01-16 18:31:05] googleguy@php.net This is not a bug, because the condition of the loop is dependent upon curl_multi_select. If the curl_multi_select returns -1 the code within the loop body is simply not executed. This still does not create an infinite loop under normal conditions because eventually if all of the curl handles timeout they are freed from the select resource handle. ------------------------------------------------------------------------ [2013-01-16 15:05:07] googleguy@php.net Related To: Bug #63936 ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=63842 -- Edit this bug report at https://bugs.php.net/bug.php?id=63842&edit=1