Setting millisecond-timeouts with curl

I'm currently working on a project where I need to curl to an external server to get some information. If this takes too long, I fall back to a local solution. The timeout for this should be really, really low, so we decided on a 250ms timeout. While testing with this timeout feature, for some reason it *always* used the local fallback. I couldn't figure out why, as when I did a manual curl to the external server, it took 50ms at maximum, way below the timeout value. Turns out it is a problem with libcurl.

So how did I found out about this? Thanks to Steve Kamerman, who took the time to comment to the PHP documentation. It turns out this issue is caused by the way libcurl behaves on linux and unix systems, where a SIGALRM is raised during the name resolution that is being caught by libcurl as a timeout alarm. Because of this, the request times out immediately instead of after the actual timeout.

The solution is to tell curl to ignore signals alltogether. This is not a perfect solution of course, because you're now suppressing something that can be useful in other situations, but in this case we decided the timeouts to be too important for the software to not use timeouts. So now it looks like this:

$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, $url);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_TIMEOUT_MS, 250);
curl_setopt($curl, CURLOPT_NOSIGNAL, 1);

It now works like a charm!