if file not loaded? set timeout for single function or part of script?

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Hi, I'm looking for a function or any solution that enables me to check if an xml feed url is live (server not down) so i can provide alternate content if it's not available. I've found pgp timerout functions that kill the script entirely after a preset length of time, but i want to merely kill the processing of a single function if it's not completed after a certain amount of time.

 

i've tried using file_exists but it always fails even when the file does exist so i'm looking for any solution to provide alternate content if an xml file can't be loaded.