As you said, php really isn't build for this kind of tasks. That being said, I do actually have something similar running at the day job. Fixed it by creating a lockfile in the php script; if the script fails the file gets 'unlocked' automatically. The first line in the script just checks if the lockfile is locked, if it is the script then quits; otherwise it'll start processing. Using cron I scheduled the script to start every minute; which will actually only run if the lockfile isn't locked. No high-tech solution in any sense, but it's been running for years without issue now.
As you said, php really isn't build for this kind of tasks. That being said, I do actually have something similar running at the day job. Fixed it by creating a lockfile in the php script; if the script fails the file gets 'unlocked' automatically. The first line in the script just checks if the lockfile is locked, if it is the script then quits; otherwise it'll start processing. Using cron I scheduled the script to start every minute; which will actually only run if the lockfile isn't locked. No high-tech solution in any sense, but it's been running for years without issue now.