[thredds] Checking if a THREDDS url is live?

[John Kerfoot <johnkerfoot@xxxxxxxxx>]

How would I go about checking to see if a TDS url is live or not?  A few 
of the TDS urls I regularly use (in addition to my own) are having 
problems with caching on very large aggregated datasets, but the request 
just kind of hangs there for a while.  What I'd like to do is make sure 
a TDS url is good before I attempt to grab data from it.

Is this possible?

Thanks,
John