Do two (or more) apps using GPS share the same location data stream? When an app calls for GPS data, does it activate the GPS call itself and then when another app simultaneously running calls it does it make a separate call? Or when the second app accesses the GPS does it get the data that's already there (or something similar, like a channel is opened in both apps which the GPS system sends all data to each channel when data is available)?

I'm wondering, because if each app only gets control of the GPS half the time it could certainly result in a less effective GPS. So I'm guessing that the iPhone was built with this in mind and the same GPS data would be available to each app, but I don't know if that's what's being done. 

Does anyone know the internal workings of GPS on iOS?
In iOS, Location Services sits between all the location radios (cellular tower info, nearest wifi, GPS) and the apps, and caches the fused results between getting new information from those radios at a rate determined by the OS for decent battery life versus requested accuracy.  Apps never "control" or talk to the GPS hardware or OS driver directly.  The location information an app gets is time-stamped, so an app can check to see if it's old info or not.