Do I need to worry about thread safe methods?

[DaveJ]

My boss at my new job is mentoring me on making my methods 'thread safe' and such, which I never had to worry about before. I don't understand what he's trying to say. I thought that 'thread safe' pertained to applications where you intentionally create threads. We are not creating any threads. He seems to think that a website has the potential of overwriting variables when multiple users log on. He likes to make methods static and then he started talking about the heap and stack where variables are stored. If we never create a thread, I don't see how that would happen...???