Thread safety is a concern when a resource is shared among multiple threads
and these threads try to access the same resource at the same time. If you
don't do this then you are probably thread safe. If you do have a shared
resource it may still not be a problem is all the accesses are read-only.
The problem usually occurs when one or more threads are trying to modify the
resource simultaneously, or when one is modifying it while other threads are
reading it. It may not always be obvious when you are accessing a shared
resource - that is part of your job as a developer.

One simple approach to making your code thread-safe is to take a lock on a
private object whenever you access the shared resource.