Is it possible to detect context in relation to a threadvar?

[JohnAD]

I'm developing a library that maintains a global pool of resources that can be 
seen in both thread and non-threaded contexts. Rather than jump into great 
detail, let show this with a silly example:
    
    
    import strutils
    import jester
    
    var someGlobal: string = "value at the moment"
    
    var someThread {.threadvar.}: string
    
    proc getSomeMain(): string =
      result = "copy of $1".format(someGlobal)
    
    proc getSomeFromThread(): string {.gcsafe.} =
      someThread = "copy of $1".format(someGlobal)
      return someThread
    
    someGlobal = "another change"
    
    var x = getSomeMain()
    echo x
    
    routes:
      get "/":
        var y = getSomeFromThread()
        resp y
    
    
    Run

Everything works great.

But, I ask, would it be possible to write a generic equivalent of "getSome". 
Something like:
    
    
    proc getSome(): string =
      if MAGIC_DETECT_METHOD:
        return "copy of $1".format(someGlobal)
      else:
        someThread = "copy of $1".format(someGlobal)
        return someThread
    
    
    Run

Or, if not at runtime, some kind of compile-time thing that detects whether 
"getSome" is being called from a thread, such as a Macro or Template.

I apologize if the answer to this is well documented somewhere. I've not been 
able to find an answer yet.