In [Tcl]-land, we often discourage use of [threads], for reasons documented 
elsewhere [[explain]].  Here's an example of how to think about design involving
threads:

Briefly, Tcl applications need threads when they rely on long-running external
resources, like database look-up or communications with physical devices 
[[references]].  Even in the latter case, though, there are a number of 
alternatives:
   * [[first]]
   * [[second]]