non-blocking reads/writes and event loops

[Jim Blandy]

> The question about whether we *should* use threads is a different
> one altogether.  The real question splits into "Are there parts of
> gdb where we could be doing processing that isn't dependent on other
> processing, and we therefore are possibly wasting time on MP systems
> by not having each done in a thread" and "Are there parts of GDB
> where we could simplify code flow by using threads".

Srikanth at HP has mentioned the idea of doing symbol table reads in
the background.  I thought that sounded pretty cool.