1 file, multiple threads

[Jive]

    Other folks have answered your questions, although some of the answers
may be open to interpretation.

    I just want to throw in a warning.  Multi-threaded programming can be a
little tricky.
If you don't know what you are doing, or if you are not careful, you can
program
bugs that manifest themselves very rarely.  I've seen them that cropped up
only about
once every two months on average in a continuously running program.
Reproducing
the failure can be next to impossible.  Finding the bugs can be a nightmare.

    You can even write a program that works correctly "by accident".
Later you introduce an apparently innocuous change that introduces a bug,
but
it does not show up in testing.  Over the course of days or months you make
more
changes to the program.  The bug you introduced way back when finally
manifests
itself.  You will assume the problem was caused by the last change you made.
Big trouble.

Look before you leap.