RFC, fix for bogus timeouts in select()

[Andrew Lunn]

> So what I should look for is(i.e. a bug exists if):
> 
> 1. select() sleeps
> 2. data arrives
> 3. thread on which select() executes is starved until after timeout
> expires
> 4. select() wakes up after timeout has expired *and* data has arrived
> 5. select() returns a timeout instead of "data arrived"
> 
> I claim the above happens, but I have not provided evidence.

If you can prove that is happening, then this is a bug. 

You should be able to prove this with kernel Instrumentation. See

http://ecos.sourceware.org/docs-latest/user-guide/debugging-techniques.html

You are interested in CYG_INSTRUMENT_CONDVAR() and
CYG_INSTRUMENT_THREAD()

You might find packages/kernel/current/host/instr usefull in helping
decrypt the results.

        Andrew