[LAD] random curiosity

[Gabriel M. Beddingfield]

On Tue, 26 Jan 2010, cal wrote:

> old seed/sequence on every note. I've now got random_r in 
> there and I'm comfortable with it, but at this stage I've 
> no clear indication I've achieved anything valuable or 
> even better :-).

>From 'man 3 random_r':

     These functions are the reentrant equivalents of the
     functions described in random(3).  They are suitable for
     use in multithreaded programs where each thread needs to
     obtain an independent, reproducible sequence of random
     numbers.

That is to say, if you need a reproduceable string of 
"random" numbers on each thread (e.g. for unit testing), 
then random_r() is your man.  Otherwise, it sounds like more 
trouble than it's worth.

I.e. if every thread is just doing srandom_r(time(),buf), 
it's probably not worth it.

If random() is implemented without memory guards (atomic 
ops) on the global variable... then it's possible that 
calling random() from two different threads at the same time 
could give the same answer -- but so what?

-gabriel