Re: Threads: better condition variables?

From: William Kempf (sirwillard_at_[hidden])
Date: 2000-08-10 16:36:57

--- In boost_at_[hidden], jsiek_at_l... wrote:
> William Kempf writes:
>  > I wouldn't attach it to the condition, however.  I'd pass the 
>  > predicate into the wait.  Thus the condition can be used to 
track 
>  > different criteria.
>  > 
>  >    cond.wait((free1 > 10)(a));
> 
> Why would you want to use the same condition variable with different
> criteria? (why not just use a different condition variable)

It's a complexity trade off.  A condition variable is a complex 
primitive (oxymoron not intentional) that on some platforms exacts a 
rather large resource overhead.  So you have a choice between 
sacrificing speed for resource optimizations or the other way 
around.  Either method will work for all cases, the only question 
remains which is the better approach for a specific case.

Also, as pointed out by others, using multiple condition variables 
can lead to deadlock if not carefully coded.  The single condition 
variable multiple criteria approach is conceptually easier to 
code "correctly".

William Kempf