From: Peter Dimov (pdimov_at_[hidden])
Date: 2007-08-20 19:37:51
Howard Hinnant wrote:
> I realize that this is stricter than POSIX, however I'm not sure that
> the difference in strictness has a practical consequence. We're
> talking about a condition which would be waited on with mutex1 by a
> group of threads, and then at some later date (synchronized properly
> so as not to overlap) waited on with mutex2. Do you have motivating
> use cases needing this functionality?
No, but I also have no motivating use cases needing the check when the
condition has been default-constructed.
> As far as overhead goes, I'm more concerned about space overhead than
> performance overhead. On Mac, sizeof(pthread_cond_t) is 28, and
> sizeof(pthread_mutex_t) is 44. I would really like for there to be be
> an option for sizeof(std::condition) to be as close to 44 as
> possible. Consider:
>
> class MyClass
> {
> std::tr2::upgrade_mutex mut_;
> ...
> };
>
> MyClass already has two std::condition's buried under the
> upgrade_mutex (at least by my reference implementation).
I believe that the main cost of a mutex or a condition is measured in kernel
objects, not bytes. One will typically run out of kernel memory much
earlier, IMO.