Queue.Queue-like class without the busy-wait

[Nick Craig-Wood]

Paul Rubin <http> wrote:
>  Nick Craig-Wood <nick at craig-wood.com> writes:
> > I believe futex is the thing you want for a modern linux.  Not
> > very portable though.
> 
>  That's really cool, but I don't see how it can be a pure userspace
>  operation if the futex has a timeout.  The kernel must need to keep
>  track of the timeouts.  However, since futexes can be woken by any
>  thread, the whole thing can be done with just one futex.  In fact the
>  doc mentions something about using a file descriptor to support
>  asynchronous wakeups, but it's confusing whether that applies here.

No it isn't pure user space, only for the non-contended case which for
most locks is the most frequent operation.

       Futex operation is entirely userspace for the non-contended
       case.  The kernel is only involved to arbitrate the contended
       case. As any sane design will strive for non-contension,
       futexes are also optimised for this situation.

-- 
Nick Craig-Wood <nick at craig-wood.com> -- http://www.craig-wood.com/nick