Johan Torp <johan.torp@gmail.com> writes:
Anthony Williams-4 wrote:
After thinking more carefully on the problem I've realized it is implementable using condition variables. Here is a revised proposal, which - for now - excludes barriers.
Given wait_for_any and wait_for_all (see my latest revision), I don't think we need these more complex composite classes in many cases, and where we do they might be better implemented specifically for the case at hand.
I agree we do not need this complex functionality in most cases. I too want to find a minimal interface which we can implement and get accepted into boost first, then we can add rich functionality - as Gaskill's proposal - on top of it. I hope we can find something much simpler than what I proposed without exposing the "completed callback". I fear that it might be difficult though.
I don't think your proposed interface is powerful enough to implement composed futures, but I might be wrong. For instance, how would you implement future operators with it?
future<bool> operator||(future<bool> lhs, future<bool> rhs);
Using wait callbacks: namespace detail { template<typename R> class future_or { boost::shared_ptr<packaged_task<R> > task; shared_future<R> lhs; shared_future<R> rhs; public: future_or(boost::shared_ptr<packaged_task<R> > const& task_, shared_future<R> const& lhs_, shared_future<R> const& rhs_): task(task_),lhs(lhs_),rhs(rhs_) {} R operator()() { unsigned const index=wait_for_any(lhs,rhs); return index?rhs.get():lhs.get(); } static void run(jss::packaged_task<int>& pt) { try { pt(); } catch(task_already_started&) { } } }; } template<typename R> unique_future<R> operator||(shared_future<R> const& lhs,shared_future<R> const& rhs) { boost::shared_ptr<packaged_task<R> > task(new packaged_task<R>); *task=packaged_task<R>(detail::future_or<R>(task,lhs,rhs)); task->set_wait_callback(detail::future_or<R>::run); return task->get_future(); } Alternatively, you could have future_or spawn a thread to run the task rather than do it lazily as a wait callback. Anthony -- Anthony Williams | Just Software Solutions Ltd Custom Software Development | http://www.justsoftwaresolutions.co.uk Registered in England, Company Number 5478976. Registered Office: 15 Carrallack Mews, St Just, Cornwall, TR19 7UL