Re: [boost] Futures Review - Allowing partial specialization of wait_for_any

Subject: Re: [boost] Futures Review - Allowing partial specialization of wait_for_any
From: vicente.botet (vicente.botet_at_[hidden])
Date: 2009-01-16 12:48:08

Hi,

The functions wait_for_all and wait_for_any seams quite generic and could be applied to other asynchronous completion tokens (ACT), as for example the tp::task from Boost.ThreadPool. 

In order to do that we need to be able to partialy specialize these functions or use traits:

Let me start with a partial specialization proposal 

    template<typename F1,typename F2,typename F3>
    unsigned wait_for_any(F1& f1,F2& f2,F3& f3)
    {
        return partial_specialization_workaround::wait_for_any::apply(f1,f2, f3);
    }

    namespace partial_specialization_workaround {
        template<typename Types>
        struct wait_for_any;
        template<typename F1,typename F2,typename F3>
        struct wait_for_any<vector3<F1,F2,F3> > {
            unsigned apply(F1& f1,F2& f2,F3& f3) {
                detail::future_waiter waiter;
                waiter.add(f1);
                waiter.add(f2);
                waiter.add(f3);
                return waiter.wait();
            }
        };
    }

With traits thing simpler . The traits class will have a function that gets a unique/shared_future from the ACT.

    template<typename F1,typename F2>
    typename boost::enable_if<is_future_type<F1>,unsigned>::type wait_for_any(F1& f1,F2& f2)
    {
        detail::future_waiter waiter;
        waiter.add(traits::get_future(f1));
        waiter.add(traits::get_future(f2));
        return waiter.wait();
    }

The default get_future traits will return its parameter
    template <typename ACT>
    struct traits {
        ACT& get_future(ACT& act) { return act; }
    };

What do you think?

Vicente