C++ future类代码示例

 void apply(future<void> f) const
 {
     if (f.ready())
         return;
     
     task_context* ctx = current_task_context::get();
     if (!ctx)
     {
         f.wait();
         return;
     }
     
     auto&& resume_task = [=]() {
         ctx->resume();
     };
     
     auto s = f.get_state(detail::use_private_interface);
     
     s->continue_with([&]() {
         s->await_queue()->push_front([=]() {
             resume_task();
         });
     });
     
     ctx->yield();
 }

 void future_answer()
 {
     //int x=the_answer_to_life_the_universe_and_everything.get_future().get();
     //如果上面注释的这句话就会出错！
     int x=fut.get();
     cout<<x<<endl;
 }

 type operator()(future<T> const& x) const
 {
     if (auto&& state = x.get_state(use_private_interface))
         return state->template then<future<void>>(std::bind([](){}));
     else
         return make_ready_future();
 }

        future<naming::id_type> migrate_component_postproc(
            future<boost::shared_ptr<Component> > f,
            naming::id_type const& to_migrate,
            naming::id_type const& target_locality)
        {
            using components::stubs::runtime_support;

            boost::shared_ptr<Component> ptr = f.get();
            boost::uint32_t pin_count = ptr->pin_count();

            if (pin_count == ~0x0u)
            {
                HPX_THROW_EXCEPTION(invalid_status,
                    "hpx::components::server::migrate_component",
                    "attempting to migrate an instance of a component which was "
                    "already migrated");
                return make_ready_future(naming::invalid_id);
            }
            if (pin_count > 1)
            {
                HPX_THROW_EXCEPTION(invalid_status,
                    "hpx::components::server::migrate_component",
                    "attempting to migrate an instance of a component which is "
                    "currently pinned");
                return make_ready_future(naming::invalid_id);
            }

            return runtime_support::migrate_component_async<Component>(
                        target_locality, ptr, to_migrate)
                .then(util::bind(
                    &detail::migrate_component_cleanup<Component>,
                    util::placeholders::_1, ptr, to_migrate));
        }

static
void crypto_one_test(const string &name, future<ContextReply> context, const vector<uint8_t> expected)
{
	auto result = context.get().data;
	if (!equal(expected.begin(), expected.end(), result.begin())) {
		throw runtime_error(name + ": Ошибка тестирования");
	}
}

 naming::id_type migrate_to_storage_here_cleanup(
     future<naming::id_type> f,
     boost::shared_ptr<Component> ptr,
     naming::id_type const& to_migrate)
 {
     ptr->mark_as_migrated();
     return f.get();
 }

/* Asynchronously provide data with promise */
int factorial(future<int>& f) {
	// do something else

	int N = f.get();     // If promise is distroyed, exception: std::future_errc::broken_promise
	cout << "Got from parent: " << N << endl; 
	int res = 1;
	for (int i=N; i>1; i--)
		res *= i;

	return res;
}

int promiseDependingFunction(future<int>& fu) {
	//... do some work setting up the environment...
	this_thread::sleep_for(chrono::milliseconds(100));

	//ready to wait for promise to be fufilled
	int value = fu.get();

	//use value
	value *= 16;

	return value;
}

template<typename T> inline exception_ptr get_exception_ptr(future<T> &f)
{
#if 1
    // Thanks to Vicente for adding this to Boost.Thread
    return f.get_exception_ptr();
#else
    // This seems excessive but I don't see any other legal way to extract the exception ...
    bool success=false;
    try
    {
        f.get();
        success=true;
    }
    catch(...)
    {
        exception_ptr e(afio::make_exception_ptr(afio::current_exception()));
        assert(e);
        return e;
    }
    return exception_ptr();
#endif
}

 void operator()(future<double> r) const
 {
     global_scratch += r.get();
 }

 HPX_FORCEINLINE result_type
 operator()(future<Derived> f) const
 {
     return f.get().share();
 }

void
producer( future & f )
    {
    f.set_exception (boost::copy_exception (err () << answer(42)));
    }

 future(const future<T> &other)
     : m_event(other.get_event())
 {
 }

int future_int_f1(future<void> f1)
{
    HPX_TEST(f1.is_ready());
    ++future_int_f1_count;
    return 1;
}

 static future<Result> call(future<Result> f)
 {
     HPX_ASSERT(f.has_exception());
     // Intel complains if this is not explicitly moved
     return std::move(f);
 }