Re: [boost] Executor associated to the future continuations (was [thread] boost::future::then)

Subject: Re: [boost] Executor associated to the future continuations (was [thread] boost::future::then)
From: Vladimir Prus (vladimir.prus_at_[hidden])
Date: 2015-10-30 03:08:26

On 29-Oct-15 11:00 PM, Vicente J. Botet Escriba wrote:
> Le 29/10/15 14:09, Vicente J. Botet Escriba a écrit :
>> Le 29/10/15 11:13, Vladimir Prus a écrit :
>>> On 29-Oct-15 12:49 PM, Vicente J. Botet Escriba wrote:
>>>> Le 29/10/15 10:08, Vladimir Prus a écrit :
>>>>> On 11-Oct-15 9:30 PM, Vicente J. Botet Escriba wrote:
>>>>>> Le 10/10/15 16:58, Vicente J. Botet Escriba a écrit :
>>>>>>> Le 10/10/15 15:26, Vicente J. Botet Escriba a écrit :
>>>>>>>> Le 10/10/15 07:57, Vladimir Prus a écrit :
>>>>>>>>>
>>>>> Vicente,
>>>>>
>>>>> I've created a very early experiment, here:
>>>>>
>>>>>     https://gist.github.com/vprus/3a7bea25e4c0a0e4222d
>>>>>
>>>>> Does it look generally right for you?
>>>> I don't know Qt. It seems ok beside tht fact that you create an Executor for each Task. Maybe this is not important for
>>>> you as your Executor class is adapting Qt.
>>>
>>> It's not hugely important, since in practice the work performance is orders of magnitude longer
>>> than QObject creation. Anyway, I possibly can create an executor per thread on demand, and reuse them.
>> Don't worry with the new version where you will give the Executor at promise creation the cost will be minimal in your
>> case.
>>>
> Hrr, I'm not able to remove completely the Executor type erasure as the type of f2 would depend on the Executor
> associated to the shared state of f1, that is unknown.
>
>      MyExecutor ex;
>      auto f1 = async(ex, cont);
>      auto f2 = f1.then(launch::inherit, cont);
>
> So, f1 could have a shared_state that depends on MyExecutor, however f2 would have an shared state that depends on the
> type erased boost::executor.

Okay, but does it matter much for performance?

> That means that it is better for the user to store the specific executor in some way and use it as follow
>
>      auto f2 = f1.then(ex, cont);

I've tried to do so, at:

        https://gist.github.com/vprus/7bb55cc6c6a1d4bbd3c4

This initial version was straight-forward, though it will probably need further tweaks for production use.

What does boost::future::then do right now if the continuation returns boost::future, is it unwrapped
automatically?

-- 
Vladimir Prus
http://vladimirprus.com