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: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2015-10-17 12:41:18

Le 16/10/15 01:19, Vicente J. Botet Escriba a écrit :
> Le 13/10/15 19:33, Vicente J. Botet Escriba a écrit :
>> Le 13/10/15 10:34, 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 :
>>>>>>>
>>>>>>> So, the function must be executed in different thread from all 
>>>>>>> the continuations,
>>>>>>> and it would seem I'd need to something set executor on promise 
>>>>>>> for that to work?
>>>>>>>
>>>>>>
>>>>>> I will see how adding an Executor parameter to promise, 
>>>>>> packaged_task constructors and
>>>>>> make_ready_future/make_exceptional_future could be implemented if 
>>>>>> this will solve your use case.
>>>>>>
>>>>> I've create https://svn.boost.org/trac/boost/ticket/11717 to track 
>>>>> this feature request
>>>>>
>>>>>
>>>> This commit contains a fix for this issue as well as the addition 
>>>> of the VERY-EXPERIMENTAL promise::set_executor and
>>>> packaged_task::set_executor. These should be replaced by 
>>>> constructors having an executor as parameter.
>>>>
>>>> https://github.com/boostorg/thread/commit/b8db8fef8b28414d16c66761badc1c6fcadfc38f 
>>>>
>>>
>>> Vicente,
>>>
>>> thanks for the addition. I'll take a look at implementing 
>>> Qt-friendly future on top of this, and report
>>> how it goes.
>>>
>>> Thanks,
>>> Volodya
>>>
>> You are welcome.
>>
>> Note that I've not implemented the constructors as it need to change 
>> the hierarchy of classes, but promise::set_executor and 
>> packaged_task::set_executor which is more expensive as I need to 
>> type-erase the executor.
>>
>> Any feedback would be much appreciated.
>>
>>
>
> After looking at the Concurrency TS, I'm not sure if it is not a good 
> idea to store the executor so that
>
>     f.then(cont)
>
> launch cont on the executor associated to f.
>
>
> In the Concurrent TS, ::then() can execute the continuation on any 
> thread.
>
>
> "
>
>  * When the object's shared state is ready, the continuation
>    |/INVOKE/(/DECAY_COPY/(std::forward<F>(func)), std::move(*this))| is
>    called on an unspecified thread of execution with the call to
>    |/DECAY_COPY/()| being evaluated in the thread that called |then|.
>
> "
>
> What do you think?
>
Hi again,

I believe that it would be better if the use states explicitly that she 
wants to inherit the policy unsing a specific policy

     f.then(launch::inherit, cont);

I have not implemented this already, but I have already the possibility 
to use the undocumented executor policy

     f.then(launch::executor, cont);

This would launch cont using the inherited executor.

Best,
Vicente