Re: [Boost-users] [Thread] Constructing a move-only object asyncronously

Subject: Re: [Boost-users] [Thread] Constructing a move-only object asyncronously
From: Alexander Lamaison (awl03_at_[hidden])
Date: 2013-03-20 13:56:52

"Vicente J. Botet Escriba" <vicente.botet_at_[hidden]> writes:

> Le 20/03/13 13:26, Vicente J. Botet Escriba a écrit :
>> Le 20/03/13 00:22, Alexander Lamaison a écrit :
>>> "Vicente J. Botet Escriba" <vicente.botet_at_[hidden]> writes:
>>>
>>>> Le 19/03/13 20:30, Alexander Lamaison a écrit :
>>>>> "Vicente J. Botet Escriba" <vicente.botet_at_[hidden]> writes:
>>>>>
>>>>>> Le 19/03/13 19:40, Alexander Lamaison a écrit :
>>>>>>> I'm trying to create a move-only object asyncronously using
>>>>>>> Boost.Thread
>>>>>>> unique_future but I'm running into trouble:
>>>>>>>
>>>>>>> error C2248: 'A::A' : cannot access private member declared in
>>>>>>> class 'A'
>>>>>>> c:\users\awl03\documents\visual studio
>>>>>>> 2005\projects\boost_1_51_0\boost\thread\future.hpp 493
>>>>>>>
>>>>>>> I've tried all sorts of ways to work around this but always end
>>>>>>> up with
>>>>>>> some variation or other of this error message.  What am I doing
>>>>>>> wrong?
>>>>>>>
>>>>> snip
>>>>>
>>>>>> you need to use version 4 to got this functionality.
>>>>> I assume this requires Boost 1.53?
>>>>>
>>>>>> I have modified your example to use boost::future (*) and use
>>>>>> packaged_task with a signature parameter (**). With this change it to
>>>>>> works for the following toolsets.
>>>>> Thanks!  Can you give me an idea of what changed in v4 to enable this?
>>>>> I've looked through the history but nothing stands out.
>>>>>
>>>>> I tried to make it work using just class thread rather than
>>>>> anything in
>>>>> <future.hpp>, but I couldn't work out how for a non-default
>>>>> constructible class.
>>>>>
>>>>>
>>>> I have just tried your example defining
>>>>
>>>> #define BOOST_THREAD_USES_MOVE
>>>>
>>>> and it works also.
>>> Perfect.  Thanks :)
>>>
>>> I'm assuming this solves the problem because the previous
>>> thread-internal move emulation didn't realise class A was movable and so
>>> tried to copy it.  Is that right?
>>>
>>>
>> Yes, your code declared a move only class using the Boost.Move
>> emulation. Boost.Thread has defined equivalent macros that use both
>> emulations. Could you try with the following without defining
>> BOOST_THREAD_USES_MOVE
>>
>> //#define BOOST_THREAD_USES_MOVE
>>
>>
>> class A : public noncopyable
>> {
>>   BOOST_THREAD_MOVABLE_ONLY(A)
>>
>> public:
>>     A(int ) {}
>>
>>     A(BOOST_THREAD_RV_REF(A) ) {}
>>
>>     A& operator=(BOOST_THREAD_RV_REF(A) ) { return *this;}
>>
>> };
>>
>
> Ah, you will need to add
>
> BOOST_THREAD_DCL_MOVABLE_BEG(T) A BOOST_THREAD_DCL_MOVABLE_END
>
> so that there is no conflict with Boost.Move.

This second version is working for me without those two defines.  No
conflicts occuring.

Alex

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