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

Subject: Re: [Boost-users] [Thread] Constructing a move-only object asyncronously
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2013-03-20 08:26:06

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;}

};

Vicente