Re: [boost] [thread] using Boost.Thread with move-only arguments

Subject: Re: [boost] [thread] using Boost.Thread with move-only arguments
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2013-04-07 18:36:34

Le 08/04/13 00:33, Vicente J. Botet Escriba a écrit :
> Le 08/04/13 00:15, Fernando Pelliccioni a écrit :
>> On Thu, Apr 4, 2013 at 3:19 AM, Vicente J. Botet Escriba <
>> vicente.botet_at_[hidden]> wrote:
>>
>>> Le 04/04/13 04:40, Fernando Pelliccioni a écrit :
>>>
>>>   Hi Vicente,
>>>> I have an issue with Boost.Thread contructor using move-only type
>>>> arguments.
>>>>
>>>> The "Thread Constructor with arguments" section of the 
>>>> documentation says
>>>> ...
>>>>
>>>> template <class F,class A1,class A2,...>
>>>> thread(F f,A1 a1,A2 a2,...);
>>>>
>>>> Preconditions:
>>>> F and each An must by copyable or movable.
>>>>
>>>> http://www.boost.org/doc/libs/**1_53_0/doc/html/thread/thread_**
>>>> management.html#thread.thread_**management.thread.multiple_**
>>>> argument_constructor<http://www.boost.org/doc/libs/1_53_0/doc/html/thread/thread_management.html#thread.thread_management.thread.multiple_argument_constructor> 
>>>>
>>>>
>>>> "An" could be copyable or movable, but the following example fails to
>>>> compile...
>>>>
>>>> error: use of deleted function 'A::A(const A&)'
>>>>
>>>>   Sorry,  if the documentation is not clear.  I should add a link 
>>>> to the
>>> Move emulation section (http://www.boost.org/doc/**
>>> libs/1_53_0/doc/html/thread/**emulations.html#thread.**emulations.move<http://www.boost.org/doc/libs/1_53_0/doc/html/thread/emulations.html#thread.emulations.move>) 
>>>
>>> for each function having rvalue references if the documentation is not
>>> clear. Please could you create a Ticket for that?
>>>
>>> Which Boost.Thread version are you using? That is, 
>>> BOOST_THREAD_VERSION is
>>> 2, 3 or 4?
>>> Could you try by defining BOOST_THREAD_USES_MOVE, 
>>> BOOST_THREAD_VERSION 3
>>> or BOOST_THREAD_VERSION 4?
>>>
>>>
>>>>
>>>> I think we should modify ...
>>>>
>>>>       template <class F,class A1>
>>>>       thread(F f,A1 a1,typename
>>>> disable_if<boost::thread_**detail::is_convertible<F&,**thread_attributes 
>>>>
>>>>> ,
>>>> dummy* >::type=0):
>>>> thread_info(make_thread_info(**boost::bind(boost::type<void>(**
>>>> ),f,a1)))
>>>>       {
>>>>           start_thread();
>>>>       }
>>>>
>>>>
>>>> ... by ...
>>>>
>>>>       template <class F,class A1>
>>>>       thread(F&& f,A1&& a1,typename
>>>> disable_if<boost::thread_**detail::is_convertible<F&,**thread_attributes 
>>>>
>>>>> ,
>>>> dummy* >::type=0):
>>>>
>>>> thread_info(make_thread_info(**boost::bind(boost::type<void>(**
>>>> ),f,boost::forward<A1>(a1))))
>>>>       {
>>>>           start_thread();
>>>>       }
>>>>
>>>> ( In the all family of related ctors in 
>>>> "boost/thread/detail/thread.**hpp"
>>>>   )
>>>>
>>>> But, I don't know if boost::bind is forwarding its arguments
>>>>
>>> No. The problem is that boost::bind doesn't supports move semantics
>>> (Boost.Move).
>>>
>>>   I think we should modify Boost.Bind to be similar to std::bind.
>>>> Is there any reason why Bind has not changed so far? Have you found 
>>>> any
>>>> limitations?
>>>>
>>> IIRC, I requested the feature long-long time ago.
>>>
>>>
>>>> If Bind can not be changed, I think Boost.Thread should use some other
>>>> tool
>>>> similar to Bind to make forwarding parameters.
>>>> GCC Libstdc++ use a Bind-lite tool for std::thread.
>>>>
>>> I have taken in account some cases, but not everything works yet. 
>>> E.g the
>>> prototype that you need is
>>>
>>>          template <class F>
>>>          explicit thread(BOOST_THREAD_RV_REF(F) f
>>>          , typename disable_if<is_same<typename decay<F>::type, 
>>> thread>,
>>> dummy* >::type=0
>>>          );
>>>
>>> I suspect that you need to follow the instructions given in
>>> http://www.boost.org/doc/libs/**1_53_0/doc/html/thread/**
>>> emulations.html#thread.**emulations.move.portable<http://www.boost.org/doc/libs/1_53_0/doc/html/thread/emulations.html#thread.emulations.move.portable>to 
>>> make your class A movable :(
>>>
>>>   I can work on this if you want.
>>>> What do you think?
>>>>
>>>>   I'm all for a boost::bind or boost::bind-lite supporting boost 
>>>> semantics
>>> (using Boost.Move). If you can work on this a propose a patch to 
>>> boost bind
>>> I'm sure all the Boost community will thank you.
>>> There are a lot of basic Boost libraries that need an update to support
>>> move semantics (as Tuple, Fusion, SmartPtr, Exception?) so that other
>>> libraries can built on them. Any effort on this sens will be much
>>> appreciated.
>>>
>>> Please, let me know if you have some trouble after defining one of the
>>> following
>>>
>>> #define BOOST_THREAD_USES_MOVE
>>> #define BOOST_THREAD_VERSION 3
>>> #define BOOST_THREAD_VERSION 4
>>>
>>> Best,
>>> Vicente
>>>
>>> ______________________________**_________________
>>> Unsubscribe & other changes: http://lists.boost.org/**
>>> mailman/listinfo.cgi/boost<http://lists.boost.org/mailman/listinfo.cgi/boost> 
>>>
>>>
>>
>> Hi Vicente,
>>
>> I had not set BOOST_THREAD_VERSION. I just realized that is set to 2 by
>> default.
>> Sorry, I had no idea about Boost Thread Move emulations. I tested the 
>> code
>> using a C++11 movable-only type and a Boost.Move movable-only type.
>>
>> Same compilation error if I define BOOST_THREAD_USES_MOVE and
>> BOOST_THREAD_VERSION to 3 or 4 ( using Boost Thread Move Emulation )
>>
>> #define BOOST_THREAD_USES_MOVE
>> //#define BOOST_THREAD_VERSION 3
>> #define BOOST_THREAD_VERSION 4
>>
>> #include <iostream>
>> #include <boost/thread.hpp>
>>
>> struct A
>> {
>>      BOOST_THREAD_MOVABLE_ONLY(A)
>>
>>      A() {}
>>
>>      void run() { }
>> };
>>
>>
>> void f( A a )
>> {
>>      a.run();
>> }
>>
>> void exec_boost()
>> {
>>      A a;
>>      boost::thread t( f, std::move(a) );
>> t.join();
>> }
>>
>> error: use of deleted function 'A::A(const A&)'
>>
>> I'll wok on Boost.Bind trying to make it move-enabled.
>>
>> Thank you for your dedication and patience.
> You are welcome.
>
> Could you try with
>
> 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;}
>
> };
>
> BOOST_THREAD_DCL_MOVABLE_BEG(T) A BOOST_THREAD_DCL_MOVABLE_END
>
>
Sorry I meant

BOOST_THREAD_DCL_MOVABLE(A)

Vicente