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

Subject: Re: [boost] [thread] using Boost.Thread with move-only arguments
From: Fernando Pelliccioni (fpelliccioni_at_[hidden])
Date: 2013-04-07 18:15:55

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
>
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>

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.

Regards,
Fernando.