Re: [Boost-users] [Thread] Problems compiling an example from the docs

Subject: Re: [Boost-users] [Thread] Problems compiling an example from the docs
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2015-10-15 19:35:31

Le 14/10/15 19:02, Malko a écrit :
> Hi, I am trying to compile the following example:
> http://www.boost.org/doc/libs/1_59_0/doc/html/thread/synchronization.html#thread.synchronization.futures.async
>
>
> #include <boost/thread.hpp>
> #include <boost/thread/future.hpp>
>
> int parallel_sum(int* data, int size)
> {
>    int sum = 0;
>    if ( size < 1000 )
>      for ( int i = 0; i < size; ++i )
>        sum += data[i];
>    else {
>      boost::future<int> handle = boost::async(parallel_sum, data+size/2,
> size-size/2);
The example uses auto ;-)
>      sum += parallel_sum(data, size/2);
>      sum += handle.get();
>    }
>    return sum;
> }
>
>
> int main() {
>    int data[] = {1,2,3,4,5,6,7,8,9,10};
>    int a(parallel_sum, data, 10);
>    return 0;
> }
>
> It does not compile because future is not a type in boost and async has the
> wrong signature.
> The future error goes away by defining BOOST_THREAD_PROVIDES_FUTURE, but I
> can not find this mentioned anywhere in the docs, I found out only looking
> on stack overflow.
http://www.boost.org/doc/libs/1_59_0/doc/html/thread/build.html#thread.build.configuration.future 

> The async signature seems to require a function of arity 0.
In 
http://www.boost.org/doc/libs/1_59_0/doc/html/thread/synchronization.html#thread.synchronization.futures.reference.async

the variadic prototype is provided only on C++11 compilers supporting 
rvalue references, variadic templates, decltype and a standard library 
providing <tuple> (waiting for a boost::tuple that is move aware), and 
BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK is defined.

http://www.boost.org/doc/libs/1_59_0/doc/html/thread/build.html#thread.build.configuration.deprecated
>
> This is clang 3.4 output using Boost.1.59 and C++03:
>
>
<snip>
>
>
> Is there more macro to be used to enable this to compile?
The easiest way, define before including any Boost.Thread file

BOOST_THREAD_VERSION 4

http://www.boost.org/doc/libs/1_59_0/doc/html/thread/build.html#thread.build.configuration.version 

>
> Thanks
>
>
> P.S.
> It would be nice to have all the info about macro configuration for future
> (and async, if it has any) in the docs.
>
>
>
:)

I recognize that all these macros area nightmare. They exist in order to 
ensure backward compatibility with version 2 and 3. An alternative 
approach I didn't considered when I developed it is to have multiple 
versions. To late for Boost.Thread versions 2,3,4.

I would like to create a version 5 that coexists with version 2, 3 and 4 
but I have not find the needed time.
Best,
Vicente