Re: [Boost-users] Using object_pool with a constructor with more that 3 arguments with MSVC

Subject: Re: [Boost-users] Using object_pool with a constructor with more that 3 arguments with MSVC
From: Gabriel Redner (gredner_at_[hidden])
Date: 2012-08-23 13:30:02

Hi Pico,

I ran into the same limitation of object_pool in my own project.
Rather than mess with m4, I ended up sidestepping the problem like so:

void *mem = myPool.malloc();
Object *obj = new (mem) Object(arg1, arg2, etc.);

This works well for my use case because my Object's has no destructor,
so I can just call object_pool::free to free the memory, or wait until
the whole pool is destroyed.  If you need destructors to run, you'll
have to do something like (untested):

obj->~Object();
myPool.free(obj);

-Gabe

On Thu, Aug 23, 2012 at 1:02 PM, Pico Geyer <picogeyer_at_[hidden]> wrote:
> Hi all.
>
> I'm using object pools in some code of mine. The code needs to build
> on unix (gcc) and on Windows(Visual C++).
> The objects that I'm constructing take 4 arguments so I needed to use
> the scripts mentioned in the note on this page:
> http://www.boost.org/doc/libs/1_51_0/libs/pool/doc/html/boost/object_pool.html
>
> <quote>
> Since the number and type of arguments to this function is totally
> arbitrary, a simple system has been set up to automatically generate
> template construct functions. This system is based on the macro
> preprocessor m4, which is standard on UNIX systems and also available
> for Win32 systems.
>
> detail/pool_construct.m4, when run with m4, will create the file
> detail/pool_construct.ipp, which only defines the construct functions
> for the proper number of arguments. The number of arguments may be
> passed into the file as an m4 macro, NumberOfArguments; if not
> provided, it will default to 3.
>
> For each different number of arguments (1 to NumberOfArguments), a
> template function is generated. There are the same number of template
> parameters as there are arguments, and each argument's type is a
> reference to that (possibly cv-qualified) template argument. Each
> possible permutation of the cv-qualifications is also generated.
>
> Because each permutation is generated for each possible number of
> arguments, the included file size grows exponentially in terms of the
> number of constructor arguments, not linearly. For the sake of
> rational compile times, only use as many arguments as you need.
>
> detail/pool_construct.bat and detail/pool_construct.sh are also
> provided to call m4, defining NumberOfArguments to be their
> command-line parameter. See these files for more details."
> </quote>
>
> So I ran this script like so:
> ./pool_construct.sh 4
> And I made sure that Visual C++ is using the right include directory.
> But I still get the error:
> error C2660: 'boost::object_pool<T>::construct' : function does not
> take 4 arguments
>
> I then starting digging into the header files to see why
> pool_construct.ipp is not being included. I then found these two
> interesting parts in object_pool.hpp:
> #if defined(BOOST_MSVC) || defined(__KCC)
> # define BOOST_NO_TEMPLATE_CV_REF_OVERLOADS
> #endif
>
> and
> #ifndef BOOST_NO_TEMPLATE_CV_REF_OVERLOADS
> #   include <boost/pool/detail/pool_construct.ipp>
> #else
> #   include <boost/pool/detail/pool_construct_simple.ipp>
> #endif
>
> I don't really understand why the pool_construct_simple.ipp file
> should instead be included for windows.
> But if there is a good reason for it, shouldn't the documentation be
> updated to tell you to instead run the pool_construct_simple.sh script
> instead?
> Can anyone provide any information to help me understand this?
>
> Thanks in advance.
> Pico
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