[Boost-bugs] [Boost C++ Libraries] #7654: offset_ptr can't be evaluated a pointer to a container in shared memory

Subject: [Boost-bugs] [Boost C++ Libraries] #7654: offset_ptr can't be evaluated a pointer to a container in shared memory
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-11-06 17:53:28

#7654: offset_ptr can't be evaluated a pointer to a container in shared memory
-----------------------------------------+----------------------------------
 Reporter:  hongchenbo@…                 |       Owner:  igaztanaga  
     Type:  Bugs                         |      Status:  new         
Milestone:  To Be Determined             |   Component:  interprocess
  Version:  Boost 1.52.0                 |    Severity:  Problem     
 Keywords:  offset_ptr boost::container  |  
-----------------------------------------+----------------------------------
 i created a container(boost::container::set) in shared memory by
 managed_shared_memeory::construct,i wanted to put the pointer of container
 into a offset_ptr，codes as：
 typedef boost::container::set<int, less<int>, int_allocator_type>
 values_type;
 values_ptr_ = segment_manager_->construct<values_type>(
 boost::interprocess::anonymous_instance )( std::less<int>(),
 int_allocator_type( segment_manager_ ) );

 when compiling：
 error C2512: 'boost::interprocess::allocator<T,SegmentManager>' : no
 appropriate default constructor available
           with
           [
               T=boost::container::container_detail::rbtree_node<unsigned
 __int64,boost::interprocess::offset_ptr<void>>,
               SegmentManager=segment_manager_type
           ]

 the related codes as：
 template <class T>
    offset_ptr( T *ptr
              , typename ipcdetail::enable_if<
 ipcdetail::is_convertible<T*, PointedType*> >::type * = 0)
    {  this->set_offset(static_cast<PointedType*>(ptr)); }

 template <bool B, class T = void>
 struct enable_if_c {
   typedef T type;
 };

 template <class T>
 struct enable_if_c<false, T> {};

 template <class Cond, class T = void>
 struct enable_if : public enable_if_c<Cond::value, T> {};

 template <class Cond, class T = void>
 struct disable_if : public enable_if_c<!Cond::value, T> {};

 template <class T, class U>
 class is_convertible
 {
    typedef char true_t;
    class false_t { char dummy[2]; };
    static true_t dispatch(U);
    static false_t dispatch(...);
    static T trigger();
    public:
    static const bool value = sizeof(dispatch(trigger())) ==
 sizeof(true_t);
 };

 i thougnt that T and U are values_type*,it's unnecessary to instantiate a
 values_type,but why called allocator's constructor ？

 the boost::container's allocator must have a default constructor，but,in
 fact,boost::interprocess::allocator is stateful，its constructor need the
 pointer to segment_manager。is it a bug? or my codes is fault?

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7654>
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