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Re: Wading through template instantiation errors for allocator

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Am 07.01.2020 um 10:36 schrieb Bonita Montero:
> Forget writing an allocator that doesn't have full heap-semantics.
> The C++-containers often rebind the allocator-type for orther
> allocators; f.e. an unordered_map might do a rebind for the
> bucket-nodes (it gets only a allocator<pair<const Key, T>,
> which isn't sufficient for everything a unordered_map needs).

I tried to write my own allocator that relies on VirtualAlloc() or
mmap(). But it doesn't work for the above reason; i.e. the allocator
might get rebound and the new allocator might be used for tiny amounts
of memory, rounded up to a page-size.

#ifdef _MSC_VER
     #include <Windows.h>
#elif __unix__
     #include <sys/mman.h>
#endif
#include <cstddef>
#include <exception>
#include <cassert>
#include <new>

#include <iostream>

template<class T>
class virtual_allocator
{
public:
     typedef T               value_type;
#if __cplusplus < 201703L
     typedef T              *pointer;
     typedef const T        *const_pointer;
     typedef T              &reference;
     typedef const T        &const_reference;
#endif
     typedef std::size_t     size_type;
     typedef std::ptrdiff_t  difference_type;
#if __cplusplus < 201703L
     template<typename U>
     struct rebind
     {
         typedef virtual_allocator<U> other;
     };
#endif

     explicit              virtual_allocator() = default;
     explicit              virtual_allocator( virtual_allocator const 
&other ) = default;
                           template<typename U>
                           virtual_allocator( virtual_allocator<U> const 
&other );
#if __cplusplus < 201703L
     static pointer        address( reference value );
     static const_pointer  address( const_reference value );
     static size_type      max_size() throw();
#endif
#if __cplusplus >= 201703L
     T                    *allocate( size_type n, void *hint = nullptr );
     void                  deallocate( T *p, size_type num = 1 );
#else
     pointer               allocate( size_type n, void *hint = nullptr );
     void                  deallocate( pointer p, size_type num = 1 );
#endif
#if __cplusplus < 201703L
     static void           construct( pointer p, const T&value );
     template<typename U>
     static void           destroy( U *p );
#endif
};

template<typename T>
template<typename U>
inline
virtual_allocator<T>::virtual_allocator( virtual_allocator<U> const 
&other ) :
     virtual_allocator()
{
}

#if __cplusplus < 201703L
template<typename T>
inline
typename virtual_allocator<T>::pointer virtual_allocator<T>::address( 
reference value )
{
     return &value;
}

template<typename T>
inline
typename virtual_allocator<T>::const_pointer 
virtual_allocator<T>::address( const_reference value )
{
     return &value;
}

template<typename T>
inline
typename virtual_allocator<T>::size_type 
virtual_allocator<T>::max_size() throw()
{
     return (size_t)(ptrdiff_t)-1 / sizeof(T);
}
#endif

template<typename T>
#if __cplusplus >= 201703L
T *virtual_allocator<T>::allocate( size_type n, void *hint )
#else
typename virtual_allocator<T>::pointer virtual_allocator<T>::allocate( 
size_type n, void *hint )
#endif
{
     std::cout << "allocate" << n << std::endl;
#if defined(_MSC_VER)
     T *p = (T *)VirtualAlloc( hint, n * sizeof(T), MEM_RESERVE | 
MEM_COMMIT, PAGE_READWRITE );
     if( !p )
         throw std::bad_alloc();
     return p;
#elif __unix__
     void *p = mmap( hint, n * sizeof(T), PROT_READ | PROT_WRITE, 
MAP_SHARED | MAP_ANONYMOUS, -1, 0 );
     if( p == MAP_FAILED )
         throw std::bad_alloc();
     return (pointer)p;
#else
     #error no implementation for your OS
#endif
}

template<typename T>
#if __cplusplus >= 201703L
inline
void virtual_allocator<T>::deallocate( T *p, size_type n )
#else
inline
void virtual_allocator<T>::deallocate( pointer p, size_type n )
#endif
{
     std::cout << "dellocate " << n << std::endl;
#if defined(_MSC_VER)
     BOOL ret = VirtualFree( p, 0, MEM_RELEASE );
     assert(ret);
#elif __unix__
     int ret = munmap( p, n * sizeof(T) );
     assert(ret == 0);
#else
     #error no implementation for your OS
#endif
}

#if __cplusplus < 201703L
template<typename T>
inline
void virtual_allocator<T>::construct( pointer p, const T&value )
{
     new( (void*)p ) T( value );
}

template<typename T>
template<typename U>
inline
void virtual_allocator<T>::destroy( U *p )
{
     p->~T();
}
#endif

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Thread

Wading through template instantiation errors for allocator Frederick Gotham <cauldwell.thomas@gmail.com> - 2020-01-03 07:04 -0800
  Re: Wading through template instantiation errors for allocator Melzzzzz <Melzzzzz@zzzzz.com> - 2020-01-03 16:57 +0000
  Re: Wading through template instantiation errors for allocator Paavo Helde <myfirstname@osa.pri.ee> - 2020-01-03 21:32 +0200
    Re: Wading through template instantiation errors for allocator Frederick Gotham <cauldwell.thomas@gmail.com> - 2020-01-04 06:12 -0800
      Re: Wading through template instantiation errors for allocator Bo Persson <bo@bo-persson.se> - 2020-01-04 15:53 +0100
        Re: Wading through template instantiation errors for allocator Frederick Gotham <cauldwell.thomas@gmail.com> - 2020-01-04 14:34 -0800
          Re: Wading through template instantiation errors for allocator Manfred <noname@add.invalid> - 2020-01-05 22:31 +0100
  Re: Wading through template instantiation errors for allocator Frederick Gotham <cauldwell.thomas@gmail.com> - 2020-01-06 02:12 -0800
    Re: Wading through template instantiation errors for allocator Frederick Gotham <cauldwell.thomas@gmail.com> - 2020-01-06 23:52 -0800
  Re: Wading through template instantiation errors for allocator Ian Collins <ian-news@hotmail.com> - 2020-01-07 21:15 +1300
    Re: Wading through template instantiation errors for allocator Frederick Gotham <cauldwell.thomas@gmail.com> - 2020-01-07 01:01 -0800
      Re: Wading through template instantiation errors for allocator Ian Collins <ian-news@hotmail.com> - 2020-01-08 07:31 +1300
        Re: Wading through template instantiation errors for allocator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-07 19:50 +0100
        Re: Wading through template instantiation errors for allocator Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-01-10 07:06 -0800
          Re: Wading through template instantiation errors for allocator Frederick Gotham <cauldwell.thomas@gmail.com> - 2020-01-14 02:25 -0800
    Re: Wading through template instantiation errors for allocator Melzzzzz <Melzzzzz@zzzzz.com> - 2020-01-07 09:20 +0000
    Re: Wading through template instantiation errors for allocator boltar@nowhere.org - 2020-01-08 10:12 +0000
    Re: Wading through template instantiation errors for allocator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-08 09:22 -0800
      Re: Wading through template instantiation errors for allocator Melzzzzz <Melzzzzz@zzzzz.com> - 2020-01-08 17:44 +0000
      Re: Wading through template instantiation errors for allocator "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2020-01-08 23:00 +0100
    Re: Wading through template instantiation errors for allocator Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-01-10 06:48 -0800
  Re: Wading through template instantiation errors for allocator Melzzzzz <Melzzzzz@zzzzz.com> - 2020-01-07 09:20 +0000
    Re: Wading through template instantiation errors for allocator Melzzzzz <Melzzzzz@zzzzz.com> - 2020-01-07 09:35 +0000
      Re: Wading through template instantiation errors for allocator Melzzzzz <Melzzzzz@zzzzz.com> - 2020-01-07 09:43 +0000
        Re: Wading through template instantiation errors for allocator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-07 10:47 +0100
          Re: Wading through template instantiation errors for allocator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-07 10:59 +0100
            Re: Wading through template instantiation errors for allocator Melzzzzz <Melzzzzz@zzzzz.com> - 2020-01-07 10:15 +0000
              Re: Wading through template instantiation errors for allocator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-07 11:21 +0100
                Re: Wading through template instantiation errors for allocator Melzzzzz <Melzzzzz@zzzzz.com> - 2020-01-07 10:25 +0000
          Re: Wading through template instantiation errors for allocator Melzzzzz <Melzzzzz@zzzzz.com> - 2020-01-07 10:02 +0000
          Re: Wading through template instantiation errors for allocator Bo Persson <bo@bo-persson.se> - 2020-01-07 15:27 +0100
  Re: Wading through template instantiation errors for allocator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-07 10:36 +0100
    Re: Wading through template instantiation errors for allocator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-07 10:42 +0100

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