/*!

\page devman_memory_management Memory Management

\authors Michael Seel (<TT>seel@mpi-sb.mpg.de</TT>)
\authors Efi Fogel (<TT>efif@post.tau.ac.il</TT>)

One of the design goals of \cgal (Section  \ref secdesign_goals ) is 
efficiency,
and this means not only implementing efficient algorithms
but also implementing them efficiently. One way to improve the efficiency
of an implementation is through efficient memory management. This can be
done by making the library data structures independent of the underlying
memory model. However, to avoid unacceptable efficiency degradations
complete abstraction of the memory model should be avoided. Here we
describe one way to address this using allocators. An allocator 
encapsulates the information about an allocation model.

We adopted the definition of the Standard \cpp
allocator \cgalCite{cgal:ansi-is14882-98}. The `std::allocator` is the
only predefined and required allocator imposed by [\cpp] on all \cpp
compiler implementations. The exact specification can also be found at
<A HREF="https://en.wikipedia.org/wiki/Allocator_(C++)"><TT>https://en.wikipedia.org/wiki/Allocator_(C++)</TT></A>.

Objects of type `std::allocator<T>` can be used to obtain small, typed 
chunks of memory to be used, for example, as static members of a class. 
This is especially interesting with classes of a constant size that are
frequently allocated and deallocated (e.g., points, lines, circles),
since a memory allocator can maintain the corresponding memory chunks
in local blocks and thus can answer allocation and deallocation calls
much faster than the corresponding system calls.

\section secallocator_macro The allocator macro 

The macro `CGAL_ALLOCATOR(T)`
is defined as `std::allocator<T>` in the file `<CGAL/memory.h>`.
`CGAL_ALLOCATOR` is used
as the default allocator for all \cgal components. You can redefine it,
for example, if \leda is present, you can define it (before including
any \cgal header file) as follows:

\code{.cpp}
#include <LEDA/allocator.h>
#define CGAL_ALLOCATOR(t) leda_allocator<t>
\endcode

\section secusing_memory_allocator Using the allocator 

How should a data structure use the allocator mechanism? Just make the
allocator one of the template arguments of the data structure. Then
use a static member object to allocate items on the heap that you
want to keep optimized regarding allocation and deallocation. We
show an example using a trivial list structure:

\code{.cpp}
#include <CGAL/memory.h>

template <typename T> 
class dlink 
{ T some_member; };

template < typename T, typename Alloc = CGAL_ALLOCATOR(dlink<T>) >
class list 
{
public:
  typedef dlink<T>* dlink_ptr;
  typedef Alloc list_allocator;

  static list_allocator M;

list() {
  p = M.allocate(1);          // allocation of space for one dlink
  M.construct(p,dlink<T>());  // inplace construction of object
}

~list() {
  M.destroy(p);      // destroy object
  M.deallocate(p,1); // deallocate memory
}

private:
  dlink_ptr p;
};

// init static member allocator object:
template <typename T, typename Alloc>
typename list<T,Alloc>::list_allocator list<T,Alloc>::M =
             typename list<T,Alloc>::list_allocator();

int main()
{
  list<int> L;
  return 0;
}
\endcode

\section secmemory_req_and_rec Requirements and recommendations 

Recommendations:
<UL>
   <LI>Use an allocator template parameter (which defaults to
         `CGAL_ALLOCATOR`) for data structures for which an optimization
         with regard to allocation and deallocation is beneficial.
</UL>

*/
