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panda/src/putil/globalPointerRegistry.h

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// Filename: globalPointerRegistry.h
// Created by:  drose (03Feb00)
//
////////////////////////////////////////////////////////////////////
//
// PANDA 3D SOFTWARE
// Copyright (c) 2001, Disney Enterprises, Inc.  All rights reserved
//
// All use of this software is subject to the terms of the Panda 3d
// Software license.  You should have received a copy of this license
// along with this source code; you will also find a current copy of
// the license at http://www.panda3d.org/license.txt .
//
// To contact the maintainers of this program write to
// panda3d@yahoogroups.com .
//
////////////////////////////////////////////////////////////////////

#ifndef GLOBALPOINTERREGISTRY_H
#define GLOBALPOINTERREGISTRY_H

#include <pandabase.h>

#include "typedObject.h"

#include "pmap.h"

////////////////////////////////////////////////////////////////////
//       Class : GlobalPointerRegistry
// Description : This class maintains a one-to-one mapping from
//               TypeHandle to a void * pointer.  Its purpose is to
//               store a pointer to some class data for a given class.
//
//               Normally, one would simply use a static data member
//               to store class data.  However, when the static data
//               is associated with a template class, the dynamic
//               loader may have difficulty in properly resolving the
//               statics.
//
//               Consider: class foo<int> defines a static member, _a.
//               There should be only one instance of _a shared
//               between all instances of foo<int>, and there will be
//               a different instance of _a shared between all
//               instances of foo<float>.
//
//               Now suppose that two different shared libraries
//               instantiate foo<int>.  In each .so, there exists a
//               different foo<int>::_a.  It is the loader's job to
//               recognize this and collapse them together when both
//               libraries are loaded.  This usually works, but
//               sometimes it doesn't, and you end up with two
//               different instances of foo<int>::_a; some functions
//               see one instance, while others see the other.  We
//               have particularly seen this problem occur under Linux
//               with gcc.
//
//               This class attempts to circumvent the problem by
//               managing pointers to data based on TypeHandle.  Since
//               the TypeHandle will already be unique based on the
//               string name supplied to the init_type() function, it
//               can be used to differentiate foo<int> from
//               foo<float>, while allowing different instances of
//               foo<int> to guarantee that they share the same static
//               data.
////////////////////////////////////////////////////////////////////
class EXPCL_PANDA GlobalPointerRegistry {
public:
  INLINE static void *get_pointer(TypeHandle type);
  INLINE static void store_pointer(TypeHandle type, void *ptr);
  INLINE static void clear_pointer(TypeHandle type);

private:
  // Nonstatic implementations of the above functions.
  void *ns_get_pointer(TypeHandle type) const;
  void ns_store_pointer(TypeHandle type, void *ptr);
  void ns_clear_pointer(TypeHandle type);

  INLINE static GlobalPointerRegistry *get_global_ptr();
  static GlobalPointerRegistry *_global_ptr;

private:
  typedef pmap<TypeHandle, void *> Pointers;
  Pointers _pointers;
};

#include "globalPointerRegistry.I"

#endif

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