Panda3D

globalPointerRegistry.h

00001 // Filename: globalPointerRegistry.h
00002 // Created by:  drose (03Feb00)
00003 //
00004 ////////////////////////////////////////////////////////////////////
00005 //
00006 // PANDA 3D SOFTWARE
00007 // Copyright (c) Carnegie Mellon University.  All rights reserved.
00008 //
00009 // All use of this software is subject to the terms of the revised BSD
00010 // license.  You should have received a copy of this license along
00011 // with this source code in a file named "LICENSE."
00012 //
00013 ////////////////////////////////////////////////////////////////////
00014 
00015 #ifndef GLOBALPOINTERREGISTRY_H
00016 #define GLOBALPOINTERREGISTRY_H
00017 
00018 #include "pandabase.h"
00019 
00020 #include "typedObject.h"
00021 
00022 #include "pmap.h"
00023 
00024 ////////////////////////////////////////////////////////////////////
00025 //       Class : GlobalPointerRegistry
00026 // Description : This class maintains a one-to-one mapping from
00027 //               TypeHandle to a void * pointer.  Its purpose is to
00028 //               store a pointer to some class data for a given class.
00029 //
00030 //               Normally, one would simply use a static data member
00031 //               to store class data.  However, when the static data
00032 //               is associated with a template class, the dynamic
00033 //               loader may have difficulty in properly resolving the
00034 //               statics.
00035 //
00036 //               Consider: class foo<int> defines a static member, _a.
00037 //               There should be only one instance of _a shared
00038 //               between all instances of foo<int>, and there will be
00039 //               a different instance of _a shared between all
00040 //               instances of foo<float>.
00041 //
00042 //               Now suppose that two different shared libraries
00043 //               instantiate foo<int>.  In each .so, there exists a
00044 //               different foo<int>::_a.  It is the loader's job to
00045 //               recognize this and collapse them together when both
00046 //               libraries are loaded.  This usually works, but
00047 //               sometimes it doesn't, and you end up with two
00048 //               different instances of foo<int>::_a; some functions
00049 //               see one instance, while others see the other.  We
00050 //               have particularly seen this problem occur under Linux
00051 //               with gcc.
00052 //
00053 //               This class attempts to circumvent the problem by
00054 //               managing pointers to data based on TypeHandle.  Since
00055 //               the TypeHandle will already be unique based on the
00056 //               string name supplied to the init_type() function, it
00057 //               can be used to differentiate foo<int> from
00058 //               foo<float>, while allowing different instances of
00059 //               foo<int> to guarantee that they share the same static
00060 //               data.
00061 ////////////////////////////////////////////////////////////////////
00062 class EXPCL_PANDA_PUTIL GlobalPointerRegistry {
00063 public:
00064   INLINE static void *get_pointer(TypeHandle type);
00065   INLINE static void store_pointer(TypeHandle type, void *ptr);
00066   INLINE static void clear_pointer(TypeHandle type);
00067 
00068 private:
00069   // Nonstatic implementations of the above functions.
00070   void *ns_get_pointer(TypeHandle type) const;
00071   void ns_store_pointer(TypeHandle type, void *ptr);
00072   void ns_clear_pointer(TypeHandle type);
00073 
00074   INLINE static GlobalPointerRegistry *get_global_ptr();
00075   static GlobalPointerRegistry *_global_ptr;
00076 
00077 private:
00078   typedef phash_map<TypeHandle, void *> Pointers;
00079   Pointers _pointers;
00080 };
00081 
00082 #include "globalPointerRegistry.I"
00083 
00084 #endif
00085 
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