Include/objimpl.h

   1
   2 #ifndef Py_OBJIMPL_H
   3 #define Py_OBJIMPL_H
   4
   5 #include "pymem.h"
   6
   7 #ifdef __cplusplus
   8 extern "C" {
   9 #endif
  10
  11 /*
  12 Functions and macros for modules that implement new object types.
  13 You must first include "object.h".
  14
  15  - PyObject_New(type, typeobj) allocates memory for a new object of
  16    the given type; here 'type' must be the C structure type used to
  17    represent the object and 'typeobj' the address of the corresponding
  18    type object.  Reference count and type pointer are filled in; the
  19    rest of the bytes of the object are *undefined*!  The resulting
  20    expression type is 'type *'.  The size of the object is actually
  21    determined by the tp_basicsize field of the type object.
  22
  23  - PyObject_NewVar(type, typeobj, n) is similar but allocates a
  24    variable-size object with n extra items.  The size is computed as
  25    tp_basicsize plus n * tp_itemsize.  This fills in the ob_size field
  26    as well.
  27
  28  - PyObject_Del(op) releases the memory allocated for an object.
  29
  30  - PyObject_Init(op, typeobj) and PyObject_InitVar(op, typeobj, n) are
  31    similar to PyObject_{New, NewVar} except that they don't allocate
  32    the memory needed for an object. Instead of the 'type' parameter,
  33    they accept the pointer of a new object (allocated by an arbitrary
  34    allocator) and initialize its object header fields.
  35
  36 Note that objects created with PyObject_{New, NewVar} are allocated
  37 within the Python heap by an object allocator, the latter being
  38 implemented (by default) on top of the Python raw memory
  39 allocator. This ensures that Python keeps control on the user's
  40 objects regarding their memory management; for instance, they may be
  41 subject to automatic garbage collection.
  42
  43 In case a specific form of memory management is needed, implying that
  44 the objects would not reside in the Python heap (for example standard
  45 malloc heap(s) are mandatory, use of shared memory, C++ local storage
  46 or operator new), you must first allocate the object with your custom
  47 allocator, then pass its pointer to PyObject_{Init, InitVar} for
  48 filling in its Python-specific fields: reference count, type pointer,
  49 possibly others. You should be aware that Python has very limited
  50 control over these objects because they don't cooperate with the
  51 Python memory manager. Such objects may not be eligible for automatic
  52 garbage collection and you have to make sure that they are released
  53 accordingly whenever their destructor gets called (cf. the specific
  54 form of memory management you're using).
  55
  56 Unless you have specific memory management requirements, it is
  57 recommended to use PyObject_{New, NewVar, Del}. */
  58
  59 /*
  60  * Core object memory allocator
  61  * ============================
  62  */
  63
  64 /* The purpose of the object allocator is to make the distinction
  65    between "object memory" and the rest within the Python heap.
  66
  67    Object memory is the one allocated by PyObject_{New, NewVar}, i.e.
  68    the one that holds the object's representation defined by its C
  69    type structure, *excluding* any object-specific memory buffers that
  70    might be referenced by the structure (for type structures that have
  71    pointer fields).  By default, the object memory allocator is
  72    implemented on top of the raw memory allocator.
  73
  74    The PyCore_* macros can be defined to make the interpreter use a
  75    custom object memory allocator. They are reserved for internal
  76    memory management purposes exclusively. Both the core and extension
  77    modules should use the PyObject_* API. */
  78
  79 #ifdef WITH_PYMALLOC
  80 #define PyCore_OBJECT_MALLOC_FUNC    _PyCore_ObjectMalloc
  81 #define PyCore_OBJECT_REALLOC_FUNC   _PyCore_ObjectRealloc
  82 #define PyCore_OBJECT_FREE_FUNC      _PyCore_ObjectFree
  83 #define NEED_TO_DECLARE_OBJECT_MALLOC_AND_FRIEND
  84 #endif /* !WITH_PYMALLOC */
  85
  86 #ifndef PyCore_OBJECT_MALLOC_FUNC
  87 #undef PyCore_OBJECT_REALLOC_FUNC
  88 #undef PyCore_OBJECT_FREE_FUNC
  89 #define PyCore_OBJECT_MALLOC_FUNC    PyCore_MALLOC_FUNC
  90 #define PyCore_OBJECT_REALLOC_FUNC   PyCore_REALLOC_FUNC
  91 #define PyCore_OBJECT_FREE_FUNC      PyCore_FREE_FUNC
  92 #endif
  93
  94 #ifndef PyCore_OBJECT_MALLOC_PROTO
  95 #undef PyCore_OBJECT_REALLOC_PROTO
  96 #undef PyCore_OBJECT_FREE_PROTO
  97 #define PyCore_OBJECT_MALLOC_PROTO   PyCore_MALLOC_PROTO
  98 #define PyCore_OBJECT_REALLOC_PROTO  PyCore_REALLOC_PROTO
  99 #define PyCore_OBJECT_FREE_PROTO     PyCore_FREE_PROTO
 100 #endif
 101
 102 #ifdef NEED_TO_DECLARE_OBJECT_MALLOC_AND_FRIEND
 103 extern void *PyCore_OBJECT_MALLOC_FUNC PyCore_OBJECT_MALLOC_PROTO;
 104 extern void *PyCore_OBJECT_REALLOC_FUNC PyCore_OBJECT_REALLOC_PROTO;
 105 extern void PyCore_OBJECT_FREE_FUNC PyCore_OBJECT_FREE_PROTO;
 106 #endif
 107
 108 #ifndef PyCore_OBJECT_MALLOC
 109 #undef PyCore_OBJECT_REALLOC
 110 #undef PyCore_OBJECT_FREE
 111 #define PyCore_OBJECT_MALLOC(n)      PyCore_OBJECT_MALLOC_FUNC(n)
 112 #define PyCore_OBJECT_REALLOC(p, n)  PyCore_OBJECT_REALLOC_FUNC((p), (n))
 113 #define PyCore_OBJECT_FREE(p)        PyCore_OBJECT_FREE_FUNC(p)
 114 #endif
 115
 116 /*
 117  * Raw object memory interface
 118  * ===========================
 119  */
 120
 121 /* The use of this API should be avoided, unless a builtin object
 122    constructor inlines PyObject_{New, NewVar}, either because the
 123    latter functions cannot allocate the exact amount of needed memory,
 124    either for speed. This situation is exceptional, but occurs for
 125    some object constructors (PyBuffer_New, PyList_New...).  Inlining
 126    PyObject_{New, NewVar} for objects that are supposed to belong to
 127    the Python heap is discouraged. If you really have to, make sure
 128    the object is initialized with PyObject_{Init, InitVar}. Do *not*
 129    inline PyObject_{Init, InitVar} for user-extension types or you
 130    might seriously interfere with Python's memory management. */
 131
 132 /* Functions */
 133
 134 /* Wrappers around PyCore_OBJECT_MALLOC and friends; useful if you
 135    need to be sure that you are using the same object memory allocator
 136    as Python. These wrappers *do not* make sure that allocating 0
 137    bytes returns a non-NULL pointer. Returned pointers must be checked
 138    for NULL explicitly; no action is performed on failure. */
 139 extern DL_IMPORT(void *) PyObject_Malloc(size_t);
 140 extern DL_IMPORT(void *) PyObject_Realloc(void *, size_t);
 141 extern DL_IMPORT(void) PyObject_Free(void *);
 142
 143 /* Macros */
 144 #define PyObject_MALLOC(n)           PyCore_OBJECT_MALLOC(n)
 145 #define PyObject_REALLOC(op, n)      PyCore_OBJECT_REALLOC((void *)(op), (n))
 146 #define PyObject_FREE(op)            PyCore_OBJECT_FREE((void *)(op))
 147
 148 /*
 149  * Generic object allocator interface
 150  * ==================================
 151  */
 152
 153 /* Functions */
 154 extern DL_IMPORT(PyObject *) PyObject_Init(PyObject *, PyTypeObject *);
 155 extern DL_IMPORT(PyVarObject *) PyObject_InitVar(PyVarObject *,
 156                                                  PyTypeObject *, int);
 157 extern DL_IMPORT(PyObject *) _PyObject_New(PyTypeObject *);
 158 extern DL_IMPORT(PyVarObject *) _PyObject_NewVar(PyTypeObject *, int);
 159 extern DL_IMPORT(void) _PyObject_Del(PyObject *);
 160
 161 #define PyObject_New(type, typeobj) \
 162                 ( (type *) _PyObject_New(typeobj) )
 163 #define PyObject_NewVar(type, typeobj, n) \
 164                 ( (type *) _PyObject_NewVar((typeobj), (n)) )
 165 #define PyObject_Del(op) _PyObject_Del((PyObject *)(op))
 166
 167 /* Macros trading binary compatibility for speed. See also pymem.h.
 168    Note that these macros expect non-NULL object pointers.*/
 169 #define PyObject_INIT(op, typeobj) \
 170         ((op)->ob_type = (typeobj), _Py_NewReference((PyObject *)(op)), \
 171          (PyType_SUPPORTS_WEAKREFS((typeobj)) \
 172               ? *(PyObject_GET_WEAKREFS_LISTPTR(op)) = NULL \
 173               : NULL), \
 174          (op))
 175 #define PyObject_INIT_VAR(op, typeobj, size) \
 176         ( (op)->ob_size = (size), PyObject_INIT((op), (typeobj)) )
 177
 178 #define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )
 179 #define _PyObject_VAR_SIZE(typeobj, n) \
 180         ( (typeobj)->tp_basicsize + (n) * (typeobj)->tp_itemsize )
 181
 182 #define PyObject_NEW(type, typeobj) \
 183 ( (type *) PyObject_Init( \
 184         (PyObject *) PyObject_MALLOC( _PyObject_SIZE(typeobj) ), (typeobj)) )
 185 #define PyObject_NEW_VAR(type, typeobj, n) \
 186 ( (type *) PyObject_InitVar( \
 187         (PyVarObject *) PyObject_MALLOC( _PyObject_VAR_SIZE((typeobj),(n)) ),\
 188         (typeobj), (n)) )
 189
 190 #define PyObject_DEL(op) PyObject_FREE(op)
 191
 192 /* This example code implements an object constructor with a custom
 193    allocator, where PyObject_New is inlined, and shows the important
 194    distinction between two steps (at least):
 195        1) the actual allocation of the object storage;
 196        2) the initialization of the Python specific fields
 197           in this storage with PyObject_{Init, InitVar}.
 198
 199    PyObject *
 200    YourObject_New(...)
 201    {
 202        PyObject *op;
 203
 204        op = (PyObject *) Your_Allocator(_PyObject_SIZE(YourTypeStruct));
 205        if (op == NULL)
 206            return PyErr_NoMemory();
 207
 208        op = PyObject_Init(op, &YourTypeStruct);
 209        if (op == NULL)
 210            return NULL;
 211
 212        op->ob_field = value;
 213        ...
 214        return op;
 215    }
 216
 217    Note that in C++, the use of the new operator usually implies that
 218    the 1st step is performed automatically for you, so in a C++ class
 219    constructor you would start directly with PyObject_Init/InitVar. */
 220
 221 /*
 222  * Garbage Collection Support
 223  * ==========================
 224  */
 225
 226 /* To make a new object participate in garbage collection use
 227    PyObject_{New, VarNew, Del} to manage the memory.  Set the type flag
 228    Py_TPFLAGS_GC and define the type method tp_traverse.  You should also
 229    add the method tp_clear if your object is mutable.  Include
 230    PyGC_HEAD_SIZE in the calculation of tp_basicsize.  Call
 231    PyObject_GC_Init after the pointers followed by tp_traverse become
 232    valid (usually just before returning the object from the allocation
 233    method.  Call PyObject_GC_Fini before those pointers become invalid
 234    (usually at the top of the deallocation method).  */
 235
 236 #ifndef WITH_CYCLE_GC
 237
 238 #define PyGC_HEAD_SIZE 0
 239 #define PyObject_GC_Init(op)
 240 #define PyObject_GC_Fini(op)
 241 #define PyObject_AS_GC(op) (op)
 242 #define PyObject_FROM_GC(op) (op)
 243
 244 #else
 245
 246 /* Add the object into the container set */
 247 extern DL_IMPORT(void) _PyGC_Insert(PyObject *);
 248
 249 /* Remove the object from the container set */
 250 extern DL_IMPORT(void) _PyGC_Remove(PyObject *);
 251
 252 #define PyObject_GC_Init(op) _PyGC_Insert((PyObject *)op)
 253 #define PyObject_GC_Fini(op) _PyGC_Remove((PyObject *)op)
 254
 255 /* Structure *prefixed* to container objects participating in GC */
 256 typedef struct _gc_head {
 257         struct _gc_head *gc_next;
 258         struct _gc_head *gc_prev;
 259         int gc_refs;
 260 } PyGC_Head;
 261
 262 #define PyGC_HEAD_SIZE sizeof(PyGC_Head)
 263
 264 /* Test if a type has a GC head */
 265 #define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_GC)
 266
 267 /* Test if an object has a GC head */
 268 #define PyObject_IS_GC(o) PyType_IS_GC((o)->ob_type)
 269
 270 /* Get an object's GC head */
 271 #define PyObject_AS_GC(o) ((PyGC_Head *)(o)-1)
 272
 273 /* Get the object given the PyGC_Head */
 274 #define PyObject_FROM_GC(g) ((PyObject *)(((PyGC_Head *)g)+1))
 275
 276 extern DL_IMPORT(void) _PyGC_Dump(PyGC_Head *);
 277
 278 #endif /* WITH_CYCLE_GC */
 279
 280 /* Test if a type supports weak references */
 281 #define PyType_SUPPORTS_WEAKREFS(t) \
 282         (PyType_HasFeature((t), Py_TPFLAGS_HAVE_WEAKREFS) \
 283          && ((t)->tp_weaklistoffset > 0))
 284
 285 #define PyObject_GET_WEAKREFS_LISTPTR(o) \
 286         ((PyObject **) (((char *) (o)) + (o)->ob_type->tp_weaklistoffset))
 287
 288 #ifdef __cplusplus
 289 }
 290 #endif
 291 #endif /* !Py_OBJIMPL_H */